DUE to some natural effect or external agency, the flow is known as vortex flow.Types of vortex flows:Free vortex flowForced vortex flowFree vortex flow:When the fluid passes rotating about the particular axis without any external torque then such flows are known as free vortex flow.It takes PLACE due to the natural effect. It means no external energy is given.Bernoulli equation is valid in a free vortex flow. That means free vortex flow is an irrotational flow.As we move away from the centerline, streamline spacing increases.TExternal = 0Rate of change of angular momentum is called torque.Angular moment = constantMass × Velocity × RADIUS = constant (Mass is also constant)Velocity × Radius = constantVelocity = 1/RadiusForced vortex flow:In this type of vortex flow, some external torque is required to rotate the fluid mass at constant angular velocity about a particular axis.All fluid particles rotate with same angular velocity like a solid hence FORCED vortex flow is also known as solid body rotation.To maintain a forced vortex flow mechanical energy has to be spent from outside and thus an external torque is always necessary.Bernoulli equation is invalid in a forced vortex flow. That means forced vortex flow is a rotational flow.As we move away from the centerline, streamline spacing decreases.ω = constantV/r = constant