CFD Simulations of Liquid Rocket Coaxial Injector Hydrodynamics

Abstract

It is well recognized that dynamic processes occurr ing inside liquid rocket coaxial injectors are majo r contributors to combustion instabilities exhibited inside the thrust chambers of large liquid bi-prope llant rocket engines. Pressure and propellant mass flow f luctuations from the injector may lead to droplet atomization and vaporization perturbations which can potentially couple with the thrust chamber acoust ic modes and lead to unacceptable levels of combustion instability. Liquid rocket shear coaxial injector elements are subject to a wide range of hydrodynamic instabilities including vena contracta instabilities insid e the manifold feed line passages, LOX post tip vortex sh edding and injector faceplate region vortex formati on to name a few. For these reasons, the basic unforced r esponse of liquid rocket coaxial injectors is of in terest to designers of liquid rocket engines. The Loci/CHEM code was used to perform single-element, 2-D unsteady CFD simulations on the Hydrogen/Oxygen Multi-Element Experiment (HOMEE) injector which was hot-fire tested at Purdue University. An in-depth look insid e the injector recess region was performed in an ef fort to characterize the frequency response of a shear co-a xial injector element using real fluids model formu lation for the liquid oxygen stream. The effects of varyin g the O/F ratio, LOX post thickness, LOX post lengt h, and LOX post acoustic frequency on injector frequency response were investigated.