The WDY (Turbulence and Vortex Dynamics) and MTP (Mesoscopic Transport Phenomena) groups of the Department of Applied Physics would like to invite you to our seminar series. The seminar takes place every first week of the month, preferably on Mondays in Cascade 2.21 (building 23 on the campus map, grid square D5) at 12:45.
If you would like to receive email announcements of these seminars, feel free to contact one of the organizers. You are also invited to subscribe to our calendar.
Week  Date  Speaker  Title / abstract 

50  20161212  dr. Roger Jaspers Science and Technology of Nuclear Fusion (FUSION), TU Eindhoven 

45  20161107  Ir. Sabine Rijnsburger Environmental Fluid Mechanics, Civil Engineering, TU Delft  Frontal dynamics in the midfield region of the Rhine river plume
Freshwater fronts in coastal areas can impact the transport of fine sediment. They can transport fine sediment offshore or exert a high stress on the bottom what causes resuspension. During the presentation I will show which processes change the frontal dynamics off the Dutch coast and under which conditions the fronts are strong enough to impact the fine sediment transport. The study uses Xband radar images and field data, which is collected 10 km north of the Rhine river outflow at 1.5 and 6 km offshore. 
40  20161006  dr. Ad Stoffelen KNMI  Earth's winds from space
Knowledge and measurement of winds is essential for, among others, atmospheric dynamics, mesoscale weather analysis, atmospheric dispersion, oceanography, marine forecasting of winds, waves and storm surges, offshore wind energy applications, and from cloud to climatescale processes. But how can we measure winds in the Earth's atmosphere?

22  20160602  ir. Johan Bosschers Research & Development MARIN  Vortex cavitation on ship propellers and its radiated noise
High propulsive efficiency of marine propellers goes with increasing cavitation extents, cavitation being the process of water evaporation and condensation. The dynamics of cavitation, especially the collapse, is an efficient noise source and it may lead to erosion on the propeller blade. Ships with high comfort class requirements, e.g. cruise vessels, or underwater signature requirements (e.g. naval vessels) optimize their propellers to achieve minimum cavitation such that often only a cavitating tip vortex remains. There is however remarkably little known on vortex cavitation as most cavitation research has and still is focused on either bubble cavitation or sheet cavitation as their nuisance is typically higher than of vortex cavitation. The presentation will give a short introduction on various types of vortex cavitation observed on marine propellers and will focus on some fundamental aspects of vortex cavitation describing both the kinematics and the dynamics. A practical method in development to predict hull pressure fluctuations and radiated noise for industrial applications will be presented and future challenges will be addressed. 
14  20160404  dr. ir. Chiel C. van Heerwaarden Wageningen University  Growth and decay of a convective boundary layer over a surface with a constant temperature
The growth and decay of a convective boundary layer (CBL) over a surface with a constant surface temper ature that develops into a linear stratification is studied, and a mathematical model for this system is derived. The study is based on direct numerical simulations with four different Reynolds numbers; the two simulations with the largest Reynolds numbers display Reynolds number similarity, suggesting that the results can be extrapolated to the atmosphere. Due to the interplay of the growing CBL and the gradually decreasing surface buoyancy flux, the system has a complex time evolution in which integrated kinetic energy, buoyancy flux and dissipation peak and subsequently decay. The derived model provides characteristic scales for bulk properties of the CBL. Even though the system is unsteady, selfsimilar vertical profiles of buoyancy, buoyancy flux and the velocity variances are recovered. There are two important implications for atmospheric modeling. First, the magnitude of the surface buoyancy flux sets the time scale of the system, thus over a rough surface the roughness length is a key variable. Therefore, the performance of the surface model is crucial in largeeddy simulations of convection over water surfaces. Second, during the phase in which kinetic energy decays, the integrated kinetic energy never follows a power law, because the buoyancy flux and dissipation balance until the kinetic energy has almost vanished. Therefore, the applicability of power law decay models to the after noon transition in the atmospheric boundary layer is questionable; the presented model provides a physically sound alternative. 
10  20160308  Dave Weij Delft University of Technology  Unstable breaching
Breaching is a gradual retreat of a subaqueous slope, which is steeper than the angle of repose. While mainly investigated due to the application of this process in the breaching process, the breaching process can also be a cause for unwanted slope instability and failure. These failures are usually caused by unstable breaching, where the size of the retreating slope increases during the process. The aim of this project is to investigate the unstable breaching process using numerical methods. 
10  20160308  Frans van Grunsven Delft University of Technology  Modeling offshore turbidity sources
Accurate predictions of the environmental impact remain a major challenge in the licensing phase of offshore mining projects. A significant part of the environmental impact of offshore mining is caused by an increase in turbidity of the oceanic waters. Turbidity levels are increased by the suspension of sediment during the excavation process and due to the discharge of return water and possibly tailings into the ocean. Current consensus prescribes releasing discharges in close proximity of the seafloor to decrease the impact area of the turbidity plume. Main engineering choices remain a challenge. Available engineering models and software are unable to include the interaction between the turbulent slurry mixture and the (deep) seafloor. This introduces an uncertainty into the predictions of the turbidity source. Uncertainties increase as the source is used as input for longterm and farfield environmental impact calculations.

9  20160301  dr. ir. Werner M.J. Lazeroms IMAU / Utrecht University  Describing subgridscale processes in geophysical models with focus on atmospheric turbulence
Numerical models of weather and climate are important application areas for fluid dynamics. These models aim at describing a vast amount of physical processes on Earth and are very computationally expensive. Therefore, it is impossible to completely resolve all the processes and subgridscale models are needed in many cases. The prime example of a process that needs to be modelled is turbulence, both in the atmosphere and in the ocean, but also at engineering scales. This talk will focus on the new explicit algebraic turbulence model for stratified flows that has recently been developed at KTH in Stockholm. I briefly explain the differences between this model and the more classical eddyviscosity approach. A significant improvement is obtained when the model is tested in various test cases, e.g. turbulent channel flow and a stably stratified atmospheric boundary layer. If time allows it, I will briefly discuss ongoing modelling work in Utrecht for a different geophysical process, namely the melting of the Antarctic ice sheet by ocean circulations. 
5  20160203  dr. Giordano Lipari Watermotion  Waterbeweging  From academic knowledge to tradable knowledge  Clues from experience. Cues from fluid dynamics
Moving to a consultancy job after an extended academic experience is a change of habitat that has many dimensions. At a personal level, it requires willingness to reformulate one's own experience according to different expectations, demands and needs. At a social level, it demands the ability to articulate and embody this willingness while maintaining and accruing your expertise, lest performance outplays learning. Without pretence on general applicability, I will try to suggest some mindset adaptations and bring forth some heuristic tools that might give orientation when consultancy is the new setting where knowledge is being produced. I hope to promote the relevance of three vaguelydefined attitudes: serendipity, sagacity and integrity. I will even endeavour to instil motivation as to why scholars in fluid dynamics can use their acquaintance (wrestling?) with it to their advantage, prime a disposition to versatility and have a better grip on chances for professional development. My considerations will hint at a personal repertoire of experiences in research and consultancy. As underpinnings for the conversation, I will recall fragments of topics in environmental fluid dynamics that I happened to investigate:

45  20151102  Prof. Murray Rudman Monash University Melbourne  Turbulent Pipe Flow of nonNewtonian Fluids  Direct Numerical SImulation et al.
All of us are familiar with Newtonian fluids such as air and water  they are part of our daily life. What we may not realise is that we are also quite familiar with nonNewtonian fluids, i.e. fluids in which the ratio of fluid stress to fluid strain rate is not a constant (this ratio is normally called "viscosity"). Examples from everyday life include toothpaste, mayonnaise, shampoo, hair gel  the list is large.
While nonNewtonian fluids may often display phenomena such as viscoelasticity (i.e. "memory" effects), there is an important class of nonNewtonian fluids which are simpler. In socalled Generalised Newtonian Fluids (or GNFs) there are no elastic effects and the the fluids stress is still written as a viscosity multiplied by a fluid strain rate, however the viscosity is no longer constant. Typically it is a function of strain rate, and numerous models have been proposed to capture this physics including power law, Bingham, HerschelBulkley, Carreau, and so on. This study is motivated by an important subset of GNFs that are important to the Australian economy  mining tailings slurries.
In this talk I will describe the basics of how these slurries are created, what kind of properties they have and why their flow (usually in a pipe) is important. I describe how important rheological characterision is and how it has usually been treated quite crudely. Using Direct Numerical SImulation we investigate the turbulent flow of GNFs in an attempt to understand how and why rheological parameters such as yield stress, shear thinning/thickening modify the turbulence and consequently basic engineering quantities such as friction factor. The open questions and next steps will also be briefly mentioned.
