Turbulent Boundary Layer Investigations with Conventional and Stereoscopic Particle Image Velocimetry

Abstract

Stereoscopic PIV (SPIV) measurements from an artificially tripped boundary layer flow along a flat plate with zero pressure gradient are presented to demonstrate the power of SPIV in turbulence research. The components of the double correlation tensor of fluctuating velocities are calculated in stream-wise span-wise planes at three vertical locations (y=220, 100, 30) to deduce the average dimensions of the dominant flow structures. A side from this statistical approach, instantaneous velocity fields are examined in order to retrieve the contribution of the various flow structures to the Reynolds stress and their significance for existing vortex models. The shape, extent and spatial distribution of slightly twisted low-speed streaks is clearly visible and in quantitative agreement with experimental and numerical results. However, the distribution of the out-of plane motions shows that no pairs of long stream-wise counter-rotating vortices flank the low speed regions. Furthermore, it seems that the outward migration of low momentum fluid is a result of an interaction between high and low speed fluids.