On relation between Reynolds number and Kلrmلn vortex formation on a bluff body in natural wind

Measurements on three rectangular prisms in natural winds at Reynolds numbers from 3×104 to 3×106 reveal the variation of conditions in which Kلrmلn vortices are generated. In this experiment, the Strouhal number and the Reynolds number had to be modified to fit the concept of stream path so that they could be defined even in such an unstable flow as natural wind. Under the condition with higher Reynolds numbers, the Strouhal numbers were found to be larger and the coefficients of lift and drag were found to be smaller. These results may explain the unsteadiness of surface pressures on a bluff body in natural wind.