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Old 12-18-2015, 05:57 PM   #11 (permalink)
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completely eliminating trail wake

Quote:
Originally Posted by cyclopathic View Post
Vortex generators are the devices for remixing and increasing speed of boundary layer. As such they need to be applied in the place where they improve aero efficiency of existing design, not to alter it as they are really not capable of doing it.

The was a study which used a combination of VG and spoiler an succeeded in completely eliminating trail wake. But as I recall they tried 26 different combinations in wind tunnel, something we can't.
If you can rediscover that study,it would be invaluable to us.

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Old 12-19-2015, 12:38 AM   #12 (permalink)
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The Bonneville spoiler and half-tonneau works because as Frank Lee says, the pickup cab is too short (the wagon body is much longer), and the half-tonneau provides a surface for the airflow to reattach after lofting over that rolling bale of air.

With the hitch mount, you can have the open front half or the closed back half. Or maybe a tall box with a teensy little half-tonneau.
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Old 12-19-2015, 11:39 AM   #13 (permalink)
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Quote:
Originally Posted by aerohead View Post
If you can rediscover that study,it would be invaluable to us.
I posted link in VG thread, take a look.
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Old 12-19-2015, 01:16 PM   #14 (permalink)
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thread

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Originally Posted by cyclopathic View Post
I posted link in VG thread, take a look.
I did an EcoModder search.
There are 10-pages of threads for VGs,and no link to the author to sort by.Can you link that for us please?
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Old 12-19-2015, 01:16 PM   #15 (permalink)
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An hyperlink would be nice. Via your Profile page I see 5 posts in http://ecomodder.com/forum/showthrea...ors-32641.html between the third and the fifth. Was it one of those?

Simulpost!!!
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Old 12-19-2015, 01:38 PM   #16 (permalink)
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Sagar et al. document

I found the "Aerodynamic Effects of Rear Spoiler and Vortex Generators on Passenger Cars",from India.
*It's good that you did some fact-finding.
*Unfortunately for the researchers,they didn't understand what they were doing.
*A 1/15-scale model requires a minimum 300-mph air velocity to test.
*The model blockage ratio way exceeded the 5% maximum.
*Surface details this small cannot be analysed with anything below a 1/2-scale model.
*Nowhere do they claim to have eliminated the wake drag.
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Old 12-19-2015, 07:27 PM   #17 (permalink)
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Quote:
Originally Posted by aerohead View Post
I found the "Aerodynamic Effects of Rear Spoiler and Vortex Generators on Passenger Cars",from India.
*It's good that you did some fact-finding.
*Unfortunately for the researchers,they didn't understand what they were doing.
*A 1/15-scale model requires a minimum 300-mph air velocity to test.
*The model blockage ratio way exceeded the 5% maximum.
*Surface details this small cannot be analysed with anything below a 1/2-scale model.
*Nowhere do they claim to have eliminated the wake drag.
So the fact they have PhD is invalidated because it is in India? What type of degree do you have?

With respect to "Surface details this small cannot be analysed with anything below a 1/2-scale model" were exactly this was discussed? That is a clay model not a car!

Last edited by cyclopathic; 12-19-2015 at 07:42 PM..
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Old 12-20-2015, 12:56 AM   #18 (permalink)
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Quote:
So the fact they have PhD is invalidated because it is in India? What type of degree do you have?
Argumentative. Assumes facts not in evidence.

Quote:
Originally Posted by PaulB2@12-17-2015, 12:34 PM
There is that diagram floating around here about pickup aerodynamics, which shows the small wing on the roof and a half tonneau being the best aerodynamically. I imagine (correct me if I'm wrong) it establishes a stable vortex in the pickup bed, and the air just flows over that vortex down to the tonneau cover. I just wondered if we could move this to the back of my volvo (if I buy one).
Quote:
Originally Posted by cyclopathic@12-17-2015, 01:41 PM
This is very interesting subject with some claiming improvements and others stopping short of calling VGs snake oil. There is an existing three on vortex generators chech it out.
Compare and contrast the Original Post and the First Post. Therein lies the crux of our dilemma. Need I post the diagram?

I think aerohead was gently poking a little fun at first. But he knows the relationship between scale and wind speed.

I have a degree but I'm not sayin' because with that and my mother's maiden name someone could triangulate my identity.

With respect to "Surface details this small cannot be analysed with anything below a 1/2-scale model" they can so be, down to 1/24th. But it's done in a water tunnel. Upside down. With hydrogen bubbles.
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Old 12-20-2015, 09:50 AM   #19 (permalink)
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putting aside discussion on how flawed the study is or isn't it had shown that vortex generators can improve existing aerodynamic features and may produce better results than spoilers alone, when applied properly.

With respect to critique.. Scale is wrong? may well be, if it were a replica of real car. But they used generic "sedan" shape, so wrong comparing to what? "Surface details this small cannot be analysed with anything below a 1/2-scale model" would have been the case if once again we were looking at real car, with panel gaps or window seals or wipers or grills to look at, but on clay model? You can argue that 68.1% drag reduction is unrealistic in real car applications, that if the real car model was used and you were trying to scale result to original. But these arguments just point out the limitations of lab experiment results; it is not like the general principle is invalid.

Perhaps you could make an argument that vortex generators only work at high flow speeds, but this is not a case. The existing applications in aviation on small planes like Cressna had shown that VGs help to reduce wind stall speed from 60 to 45MPH. Well within general car speeds. They also reduced top speed by a couple MPH, so there is no question that VG generate additional drag.
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Old 12-20-2015, 12:53 PM   #20 (permalink)
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I say again: You are talking about small-scale vortex generators. The request for discussion is about the Bonneville roof spoiler and half-tonneau in combination.

Y'all been sucked into a vortex of your own.

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