Is there any relation between the model and the test section area?. How much is the size of the Model if we comparing to the test section? any percentage?
Yes Ashraf, it has. Good practice indicates that the frontal area of the model must has between 5 to 10% of the wind tunnel cross sectional area. 7% is a good choice. More than 10% you'll need to do some corrections because of the streamlines compression. Reference: Barlow, J. B.; Rae Jr., W. H.; Pope, A., 1999, Low-speed wind tunnel testing, 3rd Edition, John Wiley & Sons, New York.
For subsonic flows,the projected area (frontal) less than 5% of wind tunnel area is mostly accepted provided the model is 2D. Beyond this you may need wind tunnel corrections. For 3D models, end effects need to be considered in addition to blockage effects. In supersonic flow regimes, the reflected shocks (originated from model) should not interfere with model.
Dear @antonio , @mahasidha , @murugan i am thankful for fast reply i will check my model ratio
I strongly recommend to read the AGARD Advisory Group reports (AGARDograph) on wind tunnel wall corrections, namely:
AGARD AG 109: Subsonic Wind Tunnel Wall Corrections: http://www.dtic.mil/dtic/tr/fulltext/u2/657092.pdf
AGARD AG 336: Wind Tunnel Wall Corrections: http://www.dtic.mil/dtic/tr/fulltext/u2/a356695.pdf
They on the one hand may guide you on the appropriate model size for your purpose, on the other Hand instruct you how to proceed in case you need to have a model larger than to be expected ideal.
By the way, I doubt that generally a 5-10% blockage can give you proper results without applying correction methods - and it will strongly depend on the speed regime of your tunnel.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Plating