Heat flux evaluation in a multi-element CH4/O2 rocket combustor using an inverse heat transfer method

Abstract

Heat load measurements in experimental lab-scale rocket combustors are essential in order to obtain information about the mixing and energy release of the propellants, the injector/injector interaction as well as the injector/wall interaction. The present work demonstrates an efficient inverse method for estimating the spatially resolved heat flux distribution at the hot gas wall of multi-element, actively cooled engines using the information provided by temperature measurements in the material. This inverse method implements Nusselt-correlations for the estimation of the wall heat transfer coefficient in the cooling channels and a Jacobi-matrix based optimization algorithm for the calculation of the hot gas side heat flux. The method is applied for the evaluation of CH4/O2 test data. A water-cooled 7-injector rocket combustor is investigated, which is operated at the Chair of Turbomachinery and Flight Propulsion (LTF) of the Technical University of Munich (TUM). The use of the inverse method gives significant information about the axial and azimuthal distribution of the heat flux. The azimuthal distribution sheds light into the interaction between the individual flames. Specifically, the angular position of maximal heat flux appears to shift from directly above the injector elements towards the positions between two neighboring elements, implying the presence of a strong vortex system pushing hot gas directly onto the wall. The obtained results agree qualitatively with RANS simulations of the hot gas flow.