A method is presented for the visual indication, of boundary—layer transition by use of a luminescent lacquer. The method consists of spraying a thin, uniform film of lacquer containing a phosphor pigment on the model and irradiating the model with ultraviolet light. The phosphor used has the property of fluorescing with a bright yellow, light when dry ari remaining dark when wet. Since the drying time (or evapo ration rate) is different for laminar and turbulent boundary layers, patterns of light and dark areas are established which identify the, type of boundary layer and, consequently, the location of transition from laminar to turbulent flow. The contrast between the light and dark regions is pronounced and good photographs of the patterns may be obtained. Usually, special preparation of the model surface is not required.
展开▼
