Control strategies targeting azimuthal flow separation over the inner windward surface of an engine nacelle inlet in the presence of a crossflow are explored in a wind tunnel investigation at inlet Mach numbers up to Formula: see text and crossflow Formula: see text. Three fluidic control approaches using arrays of surface jet actuators are considered, which include steady jets and fluidically oscillating jets with and without internal feedback flow. The effects of each of the jet types are evaluated using the same array configuration over a range of Formula: see text, Formula: see text, and the control mass flow rate parameter Formula: see text. Although each actuation approach engenders significant improvements in distortion Formula: see text compared to the base flow, unsteady actuation using fluidically oscillating jets generally outperforms steady jet actuation at the same actuation mass flow rate. Furthermore, it is found that fluidically oscillating jet actuation is more effective at low Formula: see text in the presence of internal feedback and at high Formula: see text in the absence of internal feedback. Specifically, fluidic actuation in the absence of internal feedback reduces the distortion measure Formula: see text by 50–55% across the present range of Formula: see text, at Formula: see text lower than 0.3%. The present investigations also showed that changes in the topology of flow separation with varying Formula: see text and Formula: see text underscored the need for reconfiguration of the active jet actuators within the jet array to conform to the flow separation pattern to achieve optimal effectiveness.
Nichols et al. (Sun,) studied this question.