Generating an artificially thickened boundary layer to simulate the neutral atmospheric boundary layer

Abstract

We aim to generate an artificially thickened boundary layer in a wind tunnel with properties similar to the neutral atmospheric boundary layer. We implement a variant of Counihan's technique which uses a combination of a castellated barrier, elliptical vortex generators, and surface roughness to create a thick boundary layer in a relatively short wind tunnel. We demonstrate an improved spanwise uniformity when compared to Counihan's original design by using a tighter vortex generator spacing with a smaller wedge angle which keeps the frontal area approximately constant while keeping the turbulence intensity and power spectral density unchanged. With this arrangement we were able to generate a 1:1000 scale atmospheric boundary layer at Reθ∼106 displaying logarithmic mean velocity behavior, a constant stress region, and turbulence intensities consistent with atmospheric boundary layer measurements and high Reynolds number laboratory rough-wall boundary layers. In addition, the power spectral density of the longitudinal velocity fluctuations agrees well with von Kármán's model spectrum, and the turbulence integral length scale agrees well with data from atmospheric boundary layer measurements.