The effect of model size on measurements in the R.A.E. high speed tunnel. Drag of two-dimensional symmetrical aerofoils at zero incidence

Abstract

Pitot traverse drag measurements were made at zero incidence on three NACA 0015 aerofoils of different sizes. Pressures at the tunnel walls were also measured. For each aerofoil, tests were made at two different Reynolds numbers by changing the tunnel pressure. From the results it has been possible to separate the effects of varying Reynolds number and tunnel wall interference. It has been shown that the blockage corrections in current use (based on linear theory) are not large enough to equalise drag measurements made on different sizes of aerofoil at the same Reynolds number. Empirically increased corrections which bring the results into agreement have been found. The results have also shown that at high Mach numbers there is a fairly large variation of drag coefficient with Reynolds number, especially between Reynolds numbers of about 0.2 x 10power6 and 1.4 x 10power6.