15th European Turbulence Conference 2015
August 25-28th, 2015, Delft, The Netherlands

Invited speakers:

Prof. Marc Brachet. Ecole Normale Superieure, Paris, France

Prof. Peter G. Frick, Institute of Continuous Media Mechanics, Perm, Russia

Prof. Bettina Frohnapfel,  Karlsruher Institut fur Technology, Germany

Prof. Andrea Mazzino, Dipartimento di Fisica, University of Genova, Italy

Prof. Bernhard Mehlig. Department of Physics, University of Gothenburg, Sweden

Prof. Lex Smits, Mechanical and Aerospace Engineering, Princeton University, USA

Prof. Chao Sun Physics of Fluids, University of Twente, The Netherlands

Prof. Steve Tobias, Applied Mathematics, University of Leeds, United Kingdom

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10:30   Multiphase and non-Newtonian flows 4
Chair: Wim Paul Breugem
15 mins
The turbulent dissipation rate from PIV measurements
Guus Bertens, Dennies van der Voort, Willem van de Water
Abstract: The result of a particle-image velocimetry (PIV) measurement is a velocity field averaged over interrogation windows. This severely affects the measurement of small-scale turbulence quantities when the interrogation window size is much larger than the smallest length scale in turbulence. A direct measurement of the dissipation rate demands the measurement of gradients of the velocity field, which are now underestimated because the small-scale motion is not resolved. A popular procedure is to relate the statistical properties of the measured, but underresolved gradients to those of the true ones, invoking a large-eddy argument [3]. We show that the used proportionality constant, the Smagorinsky constant, should depend on the window overlap, on the used elements of the strain tensor, and on the way in which derivatives are approximated
15 mins
Minh Quan NGUYEN, Serge Simöens, Alexandre Delache, Mahmoud El Hajem, Wouter Bos, Robert Poole
Abstract: The comparison of the results of direct numerical simulations of isotropic turbulence of Newtonian and viscoelastic fluid, based on the FENE-P model, provide evidence that viscoelasticity modifies qualitatively the behavior of the smallest scales: we observe a k−6 law in the far dissipation range of the energy spectrum and we show that it is a robust feature, roughly independent of the large-scale dynamics. It is further shown that the drag-reduction in such flows, as measured by the difference in energy dissipation between Newtonian and viscoelastic flow, strongly depends on the initial conditions.
15 mins
Rate of breakup of small inertial aggregates in homogeneous turbulence
Matthaus Babler, Luca Biferale, Alessandra S. Lanotte
Abstract: The hydrodynamic breakup of small inertial aggregates in homogenous and isotropic turbulence is studied through numerical simulations. Small inertial aggregates are subject to shear stress caused by the local velocity gradient and drag stress caused by the relative velocity of the aggregate and the fluid flow. In our simulations, we follow aggregates moving through the flow and record the total stress acting on them. Breakup is assumed to occur when the total stress overcomes a predefined threshold representing the aggregate strength. By determining how long it takes for an aggregate to reach a stress exceeding its strength for the first time, we are able to derive a breakup rate. It is found that with increasing aggregate inertia, the drag stress rapidly becomes the dominant stress resulting in an increase of the breakup rate with increasing the aggregate inertia.
15 mins
Preferential concentration of particles in compressible turbulence
Qingqing Zhang, Han Liu, Zuoli Xiao
Abstract: The behavior of particles in compressible turbulence has been seldom investigated to date despite its importance in many natural and industrial flows. Direct numerical simulations of particle-laden compressible isotropic turbulence are performed to study the preferential concentration of particles and the underling mechanisms. It turns out that heavy particles tend to concentrate in regions of low enstrophy and high fluid density (i.e, strain regions between vortex rings), especially the particles of Kolmogorov scale, which show the largest number density. Due to the compressibility, fluid particles do not distribute uniformly as in incompressible case, but show a tendency to bunch up in high density zones. The preliminary result might give some insights into compressible turbulent transport, dispersion and mixing as well as the subgrid-scale modeling for large-eddy simulation of particle-laden compressible flows.
15 mins
Mechanics of dense suspensions in turbulent channel flows
Francesco Picano, Pedro Costa, Wim-Paul Breugem, Luca Brandt
Abstract: Dense suspensions are usually investigated in the laminar limit where inertial effects are insignificant. When the flow rate is high enough, i.e. at high Reynolds number, the flow may become turbulent and the interaction between solid and liquid phases modifies the turbulence we know in single-phase fluids. In the present work, we study turbulent channel flows laden with finite-size particles at high volume fraction by means of Direct Numerical Simulations. A direct-forcing Immersed Boundary Method has been adopted to couple liquid and solid phases. We will show that the turbulence is attenuated in dense cases, even though the overall drag is increased because of the particle contribution to the total stress.
15 mins
Influence of viscosity anisotropy on turbulence large scale statistics
Tim Grünberg, Thomas Rösgen
Abstract: We report experiments on a turbulent flow of a fluid with anisotropic viscosity. The fluid is an aqueous suspension of paramagnetic nanoparticles which can be aligned by an external magnetic field. We explore the flow at various Reynolds numbers and magnetic field strengths and see pronounced changes in turbulence statistics even at the largest scales.
15 mins
Spinodal decomposition in the inverse cascade of two-dimensional, binary-fluid turbulence
Prasad Perlekar, Nairita Pal, Rahul Pandit
Abstract: We study spinodal decomposition in the inverse-cascade regime of two dimensional turbulence in symmetric, binary fluid mixtures. We show that turbulence leads to break up of domains whose size, in the inverse cascade regime, is proportional to the Hinze scale. Even more strikingly, we show that the inverse cascade of energy is blocked by the formation of domains.
15 mins
Francesco Battista, Roberta Messina, Paolo Gualtieri, Carlo Massimo Casciola
Abstract: Many technological applications are characterized by turbulent bounded flows with dispersed particles. For high mass load (particle/fluid mass ratio) a significant inter-phase momentum exchange occurs (two-way coupling regime), inducing a significant alteration of the turbulent field which, in turn, modifies the dynamics of the suspended phase. Aim of the present study is exploring the potentially of recently developed momentum coupling method, dubbed the Exact Regularized Point Particle (ERPP) method, in reproducing via Direct Numerical Simulation (DNS) the detailed dynamics of a particles laden turbulent pipe flow. The comparison with available experimental and numerical data confirms the ability of the new approach in reproducing the relevant dynamics also in parameter ranges which are unaccessible to standard techniques.