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30  20150720  Riccardo Scatamacchia Univ. Tor Vergata, Rome  Dispersion of particles from localized sources in turbulence
We present a detailed investigation of particles relative separation in homogeneous isotropic turbulence. We use data from a 3D direct numerical simulations with 1024^3 collocation points and Re = 300 following the evolution of a large number of passive tracers and heavy inertial particles, with Stokes numbers in the range St = [0:5; 5]. Many studies have focused on the subject, including extensions to the case of particles with inertia. In particular, our simulation aims to investigate extreme events characterizing the distribution of relative dispersion in turbulent flows. To do that, we seed the flow with hundred millions of particles emitted from localized sources in time and in space. Thanks to such huge statistics, we are able to assess in a quantitative way deviations from Richardson’s prediction for tracers. Furthermore, we present the same kind of measures for heavy particles to understand how the inertia affects the pair separation statistics. 
20  20150511  Dr. Carles Panadés IMAU  THE 1:2 SPATIAL RESONANCE IN CYLINDRICAL FLOWS DRIVEN BY SIDEWALL OSCILLATIONS
Besides the per se appealing interest of the instability phenomena occurring in a periodically driven cylindrical cavity, the flow that is engendered in this system is analogous to the von Kármán vortex sheet from the point of view of the symmetries. The streamwise flow at any time is reflected respect to the mid plane after advancing half of the forcing period (spatiotemporal symmetry). Additionally, the flow is also invariant to translations and reflections in the spanwise direction (spatial symmetry). Thus, the basic flow is axisymmetri c and periodic with the sidewall oscillation. Depending on the Reynolds number and the Stokes number, which are proportional to the amplitude and frequency of the forcing respectively, the spatial symmetry is broken via different Fourier modes, resulting in various threedimensional states. Furthermore, several c odimension2 points, where two different modes are unstable at the same time, have been found. The dynamics around one of these points (C1) have been studied, yielding a wide variety of possible states. In C 
14  20150331  Henk Schuttelaars TU Delft  
 
9  20150223  Andrea Cimatoribus NIOZ  Statistics of temperature from high resolution ocean measurements.
Thermistors with high precision and high sampling rate have been developed at NIOZ over the last decade. These autonomous instruments can be deployed for several months on moorings in the deep, open ocean. The high resolution datasets produced by these instruments provide a unique view on turbulence and internal waves in the open and deep ocean. I will discuss in particular the results from a mooring approximately 100m tall, with 144 thermistors, deployed above the slopes of a seamount in the North Eastern Atlantic Ocean. Turbulence at this location is strongly affected by the semidiurnal tidal wave. The statistics of temperature fluctuations and temperature increments obtained from observations are compared with those measured in the laboratory and available in the literature. In particular, we try to asses the passive/active nature of the scalar, characterising intermittency in this strongly stratified environment. 
7  20150211  Martijn van Rijsbergen MARIN  Microscale challenges in cavitation research
Although cavitation inception (the start of evaporation of a liquid by a decrease in pressure) has been studied for several decades, the exact working mechanism of sheet cavitation inception is not yet understood. Highspeed microscale observations on a foil have shown that the surface characteristics of the foil play a major role in the inception process as well as the free stream nuclei. RANS simulations have shown a minimum pressure coefficient at an isolated roughness element which is 1.5 times lower than on a smooth surface. To investigate the effect of the nuclei content on cavitation on propeller models a nuclei measurement system will be developed. 
41  20141006  MarieJean Thoraval UT  Breakup of submicron air films in a liquid
We use ultrahighspeed video imaging, at framerates up to 1 million fps, to study the dynamics and breakup of submicron films of air in a liquid pool. When a drop impacts at very low impact velocities, the air under it can cushion the impact and prevent direct contact between the drop and the pool. The thin air layer under the drop is then stretched into a hemisphere and only ruptures when it becomes of the order of 100 nm thick. The breakup of this air is extremely rapid, but the highspeed imaging allows for well controlled studies of the air film puncturing and resulting entrapment of microbubbles. We discuss the possible influence of van der Waals forces in the breakup mechanism, and the similarities with dewetting patterns of a liquid film on a solid plate. 
36  20140901  Bernard J. Geurts and Rudie P.J. Kunnen UT and TU/e  Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals
The characteristics of turbulent flow in a cylindrical Rayleigh–Bénard convection cell can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by nonconstant rotation rates, a remarkably strong intensification of the heat transfer efficiency can be achieved. We consider turbulent convection at Rayleigh number Ra = 10^9 and Prandtl number = 6.4 under a harmonically varying rotation, allowing complete reversals of the direction of the externally imposed rotation in the course of time. Both slow and fast flowstructuring and heat transfer intensification are induced due to the forced flow reversals. Depending on the magnitude of the Euler force, increases in the Nusselt number of up to 400 % were observed, compared to the case of constant or no rotation. It is shown that a large thermal flow structure accumulates all along the centreline of the cylinder, which is responsible for the strongly increased heat transfer. This dynamic thermal flow structure develops quite gradually, requiring many periods of modulated flow reversals. In the course of time the Nusselt number increases in an oscillatory fashion up to a point of global instability, after which a very rapid and striking collapse of the thermal columnar structure is seen. Following such a collapse is another, quite similar episode of gradual accumulation of a next thermal column. We perform direct numerical simulation of the incompressible NavierStokes equations to study this system. Both the flow structures and the corresponding heat transfer characteristics are discussed at a range of modulation frequencies. We give an overview of typical time scales of the system response. 
28  20140707  Dr. Willem van de Water TU/e  Writing in turbulent air
When a Gaussian blob of passive scalar is released in turbulence, it will spread due to the combined action of turbulence and molecular diffusion. The question is if diffusion helps the spreading due to turbulence, or suppresses it. To answer this elementary question, we make a Gaussian blob in a turbulent flow of air by painting the molecules (which are normally blue) in a different color using strong lasers, and then see where the colored ones go. It is an example of the flow tagging technique, that needs no tracers as we use the molecules of air itself as tracers. We will see the tagging process in action, and answer the question about the joint action of dispersion and diffusion at short times. 
23  20140602  George Schramkowski and Tomas Van Oyen Flanders Hydraulics Research  Upcoming hyperturbidity reseach at FHR
This talk describes a four years research project that will start later this year. It is devoted to modeling and understanding the shift that has been observed in some estuaries from relatively low to rather high sediment concentrations (~ 1 g/l). This situation is undesired from both an economical and ecological point of view. The aim of the research is to develop a reduced mathematical model (aka idealized model) that still includes all relevant physical mechanisms but describes the abovementioned shift. Muddy problems in tidal harbors
 
9  20140226  Dr. Ton Hoitink Wageningen University  Monitoring flow, turbulence and suspended sediment concentration using coupled ADCPs
Turbulence strongly controls the exchange of momentum and suspended sediment in geophysical surface flows occurring in rivers, estuaries and in the coastal ocean. Acoustic Doppler current profilers offer a promising means of measuring turbulent quantities. We introduce a new technique to measure profiles of each term in the Reynolds stress tensor using two coupled ADCPs. The technique is based on the variance method which is extended to the case with eight acoustic beams. Using the acoustic backscatter of the ADCPs, vertical profiles of suspended sediment concentration can be obtained continuously. The covariances between radial velocities and calibrated acoustic backscatter allow the determination of the three Cartesian components of the turbulent flux of suspended sediment. The main advantage of this new approach is that flow velocity and sediment concentration measurements are exactly collocated, and allowing for profiling over long ranges. Results show that vertical profiles of the inverse turbulent PrandtlSchmidt number are coherent with corresponding profiles of the sediment diffusivity, rather than with profiles of the eddy viscosity. 
8  20140219  Prof. Dr. ir. GertJan van Heijst TU/e  When Waves collide, an experimental investigation of people waves in a football stadium
 
6  20140205  Dr. Hanneke Gelderblom Physics of Fluids, University of Twente  Drop deformation and fragmentation by laser impact
In Extreme Ultraviolet (EUV) lithography EUV light is generated by hitting liquid tin drops with a pulsed laser. The laserdrop interaction results in a strong pressure pulse exerted on the drop. As a consequence, the drop is propelled in horizontal direction and deforms into a thin sheet which expands, becomes unstable and eventually fragments into tiny droplets. To study this process, we perform experiments with both liquid tin and water drops that are hit by a 10ns laser pulse. The drop deformation and displacement are captured by two CCD cameras with stroboscopic illumination. From these images, we extract the drop shape, velocity and fragmentation moment. In addition, we develop a theoretical model to characterize the drop deformation and fragmentation in terms of the laser energy, pulse duration, liquid properties and initial drop size. 
Show previous talks.  
