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Hybrid Flow Control of a Transonic Diffuser Boundary Layer

The formation of streamwise vorticity concentration by exploiting the interaction of surface-mounted passive and active flow control elements with the cross flow is investigated experimentally in a small-scale wind tunnel at high subsonic speeds (up to M = 0.5). Controlled formation of streamwise vortices can be a key element in the mitigation of the adverse effects of secondary flows in embedded propulsion system with complex inlet geometries that can affect pressure recovery and distortion at the engine inlet face. The evolution of these vortices is investigated on a converging-diverging insert along one of the test section walls that is designed to provide an adverse pressure gradient that mimics the pressure gradient within a typical offset diffuser. Counter-rotating vortex pairs and single-sense vortices are formed and characterized using conventional passive micro-ramps and micro-vanes, respectively. It is demonstrated that similar streamwise vortices can also be realized using synthetic jet actuators having rectangular orifices that are slanted or skewed to produce single-sense vortices, or streamwise aligned to produce vortex pairs. Hybrid actuation is demonstrated by combining the passive and active actuation approaches to yield a “fail-safe” device with significant degree of controllability.

Supported by Boeing