Molecular Mixing and Flowfield Measurements in an Expansion-Ramp Combustor: Supersonic Flow

Abstract

This paper studies the level of molecular mixing and aerodynamic effects for supersonic flow in an "air" stream, with variable "fuel" mass injection and chemical heat release, in a flow configuration that has potential utility in dual-mode ramjet/scramjet combustors. "Fuel" is injected through a backward-facing expansion ramp at a rate insufficient to provide the entrainment requirements of the shear layer produced by the flow separation, which attaches to the lower guide wall. Part of the shear layer flow is directed upstream forming a recirculation zone that enhances mixing and provides flameholding benefits. Significant (passive) control authority over the flow is demonstrated by using variable mass injection through the ramp, and also by varying the level of heat release in the flow. molecular mixing was measured employing the hypergolic hydrogen-fluorine chemical reaction. The amount of mixing for the expansion-ramp geometry is found to be higher than in classical free shear layers. However, as in free shear layers, the level of mixing is found to decrease with increasing top-stream velocity.

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