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23  20130605  Dr. Jan ten Thije Boonkkamp (TU/e)  Complete flux schemes for advectiondiffusionreaction problems
Conservation laws of advectiondiffusionreaction type are ubiquitous in continuum physics, describing the interplay between different processes such as advection or drift, diffusion or conduction and chemical reactions or ionization. They occur in disciplines like fluid mechanics, combustion theory, plasma physics, semiconductor physics etc. Complete flux schemes are are finite volume discretizations for these equations. The key idea is to determine the numerical flux from a local boundary value problem for the entire equation, including the source term. This implies that the numerical flux is the sum of a homogeneous and an inhomogeneous flux, corresponding to the advectiondiffusion operator and the source term, respectively. I will present the derivation for a stationary, onedimensional model problem, and present extensions to timedependent equations and (coupled) systems of equations. The performance of the schemes is demonstrated for several test problems. 
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46  20131113  Dr. ir. Johan Padding TU/e  Direct Simulation Monte Carlo of particles and droplets in a spray drying device
Spray drying is used to convert liquid feed materials into a dry powder form, e.g. to produce milk powder. The liquid feed is sprayed through high pressure nozzles in a spray chamber and the resulting droplets are mixed with hot gas to evaporate the liquid content. At the Multiphase Modeling of Multiphase Flow group, we are developing a simulation tool that can predict the droplet and particle flow, agglomeration, and size distribution for a section of a largescale spray dryer, with full twoway coupling between the droplets/particles and the gas. To be able to handle many billions of droplets and particles, we have adapted a direct simulation monte carlo method, in which droplets and particles (1) are represented by a much lower number of simulated particles and (2) collide stochastically according to predictions from kinetic theory. I will show some encouraging preliminary results 
43  20131023  Dr. Evgeny Asmolov (MSU)  Effective slip lengths of superhydrophobic surfaces.
Laminar shear flows over smooth anisotropic surfaces with arbitrary scalar slip, varying in only one direction, are studied. General expressions for eigenvalues of the effective sliplength tensor are derived. The flow along any direction of 1D surface can be easily determined, once the longitudinal component of the effective slip tensor is found. The expression for eigenvalues is verified for various textures (stripes, cosine, trapezoidal, triangular) using different methods (Fourier series, LBM, DPD). Large effective slip is obtained for profiles of local slip length with wide base and small noslip region. Velocity gradient and pressure are singular near the edge of noslip and partial slip regions. 
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19  20130508  Dr. Peichun Amy Tsai (UT)  Controlling Splashing and Slippage on Superhydrophobic Surfaces
In this talk, I will demonstrate how to modify surfaces to alter bulk flow using hydrophobic microstructures. The waxlike microtextures display superhydrophobicity, yielding a large static contact angle of water droplet with a low contact angle hysteresis. Two dynamical scenarios: drop impact and laminar flow on superhydrophobic surface, will be presented. At a high impact velocity splashing of water droplet can occur, emitting secondary droplets. Moreover, the splashing dynamics is strongly influenced by the micropatterns of the substrate. In microfluidic laminar flow, the geometry of the liquidgas interface affects slippage, i.e. drag reduction, using hydrophobic microstructures. We found that air and air flow play an important role in these two scenarios, revealing the importance of developing an active control of the gasliquid interface at the flow boundary. 
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14  20130403  Prof. Dr. Ir. Mico Hirschberg (TU/e)  We Whistle While We Work 
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10  20130306  Dr. Roger Jaspers (TU/e)  Flows in Fusion
To tame a hot plasma in a fusion reactor is quite a challenge, which keeps the fusion community busy already for several decades. The progress in understanding has culminated in the design of ITER, the first fusion reactor which will produce 500 MW of fusion power for an input of 50 MW of heating power. The demonstration of this will be a tremendous success, but even then a demonstration fusion power reactor is still a step away. ITER is big, inefficient, prone to instabilities and the huge heat fluxes arriving at the reactor wall causes a serious headache for the engineers. Are flows the solution to these issues?

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8  20130220  Dr. Ir. Jasper van der Gucht (WUR)  Spherical colloids on an interface with anisotropic curvature: ordering driven by capillarity
Objects floating at a liquid interface, such as breakfast cereals floating in a bowl of milk or bubbles at the surface of a soft drink, clump together as a result of capillary attraction. This attraction arises from deformation of the liquid interface due to gravitational forces; these deformations cause excess surface area that can be reduced if the particles move closer together. For micrometersized colloids, however, the gravitational force is too small to produce significant interfacial deformations, so that capillary forces between spherical colloids at a flat interface are negligible. Here, we show that this is different when the confining liquid interface has a finite curvature which is also anisotropic. In that case, the condition of constant contact angle along the threephase contact line can only be satisfied when the interface is deformed. We present experiments and numerical calculations that demonstrate how this leads to quadrupolar capillary interactions between the particles, giving rise to organization into regular square lattices. 
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6  20130206  Prof. Bendiks Jan Boersma (TUD)  Very large scale motion in turbulent pipe flows at moderate Reynolds numbers
Large scale meandering structures have been observed in turbulent boundary layers and channel flows. They are also experimentally observed in pipe flows however two point correlations indicate that these structures are considerably longer in pipes than in channels. Hutchins & Marusic (2007) argue that these large scale structures can penetrate into the near wall layer and can make a significant contribution to the kinetic energy in this layer, even down to D/2  r = 15v/u*, (where u* is the friction velocity, D the pipe diameter and v the kinematic viscosity). This is the location where in general the peak of the turbulent kinetic energy is observed. This statement is consistent with the attachededdy hypothesis of Townsend (1976). Therefore, it could thus be argued that the long meandering structures could have some influence on the peak value of the axial rms. 
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3  20130116  Dr. Chao Sun (UT)  Highly Turbulent TaylorCouette Flow
Strongly turbulent TaylorCouette flow with independently rotating inner and outer cylinder with a radius ratio of η = 0.716 is experimentally analyzed. From global torque measurements, the maximum in the angular velocity transport from the inner to the outer cylinder is found at slight counterrotation, namely at an angular velocity ratio of a_{opt} =  (ω_{o}/ω_{i})_{opt} ~ 0.33. With the help of laser Doppler anemometry, we in addition provide angular velocity profiles. The ratio a_{opt} ~ 0.33 is distinguished by zero angular velocity gradient in the bulk. For stronger counterrotation ω_{o} > 0.33 ω_{i} the probability distribution function of the bulk angular velocity becomes bimodal, reflecting intermittent bursts of turbulent structures beyond the neutral line into the outer flow domain, which otherwise is stabilized by the counterrotating outer cylinder. In addition, I will also discuss the measurements of local angular velocity flux, boundary layer properties, and statics of turbulent fluctuations. 
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51  20121219  Prof. Luca Biferale (Department of Physics University of Rome 'Tor Vergata') 
Inverse and Direct cascades in turbulence, revisited
By performing numerical investigations of NavierStokes (NS) equations decimated on a HelicalFourier basis we show that all 3D flows in nature possess a subset of nonlinear evolution leading to a reverse energy transfer : from small to large scales. Up to now, such inverse cascade was only observed in flows under strong rotation and in quasi twodimensional geometries. We show here that the energy flux is always reversed when the mirror symmetry is broken, leading to a distribution of helicity in the system with a definite sign at all wavenumbers. Our findings broaden the range of flows where an inverse energy cascade may be detected and rationalize the role played by helicity in the energy transfer process, showing that both 2D and 3D properties naturally coexist in all flows in nature. The numerical methodology here proposed is based on a Galerkin projection of the NSdynamics on a given class of HelicalFourier modes. Discussion about how to apply it to study the influence of helicity on smallscales intermittency, to investigate the regularity properties of NavierStokes solutions and to improve subgridscale models for LargeEddySimulations will be presented. Finally, it may play a key role also to understand the role of the three inviscid invariants in magnetohydrodynamics. 
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47  RESCHEDULED 20121121  Prof. Bendiks Jan Boersma (TUD)  Very large scale motion in turbulent pipe flows at moderate Reynolds numbers
Large scale meandering structures have been observed in turbulent boundary layers and channel flows. They are also experimentally observed in pipe flows however two point correlations indicate that these structures are considerably longer in pipes than in channels. Hutchins & Marusic (2007) argue that these large scale structures can penetrate into the near wall layer and can make a significant contribution to the kinetic energy in this layer, even down to D/2  r = 15v/u*, (where u* is the friction velocity, D the pipe diameter and v the kinematic viscosity). This is the location where in general the peak of the turbulent kinetic energy is observed. This statement is consistent with the attachededdy hypothesis of Townsend (1976). Therefore, it could thus be argued that the long meandering structures could have some influence on the peak value of the axial rms. 
