Influence surface finish on airfoil design

In this study has been undertaken to determine the suitability of effects surface roughness models for use in subsonic and transonic wind tunnel testing. The geometry used for the precursor study was that of a vertical lander concept. The vertical lander was a generic blunted cone followed by a bread-loaf-shaped base with two fins, or fairings, on the base’s upper surface. Three surface roughness were fabricated from Steel 17-4PH H900 by a CNC machining and grinding. The roughness average (Ra) of surfaces for each model was 0.8 μm, 1.6μm and 6.3μm that determined by optical surface profilometer. Testing covered the Mach range of Mach 0.3 to Mach 1.2 at an angle-of-attack range of −4° to +16° at zero sideslip. Coefficients of pitching moment, axial force, normal force, and lift over drag are shown at each of these Mach numbers. The study showed that between Mach numbers of 0.3 to 1.2 the longitudinal aerodynamic data in pitching moment and normal force showed very good agreement between the three models. The surface finish does have more effect on the aerodynamic characteristics such as axial force and lift over drag.