Velocity effects in transverse mode liquid propellant rocket combustion instability

Abstract

Analytical and experimental studies have confirmed the application of the pressuresensitive combustion time lag to transverse as well as longitudinal modes of high-frequency combustion instability in liquid propellant rocket engines. However, a recent series of tests at Princeton University has demonstrated that an additional combustion rate sensitivity must be considered in the transverse mode case. In the present paper, an extension of the theory of transverse mode combustion instability, which includes linearized velocity effects, is described. Fluctuations of the radial and tangential velocity components are assumed to influence the combustion process rates in a manner analogous to that previously proposed by Crocco for pressure perturbations. A physical mechanism is suggested in the enhancement of the reactant mixing, which can be affected by the transverse components of the gas velocity. The analysis predicts that the tangential velocity perturbation may have a strong destabilizing effect on spinning tangential modes but will have no effect on standing modes. The radial velocity fluctuation is shown to have a smaller but significant influence. Experimental verification of the predicted effects has been obtained for a fuel-on-oxidizer impinging doublet injector pattern and for like-on-like injection using close spacing (0.1 in.) of the liquid spray fans.