Field and wind tunnel study of the flow and diffusion around a model cube—I. Flow measurements

Abstract

Field and wind tunnel studies of the flow and diffusion around a cube were conducted. Part I of this study investigated the flow patterns behind the model. In the field study, the nondimensionalized cavity wake length (the longitudinal distance from the model center to the flow reattachment point normalized by the model height H), L c / H, was determined using 61 small vanes arranged on the cube roof and nearby ground. Eighty three field tests were conducted and it was found that as the wind angle increased, L c / H increased, and as the upwind turbulence intensity increased, L c / H decreased. To isolate the most significant parameters for L c / H, a statistical analysis was performed and it was found that wind direction had the largest positive correlation followed by Re turb , while u∗/U had the largest negative correlation followed by σ v / U, σ u / U and σ w / U. For the range of stabilities tested (−0.54 ⩽ Ri f ⩽ 0.13), thermal stratification had a negligible effect on the value of L c / H. Among these variables, the contribution of the wind direction was 62 % while that of the crosswind turbulence intensity was 12% according to a step-by-step multiple regression analysis. To clarify the results found in the field, a scale model of the cube was investigated in the wind tunnel, changing wind direction and upwind surface roughness. Similar results were noted and comparing the two studies it was found that when wind direction and upwind turbulence intensity, preferably σ u / U, σ v / U and u∗/U, were matched, the values of L c / H in the field and wind tunnel agreed.