The influence of actuator spacing on separation control using fluidic oscillators is experimentally investigated on a wall-mounted hump. Momentum inputs up to Cμ 2.5% are tested at four different spacings (Δz∕c 2.27, 4.55, 6.82, and 9.09%), at Re 1.0 ⋅ 106 and M∞ 0.09. For all spacings, the control authority is characterized by two distinct regimes associated with boundary-layer control and circulation control. The two narrow spacings show steep control authority gradients in the transition between boundary-layer control and circulation control. The time-averaged flowfields from spanwise stereoscopic particle image velocimetry (PIV) vary significantly between the presented spacings, but the circulation normalized by mass flow rate per jet remains constant for a given momentum input in the boundary-layer control regime. When the spacing is too small for a given oscillator design, the introduced vorticity is unorganized and actuation is less effective for a given momentum input. Once the flow is attached, the circulation reduces for larger momentum inputs (circulation control). This indicates a connection between increased control authority and decreased circulation in the circulation control regime. These findings are supported by novel circulation metrics that describe the level of organization in the flowfield.
ASJC Scopus subject areas
- Aerospace Engineering