Modelling gas radiation within the numerical analysis of combustion processes and reacting high enthalpy flows respectively is often neglected due to the complex mathematics of the radiative transport equation, the lack of detailed information on the spectral properties of the radiatively participating gas and the strong increase of computation time. The challenge is to identify approximative models of the radiative transport equation, as well as suitable spectral approximations, which provide the best compromise between fastness and accuracy for the present problem.\r\nThis thesis investigates the impact of gas radiation on a turbulent, reacting flow in a rocket combustion chamber based on the main combustion chamber of the Space Shuttle Main Engine (SSME). Due to the high characteristic temperature (≈ 3800 K) and pressure (≈ 21 MPa) and presence of strong radiating species, gas radiation plays a significant role in the heat transfer analysis of rocket combustion chambers. To investigate the influence of the radiatively participating species, two different combustion systems are considered: hydrogen-oxygen (H2-O2) and methane-oxygen (CH4-O2). Within the first system only water vapour (H2O) and in the second system both water vapour and carbon dioxide (CO2) mainly contribute to the radiative heat transfer, via absorption and emission of radiation. Methane is currently under discussion for future rocket engines due to its advantages compared to hydrogen. It is expected that the contribution of gas radiation in hydrocarbon systems such as methane-oxygen increases. The present study reveals that both combustion systems are optically thick; the hydrogen-oxygen system has an optical thickness of 17 and the methane-oxygen system has a value of 32. Due to the optical thick situation this study demonstrates that the Rosseland model can be applied for the approximation of the radiative transfer equation and delivers physical meaningful results. To take the operating conditions of the SSME main combustion chamber into account an semi-empirical jump-correlation for the solid wall boundary condition of the Rosseland approximation is introduced and a modified Rosseland formulation in conjunction with the weighted-sum-of-gray-gases (WSGG) approach for the spectral modelling is presented. This newly derived Rosseland approximation is then implemented into the NSMB research CFD code. The results of the NSMB Rosseland model are on the one hand compared with computations of the CFX and FLUENT commercial CFD solvers, using the radiative transport models “P1-moment method” and “Discrete Transfer Method (DTM)” and on the other hand to benchmark calculations from literature. The results reveal that gas radiation has a relatively small influence on the flow field within the SSME main combustion chamber. The thermal boundary layer is increased slightly due to gas radiation. The influence of the gas radiation on the axial temperature in the core flow and wall shear stress is neglectable. However gas radiation contributes significantly to the total wall heat flux. The results of CFX and FLUENT for the H2-O2 study reveal that nearly 7.7 % and for the CH4-O2 study nearly 8.8 % of the total wall heat flux is caused by gas radiation. The NSMB Rosseland case induces a gas radiation impact of 32 % for the H2-O2 study. Including gas radiation increases the computational costs significantly for all three CFD solvers compared to a calculation without radiation. The NSMB Rosseland combination increases the CPU time by approximately 22 %, CFX and P1 by 51 % and CFX and DTM by 466 % compared to a calculation without gas radiation.\r\nThe NSMB Rosseland case overestimates the influence of gas radiation on the wall heat loads but it results in significantly lower CPU time costs. A further development of the Rosseland solid wall boundary condition could decrease the overestimation of the fraction of gas radiation. The lower CPU time costs of the Rosseland model...    «

Modelling gas radiation within the numerical analysis of combustion processes and reacting high enthalpy flows respectively is often neglected due to the complex mathematics of the radiative transport equation, the lack of detailed information on the spectral properties of the radiatively participating gas and the strong increase of computation time. The challenge is to identify approximative models of the radiative transport equation, as well as suitable spectral approximations, which provide t...    »