Experimental study of discrete jet forcing for flow separation control on a wall mounted hump

An experimental study was conducted in a subsonic wind tunnel on a wall mounted hump at chord Reynolds numbers of 0.68 · 10⁶ < Re < 2.02 · 10⁶ (Ma < 0.2). The vast majority of the results were recorded at Re = 1.01 · 10⁶ (Ma = 0.09). A baseline characterization was performed prior to studies on separation control using spatially distributed steady jet actuation and fluidic oscillators. Time-averaged surface pressure was measured along the chord and span of the model and stereo PIV data was acquired in a plane just downstream of actuation. Spanwise measurements showed the time-averaged baseline flow as two-dimensional and in good agreement with the established literature. Steady jet actuation offers good control authority for a spacing of Δz = 0.25 in. ((formula Presented) = 1.14 %) at Cµ > 0.9 %. Larger spacing (Δz = 0.5 in., (formula Presented) = 2.27 %) results in 3D behavior and the flow could not be fully reattached. Fluidic oscillators reattach the flow at relatively low Cm values (Cm = 0.6 %) for spacings at which the steady jets showed 3D behavior (Δz = 0.5 in., (formula Presented) = 2.27 %). In fact good control authority was observed for even larger spacing (Δz = 1 in., (formula Presented) = 4.45 %). Stereo-PIV showed the fluidic oscillator control mechanism to be related to the generation of steady streamwise vorticies in the nominally separated region. Finally, figures of merit are introduced to estimate the quality of the applied actuation relative to the baseline and an inviscid solution while also considering the necessary momentum and energy requirements.