LOCAL ENTROPY PRODUCTION IN TURBULENT SHEAR FLOWS: A TOOL FOR EVALUATING HEAT TRANSFER PERFORMANCE

摘要

Entropy production in turbulent shear flows with heat transfer is calculated locally and afterwards integrated over the whole flow domain. This quantity can serve as a parameter to determine the efficiency of turbulent heat transfer processes. Based on the time averaged entropy balance equation, four different mechanisms of entropy production can be identified and cast into mathematical equations. They are: dissipation in the mean and the fluctuating velocity fields and heat flux due to the mean and the fluctuating temperature fields. Since all four entropy production rates show very steep gradients close to the wall numerical solutions are far more effective with wall functions for the production terms. These wall functions are mandatory when high Reynolds number turbulent models are used, as for example the high Reynolds number k — ε model, like in our case.