Navier-Stokes numerical simulation of supersonic hydrogen-fluorine combustion in CW chemical lasers

Abstract

Results are presented of numerical simulations of nonpremixed supersonic combustion with an accountof nonequilibrium vibration energy exchange and stimulated radiation in the continuous-wave (CW) HF chemical lasers with different fuel/oxidant mixing devices. The main goal of the study was to obtain better insight into the mechanism of coupling between the processes in the combustion region (laser cavity) and in the supersonic supply system (nozzle array). In order to take into account this effect, which is caused by the upwind influence of the cavity processes on the nozzle array flow, a coupled one-domain approach is used, i.e., a simultaneous Navier-Stokes simulation of both nozzle and cavity flows. The results of the computations clearly show that coupling or, more exactly, the feedback mentioned above, is explained mainly by the fuel and oxidant nozzle flows interaction due to propagation of the pressure disturbances from one nozzle to another through the nozzle array base recirculation zone and subsonic part of the nozzle boundary layers. It causes significant deformation of the mixing zone and flame configuration and turns out to be crucial when the difference between the nozzle exit pressure levels is large. In this case, separation of the nozzle boundary layer may occur, which leads to the ignition of the mixture inside the nozzle array. The results illustrate also the influence of the regime parameters and the design of the nozzle array on the flow wave pattern, flame configuration, structure of the base recirculation zones, and the laser output characteristics.