The use of the dye-layer technique for unsteady flow visualization

The unsteady flow around three-dimensional lifting surfaces undergoing a harmonic pitching motion was studied in a towing tank using the dye-layer technique. Different color fluorescent dyes were placed in the flow field by laying several thin, horizontal sheets prior to towing the lifting surface. The fluorescent dyes were excited using a sheet of laser light projected in the desired plane. The technique allowed the visualization of the flow in the separation zone on the low-pressure side of the lifting surface, the wake region, as well as the potential flow away from the surface. The complex unsteady flow structures were gleaned from observing the visualization results recorded on cine films.