compressible and incompressible flow and rotational and irrotational flow

Compressible flow is that type of flow in which the density of the fluid change from point to point.


Incompressible flow is that type of flow in which the density is constant for the fluid flow. r = constant. 

Rotational flow is that type of flow in which the fluid particles while flowing along stream lines also rotate about their axis. If the fluid particles while flowing along stream lines, do not rotate about their own axis that type of flow is called irrotational flow.