Question

What leads to shear stress between the adjacent layers of fluid inside the boundary layer adjacent to the surface?

(a) Aerodynamics drag

(b) Viscosity

(c) Pressure drag

(d) Wave drag

I got this question at a job interview.

The origin of the question is Boundary Layer Properties topic in section Boundary Layers, Laminar & Turbulent Boundary Layers, Navier Stokes Solutions of Aerodynamics

Answer 1

Correct answer is (b) Viscosity

For explanation: There is shear stress between the adjacent layers of fluid in both laminar and turbulent flow inside the boundary layer. This is due to the viscosity and it is given by the relation:

τ = μ\(\frac {∂u}{∂y}\)

Where, \(\frac {∂u}{∂y}\) is the transverse victory gradient.