Study on three-dimensional flow characteristics of flap separated flow control based on oscillating jets

Boundary layer blowing technology can suppress flow separation of simple flaps at large deflection angles and increase the wing's lift coefficient. Compared with steady jet blowing, oscillating jets with a larger spanwise sweep range allow greater actuator spacing, reducing the number of actuators and saving control air volume. However, the discrete arrangement of widely spaced actuators inevitably causes uneven spanwise jet energy injection, which adversely affects lift enhancement. In this study, a straight wing model with a simple flap and an oscillating jet actuator array was designed to study the 3D flow structure of oscillating jet-controlled flap separation. Results show that non-overlapping sweep ranges of adjacent actuators prevent full-span suppression of flap separated flow: within the jet sweep range, a certain attached area forms; outside this area, discrete oscillating jets exhibit irregular spanwise flow under local complex pressure gradients, forming two typical separation regions. Type Ⅰ regions lie between closely spaced jets, where—high-speed jets restrict separated backflow inlets, create strong shear with low-energy fluid in separations, form counter-rotating vortices at spiral points, promote jet entrainment, and reduce separations. Type Ⅱ regions lie between widely spaced jets, where separation is poorly controlled. Future flap separation control system designs should consider the relationship between the actual oscillating jet sweep range and actuator spacing to avoid Type Ⅱ regions and achieve higher lift benefits.