The effects of the upstream conditions on a low Reynolds number turbulent boundary layer with zero pressure gradient

Abstract

An experiment on turbulent boundary layers with low local Reynolds numbers in a zero pressure gradient has been carried out using the laser-Doppler anemometry technique and a similarity analysis of the Reynolds averaged Navier-Stokes equations. This experiment seeks to investigate the effect of the local Reynolds number and the upstream conditions on the downstream development of the mean flow and the turbulent quantities. It was found that by fixing the upstream conditions (i.e. such as the wind-tunnel speed and trip wire size), the mean velocity profiles and Reynolds stresses tend to collapse in the outer flow even though the Reynolds number, R θ, varied from approximately 700 up to 5321. However, when the upstream conditions were changed and the local Reynolds number was held constant, neither the profiles of the wall-normal Reynolds stress nor those of the Reynolds shear stress collapsed, thus showing the effects of the upstream conditions. Moreover, no effect on the mean velocity profiles or the longitudinal Reynolds normal stress could be seen in the present data. However an influence of the upstream conditions on the mean velocity profiles could be shown to exist by comparing the present data with those of other investigators at higher wind-tunnel speeds. In this experiment the upstream conditions were varied by changing the wind-tunnel speeds to 5, 10 and 20 m s−1, while the trip wire size and its location were held constant. This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M Sommerfeld.