Note on the Effect of Compressibility on the Profile Drag of Aerofoils at Subsonic Mach Numbers in the Absence of Shock Waves

摘要

A method is developed for calculating the profile drag of aerofoils in compressible flow at moderate Mach numbers in the absence of shock waves. The method is used to calculate the profile drag of an 18£ per cent thick symmetrical Joukowski aerofoil for a Mach number (U0/a0) of 0-685 at a Reynolds number of 107 and for a mean transition point position at 0.094c. The profile drag is also calculated for incompressible flow (Mach number zero). It is found that the calculated drag coefficient for compressible flow is only about 2 per cent, greater than that for incompressible flow. It is estimated that with the compressible-flow velocity distribution in incompressible flow the drag would be about 15 per cent, greater, but it appears that actually the increase in velocity due to compressibility is roughly balanced by the corresponding decrease in density