46  RESCHEDULED 20121114  Dr. Roger Jaspers (TU/e)  Flows in Fusion
To tame a hot plasma in a fusion reactor is quite a challenge, which keeps the fusion community busy already for several decades. The progress in understanding has culminated in the design of ITER, the first fusion reactor which will produce 500 MW of fusion power for an input of 50 MW of heating power. The demonstration of this will be a tremendous success, but even then a demonstration fusion power reactor is still a step away. ITER is big, inefficient, prone to instabilities and the huge heat fluxes arriving at the reactor wall causes a serious headache for the engineers. Are flows the solution to these issues?

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44  20121031  Dr. Steffen Berg (Shell Global Solutions International B.V.)  Multiphase flow in Porous Media at the Pore Scale  A microCT study
Fluid flow in porous media is commonly encountered in natural and technological processes. Examples are the carbon and nutrient cycling in the critical zone, the spread and longterm fate of sequestered carbon dioxide, the mobilization of trapped hydrocarbon phases in enhanced oil recovery in sedimnatary rocks, drying processes and the mass transfer in porous catalysts and membranebased fuel cells. These examples are of particular complexity problems involving nonsteady flow of multiple immiscible phases in porous structures. Commonly used approaches to model macroscopic fluid behavior are phenomenological, have many shortcomings and lacks a consistent link to elementary porescale displacement processes commonly called Haines jumps. New development of highspeed, synchrotronbased Xray computed microtomography enabled us to directly image for the first time the Haines jumps in porous rock at realtime. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found Haines jumps cascading typically through 1020 geometrically defined pores per event, accounting for 64% of the energy dissipation. Realtime imaging opens the path for a more detailed fundamental understanding of elementary process in porous media such as hysteresis, snapoff and nonwetting phase entrapment by a rigorous process upscaling on a thermodynamic model basis. 
43  20121024  Dr. Francesco Picano (KTH Royal Institute of Technology)  Transport phenomena in wall bounded particleladen flows
Understanding the transport properties of suspensions is crucial both for theoretical and applied contexts. The mutual interaction between the dispersed solid phase and the carrier fluid leads to several peculiar aspects concerning mass and momentum transport, e.g. turbophoresis, smallscale clustering or suspension effective viscosity. Volume fraction and inertia control the coupling mechanisms between the phases leading to different regimes and phenomenologies. In the present work, data from direct numerical simulations are analyzed to investigate suspensions both in the dilute and dense case. The effects of wall turbulence on the particle transport will be discussed in the dilute regime, while the influence of the solid particulate phase on the carrier fluid will be presented in the dense regime. 
42  20121017  Dr. Johannes Bleibel (Max Planck Institute for Intelligent Systems)  Cosmology in a petri dish? Simulation of collective dynamics of colloids at fluid interfaces
Interfacially trapped, micrometersized colloidal particles interact via longranged capillary attraction which is analogous to twodimensional screened Newtonian gravity with the capillary length l as the tuneable screening length. Using Brownian dynamics simulations, density functional theory, and analytical perturbation theory, we study the dynamics of an initially prepared distribution of colloids, either a random homogeneous distribution, or a finitelysized patch of colloids. Whereas the limit l → ∞ corresponds to the global collapse of a selfgravitating fluid, for smaller l the dynamics crosses over to spinodal decomposition showing a coarsening of regions of enhanced density which emerge from initial fluctuations [1,2]. For the finite patch of colloids and intermediate l we predict theoretically and observe in simulations a ringlike density peak at the outer rim of the disclike patch, moving as an inbound shock wave [1]. Experimental realizations of this crossover scenario appear to be well possible for colloids trapped at water interfaces and having a radius of around 10 micrometer [3]. Finally, the influence of hydrodynamic interactions on this capillary collapse will be discussed.

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40  20121003  Dr. Markus Rauscher (Max Planck Institute for Intelligent Systems)  Dynamics of thin liquid films: slip, viscoelasticity, and thermal fluctuations
We study the dewetting dynamics of thin liquid films. In particular, we use a mesoscopic approach, augmenting macroscopic hydrodynamic equations by taking into account hydrodynamic slip, the substrate potential (van der Waals forces), and thermal fluctuations. After a brief introduction in the topic of dewetting of nonvolative fluid films, we discuss the role of thermal fluctuations in spinodal dewetting and show clear experimental evidence for them. The second part of the talk is dedicated to the interplay of slip and viscoelasticity in dewetting films and the resulting dewetting patterns. In particular we show that the shape of the rim around holes in dewetting films is mostly determined by slip and not by viscoelasticity. In addition, we use the shape analysis to measure the slip length. 
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38  20120919  Dr. Jacco Snoeijer (UT)  Symmetric and asymmetric coalescence of drops on a substrate
The coalescence of viscous drops on a substrate is studied experimentally and theoretically. We consider cases where the drops can have different contact angles, leading to a very asymmetric coalescence process. Side view experiments reveal that the "bridge" connecting the drops evolves with selfsimilar dynamics, providing a new perspective on the coalescence of sessile drops. We show that the universal shape of the bridge is accurately described by similarity solutions of the onedimensional lubrication equation. Our theory predicts a bridge that grows linearly in time and stresses the strong dependence on the contact angles. Without any adjustable parameters, we find quantitative agreement with all experimental observations. 
37  20120912  Dr. Luis Portela (TUD)  ParticleDriven Secondary Flow in Turbulent Pipe Flows
In fullydeveloped singlephase turbulent flow in straight pipes, it is know that mean motions can occur in the plane of the pipe crosssection, when the crosssection is noncircular, or when the wall roughness is nonuniform around the circumference of a circular pipe. This phenomenon is known as secondary flow of the second kind and is associated with the anisotropy in the Reynolds stress tensor in the pipe crosssection. In this presentation, we show that in a turbulent particleladen turbulent flow the particles can also induce a secondary flow of the second kind. The forcing of the flow by the particles can lead to large changes in the turbulence. Therefore, a nonuniform particle distribution (e.g. in a horizontal pipe) can promote a nonuniform modification of the turbulence and lead to an anisotropy in the Reynolds stresses in the crosssection. Hence, a nonuniform particle distribution can induce a secondary flow of the second kind. We used Laser Doppler Anemometry (LDA) measurements and pointparticle Direct Numerical Simulations (DNS) to study the particledriven secondary flow in a welldefined controlled situation, keeping the particles at fixed positions, with different distributions inside the pipe. This way, any other possible effects are excluded, and the only effect that remains is the turbulence modification by the particles. We present the results from the experiments and simulations together with a theoretical analysis of how the particles promote the secondary flow. We show that the secondary flow is driven by the divergence of the Reynolds stress tensor in the crosssection and that the gradients of the radial and circumferential Reynolds stresses are the dominant terms. Our results indicate that two main mechanisms of turbulence modification determine the pattern of the Reynolds stress tensor in the crosssection, hence the pattern of the secondary flow: (i) a "blockage effect", associated with the mean particleforcing away from the wall, which reduces the Reynolds stresses in the crosssection, and (ii) a "roughness effect", associated with the mean particleforcing close to the wall, acting on the viscous stresses, which leads to an increase in the Reynolds stresses in the crosssection. Since these two mechanisms act in opposite directions, the pattern of the secondary flow will depend on the particle distribution inside the pipe. We show how these two mechanisms determine the different patterns and propose some simple scaling rules that allow us to estimate the magnitude of the secondary flow. 
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35  CANCELLED 20120829  Prof. Arakel Petrosyan (Space Research Institute of the Russian Academy of Sciences)  Research on Theoretical and Computational Fluid Dynamics at the Space Research Institute of the Russian Academy of Sciences
Review on fluid dynamics research at the Space Research Institute of the Russian Academy of Sciences will be given. This includes: inverse cascades in turbulent shear flows; large scale instabilities in helical turbulent flows in fluids with solid particles and in fluids with gas bubbles; transport of solid particles in geophysical boundary layers with obstacles; numerical and theoretical studies of shallowwater equations on complex boundaries, extensions of shallow water theory to compressible and magnetohydrodynamic flows; large eddy simulations of magnetohydrodynamic turbulence. 
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Summer break.  
26  20120627  Michel Riepen (ASML)  Thin film flow phenomena in Immersion and EUV Lithography
In this presentation, I will briefly give an introduction on the current and next generation lithography systems and the importance of a good understanding of thin film flow phenomena for this technology. Starting with Immersion lithography, where a thin layer of water is applied between the lens and the wafer to increase the imaging resolution, a number of aspects of contact line dynamics and thin film dynamics will be discussed. In the next generation lithography systems EUV light is used for the imaging process. EUV light is generated with Sn plasma and as a consequence "Tin management", i.e. the control of tin flow, deposition and drainage, is crucial for the performance of these systems. In the presentation the principle of the current EUV sources will be introduced briefly including some examples of Tin Management. 
