Two-dimensional potential flow through an impeller having radial vanes is considered by using the complex velocity potential. The impeller consist of radial straight vanes arranged symmetrically about center of impeller, and it rotates with a uniform angular velocity about the center. It is assumed that isolated vortices are set up at points lying between the vanes. The flow is to consist of four parts, namely; (a) discharge flow issuing from the center of impeller, (b) so-called channel vortex flow, or the flow caused by the pushing action of moving blades, (c) circulatory flow about each vane, (d) flow caused by isolated vortices, whose vortex centers lie at some point between the vanes.
By consideration of combined flow caused by these four component flows, and imposing the condition of finitude of flow-velocity at two edges of each vane, the relation between the discharge, amount of circulation and strength of isolated vortex is deduced. The result is explained by a numerical example.