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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)

Abstract:

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.

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*Frank Jacobitz, Kai Schneider, Marie Farge*

12:00

15 mins

Multiscale Statistics of Lagrangian and Eulerian Acceleration in Turbulent Stratified Shear Flows
15 mins

Session starts: Friday 28 August, 10:30

Presentation starts: 12:00

Room: Room F

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)

Abstract:

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.