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

 10:30 15 mins Influence of internal intermittency on drop breakage and coalescence in turbulent liquid-liquid dispersion Wioletta Podgorska Abstract: Break-up and coalescence of droplets in stirred dispersion is considered and the influence of highly intermittent nature of turbulence on scale-up is discussed. Drop breakup occurs when disruptive stresses overcome the stabilizing ones. Three different situations are taken into account: (a) pure liquid-liquid system with dispersed phase of low viscosity in which the only disruptive stress is due to pressure fluctuations and stabilizing stress is due to interfacial tension, (b) pure system with dispersed phase of high viscosity in which viscous stress generated within the drop increases stabilizing effect, (c) system with surfactant and additional disruptive stress. In all cases internal intermittency causes faster breakage in larger scale when average energy dissipation rate in the tank is maintained. Additionally, for system (a) coalescence was taken into account. In this system drop interfaces are partially mobile and coalescence is faster in larger scale due to intermittency. 10:45 15 mins INTERMITTENCY IN ELASTIC WAVE TURBULENCE Sergio Chibbaro, Christophe Josserand Abstract: We study numerically the long-time evolution of waves of a thin elastic plate for different energy input. In particular, we focus on the possible existence of intermittency, intended mainly as highly non-gaussian features. We show that deviations from the Kolmogorov- Zakharov scenario are present in high-order structure functions of the deplacement. This is more pronounced for higher- energy input even though the limit of small deformation so that modes of oscillations interact weakly is globally kept valid. 11:00 15 mins Stochastic simulation of non-stationary continuous multifractal time series Francois G Schmitt, Yongxiang Huang Abstract: Intermittency is an ubiquitous property of fully developed turbulence, for Eulerian and Lagrangian fields, and for velocity, passive and active scalars. Intermittency corresponds to multi-scale high fluctuations, with some underlying long-range correlations. Such property is usually characterized using scaling approaches, verified using experimental or numerical data. However there are only few studies devoted to the generation of continuous stochastic processes having non-stationary multifractal properties, able to mimic Eulerian or Lagrangian velocity or passive scalar time series. Here we review recent works on this topic, and we provide stochastic simulations in order to verify the theoretical predictions. In the lognormal framework we provide a $h-\mu$ plane expressing the scale invariant properties of these simulations. 11:15 15 mins MARKOV CLOSURE FOR THE LUNDGREN-MONIN-NOVIKOV HIERARCHY OF VELOCITY INCREMENTS IN BURGERS TURBULENCE Jan Friedrich, Rainer Grauer Abstract: A central, yet unsolved issue in the longstanding problem of hydrodynamic turbulence is the closure problem of turbulence, which is due to the nonlinear character of the Navier-Stokes equation. We formulate the closure problem for the many-increment probability distributions (PDF’s) in Burgers turbulence and introduce a new method for closing the hierarchy. To this end, we rely on the experimentally and numerically verified assumption in [1] that the turbulent cascade possesses a Markov property in scale down to the so-called Einstein-Markov length. The hierarchy is closed at the stage of the two-increment PDF corresponding to a three-point closure that allows for a description of intermittency effects, not captured by other closure approximations, i.e. Gaussian closures etc. The proposed closure also opens up a possible way to a perturbative treatment of the Navier-Stokes equation beyond the Einstein-Markov length in successively taking into account a larger and larger scale “history” of the system. 11:30 15 mins Real-space Manifestations of Bottlenecks in Turbulence Spectra, Uriel Frisch, Samriddhi Sankar Ray, Ganapati Sahoo, Debarghya Banerjee, Rahul Pandit Abstract: An energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the non-turbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence. 11:45 15 mins Dissipative Range Scaling of Higher Order Structure Functions for Velocity and Passive Scalars Michael Gauding, Jonas Boschung, Christian Hasse, Norbert Peters Abstract: Differently to Kolmogorov's second similarity hypothesis, we find that the 2n-th order velocity and scalar structure functions scale with n-th order moment of the energy dissipation and the scalar dissipation, respectively. The origins of this scaling are analyzed by the transport equations of the fourth order velocity and scalar increment moments and by direct numerical simulations.