On drag variation due to array patterns of cubic blocks

A series of wind tunnel tests were performed to investigate the variation of the surface drag caused by different array patterns of roughness elements. The drag on the rough surface using cubic blocks was directly measured by a float built in the floor of the wind tunnel. The direct measurement by the float was comparablly reliable when compared with other three different ways of drag measurement. The variation of the surface drag coefficient Cr caused by array patterns has been examined. The relationship between Cr and the 'roughness concentration' ratio λ element frontal area/surface area per element, showed that the randomarrayed distribution was equivalent to the staggered arrayed pattern with the elements facing to the wind at an angle of 45