Separation Control in 2-D Closed Channel Bends

Wind Tunnel experiments were performed in a high pressure environment simulating the bend of a centrifugal compressor.

Active flow control techniques in the forms of dielectric barrier discharge (DBD) plasma actuators, as well as passive flow control techniques in the form of counter rotating vortex generators were employed as a means of reattaching separated flow.

Additional modifications were made to the geometry of the geometry of the flow's turning radius and subsequent recurves to both improve flow characteristics and isolate significant factors of flow separation in the closed channel environment.

Experiments were conducted over a range of pressures and Mach numbers to determine applicability of flow control techniques.

Subsequent experiments were conducted in a turbulent 2-D channel flow at atmospheric pressure leading to a range of curved bends that result in an inner-radius flow separation.

The ratio of the bend centerline radius to channel height was 1.125.

The bend angle was adjustable and ranged from 0 to 150 degrees.

The approaching channel flow to the bends was approximately fully developed, and did not vary with the bend angle.

The flow conditions were adjusted to maintain a constant centerline velocity to account for the different pressure losses associated with the different bend angles.

The flow field within the bend was documented using smoke wire flow visualization, a traversable Pitot probe, and particle image velocimetry over a range of channel Reynolds numbers.

The objective was to identify characteristics of flow separation and reattachment, as well as approaches to flow separation control.

Flow separation control by both passive and active means are investigated.

Active control involves a diaphragm-driven unsteady tangential wall jet, and a pulsed-DC plasma actuator.

An optimum frequency was found in each case to minimize the reattachment length. The scaling of the optimum frequency to the separated flow characteristics is presented.