Abo Bibliothek: Guest
Ninth International Symposium on Turbulence and Shear Flow Phenomena
June 30 - July 3, 2015, University of Melbourne, Australia

DOI: 10.1615/TSFP9

ON ACCELERATION STATISTICS IN TURBULENT STRATIFIED SHEAR FLOWS

pages 329-334
DOI: 10.1615/TSFP9.560
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ABSTRAKT

The Lagrangian and Eulerian acceleration statistics in homogeneous turbulence with uniform shear and stable stratification are studied using direct numerical simulations. The Richardson number is varied from Ri = 0, corresponding to unstratified shear flow, to Ri = 1, corresponding to strongly stratified shear flow. The probability density functions (pdfs) of both Lagrangian and Eulerian accelerations show a strong and similar influence on the Richardson number and extreme values for Eulerian acceleration are stronger than those observed for the Lagrangian acceleration. A consideration of the terms in the Navier-Stokes equation shows that the Lagrangian acceleration is mainly determined by the pressure-gradient, while the Eulerian acceleration is dominated by the nonlinear term. Similarly, the Eulerian time-rate of change of fluctuating density is observed to have larger extreme values than that of the Lagrangian time-rate of change due to the nonlinear term in the advection-diffusion equation for fluctuating density. Hence, the time-rate of change of fluctuating density obtained at a fixed location by an Eulerian observer is mainly due to advection of fluctuating density through this location, while 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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