# How do I find pressure coefficient?

1. Oct 26, 2011

### gharrington44

a. A very large reservoir of pressurized air feeds a contraction and forms a free jet of air of circular cross section and diameter 60 cm in a laboratory, where the ambient pressure is atmospheric. A Pitot static tube is arranged in the jet and attached to a vertical U-tube manometer containing alcohol. If the difference in levels recorded by the manometer is 65 mm, find the air speed.

I was able to find the air speed leading the contraction to be 28.8 m/s

b. The Pitot static tube is removed and replaced by a small body, which is equipped with static pressure holes in its surface. If the minimum gauge pressure recorded on the body is found to be -310 Pa, find the maximum velocity on the body.

I found the maximum velocity of the body to be 36.5 m/s.

c. State the values of pressure coefficient on the body (i) at the stagnation point, and (ii) at a point where the velocity achieves a value 50% above the value in the jet.

I have no idea how to approach this at all. I am assuming the stagnation point is in the center of the object where the air velocity is 0. But I am not familiar with a pressure coefficient or where to find where the velocity is half of what it should be.