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

The correct option is D May have any value

Answer is D.
Turbulent flow is a fluid motion with particle trajectories varying randomly in time, in which irregular fluctuations of velocity, pressure and other parameters arise. Since turbulence is a property of the flow rather than a physical characteristic of the liquid, an energy source for maintaining turbulence is required in each case, where such flow is realized. Turbulence may be generated by the work either of shear stresses (friction) in the main (mean) flow, i.e., in the presence of mean velocity gradients (a shear flow), or of mass (buoyant, magnetic) forces.
In near-wall flows (i.e., boundary layer, as well as tube and channel flows), turbulence generates in the region of the greatest near-wall velocity gradients throughout the flow extent. The turbulent flow is much more capable for transfering momentum, heat and suspended particles, and for propagation of chemical reactions than is laminar flow.
Hence, in a turbulent flow, the velocity of the liquid molecules in contact with the walls of the tube is may have any value.