Experimental characterisation of atmospheric flows in the boundary layer wind tunnel facility at the University of Bristol

A comprehensive experimental investigation of Counihan-type passive surface treatments was conducted in the newly commissioned Boundary Layer Wind Tunnel (BLWT) at the University of Bristol to simulate atmospheric boundary layer (ABL) flows. Using castellated barriers, elliptical vortex generators, and modular roughness elements, the principal components of the surface treatment were parametrically varied to isolate and quantify their respective roles in governing mean velocity development and turbulence structure within the simulated ABL. The results show that the castellated barriers primarily govern turbulence generation in the outer region, while the roughness elements dominate near wall turbulence characteristics. Unlike findings often reported in other facilities, the vortex generators in the present study were found to have a limited influence on the mean velocity, turbulence intensities and integral length scales. Moreover, they were ineffective in controlling the boundary layer thickness. Tailored surface ABL treatment configurations for urban, suburban, and rural ABLs demonstrate close agreement with established field data, canonical models and previously published datasets, confirming the BLWT’s capability to simulate physically realistic and scalable atmospheric flow conditions. This work also establishes guidelines for optimising wind tunnel ABL simulations, supporting research in environmental aerodynamics and structural wind engineering.