Simulation numérique bidimensionnelle d'un écoulement turbulent stratifié derrière une marche

Abstract

Numerical simulations of turbulent flows in complex geometries are generally restricted to the prediction of the mean flow and use semi-empirical turbulence models. The present study is devoted to the simulation of the coherent structures which develop in a flow submitted to a velocity change, downstream of a backward facing step. Two aspect ratios (height of the step over height of the channel) are explored for two Reynolds numbers (6000 and 90 000). In this isothermal case coherent structures are obtained by the numerical simulation in the mixing layer downstream of the step. The numerical simulation provides results in fairly good agreement with available experimental results. In a second step a thermal stratification is imposed on this flow for three Richardson numbers (0, 0.25, 0.5). The Prandtl number is 0.7. The coherent structures in the three cases are produced in the immediate vicinity of the step and disappear downstream for larger Richardson numbers.