Mixing Characteristics of Active Microjet-Based Actuators in a Supersonic Backward-Facing-Step Flow

Abstract

Mixing in self-ignited supersonic combustors continues to be an important process that influences the performance and limitations for propulsion applications. A common approach for current generation combustors involves the employment of fuel-jet-injection schemes that enhance shear-layer mixing. These fuel jets issuing in a supersonic crossflow induce a bow shock coupled with an oblique shock causing total pressure losses and consequently reducing scramjet-combustor efficiency. This paper explores a novel approach for enhancing mixing using transverse active microjet-based actuators injecting in a supersonic backward-facing-step flow, while reducing pressure losses through weak-shock formation. Shear-layer mixing and flow features were characterized using particle image velocimetry and shadowgraph imaging. Relative comparisons were made with and without microjet actuation under nonreacting conditions. The main flow mechanisms attributed to enhancing mixing are explained. A triple-microjet-injection configuration, in the form of three microjet arrays supplied with different pressures, was investigated. The multiple-microjet-injection configuration formed a virtual ramp at the trailing edge of the backward-facing step that further enhanced mixing and increased the shear-layer thickness.