Numerical reproduction of OH* radiation measurements of unsteady supercritical LOx/H2 combustion

Abstract

Radiation emitted from hydroxyl radicals (OH*) in high pressure oxygen-hydrogen flames has often been used as a marker for the flame zone because it is a physical quantity which is relatively easy to capture experimentally with high-speed cameras or photomultipliers. However, quantitative comparison of CFD results with experimental data and its use as an indicator of heat release during the combustion process is still an open problem. In order to compare CFD simulation results with experimental data, a radiation modelling tool has been developed at the Institute of Space Propulsion at the German Aerospace Center (DLR). This tool takes as input the relevant field variables obtained by a CFD simulation and gives as an output the intensity of the radiation emitted by OH* molecules as a result of the thermal excitation of OH ground state molecules by applying a reverse ray-tracing algorithm. This work aims to investigate the flame response of a single injector element fed with LOx/H2 subject to acoustic forcing and the fluctuations of the intensity of the OH* radiation emitted from the flame. The results are then compated with experimental data. The main steps are running a URANS simulation and investigate the flame response to acoustic excitation and apply the radiation modelling and ray-tracing tool to extract the OH* radiation intensity flucutations recored by an optical probe of the chamber. The results show a good qualitative agreement with the experimental data and give better understanding of the flame dynamics giving rise to inherently nonlinear radiation intensity dynamics.