Liquid Films Instability Analysis of Liquefying Hybrid Rocket Fuels Under Supercritical Conditions

Abstract

Numerical analysis on the instability of liquid/dense fluid films under supercritical operating conditions is performed on methane fuel. A numerical code for compressible fluid flows, accommodated for the van der Waals equation of state, is developed in order to deal with supercritical fluid and dense fluid layers and has shown good convergence, even at a very low-Reynolds-number flow typically seen in actual hybrid rocket engines. A linear instability analysis is conducted and shows that an amplification rate has a peak at a certain wave number of initial perturbations. The perturbation becomes unstable as the Reynolds number and chamber pressure increase, and the instability region of the wave number is enlarged when an acceleration body force in the streamwise direction is imposed. A limit cycle of the amplitude of perturbations is observed at low-Reynolds-number flows, and the instability of dense fluid layers leads to the entrainment phenomena at high-Reynolds-number flows. It is deduced that the perturbation with the peak value of the amplification rate dominates in an actual hybrid rocket engine.