Fully coupled numerical simulation of a transpiration cooled rocket thrust chamber with combustion modeling

Kurzfassung

Modern developments in porous metal and ceramic composite manufacturing technology have made transpiration cooling applicable in future rocket engine thrust chamber cooling. In past years, a numerical model, the Three-Domain model, for transpiration cooling using Ansys CFX was developed at the German Aerospace Center, which has already been applied to a virtual thrust chamber demonstrator (TCD2) in the scope of the DFG Collaborative Research Center TRR40. In this case however, only a shortened chamber segment was investigated assuming completed combustion. In the scope of this thesis, the model is extended to resolve the full combustion chamber including combustion processes. Results are compared with calculations on the full geometry assuming complete combustion before injection. As the Three-Domain model could not be stabilized for the full geometry with combustion modeling, a new approach is introduced whereby the hotgas, wall and coolant domains are no longer coupled externally, but a CFX-internally coupled model is superposed using a volumetric coupling approach in the porous domain only. This new approach is validated on an experimental test case, which has previously been used to validate the Three-Domain model serving as a basis for this thesis. When using the volumetrically coupled model, it is still shown that transpiration cooling is an efficient method to reduce heat loads on combustion chamber walls and that it has a significant effect on the temperature gain in the cooling channel. In modeling the combustion processes, the choice of mixing rules can have significant effects. Uncertainties in material properties and other parameters such as the volumetric heat transfer coefficient do not allow an exact evaluation of the advantages of transpiration cooling over pure regenerative cooling. When using a porous metal material with a high thermal conductivity, higher permeabilities are necessary to achieve the same wall temperature reduction due to transpiration cooling than when using a porous ceramic material with lower permeability. Additionally, an analytical correlation is shown to be inaccurate for most applications in rocket combustion chambers.