Impact of Turbulent Prandtl and Schmidt Numbers on Numerical Heat Flux Predictions in the LUMEN Thrust Chamber

Results from ongoing modelling of the thrust chamber of the 25-kN, LOX-LNG, demonstrator rocket engine "LUMEN" of the German Aerospace Center (DLR) are presented. The DLR's computational fluid dynamics (CFD) code, TAU, is used to conduct three Favre-averaged Navier-Stokes (RANS) numerical simulations where the turbulent Prandtl and Schmidt number are set equal, and varied between values of 0.4, 0.7, and 1.0. CFD results are compared to two different Ievlev correlations and the Bartz correlation for heat flux. A calorimetric version of the LUMEN thrust chamber provides experimental heat flux data for comparison. In the cylindrical section of the chamber, the simulations with a turbulent Schmidt and Prandtl number of 1.0 provide the closest agreement with the experimental data, while a value of 0.7 yields the best match for the heat flux in the throat region. Two opposing limitations are acknowledged: the boundary conditions may have overestimated the heat flux, while the omission of recombination reactions and radiation may have underestimated it. Across the three tested correlations, the differential Ievlev correlation most closely reproduces the experimental data, however the heat flux values within the experimental measurement uncertainty are limited to regions near the nozzle throat.