25  20120620  Dr. Nicolae Tomozeiu (Océ)  Water evaporation from aqueous mixtures studied using optical spectroscopy
Evaporation of water is a fundamental process in many technologies for films fabrication from liquid phase. Although the water evaporation seems to be among the very basic physical phenomena, there is a lack of experimental data that could enrich our understanding of this process. Nicolae Tomozeiu, R&D Océ Technologies, PO box 101, 5900 MA, Venlo, The Netherlands 
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22  20120530  Dr. Davide Proment (Università degli Studi di Torino)  Rogue waves and statistical models for wave forecasting
In the framework of the Hamiltonian formulation, I will discuss the nonlinear dynamics of surface gravity waves. In the weakly nonlinear regime and in the narrow band approximation the evolution equation of the free surface reduces to the Nonlinear Schrodinger equation (NLS), a model widely used to explain the main mechanisms responsible for the formation of rogue waves in ocean. In particular I will discuss the modulational instability and exact breathers solutions of the NLS. The effect of the current will also be considered. Based on the wave turbulence theory, I will also discuss the statistical properties of the waves and present the Hasselmann energy balance model, a kinetic equation which is the base of the operational wave forecasting models. 
21  20120523  Prof. Dr. Ir. Michiel Kreutzer (TUD)  Droplet Microfluidics
In this talk, I will discuss our work on droplet and bubbles in microchannels, motivated by the use of droplets in labonchip applications. Topics include droplet formation and breakup, and the droplet physics of complex fluids. 
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19  20120509  Prof. Dr. Federico Toschi (TU/e)  Inverse Energy Cascade in ThreeDimensional Isotropic Turbulence
We study the statistical properties of homogeneous and isotropic threedimensional (3D) turbulent flows. By introducing a novel way to make numerical investigations of NavierStokes equations, we show that all 3D flows in nature possess a subset of nonlinear evolution leading to a reverse energy transfer: from small to large scales. Up to now, such an inverse cascade was only observed in flows under strong rotation and in quasitwodimensional geometries under strong confinement. We show here that energy flux is always reversed when mirror symmetry is broken, leading to a distribution of helicity in the system with a welldefined sign at all wave numbers. Our findings broaden the range of flows where the inverse energy cascade may be detected and rationalize the role played by helicity in the energy transfer process, showing that both 2D and 3D properties naturally coexist in all flows in nature. The unconventional numerical methodology here proposed, based on a Galerkin decimation of helical Fourier modes, paves the road for future studies on the influence of helicity on smallscale intermittency and the nature of the nonlinear interaction in magnetohydrodynamics. 
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17  20120425  Dr. Peter Schall (UvA)  Strong correlations in soft glasses: New criticality in material flow?
Soft materials such as suspensions and pastes show remarkable mechanical properties: they can be rigid when confined at high density (sand castle), but can flow easily when small stresses are applied (hour glass). This transition from rigidity to flow is central to phenomena in geology, and important for food and cosmetic products. We investigate the role of correlations in this transition. By using transparent colloidal and granular model systems we obtain direct microscopic images of flow and arrest: In three dimensions and real time, we track the motion of the individual particles, and we visualize correlations in the affine and nonaffine particle displacements. At the transition from rigidity to flow, shear is neither macroscopically uniform nor strongly localized: We observe systemspanning strain correlations that reveal a novel form of mechanical criticality. While our model systems allow direct imaging of these critical strain fluctuations, we expect very similar mechanisms to hold for other soft materials as well as atomic and molecular glasses. 
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14  20120404  Dr. Ir. Arthur de Jong (TU/e  MBx group)  Magnetic particle based capturing and detection for sensitive immunoassays
Assay technologies capable of detecting minute concentrations of biomolecules are crucial for discoveries in biological research and applications in medical diagnostics. In general high detection sensitivity is achieved by using multiple reaction steps; e.g. dilution, affinity capture, washing, labeling and amplification. This results in long and laborious processes and the deployment in labonchip devices is very complicated. A challenge in bioanalytical science is to detect low biomarker concentrations in complex biological matrices, without separation or fluid manipulation steps. The research in our group aims at the development of new technologies for transport and detection of biomolecules by using magnetic microparticles with an applicability in small fluidic devices. I will present the latest developments in this field. 
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12  20120321  Prof. Dr. Ir. Boudewijn Lelieveldt (TUD / LUMC) 
Magnetic resonance imaging (MRI) allows acquisition of three dimensional (3D) image volumes with encoding of blood flow or tissue velocities in three orthogonal directions throughout the cardiac cycle. When applied to the heart, this MRI technique (4D VENC MRI) can be used to depict the blood flow through all the cardiac valves simultaneously, making it a highly promising tool to assess valvular disease. In addition, 4D VENC MRI enables the visualization of the 3D timevarying intracardiac blood flow providing relevant diagnostic information on underlying cardiac pathologies such as heart failure and. However, the clinical usage of 4D VENC MRI to asses valvular and intracardiac flow abnormalities in one scan is hampered by the amount and complexity of the data per patient study (5,00010,000 images). To make 4D VENC MRI suitable for clinical application, dedicated image analysis techniques need to be developed for feature extraction, quantification and visualization that enable a timeefficient and intuitive analysis of the enormously large image data sets. In this presentation, novel image processing and visualization methods will be discussed for extraction of clinically relevant information on valve and intracardiac flow patterns, with a specific focus on vortex formation in the heart chambers and around the valves, and on flow through the valves. 
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10  20120307  Prof. Dr. Fulvio Scarano (TUD)  On the use of Tomographic PIV for the investigation of vortex dynamics and jet aeroacoustics
The talk covers the fundamental aspects of Tomographic Particle Image Velocimetry and its application for the study of the dynamical evolution of threedymensional turbulent structures. The transition from axisimmetric to threedimensional regime in circular jets is explored by timeresolved measurements where the phenomenon of vortex pairing and the growth of azimuthal instabilities dominates the transition scenario. Comparatively, the jet with chevron exit exhibits axial vortices later undergoing transition and forming Cshaped structures contouring the jet core. The experimental data offers the possibility to study both vortex dynamics (stretching and tilting) as well as some properties associated to sound production. The Lamb vector and its second temporal derivative are dynamically mapped and put in relation to the largescale coherent structures dominating the transition. Other relevant examples taken from wallbounded turbulence and separated flows will be illustrated and discussed that show the current state of technology for 3D flow diagnostics by PIV. 
9  20120229  Prof. Dr. Philip de Goey (TU/e)  Modeling turbulent combustion with Flamelet Generated Manifolds
Turbulent combustion processes can be characterized as chemicallyreacting flows where hundreds of chemical reactions take place in extremely thin reaction fronts, wrinkled and moved around by the vortical structures in the turbulent flow. Modeling such processes with DNS, LES or RANS models is extremely expensive. To reduce costs, chemical reduction techniques are used involving only a few key processes, while accuracy is maintained. One such method, referred to as Flamelet Generated Manifolds method is developed and validated stepbystep. Backgrounds, model development, validation and application of the model to a various set of problems is presented. 
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7  20120215  Dr. Hans Wyss (TU/e)  Relaxation and Flow of Soft Colloids
Suspensions of soft, deformable and compressible particles exhibit dynamics and flow behavior that is qualitatively different from that observed for hard particles. A wide range of materials including foods, creams and biological systems contain such soft particles. Nevertheless, their behavior remains poorly understood. As a basis for understanding this behavior, it is important to first quantify the properties of the particles themselves. I will give a short overview of methods used to experimentally access the elastic properties of single soft particles, focusing on a new method, Capillary Micromechanics [1], that we have recently introduced. It enables us to access both the elastic shear modulus as well as the elastic compressive modulus of a single soft particle. I will further illustrate the importance of particle softness by discussing the use of soft particle suspensions as model glass formers. Colloidal particles have been widely employed as models for understanding glass formation; their behavior is surprisingly similar to that found for molecular glass formers. However, for different molecular glassforming liquids, the dynamic behavior upon approach to the glass transition shows broad variations. These variations can be described by the socalled fragility, which describes the sensitivity of their viscosity or structural relaxation time on temperature as the glassy state is approached. In hardsphere colloids only highly fragile behavior has been observed. By using soft, deformable particles we have extend the concept of fragility to colloidal soft materials and captured the entire range of dynamic behaviors merely by varying the softness of the individual mesoscopic particles. Hard particles make "fragile" glasses and soft particles make nonfragile, or "strong", glasses [2]. Further reading:

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Due to a busy schedule, no Fluid Dynamics seminars are held in January 2012.  
