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

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

Jacobitz, F.
Schneider, K.
Farge, M.

2015-08-28

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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