Thermomechanical Concepts and Modeling for Stability Physics in Liquid-Propellant Rocket Engines

摘要

Thermomechanical concepts and modeling are used to describe the response of inert and reactive gases to transient, spatially resolved thermal energy deposition. The ultimate goal is to establish the cause-effect relationship between combustion-generated energy deposition and the mechanical disturbances responsible for operationally observed pressure oscillations in liquid-propellant rocket engine combustion chambers as well as to identify physical processes that convert thermal energy to kinetic energy. Asymptotic formulations of the nondimensional describing transient conservation equations for both inert and reactive gases are used to identify nondimensional parameters that characterize fundamental physics occurring as the gas responds to localized heating. The characteristics of the responses depend upon the magnitudes of the suite of parameters. Some are described by hyperbolic partial differential equations; others involve either nearly constant density or nearly isobaric phenomena. Thermomechanical concepts are used to explain how initially imposed small pressure, density, temperature, and velocity disturbances can be the sources of a thermal response that evolves to relatively larger thermomechanical disturbances. The competition between localized, spatially distributed chemical energy addition from a highactivation-energy, one-step, Arrhenius reaction and compressibility effects associated with localized gas compression/expansion is the driver for diverse outcomes. Sufficiently robust thermal energy addition can cause a thermal explosion after an induction time period, followed by relatively large changes in the thermodynamic variables and induced velocity (instability) on a time scale exponentially short compared to that of the induction time.