A-Priori Tests of Reynolds Stress Transport Models in Turbulent Pipe Expansion Flow

摘要

The database obtained from a direct numerical simualtion (DNS) of turbulent sudden pipe expansion flow with an expansion ratio fo ER=1.2 has been used to analyse various Reynolds stress models. The inflow conditions were provided by a DNS of fully developed turbulent pipe flow. Teh Reynolds number at the inlet thus corresponds to that in the pipe and is 360 based on diameter and friction velocity. In this DNS a mean reattachment length of 10.2 step heights was observed. various models for pressure strain correlations, turbulent transport and viscous dissipation were evaluated using the DNS database. It was found that none of the investigated redistribution models is able to predict the extraction of fluctuatign kinetic energy from the wall normal velocity component within the reattaching flow at least qualitatively correct. Improved models are needed to predict the turbulent transport of the wall normal stress component for separated flows accurately.