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50  20111214  Dr. Ir. Henk Huinink (TU/e)  Water migration through multilayered polymeric films
Polymeric layers are used to protect objects against degradation and improve their appearance. Since water plays a key role in the degradation of many substrates, such polymeric coatings have to form a barrier for water migration. In automotive and aerospace applications multilayered coatings are used to meet all requirements. Understanding the sorption kinetics of water in such multilayered structures helps to develop new coatings with better protective properties. In this lecture it will be discussed how NMR imaging is used to visualize the time evolution of water distributions on a micrometer scale. It will be shown how a combination of NMR imaging and relaxometry gives insight in the nature of the polymerwater interaction, which helps to understand the cause of water sorption. A simple model with the sorption isotherm as key ingredient is formulated that elucidates why water uptake and drying occurs on completely different timescales. Finally, the response of multilayered coatings on humidity fluctuations is predicted with the help of this model, and it is demonstrated that accelerated testing procedures as used in the coating industry can lead to erroneous results. 
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48  20111130  Dr. Ir. Christian Poelma (TUD)  Insight into the developing vitelline network with microPIV measurements
Fluid dynamics plays a critical role in the development of vascular networks, so quantitative information about e.g. wall shear stress, flow rates and velocity profiles is essential for a better understanding. During several developmental stages, subsequent measurements are performed of the network topology and velocity field using microPIV. The vitelline network (extraembryonic vessels) of a chicken embryo is used as a model for investigation of human vascular development. 
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46  20111116  Prof. Dr. Ir. Hans Kuipers (TU/e)  MultiScale Modeling of Dense ParticleLaden Flows
Dense gasparticle flows are encountered in a variety of industrially important processes for large scale production of fuels, fertilizers and base chemicals. The scaleup of these processes is often problematic, which can be related to the intrinsic complexities of these flows which are unfortunately not yet fully understood despite significant efforts made in both academic and industrial research laboratories. In dense gasparticle flows both (effective) fluidparticle and (dissipative) particleparticle interactions need to be accounted for because these phenomena to a large extent govern the prevailing flow phenomena, i.e. the formation and evolution of heterogeneous structures. These structures have significant impact on the quality of the gassolid contact and as a direct consequence thereof strongly affect the performance of the process. Due to the inherent complexity of dense gasparticles flows the authors have adopted a multiscale modeling approach in which both fluidparticle and particleparticle interactions can be properly accounted for. The idea is essentially that fundamental models, taking into account the relevant details of fluidparticle (lattice Boltzmann model) and particleparticle (discrete particle model) interactions, are used to develop closure laws to feed continuum models which can be used to compute the flow structures on a much larger (industrial) scale. Our multiscale approach (see figure below) involves the lattice Boltzmann model, the discrete particle model and the continuum model based on the kinetic theory of granular flow. In this presentation the multiscale modeling strategy for dense gasparticle flows will be presented together with illustrative computational results. In addition, areas which need substantial further attention will be highlighted. 
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44  20111102 in CC 2.10  Dr. Brock Mosovsky (University of Colorado, Boulder, USA)  Transport in Transitory Dynamical Systems
Recent years have witnessed a concerted effort by the dynamical systems community to develop new techniques for identifying structures in aperiodic timedependent flows that remain coherent in the Lagrangian sense over some finite time horizon. These coherent structures may persist only for finite time, making them inherently tied to the dynamical timescales of the flow and rendering a rigorous quantification of transport between them quite difficult. In this talk, we consider transitory systems  those that exhibit time dependence only on a compact interval in time  and present a new method for quantifying transport between pre and posttransition coherent structures in the case of exact volumepreserving flows. As examples, we consider a 2D rotating double gyre model and a 3D kinematic model of a spherical droplet in a serpentine microchannel. We present quantitative results for the transport between coherent structures in each case. These results are joint work with Dr. James D. Meiss at the University of Colorado, Boulder, USA. 
43  20111026  Prof. Dr. Hans Kuerten (TU/e)  Heat transfer enhancement by inertial particles in turbulent channel flow
Recent experimental data shows that the thermal conductivity of nanofluids increases with increasing particle size. Enhanced thermal conductivity for particle sizes up to 0.3 μm was measured. We investigated by means of direct numerical simulation of particleladen nonisothermal turbulent channel flow whether the heat transfer augmentation observed for these small particles continues to considerably larger particles with diameters in the millimeter range. The results of the simulations show an enhancement of the heat transfer when heavy inertial particles with high specific heat capacity are added to the flow. The simulations employ a coupled EulerianLagrangian computational model in which the momentum and energy transfer between the discrete particles and the continuous fluid phase are fully taken into account. The effect of turbophoresis, resulting in an increased particle concentration near a solid wall due to the inhomogeneity of the wallnormal velocity fluctuations, is shown to be responsible for an increase in heat transfer. As a result of turbophoresis the effective macroscopic transport properties in the region near the walls differ from those in the bulk of the flow. To support the turbophoresis interpretation of the enhanced heat transfer, results of simulations employing no particlefluid coupling and simulations with twoway coupling at considerably lower specific heat, or considerably lower particle concentration are also included. The combination of these simulations allows distinguishing contributions to the Nusselt number due to mean flow, turbulent fluctuations and explicit particle effects. 
42  20111019  Prof. Dr. Ir. Harald van Brummelen (TU/e)  Goaladaptive methods for multiscale flow problems
Adaptive finiteelement methods based on goaloriented aposteriori error estimates provide a very powerful paradigm for approximating goal functionals (observables) of flow problems that exhibit multiple scales, e.g., transitional molecular/continuum flows and coupled problems such as fluidstructure interaction. Based on the solution of a suitable dual problem, the contribution of local errors in the solution to the error in the goal functional is estimated, and only the regions that yield a dominant contribution are refined. In such a manner, a computational model is generated, that provides an optimal approximation to the goal functional. In this presentation, I will discuss the basics of goaloriented error estimation and goaladaptive refinement. Next, I will present applications of the methodology to a prototype Boltzmann equation and to fluidstructure interaction. Numerical results are presented for both these applications. Further reading:

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38  20110921  Dr. Herman Wijshoff (Océ)  "Drop formation and substrate interaction in inkjet printing"
Inkjet technology has evolved into a technology which plays an important role in the graphical printing industry and in many emerging new industrial and medical applications. To comply with the increasing and diverging requirements for today's inkjet technology, a fundamental understanding of the underlying processes is very important. The physics behind the chain of processes comprise the twoway coupling from the electrical to the mechanical domain through the piezo electric actuator, the coupling to the acoustic domain inside the ink channels, and the coupling to the fluid dynamic domain, i.e. the drop formation process. The presentation will focus on the last stage of the printing process, i.e. the formation, flight, impact, spreading, absorption, and solidification of the drops. Stateoftheart experimental techniques, numerical models and theoretical frameworks will be discussed. 
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36  20110907  Prof. Dr. Ir. Jaap den Toonder (Philips / TU/e)  "Microfluidics"
Microfluidics is the science and technology of the manipulation and analysis of fluids at small scales  typically smaller than a mm. Microfluidics enables to miniaturize and integrate fluidic processes while achieving ultimate control over these processes. A main application is in medical diagnosis; the ultimate vision is that processes needed for medical diagnosis, for example DNA analysis, could be integrated on a single microfluidic chip in which the biofluid to be analyzed is flown through microchannels and chambers  the lab on a chip. In this lecture I will start by addressing the general characteristics of microfluidics and point out the specific scale effects that enable effects not possible at larger scales. Then I will briefly show some examples of microfluidicbased products being developed at Philips  a DNA analysis platform, a handheld immunoassay platform and blood cell count device. Finally, I will show our work at TU/e and Philips aimed at developing approaches for next generations of microfluidics devices. I will put specific emphasis on a new fluidic actuation method inspired by nature  artificial cilia. 
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34  20110824  Prof. Dr. Xisheng Luo (University of Science and Technology of China)  "On shockbubble interaction: experiment and simulation"
The interaction of a planar shock wave with a spherical gas bubble (SF6 or helium) surrounded by air is studied experimentally and numerically. By means of the highspeed schlieren photography with high time resolutions and the numerical method VAS2D, the detailed flow field structures including the evolution of bubble and the development of wave patterns are obtained. The sequences of schlieren frames of SF6 show that the refracted shock wave converges inside the volume and causes the shock focusing within the bubble interface, resulting in an outward jet. The pressure perturbation plays an important role in the jet formation. Quantitative data of the evolving interface length, height, and vortex spacing as well as the displacements of the interface and the jet are acquired and compared. The generation and distribution of vorticity are also analyzed numerically and are found to be the dominant factors for the interface deformation and the resulting turbulent mixing. The evolution of a spherical gas interface under reshock conditions is then experimentally studied. Distinct flow structures are observed due to the additional vorticity and wave configuration caused by the reshock. In the air/helium case, the deformation of the reshocked bubble depends on the development of the penetrating air jet along the symmetry axis of the bubble. In general two separate vortex rings can be observed, i.e. one develops slowly, and the other approaches and eventually impinges on the shock tube end wall. In the air/SF6 case, two SF6 jets moving in opposite directions are generated and the oscillation of the interface is observed for small end wall distances, while small scale vortex morphologies on the gas interface are found for large end wall distances. The physical mechanisms of the baroclinic vorticity generation and the pressure perturbation are highlighted in the interface evolution process. 
