Rotational flow

A flow in which net rotation of the fluid element is not equal to zero, is known as rotational flow.

Or

The flow in which the fluid particles also rotate about their own axes while flowing, is called rotational flow.

• Distortion in this case is less than irrotational flow.

Example

In a rotational flow if a match stick is thrown on the surface of the moving fluid, it will rotate about its own axes.

Reference :

Hydraulics, fluid mechanics and hydraulic machines by R.S Khurmi