This simulation illustrates the velocity of a fluid for rigid body rotation and for irrotational flow. For rigid body rotation, the angular velocity is assumed to be constant, and the circulation is not taken into account. For irrotational flow, each contour in the vortex is assumed to have the same value of circulation, and angular velocity is not taken into account. The velocity displayed to the right of the image is the velocity of the fluid at the center of the black point.