Efficient Flow Control via Vortex-Synchronized Travelling Wave Pulsed Jet Actuation

The advent of ultra-high bypass ratio (UHBR) engines presents a promising opportunity for enhancing sustainability in commercial aviation. However, integrating these engines often necessitates a large cut-out in the wing's leading-edge slats, which can induce flow separation and degrade aerodynamic performance. This study investigates the application of active flow control (AFC) using an array of pulsed jet actuators (PJAs) distributed across the slat cut-out region. The PJAs intermittently inject high-momentum air into the boundary layer to suppress separation and improve lift yield. A central focus of the work is the implementation of a spanwise-propagating travelling wave imposed along the array, achieved by introducing a time delay between successive actuators. By synchronizing the wave frequency with the natural vortex-shedding frequency at the slat cut-out, greater lift enhancement is achieved compared to standard pulsing. Furthermore, this approach enables a reduction in array size by operating only those actuators positioned near dominant vortex structures, thereby minimizing both pneumatic and electrical power demands. Wind tunnel experiments were carried out using a 0.9 m semi-span DLR-F15 wing fitted with 44 PJAs in the slat cut-out region. Hot-wire anemometry confirmed that unsteady vortices originate at the cut-out corners, with vortex size increasing and shedding frequency decreasing beyond angles of attack of approximately 9°. When travelling wave actuation was applied to only 25% of the outboard most PJAs, a lift coefficient increase of 4.5% was observed relative to the uncontrolled baseline, and a 0.57% gain over the same actuators operating in standard pulsing mode. Additional tests examined the performance of travelling waves imposed over varying array sizes, and a figure of merit was defined to evaluate lift enhancement relative to power input. Results identify the most efficient array configuration, achieving significant aerodynamic benefits with minimal energy expenditure.