TRANSITION OF BOUNDARY-LAYER FLOWS IN THE PRESENCE OF GOERTLER VORTICES

Further experimental results on transition of boundary layer flows in the presence of streamwise counter-rotating Goertler vortices were obtained on concave test surface of 3.0 m radius of curvature. The test surface was mounted in a perspex (plexiglass) curved rectangular section duct connected to a low speed, blow down type, wind tunnel for a free-stream velocity range of 2.0 to 13.1 m/s. Velocity measurements were made using a single sensor hot-wire anemometer and boundary layer flow transitions were detected by a frequency spectrum method. The experimental results show a simple linear relationship between transition start position and free-stream velocity, and lie well between the limit lines of Goertler number transition criteria. It is found that the onset of transition at the flow upwash region occurs when the Goertler number based on the boundary layer momentum thickness reaches a value of about 7.5.