Question

What is the formula for coefficient of drag over a circular cylinder at hypersonic speed?

(a) cd = \(\frac {D}{q_∞ S}\)

(b) cd = \(\frac {D}{2q_∞ S}\)

(c) cd = \(\frac {2D}{q_∞ S}\)

(d) cd = Dq∞S

This question was posed to me during an online exam.

Question is taken from Time-Marching Technique topic in section Time-Marching Technique of Aerodynamics

Answer 1

Right choice is (a) cd = \(\frac {D}{q_∞ S}\)

To elaborate: At hypersonic speed, coefficient of drag over circular cylinder can be predicted using the Newton’s theory. It is given by:

cd = \(\frac {D}{q_∞ S}\)

Where, S = 2R is the cross – sectional area and R is the radius of the cylinder

cd = \(\frac {4}{3}\) which is obtained using Newton’s theory.