Separated flow control in diffusers using pneumatic and plasma based actuators

Flow separation is a phenomenon in which the flow encounters an adverse pressure gradient along a surface and is unable to stay attached to it. It is observed in different scenarios, like flows over wings, blades, diffusers and S-ducts and leads to undesirable outcomes like loss of lift, increase in drag, stall and decrease in pressure recovery. In particular reference to jet engines, separation of flow in its diffuser or ducting section adversely affects the performance of the engine. Flow control aims at controlling this separation by using active and/ or passive devices. Two of the many techniques employed are pneumatic actuation, in which a continuous or pulsed jet of air is forced into the core flow, and plasma actuation in which an arc discharge is created between two electrodes on the surface of the body or inside cavities to effectively inject momentum and energy into the core flow. These two actuator systems are being explored to control the flow and encourage quicker reattachment or eliminate separation altogether in open-loop and potentially closed-loop form.