Numerical Simulations of Liquid Propellant Combustion Instability: Onset and Growth

摘要

This work describes the onset and evolution of instabilities initiated at a liquid phase (reactant) gas phase (product) interface which is considered initially wrinkled by a prescribed surface perturbation. Combustion generates the vapor product region, raises its pressure, and accelerates it into the liquid fuel region, initiating Rayleigh-Taylor instabilities. The original Rayleigh-Taylor interface instabilities and subsequent, parasitic Kelvin-Helmholtz instabilities are investigated during their growth over a range of idealized initial conditions representative of liquid propellant driven gun combustion. Phase change and interphase heat and mass transfer are neglected in this study, so that combustion energy release is simulated solely by pressure rise in the gas phase. This permits a detailed study of the hydrodynamic instability growth at the fuel/gas interface through use of a Lagrangian center-of-mass formalism. The variable density field is thereby traced explicitly in space and time following the moving Lagrange contours. The bands of nearly constant density bounded by two successive Lagrange lines are however, Eulerian representations with the spanwise velocity distribution defined on a fixed grid of spatial solution points. The corresponding solution is determined by use of a fast Fourier transform collocation procedure. The dimensionless Atwood Number, characterizing the liquid/vapor interface density ratio; the perturbation amplitude to wavelength ratio; and the instability amplitude growth rate to pressure growth rate (energy release rate) as well as injection velocity and interphase slip velocity receive special attention in these investigations. (ERA citation 10:001033)