A FRAMEWORK FOR REPRODUCING FIELD-REPRESENTATIVE SHEAR IN PORTABLE WIND TUNNELS USED FOR ODOUR EMISSION MEASUREMENTS

Portable wind tunnels (PWTs) offer advantages over commonly used devices for measuring odorous gas emissions from passive liquid surfaces, such as wastewater stabilization ponds and settling basins, as they enable controlled flow conditions and more representative estimates of emission fluxes. A fundamental and largely unexplored challenge remains: how to prescribe and reproduce field-representative shear conditions within confined portable systems. This is particularly relevant because friction velocity ( ) plays a dominant role in controlling emission rates, especially for compounds with high gas-phase mass-transfer resistance. PWTs partially enclose the air–liquid interface to quantify emission fluxes while attempting to mimic atmospheric flow conditions. In this study, the internal flow within a PWT is experimentally characterized and modelled to evaluate boundary-layer development and friction velocity. High-resolution Particle Image Velocimetry measurements were conducted under a range of operating conditions. Results show that friction velocity can be predicted using boundary-layer theory. At low flow rates (mean velocities 0.12–0.61 m s -1 ), consistent with previous studies, the flow remains laminar and is well described by a modified Blasius solution. At moderate flow rates (1.92–2.27 m s -1 ), the flow is turbulent, with values comparable to field conditions, and the boundary layer is represented by an adjusted turbulent power-law profile. A key outcome is the development of predictive relationships enabling direct prescription of friction velocity through operating flow rate. This work bridges atmospheric boundary-layer flows and PWT conditions, supporting ongoing discussions on the standardization of PWTs for field odour emission measurements and providing a framework for physically based, reproducible emission studies.