Expert: Paul Soderman - 5/18/2009

Question
Mr Soderman. I must build a flow straightener but I am unsure of what the cell size must be. After doing some research, I've only found that the length of the honeycomb must be 6 to 8 times the cell size minimum, but nothing on the actual cell size and if it must be related to the tunnel diameter. I hope you can help me. Thanks in advance

Answer
Jose
Here is an answer I got from my friend Ken Mort on a similar question:

"I think the guy ought to use Barlow, Jewel B.: Rae Jr, William H.; and Pope, Alan: " Low-Speed Wind Tunnel Testing" and Pankhurst, R. C. and Holder, D. V. : "Wind-Tunnel Technique" for this even though he's designing it for a transonic wind tunnel. After all the airspeed is low in the settling chamber. If I understand Pope correctly the diameter of the honeycomb  should be less than or equal to the settling chamber diameter divided by 150. I think this results in a honeycomb diameter of on the order of a half inch or a little more than a cm. The biggest challenge is to find a cheap source of honeycomb. People have used straws and milk cartons stacked up for low speed tunnels to keep the cost down. He should locate the honeycomb upstream of the contraction at least a half diameter of the contraction if possible to minimize the wakes entering the test section."

Paul