Wake Drag of Microjet Flow Control from Pressure and Particle Image Velocimetry

Abstract

A wind-tunnel experiment was conducted to evaluate the impact of flow control on the flap of a multi-element airfoil on its wake velocity profiles and drag. The flow control strategy uses microjets (small, low-momentum jets that are nominally surface-normal and located near the trailing edge of the flap) to control lift and improve the aerodynamic performance of airplane high-lift systems. The baseline airfoil is the two-element NLR7301 with a Fowler flap deployed at 20 deg, tested in the Oran W. Nicks Low-Speed Wind Tunnel at Texas A&M University at an angle of attack of 0 deg, a nominal chord Reynolds number of 2.4 million, and a Mach number of 0.12. This study focuses on the aerodynamic performance impact of microjets with variable mass flow control on the pressure side near the trailing edge of the flap and compares them to a fixed tab in the same location. Key measurements include airfoil wake profiles made using a traversing pitot–static-pressure system and particle image velocimetry. Wake-based drag was observed to decrease significantly when microjet control was used, compared with a small fixed tab that provides equivalent lift enhancement.