This paper considers the two-dimensional vorticity creation-diffusion model for a vortex particle method. To formulate the model, we employ the asymptotic analysis and show that the outer flow has to satisfy the no-through-flow condition. The strength of the created vortex sheets on the body surface is found to be the double of the slip velocity induced by the uniform flow and the scattered vortex particles, using the conformal map from the physical plane to the outside of a circle. The present model can be applicable to a solid body of an arbitrary shape but consisting of a smoothed surface.

fluid mechanics, vortex particle method, vorticity creation - diffusion model.