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32  20110810  Prof. Dr. Olga I. Vinogradova (A. N. Frumkin Institute of Physical Chemistry and Electrochemistry  Russian Academy of Sciences)  "Superhydrophobic textures for microand nanofluidics"
The hydrodynamic slippage at a solidliquid interface is currently at the center of our understanding of fluid mechanics. For hundreds of years this science has relied upon noslip boundary conditions at the solidliquid interface that has been applied successfully to model many macroscopic experiments, and the state of this interface has played a minor role in determining the flow. However, the problem is not that simple and has been revisited recently. Due to the change in the properties of the interface this classical boundary condition could be violated, leading to a hydrodynamic slip. In this talk, I highlight the impact of hydrophobicity, roughness, and especially their combination on the flow properties. In particular, I show that hydrophobic slippage can be dramatically affected by the presence of roughness, by inducing novel hydrodynamic phenomena, such as giant interfacial slip, superfluidity, mixing, low hydrodynamic drag, and more. 
Summer break.  
26  20110629  Prof. Christos Vassilicos (Imperial College London)  "Turbulence without RichardsonKolmogorov cascade"
Wind tunnel evidence will be presented suggesting that turbulence can exist which is fully developed but where the RichardsonKolmogorov cascade is nevertheless suppressed. 
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24  20110615  Dr. Ir. Arjen Bogaerds (TU/e)  "Flow instabilities in polymer processing"
Polymeric flow instabilities, or melt flow instabilities, are the typical bottleneck that puts constraints on the production rate of, almost all, processing techniques. Characteristic for these processing flows are that inertial effects are normally quite small and that the occurrence of transient flow phenomena are generally driven by the generation of normal stresses (or discontinuities thereof) inside the polymeric fluid. In this talk two examples that are of direct practical interest, including their possible analysis, will be addressed. 
23  20110608  Tim Laagland Marijn Nijssen Sander Schreven Roald van der Vliet (InnoSportLab)  "Drag and propulsion in swimming" 
22  20110601  Dr. Ir. Patrick Anderson (TU/e)  "Drops, pairs and trains in confinement"
An important microfluidic application consist in the generation of a regular array of monodisperse drops, for example by the use of Tjunctions or flowfocusing devices, for drug delivery purposes. In this presentation, we focus on the pairing and collective dynamics of these trains of drops, and in particular on the influence of the deformability of the dispersed phase, by comparing trains of solid particles and trains of drops. Two different numerical methods are employed: boundary integrals for drops and Stokesiandynamics techniques for solid particles. Results show that isolated pairs of drops undergo pairing, while isolated pairs of rigid spheres do not cluster. By contrast, confined linear arrays of particles and drops always undergo pairing regardless of deformability. Depending on the deformability and the initial separation between the drops, the initial dynamics of the pairing behavior can be quite complex. At prolonged time scales, all drop pairs reach the same velocity, while particle pairs migrate at a different velocity due to different intraparticle distances. In addition, the response of linear arrays to particle displacements shows a qualitative dependence on deformability. 
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20  20110518  Dr. Nico Dam (TU/e)  "Laser diagnostics of combustion phenomena"
Combustion is a challenge for those who seek detail in complexity. Every combustion phenomenon is an interplay between complex chemistry, fluid flow and diffusion, each driving the others and being driven by them. Efforts to describe combustion are largely numerical, aided by experiments. In my talk I will focus on the latter, providing some examples of laser spectroscopic research on transient combustion products. 
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18  20110504  Prof. Dr. Ir. Frans van de Vosse (TU/e)  "Cardiovascular Fluid Structure Interaction"
Mathematical models of the mechanical properties of the cardiovascular system play an increasingly important role in the diagnostics and treatment of cardiovascular disease and, in addition, can provide valuable information to pathological studies aiming to understand the genesis of cardiovascular disorders like atherosclerosis, heart failure and heart valve deficiency. Biomechanics of the cardiovascular system is characterized by the interaction of blood flow with surrounding structures, like the vessel wall and the heart muscle, and immersed structures like heart valves and medical devices. In the presentation, several aspects of this fluid structure interaction, and especially the complexity of the structures involved, will be addressed. Examples of the use of arbitrary EulerLagrange methods for the flow in the left ventricle and fictitious domain methods for heart valve dynamics will be given. Depending on the kind of analysis to be performed and the detail in information that is needed, three distinct approaches (lumpedparameter models, 1D wave propagation models, and fully 3D fluidsolid interaction models) can be used to model the mechanics of the cardiovascular system. Examples of a simple heart muscle contraction model, an arterial wave propagation model and a fully 3D model of the flow in geometrically complex arteries will be presented to elucidate the difference and the relation between the three approaches. 
17  20110427  Dr. Ir. Michel Speetjens (TU/e)  "Lagrangian transport phenomena in 3D laminar mixing flows."
Transport in 3D laminar flows is key to a wide variety of industrial fluid systems of size extending from microns to meters. Examples range from the traditional mixing and heat transfer in viscous flows via compact mixing and thermalprocessing equipment down to emerging applications in the rapidlyexpanding field of microfluidics. Central question in all cases is "How to achieve efficient mixing?". Mixing by fluid motion only forms an important subclass of laminar transport problems and is an essentially Lagrangian process. This advances a Lagrangian representation based on the properties of fluid trajectories as a natural way for its description. Continuity "organises" these trajectories into coherent structures that geometrically determine the transport properties of a given flow. The formation of such coherent structures and its impact upon 3D transport is demonstrated by way of experimentally realisable examples. 
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14  20110406  Dr. Ir. Rudie Kunnen (TU/e)  "Droplet collisions in turbulent clouds."
An unresolved question in cloud physics is the quantitative effect of turbulence on the growth of rain droplets. Especially in the size range of 1050 micrometer in radius turbulence must be accounted for. It enhances the velocity of the droplets. Furthermore, droplets are swept out of the eddies which leads to a clustering of droplets in the sheardominated spaces in between the vortical regions: preferential concentration. Both the clustering and the enhanced velocity lead to larger collision probability and a faster coagulational growth. Using a Lagrangian pointparticle model in simulations of turbulence, the socalled collision kernel is evaluated for several turbulent flows. The collision kernel predicts the collision rate of droplets of two size groups given their number densities. The collision probability is enhanced by factors up to 3.4. 
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12  20110323  Prof. David Smeulders (TU/e)  "Seismoelectric coupling: experiment and theory."
When grain surfaces of rocks and soils are in contact with a fluid electrolyte, they typically acquire a surface charge that is balanced by mobile counter ions in the fluid surrounding the grains. A compressional seismic wave will create pressure gradients on the scale of the wavelength. The resulting hydraulic flow will transport the counter ions relative to the immobile bound charge. In this way, counter ions accumulate in pressure troughs, and bound charge becomes exposed in pressure peaks, creating an electric coseismic field. We note that there is no net electric current. The electric field generated by the relative motion of the counter ions with respect to the bound charge drives a conduction current that exactly balances the hydraulic convective ion current flow. This is no longer the case for interfaces. Here an electric current imbalance is produced resulting in electromagnetic waves that can propagate freely outside the support of the pressure waves. Detection of these waves can give information on the material that is complementary to acoustic surveys. We developed an experimental setup to measure the electrokinetic conversion coefficient at an interface between water and watersaturated porous material. A comparison with theoretical results is presented in the 200800 kHz range. 
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10  20110309  Prof. Dr. Ir. Willem van de Water (TU/e)  "Blowing in the wind: Aeolian patterns."
Barchan dunes can be found in the desert under steady wind conditions. They translate in the direction of the wind while their shape remains unchanged. These remarkable natural patterns are the result of the interaction between sand and wind where the wind deposits the sand in heaps, which, in turn, change the properties of the turbulent wind. These crescentshaped dunes have a minimal length in the order of ten meters, which renders laboratory experiments almost impossible. Their length scale is set by the details of the sandwind interaction. In nature, smaller dunes do not evolve into the typical barchan shape. Our experimental approach produces dramatically scaled down dunes. The idea is to modulate gravity by vertical oscillation of the sand bed. Our tiny dunes travel in the turbulent boundary layer of an open windtunnel. Particle image velocimetry on their surface reveals the flux of creeping sand, while measurement of sand grains flying through the air using a high speed camera quantifies the key mechanism that moves sand by wind: saltation. We will contrast our findings with several theories that predict the shape of dunes on earth and other planets of our solar system. 
