Low Reynolds number airfoil design and wind tunnel testing at Princeton University.

Abstract

Describes the Princeton wind tunnel for low Reynolds number aerofoil studies. No high pass filter is used, the DC component of the anemometer being subtracted off instead. Lift is measured by a mechanical force balance, drag is found indirectly by the momentum method. Notes reasonable agreement with results obtained in the Delft University and Stuttgart University tunnel. Discusses results for aerofoil shape, effects of trips, model accuracy and the effects of trailing edge thickness, making comparisons with results obtained using codes such as the Epplers and Somers codes. Considers the behaviour of the transition point on the upper surface and the effectiveness of a bubble ramp in the upper surface velocity distributions. Examines possible methods for boundary layer trips, noting that a simple two-dimensional trip performed as well or better than zig zag tape or hemispheres (bumps). Effects of contour inaccuracies are studied. Concludes that accuracy should be held to within 0. 2% of chord, with particular attention to be paid to the region from 20% to 60% on the upper surface where laminar separation bubbles form. (C.J.U.)