Question

Turbulent entrainment leads to ___________

(a) Increase in the magnitude of the velocity gradients in the flow direction

(b) Increase in the magnitude of the velocity gradients in the cross-stream direction

(c) Decrease in the magnitude of the velocity gradients in the flow direction

(d) Decrease in the magnitude of the velocity gradients in the cross-stream direction

This question was addressed to me during a job interview.

This interesting question is from Free and Wall Turbulence in portion Turbulence Modelling of Computational Fluid Dynamics

Answer 1

The correct choice is (c) Decrease in the magnitude of the velocity gradients in the flow direction

For explanation: Because of the entrainment of the surrounding fluid, the velocity gradients decrease in magnitude in the flow direction. This also decreases the difference between the speed of the wake fluid and its surroundings.