Quote:
Originally Posted by CHSGreenpower
Hi,
I'm building a small, low-speed wind tunnel to test our school's Greenpower race car designs.
Greenpower has come up on Ecomodder before I believe, it essentially involves single seat electric cars having to travel the furthest distance they can in a given time on one set of batteries. All cars use the same batteries and motor.
Anyway, I digress.
We have built the test section of a wind tunnel for 1/10th scale models of our car designs.
It measures 165 x 235 x 360mm internally, with pieces angled at 45 degrees stretching 31mm along each side from the corner to prevent pressure differences.
The largest model that it could be used for measures 120 x 120 x 280mm however typical sizes are usually about 60 x 50 x 280mm.
The wind tunnel needs to be able to produce speeds from about 25mph to 55mph or so.
I am yet to build the inlet horn, diffuser or purchase any fans yet because I didn't want to build them incorrectly so as to change the working speeds, rendering our wind tunnel almost useless to us.
What size should the inlet horn and diffuser be?
What CFM will I need to achieve these speeds?
If any of you can point me in the correct direction to find answers to either of these questions that would be great.
Thanks
Sam
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I don't have my work book with me,nor calculator but here are some considerations:
* a 1/10-scale passenger car tunnel would require a test section cross-sectional area of 4-meters-square minimum,to counter blockage effects.
*a minimum test section airspeed would be 200-mph to reach a critical Reynolds number/turbulent boundary layer.(dynamic similarity).
*at 200-mph,we have 17,600 feet/minute,and with 44-sq-ft of cross-sectional area,we get 774,400-Cubic Feet per Minute (CFM).
*high-speed tunnels have boundary layer thickness issues,and the ground borad must be elevated above the boundary layer,or suctioned off the flooor of the tunnel,as in the real world,the ground has no boundary layer.
*you'd need help from an air conditioning company to determine wall friction coefficients/losses,and total static pressure requirements to determine net horsepower for the air mover(s).
*Alan Pope published a great book on Low Speed Wind Tunnel Design.It's worth an inter-library loan if your school doesn't have it.
*small-scale model features cannot be successfully investigated except in near-full-scale CFD or wind tunnel.(Ferrari is spending 100-hours just to refine a single spoiler in their tunnel,at a cost of $4,000 (US)/hour.[$400,000]
*Texas Tech had a small tunnel and did 1/12th-scale work.With 50-hp (electric) they could get an 80-mph section velocity,not enough for a TBL Reynolds number,and they had to back things up in a water tow tank.
