A proposed free stream velocimeter would use a cylinder with pressure taps at = 180 and at

Question:

A proposed free stream velocimeter would use a cylinder with pressure taps at θ = 180° and at 150°. The pressure difference would be a measure of stream velocity U∞. However, the cylinder must be aligned so that one tap exactly faces the free stream. Let the misalignment angle be δ, that is, the two taps are at (180° + δ) and (150° + δ). Make a plot of the percent error in velocity measurement in the range –20° < δ < +20° and comment on the idea.