An Investigation of Flow Fields Over Multi-Element Aerofoils

Abstract

This paper presents results obtained from a combined experimental and computational study of the flow field over a multi-element aerofoil with and without an advanced slat. Detailed measurements of the mean flow and turbulent quantities over a multi-element aerofoil model in a wind tunnel have been carried out using stationary and flying hot-wire (FHW) probes. The model configuration which spans the test section 600mm×600mm, is made of three parts: 1) an advanced (heel-less) slat, 2) a NACA 4412 main aerofoil and 3) a NACA 4415 flap. The chord lengths of the elements were 38, 250 and 83 mm, respectively. The results were obtained at a chord Reynolds number of 3×105 and a free Mach number of less than 0.1. The variations in the flow field are explained with reference to three distinct flow field regimes: attached flow, intermittent separated flow, and separated flow. Initial comparative results are presented for the single main aerofoil and the main aerofoil with a nondeflected flap at angles of attacks of 5, 10, and 15 deg. This is followed by the results for the three-element aerofoil with emphasis on the slat performance at angles of attack α=10, 15, 20, and 25 deg. Results are discussed both for a nondeflected flap δf=0deg and a deflected flap δf=25deg. The measurements presented are combined with other related aerofoil measurements to explain the main interaction of the slat/main aerofoil and main aerofoil/flap both for nondeflected and deflected flap conditions. These results are linked to numerically calculated variations in lift and drag coefficients with angle of attack and flap deflection angle.

Flow over an aerofoil without and with a leading-edge slat at a transitional Reynolds number

“…Recent developments in this field have incorporated modern experimental and numerical means. Maddah and Bruun [13] investigated flow fields over a multi-element aerofoil with and without an (heel-less) advanced slat at Re = 3 × 10 5 and incompressible conditions. Tang and Dowell [14] numerically examined the effects of small trailing-edge strips and Gurney flaps on the steady and unsteady flow over a NACA 0012 aerofoil at Re = 1 × 10 5 and 2 × 10 5 .…”

Effect of Leading-Edge Slats at Low Reynolds Numbers

“…Early studies indicated that devices placed at the leading-edge that attenuated the suction peak and moved loading aft were effective in delaying stall [2][3][4][5][6][7][8][9][10]. Representative devices include leading-edge slats, fixed slots and auxiliary airfoils ahead and above the leading-edge, as well as flaps [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. A slat (or slot) differs from a flap in having a gap through which windward surface fluid is vented to the leeward surface.…”