Numerical Calculations and Wind Tunnel Experiments on Gas Diffusion in Thermally Stratified Flow over a Ridge

Abstract

A numerical model was proposed to simulate air flow and gas diffusion over a two-dimensional ridge in neutral and stable stabilities (bult Richardson number Rib=0.0, 0.7, 1.8). This model is based on the finite difference method and can precisely calculate the viscous convective flow over a no-slip oblique boundary.
It was found from the calculated results that a reverse flow appeared upstream of the ridge and a standing vortex disappeared downstream when bulk Richardson number Rib became greater than about 1.0, and that the gas concentration increased upstream of the ridge in stable condition.
Next, a wind tunnel experiment was performed in neutral and stable stabilities (Rib=0.0, 0.7 and 1.8) in order to verify the calculated results.
The experimental results showed that the flow patterns and concentrations significantly change with stability, in particular high concentration appeared upstream of the ridge due to the reverse flow in stable conditions.
Finally, the experimental results were compared with the calculated results and the good agreement was obtained between them.