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Old 05-28-2008, 04:08 PM   #1 (permalink)
jim-frank
EcoModding Lurker
 
Join Date: May 2008
Location: western Colorado
Posts: 59

ScabbySentra - '93 Nissan Sentra SE
90 day: 44.37 mpg (US)
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tuft testing, vortex generators, and God's own wind tunnel

I was out in the eastern plains of Colorado last week and took advantage of the stady 30+ mph winds that were blowing. They were very consistent in both direction and speed, so I parked my car facing into the wind and used a roll of masking tape and some yarn to make a tuft panel on the back window of the car. The results were pretty clear, in that the flow was smooth and attached along the top of the car, detaching about two inches down from where the window starts sloping down.

I decided to try making some simple fence type VG's out of thin aluminum flashing and taped them to the roofline just above the seperated flow region. Over the course of the next two days, I drove around and watched the tufts through the rear view mirror. The vortex generators did nothing to visibly affect the flow down the back of the glass. I tried moving them forward and aft, spacing them farther and closer apart, and angling them relative to the flow direction.

The last test of that run was to make a slot type VG, with the triangular sloped floor slots that look like NACA ducts. Again, no visible change in the flow along the glass was observed- the detached and turbulent air was spread almost all the way across the glass.

I did some looking on the UA patent office website and found a different design for VG's that has a little more information on size, angles, and orientation (Patent number 5,058,837). I plan to set up another tuft panel on the glass and make some of the VG's detailed in this patent to see if I can observe any tendency to reduce the turbulence in this area.

Tons of fun!

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