Simulation of the GOx/GCH4 Multi-Element Combustor Including the Effects of Radiation and Algebraic Variable Turbulent Prandtl Approaches

Abstract

Multi-element thrusters operating with gaseous oxygen (GOX) and methane (GCH4) have been numerically studied and the results were compared to test data from the Technical University of Munich (TUM). A 3D Reynolds Averaged Navier–Stokes Equations (RANS) approach using a 60° sector as a simulation domain was used for the studies. The primary goals were to examine the effect of the turbulent Prandtl number approximations including local algebraic approaches and to study the influence of radiative heat transfer (RHT). Additionally, the dependence of the results on turbulence modeling was studied. Finally, an adiabatic flamelet approach was compared to an Eddy-Dissipation approach by applying an enhanced global reaction scheme. The normalized and absolute pressures, the integral and segment averaged heat flux were taken as an experimental reference. The results of the different modeling approaches were discussed, and the best performing models were chosen. It was found that compared to other discussed approaches, the BaseLine Explicit Algebraic Reynolds Stress Model (BSL EARSM) provided more physical behavior in terms of mixing, and the adiabatic flamelet was more relevant for combustion. The effect of thermal radiation on the wall heat flux (WHF) was high and was strongly affected by spectral models and wall thermal emissivity. The obtained results showed good agreement with the experimental data, having a small underestimation for pressures of around 2.9% and a good representation of the integral wall heat flux.

Simulation of a GOx-GCH4 Rocket Combustor and the Effect of the GEKO Turbulence Model Coefficients

“…It is also interesting that the k-epsilon model shows similar values for the Csep = 1 model, and therefore higher values than the GEKO default model. Previously, it was observed that the standard k-epsilon model provides higher pressures than k-omega based models (the shear stress transport model, for example) due to its higher combustion efficiency, originating from the enhanced turbulent mixing [1,2,8,36]. The heat flux values for k-epsilon and GEKO Csep = 1, show the same trend as for the pressure, having higher values for k-epsilon and Csep = 1.…”

“…It has been shown that RAMEC, in general, results in higher wall heat fluxes, while the Zhukov-Kong mechanism provides better experimental pressure profiles. Due to higher estimated errors in the wall heat flux measurements, and also the absence of modeling of the radiative heat transfer, which can contribute to up to 10-15% of total wall heat flux depending on the wall properties and species concentrations [36,[41][42][43][44], the Zhukov-Kong mechanism, which better agrees with the experimental pressures, can be recommended. Regarding the GEKO coefficients, Csep = 1 can be recommended as well as the standard k-epsilon model for further usage for the same applications, which may be beneficial for engineers in terms of convergence, having turbulence models built on a different basis (k-omega and k-epsilon) and demonstrating similar performances, and, in terms of GEKO, proving to be easily adaptable for the required application.…”

“…The turbulent Prandtl and Schmidt numbers, equal to 0.9 and 0.7, respectively, are used for all simulations, regardless of their influence on the simulation results [35,36] as the current study did not require them to be varied, and it was chosen to keep constant settings throughout the simulations.…”