Question

When the Reynolds number approaches infinity, what happens to the boundary layer thickness?

(a) Approaches infinity

(b) Approaches zero

(c) Approaches once

(d) Remains same

I have been asked this question during an online interview.

This intriguing question originated from Boundary Layer Properties in chapter Boundary Layers, Laminar & Turbulent Boundary Layers, Navier Stokes Solutions of Aerodynamics

Answer 1

The correct answer is (b) Approaches zero

Explanation: As the Reynolds number increases, the boundary layer thickness decreases when compared to the length of the body. Usually for very large aircrafts, the value of \(\frac {δ}{L}\) is around 0.01 which is a very small value. So hypothetically, as Re ➔ ∞, δ ➔ 0.