Scale Effects in Swirling Flow

This paper presents the results of a study of vortex behavior in open-channel hydraulic models. The effects of model scale on steady well-developed vortices were investigated experimentally by comparing the behavior of three sizes of geometrically similar models. The models had sharp-edged circular orifices with diameters of 2 in., 4 in., and 6 in., respectively. Similarity of swirl production, discharges and air cores was considered. A general dissimilarity was found between the swirls produced in the smallest model and those in the two larger models. Also a local scale effect was detected in the region of the air core; the swirl reduction in this region was greatest in the smallest model. A theoretical explanation is given for the local scale effect. The behavior of the two larger models was similar.