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08  20110223  Dr. Guy Metcalfe  "Laminar Transport in Chaotic Periodically Reoriented Flows."
Periodically reoriented flows (PRFs) are relatively simple to use for designing scalar and reactive transport enhancement in laminar flows. Moreover, the symmetry properties of these flows have led to the development of fast optimization methods, which are several thousand times faster than traditional optimization techniques at computing the solution to the advectiondiffusion equation over the entire space of control parameters of the flow. I will show three examples of PRFs: a flow designed for a laminar flow heat exchanger, a flow designed for extraction of mass and energy from porous media, and a flow designed for electrokinetic micromixing. 
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06  Thursday 20110210 at 14:00  Dr. Chaouqi Misbah (French National Center for Scientific Research)  "Vesicles and capsules dynamics: a route towards a bottomup approach to blood flow."
Blood is a complex fluid, and is predominantly composed by red blood cells (RBCs) that dictate its rheology. Unlike simple fluids, constitutive laws describing blood flow from a bottomup approach (i.e. by taking explicitly into account the corpuscular nature of blood in order to extract macroscopic laws) remains to be done. Since the seminal work of Poiseuille (in the 19th century) until the end of the 20th century blood flow has been described by means of phenomenological continuum models that require many assumptions which are difficult both to justify and to validate. Most of the blood flow resistance occurs in the microvasculature (where oxygen is delivered by RBCs to bodily tissues) where it is clear that the corpuscular nature of blood cannot be disregarded, given the fact that the size of RBCs is of the order of that of blood vessels (but this does not exclude the relevance of the corpuscular nature in larger blood vessels, such as arteries and veins). After a general introduction, we present the current state of the art in modeling blood flow, with comparison, when possible, to experiments. We shall consider the following question (i) a single vesicle (a simple model for RBC) under unbounded and bounded shear flow, which is a priori a simple problem, but which reveals unexpected complexity, entailing a strong impact on rheology; (ii) we discuss a model of RBC by taking into account the role of cytoskeleton; (iii) we address the problem of GR in a Poiseuille flow, and we shed light on a longstanding puzzle in microcirculation: why do red blood cells adopt a non symmetric shape (called slipper) in the microvasculature; (iv) we discuss then the problem of cluster formation of RBC, which results from purely hydrodynamical interactions, and (v) we conclude the presentation with discussion of concentrated suspensions. We present a list of open problems in this field which knows nowadays a tremendous interest at the international level. 
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Due to a busy schedule, no Fluid Dynamics seminars are held in January 2011.  
52  Christmas break  
51  Christmas break  
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49  20101208  Dr. Ir. Leo Pel (TU/e)  "Moisture transport at high temperatures in porous materials: Toward understanding fire spalling of concrete." 
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47  20101124  Prof. Dr. Anton Darhuber (TU/e)  "Ongoing research projects in MTP." 
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45  20101110  Dr. Ir. Bert Blocken (TU/e)  "Computational modeling in Urban Physics."
Urban Physics is a branch of Building Physics. Building physics is the engineering discipline that covers the physical aspects related to buildings, including the transfer of heat, air, moisture, pollutants, light and sound. It aims at providing a comfortable and healthy indoor and outdoor built environment, taking into account existing and/or future economical, energetic, ecological and climatic constraints. Urban development, urban human activity and climate change inevitably change the physical processes in the urban environment. This can result in adverse effects such as the urban heat island effect, outdoor and indoor air pollution, heat stress, wind nuisance and building deterioration. Urban physics research involves computational modeling at a wide range of spatial and temporal scales. Traditionally, models were devised to operate at only one of these scales. Examples are Mesoscale Meteorological Models (MeM), Microscale Meteorological Models (MiM), Building Energy Simulation models (BES) and Building Envelope HeatAirMoisture (BEHAM) transfer models. MeM model phenomena at the mesoscale (i.e. horizontal distances between 5  5000 km), such as fronts, mesocyclones, orographic effects and landsee breezes. MiM (e.g. Computational Fluid Dynamics  CFD) models multiphase urban aerodynamics at horizontal distances below about 5 km. BES typically focus on heat and mass transfer in single buildings, while BEHAM generally only considers the HAM transfer in a single building component (e.g. facade, roof). In the traditional singlescale modeling approach, models generally include effects at other scales as parameterized boundary conditions which limits their predictive capability. This presentation addresses two main issues in computational modeling in urban physics: (1) the need for highquality and comprehensive experimental datasets for physical model validation and (2) multiscale modeling by external or internal coupling of models at different scales to lessen or remove singlescale model limitations. Existing and potential future cooperation with the Department of Applied Physics is discussed. 
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43  20101027  Folkert Boersma (TU/e, KNMI)  "Constraints on emissions and chemistry of nitrogen oxides inferred from satellite observations."
Nitrogen oxides (NOx = NO+NO2) are emitted into the atmosphere by anthropogenic and natural sources. In the presence of nitrogen oxides, photochemical oxidation of volatile organic compounds (VOCs) and CO, leads to the production of tropospheric ozone, a global air pollutant and greenhouse gas. The ozone precursors (NOx and VOCs) have large and changing anthropogenic sources and some natural sources may be perturbed by climate change. We need to better understand the factors controlling ozone but this is difficult because of complex chemistry involving a continuum of scales from local to global. That we do not understand ozone well enough is reflected by the 4th IPCC report stating that the uncertainty on presentday (radiative forcing from) ozone is larger than that of CO2 and methane! In the VIDIproject 'Attributing the sources of tropospheric ozone from space', I propose to improve this situation by exploring recently advanced satellite observations of ozone and its precursors to their full advantage. The species nitrogen dioxide and formaldehyde, closely related to emissions of nitrogen oxides and VOCs, can be optimally observed from space with sensitivity down to the boundary layer. In this presentation I will focus on NOx and show how we can use these measurements to constrain the rapidly changing anthropogenic and natural emissions of nitrogen oxides in their chemical context. 
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41  20101013  Prof. Dr. Federico Toschi (TU/e)  "Life at high Reynolds number."
We study the statistical properties of population dynamics evolving in a realistic twodimensional compressible turbulent velocity field. We show that the interplay between turbulent dynamics and population growth and saturation leads to quasilocalization and a remarkable reduction in the carrying capacity. The statistical properties of the population density are investigated and quantified via multifractal scaling analysis. We also investigate numerically the singular limit of negligibly small growth rates and delocalization of population ridges triggered by uniform advection. 
40  20101006  Dr. Ir. Bas van de Wiel (TU/e)  "Challenges in the atmospheric nocturnal boundary layer."
As a new member of the WDY group Bas van de Wiel would be pleased to inform you about the background of his research area and his future plans related to his VIDI project. Who is not familiar with the fact that on clear summer days near surface winds tend to become weak in the evening? As wind shear drives turbulent mixing, a weakening of the wind coincides with a weakening of turbulence intensity. Interestingly, this cessation of turbulence may be interrupted by chaotic bursts of turbulence: socalled globally intermittent turbulence. Turbulent bursts transport a significant amount of heat, moisture and momentum and it may act as an efficient 'venting' mechanism of pollutants (that usually accumulate in quiet periods). Besides this intermittent boundary layer two other prototypes prevail in nature: the quiet ,socalled 'radiative' (laminar) boundary layer and the continuous turbulent (windy) boundary layer. At present there is no comprehensive theory to predict those regimes. Therefore, the aim of the study is to understand and predict the transitions between those regimes based on knowledge on largescale atmospheric forcings. As a mechanism we hypothesize that both intermittent and radiative boundary layers are natural physical instabilities of the continuous turbulent boundary layer, as the latter cannot maintain its turbulence when the largescale atmospheric pressure gradient is too small. In our research we will use numerical simulations techniques and analyze atmospheric observational data. Note that suggestions for potential collaborations within WDY are highly appreciated by the speaker. 
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37  20100915  Dr. Jens Harting (TU/e)  "Lattice Boltzmann in microfluidics." 
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35  20100901  Dr. A. Pier Siebesma (KNMI)  "Why clouds are fractal."
The geometrical properties of cumulus clouds modeled by a numerical technique called largeeddy simulation are investigated. Surfacevolume analyses reconfirm previous scaling results based on satellite data. This technique allows for the first time a direct analysis of the scaling behavior of cloud boundaries of individual clouds.

Currently the seminar is being organized by Kim Alards (WDY) and Matias Duran Matute (WDY).