Wind Tunnel Vibration

[JamesEtch]

Hello there. I am currently using a small open jet wind tunnel to test 1/10 scale models of a solar powered car. Unfortunatly the flow quality from the wind tunnel is poor and so considerable vibration of the models and the force balance used is noticed. The vibration seems to be reasonably consistent in terms of frequency and so I am wondering if a tuned vibration absorber could be used to reduce vibration. I was wondering if anyone had heard of such a scheme ever being used or if anyone had any experiece with vibration on wind tunnel force balances, cheers James Etchells.

 

[DoubleGeek]

If you want a good test, you can't be fixing your air flow with other devices that could introduce even more perturbations. I wouldn't waste your time or money.

If you are getting a low-frequency "surge" type oscillation, where flow velocity is unsteady, then I would look for any place in the tunnel where eddy currents could be generated. If the flow is disrupted even way back at the fan, it may cause bubbles of air to be generated that would reflect back to your test section. Transitions in cross-sectional area need to be uniform along the length of the tunnel. A screen or honeycomb in the diffuser section might also help to even the incoming flow.

If none of these work, you may have a poorly designed tunnel. Sometimes minor changes to the diffuser or fan section can fix these problems.