Recent Experience in the Rae 5 Meter Wind Tunnel of a China Clay Method for Indicating Boundary Layer Transition

摘要

A flow visualization method using clay to study boundary layer transition on a slender body model at high Reynolds number in a pressurized, low speed wind tunnel is described. The method is based on the differential rate of evaporation, beneath laminar and turbulent boundary layers, of a liquid absorbed on a solid spread on the surface. The liquid has a similar refractive index to the solid so that the mixture appears to be transparent until evaporation takes place, when the color of the solid becomes visible. The solid layer consists of china clay powder mixture with chemicals to form a lacquer, which is sprayed on to the surface. When dry, this forms a semipermanent white absorbent film. A liquid sprayed on this film is absorbed by it, causing it to become transparent. The lacquer consists of Frigilene (100 ml), butyl acetate (100 ml), butyl alcohol (100 ml), xylene (50 ml), and china clay (100 mg).