Expert: Paul Soderman - 4/11/2008

Question
We plan to measure the forces on a cantilevered cylinder in our wind tunnel. the blockage ratio can be 5%. I wonder is it necessary to make correction for the measured Drag and Lift, and also vortex shedding frequency? I read your answer to another similar question, you suggested that different correction should be used for different quantities, e.g. drag, lift and frequency.
So, is there any reference books I can refer to?
Thanks


Answer
Hanfeng
I suggest Low-Speed Wind Tunnel Testing by William Rae and Alan Pope, 2nd edition, John Wiley and sons.  Rae and Pope go into much detail about blockage effects.  5% blockage is significant.  Vortex shedding frequency is easy to predict and will give you a clue as to what is happening if things start oscillating at that rate.   There is no correction for vortex shedding, but steps can be taken to minimize the shedding if it occurs (and usually does on cylinders).
Paul