Discussion
In a low-speed wind tunnel, the angular location(s) from the front stagnation point on a circular cylinder where the static pressure equals the free-stream static pressure, is
Answer: B
The angular locations are ±30° from the front stagnation point.
Inviscid flow over a circular cylinder gives a surface speed \(2U\sin\theta\), measured from the front stagnation point, and so a pressure coefficient
\[ C_{p} = 1 - 4\sin^{2}\theta \]
The static pressure equals the free-stream pressure where \(C_{p} = 0\): \(\sin\theta = 1/2\), so \(\theta = \pm 30^{\circ}\) on the front of the cylinder (and \(\pm 150^{\circ}\) at the rear, which the options do not offer).
At 0° the pressure is the stagnation value, \(C_{p} = 1\). At ±60°, \(C_{p} = 1 - 4(0.75) = -2\), well below free-stream pressure. ±38° does not satisfy the inviscid result that the key follows.
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