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 Direct numerical simulation of weakly spanwise-rotating turbulent plane Couette flow Jie Gai, Zhenhua Xia, Qingdong Cai Abstract: In this report, we conduct direct numerical simulations (DNS) of weakly spanwise-rotating plane Couette flows at Reynolds number $Re_w = U_wh/\nu= 1300$ (here, $U_w$ is the half the wall velocity difference, and $h$ is half-channel height). A series of simulations with different rotation numbers $Ro = 2\Omega h/U_w$ ($\Omega$ is constant angular velocity component in the spanwise direction) is carried out to investigate the effect of $Ro$ on the flow statistics. Our results show that the flow statistics are affected by the $Ro$, and a "critical" rotation number $Ro^*$ (between $Ro=0.01$ and $Ro=0.05$) is observed, where the kinetic energy of secondary flow contributes about a half of the turbulent kinetic energy, and the mean shear rate at the center line reaches a minimum value. We conjecture that different mechanisms should exist around $Ro^*$, and will be investigated further. 10:45 15 mins Wavelet analysis of broadband signals to extract amplitude and frequency modulation: an application to wall turbulence Woutijn Baars, Krishna Talluru, Nick Hutchins, Ivan Marusic Abstract: Large-scale structures in wall-bounded turbulent flows are known to exhibit a coupling with the small-scale energy in the flow. Besides a superposition of large-scale energy onto the near-wall dynamics, this coupling comprises an amplitude and frequency modulation of the small-scale fluctuations by the large-scale motions. In this work we use wavelet analysis to examine amplitude and frequency modulation. Albeit the wavelet-based approach for amplitude modulation condenses to analyses presented in earlier studies, the strength of the approach becomes evident from a convenient extension of the technique to extract local instantaneous frequency modulation. While discrete techniques were employed previously, an application of a continuous approach results in inherent advantages when phase lags between the large- and small-scale fluctuations in terms of amplitude and frequency modulation are investigated. 11:00 15 mins Spectra of turbulent energy transport in channel flows Yoshinori Mizuno Abstract: To reveal the scale-dependences of the transport of turbulent energy in a channel flow, the constituents of the budget equation of turbulent energy for the Fourier modes of velocity fluctuations are computed by using direct numerical simulations. At each height in the buffer and overlap regions, the transport in the wall-normal direction by the turbulent convection provides energy to the fluctuations at small scales, but takes it away from those at large-scales. Furthermore, energy taken from the large-scales in the overlap region is carried upward to the center of channel and also downward to the vicinity of the wall. This downward transport is expected to cause the anomaly of the turbulent intensity and the constituents of the budget equation near the wall. The transport between scales and their scaling will also be discussed in the talk. 11:15 15 mins Numerical investigation of localized exact solutions of the Navier-Stokes equations in pipe flow. Vladimir Pimanov, Nikolay Nikitin Abstract: The edge state solution in pipe flow at Re=2200 is calculated numerically. The solution has the form of spatially localized puff-like structure drifting downstream. In the moving frame it is represented by a steady average flow and time-periodic pulsation flow. It is shown, that the Kelvin-Helmholtz instability mechanism is not valid for pulsation generation in the edge state flow. 11:30 15 mins TURBULNENT STRUCTURES IN AN OPTIMAL TAYLOR-COUETTE FLOW BETWEEN TWO COUNTER-ROTATING CYLINDERS Razieh Jalalabadi, Muhammad Nadeem, Hyung Jin Sung Abstract: Taylor-Couette flow with two independently counter-rotating cylinders is investigated. Direct numerical simulation is applied to study flow structure and angular velocity transport for η = 0.714 at optimum and fully turbulent regime. The main purpose is to study the coherent structure in both axial and radial directions and its contribution to angular velocity transport in optimum condition. Visualizing the vortical structure (and other structural parameters) with the distribution of azimuthal velocity and ω-Nusselt number leads to a better understanding of turbulent flow structure at optimum condition comparing to non-optimum condition. 11:45 15 mins PREDICTING THE RESPONSE OF SMALL-SCALE NEAR-WALL TURBULENCE TO LARGE-SCALE OUTER MOTIONS Lionel Dr. Agostini, Michael Prof. Leschziner Abstract: Abstract: The paper deals with the question of how to determine – or “predict” - the near-wall-turbulence statistics from a Reynolds-number-independent, “universal”, small-scale signal, and the Reynolds-number-dependent large-scale outer motions in the log layer. An empirical model is proposed, which is intended to take into account the effect of “splatting”, not previously considered, thus offering an improved representation of the near-wall-turbulence field. 12:00 15 mins Turbulent plane Couette flow with wall-transpiration Sergio Hoyas, Stefanie V. Kraheberger, Martin Oberlack Abstract: In the present abstract, DNS results obtained for turbulent plane Couette flow with wall-normal transpiration velocity are presented. Important equations valid in such a flow are derived, describing the total shear stress and the relation between the friction velocities at the lower and upper wall. These expressions are of importance, as there are neither experimental nor DNS data to compare with. Equally important, we derive a center region and a viscous sublayer velocity scaling for the suction wall, which were both validated using the DNS data.