Analysis of Thermal Effects in Cavitating Liquid Hydrogen Inducers

Abstract

Evaporative cooling effects due to cavitation can significantly improve the performance of liquid rocket turbomachinery that operate with cryogenic fluids, in which the fluid is operating close to its critical temperature and the thermal effects resulting from phase change become important. A detailed numerical analysis to quantify these thermal effects of cavitation and to better understand their impact on cavitation flow physics in liquid hydrogen inducers is presented. Simulations were performed on a helical flat-plate inducer that was extensively tested in both liquid hydrogen and cold water. Predictions of cavitating performance over the operational range of inlet pressures were conducted and compared with experimental data. Fundamental differences were observed in the cavity for liquid hydrogen compared with the cold-water inducer; the cavity in liquid hydrogen shows far less vapor content, although spreading out further in the spanwise direction, which may generate blade-to-blade interactions. Thermal effects result in a more gradual breakdown of the head in liquid hydrogen resulting in improved overall performance; the liquid hydrogen inducer performed to a suction specific speed (N SS number) of 75,000 and the corresponding value in water is 35,000. The temperature depressions due to evaporative cooling in the liquid hydrogen fluid are found to be only on the order of 0.5-1.0 K, highlighting the strong coupling of thermodynamic properties and the phase-change process at these flow conditions.