Similitude in Free-Surface Vortex Formations

Different fluids were used to investigate the effects of fluid viscosity and surface tension on the incipient conditions for vortex formation and on vortex size and shape. Experiments were conducted in two different sizes of cylindrical tanks with adjustable vanes at the perimetry to allow varying degrees of initial circulation to be generated at the entrance to the test section. The results of the experiments demonstrated that: (1) free surface vortex flow is affected by initial circulation and viscosity, but, for the ranges tested, is not affected by surface tension; (2) the coefficient of the discharge is a function of the Reynolds and circulation numbers; and (3) regions in which an air core will or will not form can be defined by the depth of flow, orifice size, and circulation and Reynolds numbers.