tuft testing, vortex generators, and God's own wind tunnel

[jim-frank]

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!

[aerohead]

Thanks for the grunt-work.Your methodical testing will help us all be in a better position to qualify applicable technology as it avails itself.Turbulators have been an enormous topic of controversy over the years now and it will be good to hear from the trenches on this hotly-debated issue.Thanks mucho!

[cfg83]

jim-frank -

Man, that's a good idea! No other factors to get in the way. Maybe I need to go "where the wind farms are", like Palm Springs, to find me some good wind. Or maybe run out to the beach parking lots on a super-windy (non-weekend) day and go into tuft-madness mode.

CarloSW2

[ttoyoda]

That is a very interesting patent. The things described in it are worth trying.

Keep in mind that patents are written to cover all the bases. It is not neccesary for the things in the patent to actually work as described, or work at all. A good patent writer would write patents which cover all the bases for the inventor, but mislead (or at least not educate on essential finer points) anyone who tried to reverse engineer the invention using the patent as a guide. The scale and shape of items in illustrations may be distorted or grossly out of scale. Close reading of the text sometimes reveals this kind of misdirection.

Good luck with your testing and let us know how it comes out.

[jim-frank]

Thanks, all. I've been really tied up at work with no chance for experimentation with more tufts, but I'll get around to it.

I've read through a great many patents, and I know that they will fudge as much as they can to delay copycats. They have to make it at least theoretically workable, so that the actual working device is covered.

This design has the best conceptual basis for making large contrarotating vortices that I've run across so far. It also doesn't need to be oriented at any particularly critical angle to the airflow, so you have some latitude in mounting them.

The Mitsubishi paper (that is available online) specified that the simple delta wedge shaped VG's had to be oriented at 15 degrees to the airstream to work well.

This is fun stuff!

[FrankP]

I have just joined ecomodder. I found the site while searching for details of vortex generators for cars etc. I am interested in making a set to fit to my caravan (RV) which has a upright rear end which creates heaps of drag. I have seen a few caravans here in Australia fitted with VG's. They might work but it will be fun trying anyway. I would like to find out the dimensions/angles etc required to make and fit VG's. I don't believe it is cost effective to buy a set not knowing if they are going to work. Thanks in advance. Frank

[Daox]

Welcome to EM FrankP.

Nobody has ever proven VGs to actually improve mileage. Your time is much better spent elsewhere. A grill block is a great place to start.

[IndyIan]

I think the rear window angle is just too steep to keep flow attachment very far down even with VG's. Probably you need to make a Kamm back to see some results.

[jim-frank]

I never saw any increase in mileage with any of the VG designs I tried. I also never saw any notable improvement in flow attachment on the back window of my Nissan Sentra.

In fact, the only visible flow attachment improvement is on the sides of the car at the back side windows. Tufts there showed that the "Vent shade" on the drivers side smoothed airflow greatly compared to the passenger side where I removed the shade because it was broken.

I want to replace the passenger side one to see if my high speed gas mileage improves at all...

[Piwoslaw]

Originally Posted by jim-frank

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.

Using steady wind for tuft testing is a good idea. You can't change the speed, but you can do things you normally wouldn't be able to when tuft testing on the highway, like get out and look from different angles. Another is tuft testing the windshield, which probably can't be "tufted up" when the vehicle is moving on a public road.