Flow Visualization of Three-Dimensional Large Scale Motions in ZPG and APG Turbulent Boundary Layers

Abstract

This paper presents a preliminary report detailing 3-D flow visualization images of a zero-pressure gradient (ZPG) and adverse pressure gradient (APG) turbulent boundary layer. A Stratford ramp was designed and constructed to produce a moderate adverse pressure gradient on the wind tunnel wall. The boundary layer flow was seeded with smoke and a high-repetition rate laser light sheet is scanned across the flow. Using a high speed camera, 2-D images of the flow were captured which are then reconstructed into a nearlyinstantaneous 3-D flow visualization image of the turbulent boundary layer. Pressure measurements and 2-D particle image velocimetry (PIV) were performed to characterize the flow with and without the ramp. In the three-dimensional flow visualization images, the ZPG turbulent boundary layer appeared to generally have a smoother, more well-defined boundary edge, outlining larger structures compared to the APG case. In the ZPG images, the large scale vortices appear to be a well-defined shape and show streaks of freestream flow entrainment more often than in the adverse pressure gradient case.