Transition in boundary layers on a concave surface

Abstract

Transition from laminar to turbulent flow has been investigated in boundary layers along a concave surface of 2.0 m radius of curvature for a freestream velocity range of 6.0-15.0 m/s. Velocity and turbulent intermittency measurements were made using a single sensor hot-wire anemometer. Intermittency profiles at the so-called upwash and downwash regions were obtained at some streamwise positions to help determine the transition starts and ends at the regions. The experimental results show that, at both upwash and downwash regions for all of the free-stream velocities tested, the intermittency profiles at different transition stages exhibit similar behaviors. The difference between the upwash and downwash intermittency profiles obtained at the same streamwise locations decreases with increasing freestream velocity. For all of the freestream velocities, transition starts and ends earlier at the upwash regions than at the downwash regions. The transition lengths in the upwash regions are slightly longer than those in the downwash regions and decrease with increasing freestream velocity. The starts of transition at the upwash regions agree well with the transition prediction Goertler number of 6, whereas at the ends of transition for both upwash and downwash regions, the Goertler number ranges front 7.90 to 9.30.