Obtaining pseudo-OH* radiation images from CFD solutions of transcritical flames

摘要

The quantitative comparison of experimental data and results from CFD simulations is still an ongoingchallenge in the investigation of high pressure combustion in rocket combustion chambers. This is due tothe extreme environment which develops in liquid propellant rocket engines, which represent a challengefor experimental data collection. OH ? radiation emitted from the flame has often been designated as anindicator of the combustion zone, because of its relative ease of detection with appropriate cameras. Amethod was developed to compare OH ? radiation originating from cryogenic oxygen-hydrogen flamesin an experimental combustor with the CFD simulation results. Pseudo-OH ? images were obtained fromCFD results of two combustors. The method consists in obtaining the path of a ray of light by a reverseray tracing algorithm and sampling the thermodynamic properties along the path of the ray, simulatingthe emission and absorption spectra in the wavelength range of interest, in this case of OH ? emissionduring combustion. The spectral radiance is then determined by solving the differential radiative transferequation. Finally, the total radiance is calculated integrating the spectral radiance. The results obtainedapplying this method are then compared with former results of two test cases, a laminar and a turbulentflame, and with the related experimental data. An improvement of the comparison with the experimentaldata was achieved in terms of the prediction of self-absorption, which was underestimated in previousworks by a factor of 15, and in terms of radiance near the injection plane, where difference is estimatedto be about 40% when including refraction. The method allows for more direct comparison between 3DCFD results and 2D experimental images collected by the optical setup and probes.