Reynolds Stresses in Turbulent Boundary Layers at High Reynolds Number

A 2D turbulent boundary layer experiment with zero pressure gradient has been carried out over a smooth surface using two cross hot-wire probes. Wind tunnel speeds of 10 and 20 m/s were set up in order to investigate the effect of the upstream conditions and Reynolds number on the outer flow. For a given set of upstream conditions such as the wind tunnel speed, trip wire size and location, the three components of the velocity field were measured from about 14 m away from the inlet of the wind tunnel up to 30 m downstream. This experiment is unique because it achieves Reynolds numbers as high as $R_\theta$=120,000 for which measurements of the mean velocity and the Reynolds stresses profiles, <u^2>, <v^2>, <w^2> and -<uv>, are reported. It is shown that by fixing the upstream conditions, the mean velocity profiles, and the normal Reynolds stress components, particularly the <u^2> and <v^2> expressed in outer variables, tend to collapse even though the local Reynolds numbers, $R_\theta$, vary from approximately 31,000 up to 120,000. However, the spanwise component of the Reynolds stress, <w^2>, and the Reynolds shear stress component, -<uv>, showed a dependence on the Reynolds number. Moreover, these measurements will be compared with the low Reynolds number (761 &#8804; R_\theta &#8804; 5,321) data of Castillo and Johansson (2002 J. Turbulence 3 031). More importantly, it will be shown that the Reynolds stress is significantly influenced by the upstream conditions (i.e flow history, wind tunnel speed)