Question

True or False

All inviscid regions are also irrotational regions.

Please explain the answer

Answer 1

Irrotational flow is a flow in which each element of the moving fluid undergoes no net rotation with respect to a chosen coordinate axes from one instant to other. A well-known example of irrotational motion is that of the carriages of the Ferris wheel (giant wheel). In a Ferris wheel although each carriage follows a circular path as the wheel revolves, it does not rotate with respect to the earth, as a result the passengers remain upright and continue to face the same direction. Rotation of a fluid particle can be caused only by a torque applied by shear forces on the sides of the particle. Since shear forces are absent in an ideal fluid, the flow of ideal fluids is essentially irrotational. Generally when the flow is viscid, it also becomes rotational. This is due to the fact that viscosity introduces velocity gradients and introduces distortion and rotation of fluid particles, even though the fluid as a whole need not rotate about a fixed center.