Study and application of wall-roughness models in LES flows

Abstract

This paper develops a new treatment of rough walls in turbulent high-enthalpy combustion chamber environments where the effect of the roughness on the (averaged) temperature profile can no longer be neglected. As the velocity and temperature profiles are affected by the roughness, a new framework is presented to take into account the effect of normalized sand grain roughnesses on the so called downward shift of the profiles in the logarithmic region. The application of the two presented methods exploits the roughness functions which can be found in the literature. The modeling presented in this paper is among the first attempts to combine a roughness model with a chemically reacting flow. Specifically, LES simulations are performed to verify the implementation of the models proposed for two setups, a periodic channel running on air and a rocket combustion chamber running on methane and oxygen. A Flamelet combustion model is used to model the chemical reactions. At the chamber walls, a roughness model is implemented in order to observe the effects on the temperature fields. The results are compared with the available experimental data.