PART I The Effect on Transition of Isolated Surface Excrescences in the Boundary Layer PART II Brief Flight Tests on a Vampire I Aircraft to Determine the Effect of Isolated Surface Pimples on Transition

摘要

The effect of isolated surface excrescences in a laminar boundary layer in producing disturbances which may lead to turbulent flow has been examined experimentally by several methods. Photographs of some of the flow patterns visualised by smoke and china-clay techniques are given.nThe critical heights of pimple which just give rise to spreading wedges of turbulent flow have been measured on a flat plate and on two aerofoils at several angles of incidence. The results are analysed and are presented in a form which enables approximate estimates to be made of the protuberances permissible on laminar-flow surfaces at full-scale flight Reynolds numbers. The estimates suggest that at an altitude of 30,000 ft the critical pimple height is 0-004 in. for a speed of 350 m.p.h., whilst 0-002 in. may be permissible at all subsonic speeds. At sea-level, however, the tolerances are approximately halved.