Active Flow Control for Efficient Lift Enhancement in the Wing Slat Cut-Out using Pulsed Jet Actuators

The introduction of ultra-high bypass ratio (UHBR) aircraft engines and associated increased in nacelle size necessitates a cut-out in the wing leading edge slat, which induces separated flow during take-off and landing resulting in a loss of lift and increased drag. Active flow control (AFC) has been proposed as a potential solution to recover the loss in lift coefficient due to the slat cut-out region. The purpose of this study – part of the Clean Sky 2/Horizon 2020 WINGPULSE project (https://cordis.europa.eu/project/id/887092), is to experimentally and computationally investigate AFC strategies in the slat cut-out region with the goal of recovering lost maximum lift coefficient with minimal energy expenditure. This will be demonstrated by conducting experimental (wind tunnel) and numerical (CFD) tests. The effect of AFC in the form of pulsed jet actuators (PJAs) on a separated flow developed at high angle of attack on a cut-out in a representative model (swept wing with a high-speed DLR-F15 section and Fowler flap) in a off-design configuration at a chord-based Reynolds number of ~ 1 million is investigated. The model, of chord 0.34 m and span 1 m, consists of a built-in PJA module of 88 nozzles controlled by solenoid valves embedded in the wing to control the flow separation. The PJA module is designed to control each valve independently in duty cycle, pulsing frequency, and starting time relative to the first valve. Flow visualisation, force measurements and pressure distribution measurements, are conducted to examine the PJA effect on the separated flow. In addition, measurements of the PJA pneumatic and electrical power consumption is analysed. A parallel CFD study using large eddy simulations (LES) is conducted on the same geometry and conditions. It is shown that the lift coefficient is governed mainly by the dimensionless frequency F+ of the pulsing, the pulsing duty cycle, DC, and the PJA jet to freestream velocity ratio, VR. The impact of DC, F+, and the number of operating PJA nozzles on the lift improvement are examined. Also, it is found that reducing DC and F+ of the pulses remarkably improves the lift coefficient and delays the stall angle. In addition, a net cost benefit analysis is considered to identify optimal control strategies based on the balance between flow control effectiveness and power consumption.