Numerical analysis of coaxial swirl injectors

James Vincent Canino, Purdue University

Abstract

A growing recognition exists in the United States that injector dynamics play a pivotal role in the combustion instabilities of some Liquid Rocket Engines (LREs). Russian researchers believe injector dynamics can lead to unsteady mass flow from the injector to the combustion chamber resulting in unsteady heat release. Unsteady heat release coupled with the chamber modes, could cause combustion instability and the destruction of the rocket. The research described herein focused on the use of computational fluid dynamics to describe the frequency and amplitude of unsteady mass flow rate from a gas-centered coaxial swirl injector with varying geometries and fluid properties. An incompressible model, therefore, was utilized to investigate the effects of density ratio, liquid swirl velocity, liquid film thickness, collar thickness, and recess length. Present findings showed that the frequency at which the liquid film oscillates increases as the density ratio and collar thickness increase, decreases as the film thickness and liquid swirl velocity increases, and is unaffected by the recess length. Thus, the frequency seems dependent on the behavior of the vortex shedding/reattachment from the collar and the dynamic pressure imbalance on the liquid surface. The vortex behavior has been included as an important parameter for determining the behavior of the film given that the collar thickness affects the frequency. Since these studies lead to the belief that the vortex dynamics aft of the collar are important, a more fundamental study concerning the vortex dynamics behind a splitter plate/post was undertaken. For this study a compressible model was utilized to investigate the effects of momentum ratio, axisymmetry, the presence of a wall near the splitter, and swirl. Shedding frequency was found to increase as the momentum ratio varies from unity. Furthermore, axisymmetry reduced the shedding frequency over all momentum ratios. The presence of a wall near the splitter, in contrast, increased the shedding frequency when the higher momentum stream was adjacent to the wall. Finally, swirl caused complex interactions aft of the splitter rendering distinct trends in shedding frequency difficult to discern for high amounts of swirl.

Degree

Ph.D.

Advisors

Heister, Purdue University.

Subject Area

Aerospace engineering

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