Experimental Determination of Floor-Origin Equivalent Roughness Parameters from CTA Measurements in a Boundary Layer Wind Tunnel

This study presents an experimental reduction methodology for deriving the equivalent roughness parameters required by rough-wall CFD wall functions from measured turbulent-boundary-layer velocity profiles. The methodology is demonstrated using constant-temperature anemometry measurements performed in the TASL1-M Boundary Layer Wind Tunnel at the Aerodynamics and Wind Engineering Laboratory “Constantin Iamandi”, Technical University of Civil Engineering Bucharest, where rough-wall boundary layers were generated using tetrahedral spires, a castellated barrier and variable floor roughness heights between 0 and 50 mm. A smooth-wall reference profile was first used to establish the logarithmic intercept of the unshifted law of the wall. The measured velocity profiles were then reduced to estimate the friction velocity, floor-origin aerodynamic roughness length and logarithmic roughness shift. The equivalent sand-grain roughness and wall-function roughness constant were subsequently obtained as derived parameters under the adopted roughness-function convention. The corrected rough-wall profiles show a consistent alignment with the common logarithmic representation after application of the fitted roughness shift. The proposed methodology establishes a reproducible pathway from measured velocity profiles to a coherent set of equivalent roughness parameters and provides a tunnel-specific parameter set for future rough-wall CFD simulations without explicit modelling of the physical roughness geometry.