Control of a Separating Flow over a Turret

Control of flow separation over a turret comprised of hemisphere on top of a cylindrical base is demonstrated in wind tunnel experiments at Reynolds number ReD ≈ 800,000. Highfrequency actuation (StD ≈ 15) is effected using spanwise arrays of individually-addressable synthetic jet actuators and the control effectiveness is characterized using high-resolution particle image velocimetry (PIV) and surface pressure measurements. The present work has demonstrated that high-frequency synthetic jet actuation can lead to substantial separation delay, and that extent of separation delay is directly proportional to both the jet momentum coefficient and the spanwise width of the actuator array. Detailed PIV measurements near the juncture between the hemisphere and the cylinder show that in the presence of nominal actuation there is virtually no recirculating flow within the measurement window down to the level of the juncture between the hemisphere and the cylinder, and suggest that the boundary layer on the surface of the hemisphere is actually attached. However, the pressure distributions show that the static pressure levels off at elevation angle greater than 145°, which may be attributed to 3-D effects. Estimates of the turbulent kinetic energy within the flow downstream of the hemispherical cap show a rather dramatic reduction in TKE in the controlled flow, as the recirculating flow domain is pushed below the hemisphere-cylinder juncture. It is also shown that the presence of a partition plate downstream of this juncture prevents vertical advection of the reduced recirculating flow domain and forces it towards the corner much like in the flow behind a hemispherical shell on a flat plate.