An Air°injection Nethod o f fixing Transition from Laminar to Turbulent Flow in a Boundary Layer

Abstract

~The paper deals with a simple method of fixing transition by the injection of small air jets into a boundary layer from a row of surface holes, and describes experiments which establish the effectiveness of the method. A merit of the method is that the rate of air injection can be adjusted to give, at each speed of test, a minimum disturbance of flow necessary to fix transition at the position selected. The minimum rate of air injection for transition is small, about 0. 015 times the rate of mass-flow in the boundary layer. The method is especially suitable for high-speed tests since it does not give a local shock wave, which is sometimes present when a surface wire is used to fix transition. The experiments show that a large increase in drag may be caused by a very small leakage of air into the laminar boundary layer of a low-drag wing. 1. Introduction.-A standard method of fixing the posffion of transmission from laminar to turbulent flow in the boundary layer of an aerofoil is either by a fine spanwise wire or by a roughness caused by a narrow band of fine particles on the,surface. The criterion that transition occurs close behind a wire is uhh/v ~ 400, where h is the diameter of the wire and Uh is the velocity in the boundary layer, without the wire, at a distance h from the surface 1,

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Cite this paper

@inproceedings{FAGE1944AnAN, title={An Air°injection Nethod o f fixing Transition from Laminar to Turbulent Flow in a Boundary Layer}, author={y A . FAGE and Randy Sargent}, year={1944} }