Question

What is the skin friction drag for an incompressible turbulent flow with Reynolds number =  1.5 × 10^7 over a flat plate?

(a) 2.72 × 10^-3

(b) 5.41 × 10^-3

(c) 3.82 × 10^-3

(d) 2.91 × 10^-3

The question was posed to me in an online interview.

I'd like to ask this question from Turbulence Modelling in division Boundary Layers, Laminar & Turbulent Boundary Layers, Navier Stokes Solutions of Aerodynamics

Answer 1

Right answer is (a) 2.72 × 10^-3

Easy explanation: Given, Rec = 1.5 × 10^7

The skin friction drag over a flat plate for an incompressible turbulent flow is given by:

Cf = \(\frac {0.074}{Re_c^{1/5}}\)

Substituting the values,

Cf = \(\frac {0.074}{1.5 \times 10^{7^{1/5}}}  = \frac {0.074}{27.24}\) = 2.72 × 10^-3