Question

Coefficient of drag over a sphere at hypersonic speed is dependent on the Mach number.

(a) True

(b) False

I had been asked this question during an interview.

I would like to ask this question from Time-Marching Technique in division Time-Marching Technique of Aerodynamics

Answer 1

Correct choice is (b) False

The best explanation: The coefficient of drag for a sphere that is kept at hypersonic flow is given by:

cd = \(\frac {D}{q_∞ S}\)

Where, S = πR^2 (R being the radius of the sphere)

This results in the value of cd being 1. Clearly, this result is independent of the Mach number of the flow. The only condition is that the Mach number should be in the range of hypersonic regime for this result to be valid.