Pickup truck vortex used on a car?
 

I was looking at buying a volvo 850 wagon which has a nice boxy rear end. It occurred to me that that back end looks a lot like the back of a pickup cab.

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).

The wing is easy, just stick it on the roof, projecting out the back. For the "pickup box", why not just get a receiver hitch arrangement and mount a short, wide box there. The vortex would reside in the box, which could also be used sometimes for carrying stuff. One could easily add a curved surface inside the box to make the vortex even more stable.

If doable, this should be a lot easier than adding a trailer with long, sloping sides and top. The box could physically touch the bodywork so there is no gap, unlike a trailer. Also the rear view mirror still works. The back door is accessed buy simply pulling the pin and removing the box from the receiver hitch.

I'm assuming the axis of the vortex is horizontal. Is that correct?

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.

Yes the axis is horizontal.

While that set-up represents an improvement to pickups, I suspect it wouldn't for the wagon. The wagon is starting out from a better place with the nice clean cut-off. If one is willing to do the work of replicating a truck box, one could just as easily- or even moreso- hang a nice partial or full tail back there.

wing/box
 

Here's a rendering of a quasi-commercial setup which combines the wing and box into an aerodynamic boattail/box-cavity/storage container.
It rolls up to the SUV/wagon receiver hitch on four castor'd pogos,which rise and stow into the belly while on the road.
3-4 mpg.
http://i1271.photobucket.com/albums/...ntitled1-7.jpg

I am seeing improvement on aero optimized hatchback (Prius C) with VGs installed along roof spoiler, so it isn't that you have to start from very bad to see improvements.

I'm saying the pickup and wagon are two different scenarios; pickup being worse.

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.

terms
 

I think were getting our terms mixed up a little... A truck bed has a recirculation bubble, where a vortex is air spinning off a generator or wing longitudinally... Also horizontal axis, but towards rear.
That's what grays garage tought me anyways. Check out his vids.
Aerohead has done a nice rendering of your idea. Would shift center of gravity back a bit
Good luck

OK, recirculation bubble. I was not talking about those little vortex generators at all. Sorry for misleading people...

Aerohead has the right idea with his first picture, except that the top of the box is removed and the bubble sits in there, and also there needs to be a wing on top of the roof.

But I get Frank's point too; the devices are to compensate for the pickup being worse off in the first place, and may be pointless to apply to a wagon.

Interestingly, my Ram pickup is rated at 25mpg (highway) while the Volvo I am looking at is probably a bit worse, even though the Ram is a much larger and taller vehicle. I guess engine efficiency has gone up over the years.

completely eliminating trail wake
 

If you can rediscover that study,it would be invaluable to us.:D

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.

I posted link in VG thread, take a look.

thread
 

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?

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!!!

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.

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!

Argumentative. Assumes facts not in evidence.

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.

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.

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. :)

PhD/degree/were(sic)/model
 

*whether they have a PhD or are from India is not germane to the topic.
*I have a B.S.,Mechanical Engineering Technology.
*Where these criteria were discussed is nowhere in their presentation,as they obviously didn't know what they didn't know with respect to aerodynamics,or dynamic similarity,and it reflects the fact that they don't understand critical Reynolds number and verisimilitude (absolutely critical to testing success),which is discussed elsewhere in the literature I've studied over the last 40-years.
*Of course it's a model.
*The PhD's who run 'real' wind tunnels have published reports stipulating that certain body features cannot be adequately tested at scales below 1/2-scale,sometimes it requires full-scale testing,or full-scale CFD.

putting aside
 

*You are correct,in that VGs have been shown to reduce overall drag on notchback cars,SUVs,and Vans.
*The Mitsubishi Evo Lancer registered a maximum 1.7% drag reduction with delta-shaped VGs.
*An SUV and van registered 4.2% and 10% reductions respectively in a different investigation by different investigators.
*The Lockheed C-130 Hercules has undergone VG,stubs,nubs,microvane,and sub-B.L. VG drag reduction investigations for its up-swept underside to good effect.
*The report from India was extremely flawed in execution and follow through,but is no reflection on you.

Lots of pie-in-the-sky stuff on this forum. Part of its fun.

This idea should be well known. Trunk & aero devices.

The Highway Pack for the SUVs.

Would even work with trailer-Towing.

A tail is also beneficial in handling cross-winds. There’s a point where the extension becomes a lever, but it’s fairly high up there in wind speed.

Meaning: less work at the steering wheel thru the day. Today’s computer integration of drivetrain inputs isn’t going to be bettered by the driver. The driver already has enough work what with road, load, traffic and weather.

Judging conditions to alter speed to best accommodate NO lane changes and being able to maintain lane CENTER without corrections is where Interstate Highway mpg resides.

67-mph may be do-able prior to dawn and in earliest morning. But once traffic escalates, the penalty becomes too high (Safety & economy track for discussion purposes). It may only be 64-mph the better part of the day. Fuel burn will be about the same. MPG isn’t simply wind resistance.

Aero aids that allow the vehicle to more smoothly handle gusting and constant winds reduce Steering degree of input AND duration.

My day at the wheel is FAR EASIER when I have a 53’ van with skirt & tails. I get an extension against the clock of when fatigue takes over at the wheel.

.

I believe the Texas University PDF diagram shows full aero-cap on the bed being best as it retains air attachment.

In addition as I recall the diagram shows a full tonneau cover as being ever so slightly superior to a half cover in any condition including with or without roof wing.

I think you are comparing apples to oranges anyway, long body ratio station wagons are nothing like pickup trucks aerodynamically speaking.

You may wish to lengthen the cab or wagon with a rear spoiler or roof wing so the air has a clean and defined detachment point that forms partial box cavity. That is one of the only commonalities I can think of.