The formation of regions of separated flow on wing surfaces Part 1 low-speed tests on a two-dimensional unswept wing with a 10 per cent thick RAE 101 section Part 2 laminar-separation bubbles and the mechanism of the leading-edge stall

Abstract

Tests of a two-dimensional straight wing with a 10 per cent thick RAE 101 section have been made in a low-speed wind tunnel to check the validity of a criterion suggested by Owen and Klanfer for the type of bubble which will be formed when a laminar boundary layer separates from the surface of an aerofoil. The results confirm this hypothesis and show that if the boundary-layer Reynolds number based on displacement thickness at separation, calculated from an observed pressure distribution, is greater than 450 a short bubble is formed, and for (Rδ1)s less than 400 a long bubble is formed. For values of (Rδ1)s within the range 400 to 450 it is uncertain which type of bubble will occur. A method is given, based on these results, for predicting the type of bubble formed on a two-dimensional unswept wing of arbitary section shape for a given incidence and Reynolds number. A brief discussion of the physical structure of bubbles is given, and the more important problems yet to be solved are indicated. A hypothesis is put forward to explain the phenomenon of the 'leading-edge stall' of moderately thin aerofoil sections, and some remarks are added on the scale effect on the maximum lift attained by aerofoils which experience this type of stall.