Surface roughness and thermal stratification effects on the flow behind a two-dimensional fence—I. Field study

Abstract A small-scale field study was conducted to investigate the flow around a two-dimensional fence which was placed perpendicular to the oncoming flow. Characteristics of the oncoming flow and flow behind the fence were measured and, in addition, the flow behind the model was visualized with small wind vanes. The turbulent Reynolds number ( Re turb = UH K , where U is the mean velocity at model height H and K is the turbulent diffusivity) and flux Richardson number at the model height are chosen as the characteristic nondimensional numbers for the oncoming flow. These nondimensional numbers, derived from the normalized momentum and energy equations, are useful and convenient when comparing the field and wind tunnel data for similarity. The cavity wake length L c (chosen as flow characteristic) normalized by the model height H , L c H , was found to increase as Re turb increases. The effects of thermal stratification are unclear for the range of weak stratification tested. For such cases, the effect of the (weak) stratification is probably felt indirectly through its effect on the turbulence. These results will later serve as input and comparative data for a related wind tunnel study (Ogawa and Diosey, 1980) which will investigate the similarity criteria required for laboratory simulation of such phenomena.