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15 mins
Multiscale Statistics of Lagrangian and Eulerian Acceleration in Turbulent Stratified Shear Flows
Frank Jacobitz, Kai Schneider, Marie Farge
Session: Lagrangian aspects of turbulence 4
Session starts: Friday 28 August, 10:30
Presentation starts: 12:00
Room: Room F

Frank Jacobitz (Shiley-Marcos School of Engineering, University of San Diego, 5998 Alcal\'a Park, San Diego, CA 92110, USA)
Kai Schneider (M2P2-CNRS, Aix-Marseille Universit\'e, 38 rue Joliot-Curie, 13451 Marseille Cedex 20, France)
Marie Farge (LMD-IPSL-CNRS, Ecole Normale Sup\'erieure, 24 rue Lhomond, 75231 Paris Cedex 5, France)

Direct numerical simulation data of homogeneous turbulence with shear and stratification are analyzed to study the Lagrangian and Eulerian acceleration statistics. Richardson numbers from $Ri=0$, corresponding to unstratified shear flow, to $Ri=1$, corresponding to strongly stratified shear flow, are considered. The scale dependence of the acceleration statistics is studied using a wavelet-based approach. The probability density functions (pdfs) of both Lagrangian and Eulerian accelerations exhibit a strong and similar influence on $Ri$. The extreme values for Lagrangian acceleration are weaker than those observed for the Eulerian acceleration. Similarly, the Lagrangian time-rate of change of fluctuating density is observed to have smaller extreme values than that of the Eulerian time-rate of change. Thus the time-rate of change of fluctuating density obtained at a fixed location is mainly due to advection of fluctuating density through this location. In contrast the time-rate of change of fluctuating density following a fluid particle is substantially smaller, and due to production and dissipation of fluctuating density.