Aerodynamic Load Control through Blowing

Abstract

Aircraft are subject to extreme loads during gust encounters. Amelioration of these loads will allow for reduced structural weight and therefore greater efficiency. In this paper, two versions of blowing jet from suction surface, normal and upstream, are studied under steady state conditions to illustrate the effectiveness of these devices at mitigating extreme lift. Force, pressure and Particle Image Velocimetry measurements were performed at a Reynolds number of 660,000 for a NACA 0012 airfoil. A range of volumetric flow rate coefficients, below CQ = 0.44%, for a range of angles of attack 0° ≤ α ≤ 20°, are studied for five chordwise locations. It was observed that normal blowing at xJ/c = 0.95 induces a change in lift of ΔCL = -0.15 for the maximum momentum coefficient. Locations further forward produce a negligible change in lift coefficient. Whereas, upstream blowing was capable of reducing lift at all chordwise locations studied by up to ΔCL = -0.33. Upstream blowing encourages the shear layer to deflect upwards and inciting a greater adverse pressure gradient on the upper surface. Locations near the trailing edge are preferable for low angles of attack, as greater lift mitigation is obtained. Lift reduction can be augmented for higher angles of attack, with leading edge locations. As expected, increasing momentum coefficient increases the magnitude of the change in lift for all cases studied.