Question

If y is the distance in the cross-stream direction from the centre line at a particular cross-section b  → Cross-stream half width. The mean velocity gradients and all the velocity fluctuations become zero when the value \(\frac{y}{b}\) ___________

(a) goes above unity

(b) goes below unity

(c) goes above zero

(d) goes below zero

The question was posed to me in an interview for job.

This intriguing question comes from Free and Wall Turbulence in portion Turbulence Modelling of Computational Fluid Dynamics

Answer 1

The correct choice is (a) goes above unity

To explain I would say: The value \(\frac{y}{b}\) going above 1 means that y crosses b and goes out of the turbulent region. So, the velocity gradients and its fluctuations also will become zero when the value \(\frac{y}{b}\) goes above 1.