Question

In a turbulent flow, the velocity of the liquid molecules in contact with the walls of the tube is:
A. Zero
B. Maximum
C. Equal to critical velocity
D. May have any value

Answer 1

This question is based on fluid mechanics. We know that there are two kinds of flow that are Laminar and turbulent flow. The turbulent flow creates a disturbance while the laminar flow does create disturbance. The laminar flow moves parallel to the lower layer of the fluid.

Complete step by step answer:
If we find the fluid is flowing in a straight path without any disturbance, then such fluid is said to be laminar flow. These kinds of fluid are found in blood vessels, syrup flowing out of the nozzle and many more.

In contrast, if we see the fluid is flowing in an irregular manner, then the fluid is said to be turbulent flow. Those fluids found in oceans, fluid comes out from the pump or turbine and many more.

Turbulent flow is a fluid motion with particles doing random motion continuously with respect to time. In this, there are unusual fluctuations in velocity and pressure. Turbulence may be caused by the work of either shear stresses in the mean flow.

If we flow the fluid from the tube, we can observe that turbulence produces in the region of the greatest near-wall velocity gradients during the flow extent. The turbulent flow is caused due to the excess of kinetic energy generated and it is capable of transferring the momentum.

Therefore, in a turbulent flow, the velocity of the liquid molecules in contact with the walls of the tube may have any value.

Thus, the correct option is (D).

Note: In this question, students must have knowledge of turbulent flow. With the use of Reynolds number, we can find whether the flow is laminar or turbulent. If we find the Reynolds number is more than 4000, then the flow is turbulent and if Reynolds number is less than 2000, then the flow is laminar, otherwise transient.