Correct Answer - Option 4 : forced vortex at centre and free vortex outside
Explanation:
Vortex flow:
When a certain mass of fluid is rotated about a particular axis due to some natural effects or external agency, such a flow is known as vortex flow. There are two types of vortex flow;
- Free vortex flow
- Forced vortex flow
Free vortex flow:
When the fluid mass is rotating about a particular axis without any external torque, such flows are known as free vortex flows.
Forced vortex flow:
In these types of vortex flows, some external torque is required to rotate the fluid mass at a constant angular velocity about a particular axis.
Tornado:
A tornado is "a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud". For a vortex to be classified as a tornado, it must be in contact with both the ground and the cloud base.
