Spontaneous and Triggered Longitudinal Combustion Instability in a Single-Injector Liquid-Rocket Combustor

摘要

Spontaneous and triggered longitudinal combustion instability is simulated numerically in a single-injector liquid-rocket engine using a recently developed axisymmetric compressible flow solver. Turbulence is treated using delayed detached-eddy simulation, whereas chemical reactions are modeled using a compressible flamelet progress variable method. The baseline case is an unstable case that exhibits spontaneous instability and simulates well the experimental evidence. Heat loss is then introduced by imposing a isothermal boundary condition on the chamber wall. Various temperature values are used, with spontaneous longitudinal-mode instability still occurring at the higher wall temperature. Stable but inefficient combustion occurs for the lowest wall temperature. Subsequently, triggered instability of the chamber with low wall temperatures is simulated by perturbing the propellant mass flow rates. Unsteady oscillation can be triggered to higher-amplitude limit cycles. The effectiveness of various disturbances as triggers for instability is quantified through the definition of "triggered energy" and an unsteady Rayleigh-index analysis.