Question

The velocity at a point far away from the wall is defined by ____________

(a) Power law

(b) Log-law

(c) Velocity-defect law

(d) Newton’s law of viscosity

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

My question is based upon Turbulent Boundary Layer topic in portion Turbulence Modelling of Computational Fluid Dynamics

Answer 1

Right choice is (c) Velocity-defect law

The best explanation: Far away from the wall the fluid flow is retarded by the wall shear stress. The velocity (U) at such a point is defined as

\(\frac{U_{max}-U}{u_\tau} =function(\frac{y}{\delta})\)

This is called velocity-defect law.