Wind Tunnel Simulation of the Atmospheric Boundary Layer

We aim to generate an artificially thickened boundary layer in the wind tunnel with properties similar to the neutral atmospheric boundary layer (ABL). We implement a variant of Counihan's technique which uses a combination of a castellated barrier, elliptical vortex generators, and floor roughness elements to create a thick boundary layer in a relatively short wind tunnel. We demonstrate an improved spanwise uniformity than in Counihan's original design by using a tighter vortex generator spacing with a smaller wedge angle to keep frontal area approximately constant. This is achieved while keeping the turbulence intensity and power spectral density unchanged. It was found possible to generate a boundary layer at $Re_{\theta} \sim 10^{6}$, displaying logarithmic mean velocity behavior, a constant stress region, and turbulence intensities that compare favorably with full scale ABL measurements and laboratory rough-wall boundary layers. In addition, the longitudinal power spectral density agrees well with von K\'arm\'an's model spectrum and the integral length scale agrees well with data from ABL measurements.