Anyone every used these to reduce drag?

If Toyota could get an 11% increase in efficiency THEY would beat you to it.

#PTBarnumwasright

 

Though I was always amused by the "Dimple Car Experiment".

Mythbusters got a verified 14% MPG increase.

www.youtube.com/watch?v=VUiGhyHC-1A



Rob43

 

I wonder why Toyota didn't use dimples... ...Perhaps they were afraid it would make the car TOO ugly.

 

HAS to be something else......

 

Perhaps their wind tunnel tests didn't replicate Mythbuster's results? Or other automotive and aviation tests don't get sufficiently useful results?

Not having cable or satellite TV, I never had opportunity to watch that series from home. But I did see a few episodes elsewhere, and some left me quite unimpressed. They could have benefited from some better engineering consultation or wider exposure to testing methods and failure analysis.

 

Myth Busters is who they were, not necessarily what they did.
Better engineering consultation and more effective testing methods and failure analysis was not their prime motivator.

Like many (if not most) scientists, they were just in it for the bucks and the notoriety.

 

A few reasons these things are not used on mainstream cars that I can think of.
1. They give out a racer appearance so it could be a turn off for majority of car buyers.
2. There are actually rules against protruding sharp corners on production vehicles, so while some tiny versions of the dimples are used, they pretty much all stayed away from the largers ones to be placed on the roof except a few more that are more targeting racing enthusiasts.
3. They really have very little effect until you are going at higher speeds, pretty much above the speed limit in almost all places.

 

I don't have any pictures but has anyone looked closely at resident taillights on a new prius or a 2015 RAV4? There's some interesting small bump-outs.

 

Outside facing of taillights .... Not sure where 'resident' came from

 

@krmcg added some vortex generators to his Gen 4 Prius. IIRC.

 

I had them on my Gen 2 and also put them on my new Prime. not sure about drag but in my case, they greatly helped to improve the stability at higher speed (> 65MPH) when large vehicle is nearby.. such as passing a tractor trailor or going behind one.

20190826_151418 by mister2cool posted Nov 11, 2019 at 4:13 PM

20191029_151100 by mister2cool posted Oct 29, 2019 at 4:17 PM

 

I would be wary of drawing conclusions about vehicle aerodynamics from airplanes; airplanes operate in a very different flow regime. Cars travel at such low speeds (relatively) that we can treat the air they move through as an incompressible fluid; this is not the case with most airplanes. Cars are bluff bodies; airplanes are streamlined bodies.

Some of you in this thread have correctly noted that Toyota and other manufacturers use very small vortex generators in specific places on their cars, usually the taillight edges and the A-pillar sail panels inboard of the mirrors. This is done for a couple of reasons, to slightly reduce drag and to reduce noise. Vortex generators, as their name suggests, must be placed at some angle to the flow so that they create a wake behind the fin; air wants to fill this low-pressure area and the path of the streamlines turns toward the wake, setting up the rotation that is the vortex. Similar to the pressure drag that creates most of the drag force acting on a car body, there is drag associated with vortex generators--so they have to be used judiciously and placed carefully to avoid increasing drag overall; that is, the benefit of using them must outweigh the drag associated with them or you simply increase drag for no reason. Along the top edge of the rear window of a Prius as in the images above will create more drag than leaving the vortex generators off; they are most beneficial when there is an area of flow detachment, such as a too-steep rear window, where the low pressure created by the vortex generators can prolong flow attachment (flow detaches because it slows/gains pressure too quickly--reduce that pressure gain by introducing a bunch of small, low-pressure vortices and it can stay attached where it otherwise wouldn't).

I'm skeptical that the Aerohance vortex generators shown on a Prius spoiler are helping at all (I would bet money they are hurting), and if they are it's certainly not on the order of an 11% improvement in fuel economy (which requires an even greater percentage improvement in drag). I wouldn't waste the money on these.

 

Yes I would disagree that vortex generator can reduce drag at the speed that our cars travel.
The theory is that the vortex created from the top of the rear window would help air flow reach the rear spoiler and thus making the spoiler slightly more effective than it would have otherwise. A more effective spoiler would generate more downforce hence improved handling at the expense of increased drag. Even that would require a car to be traveling well above speed limit on most highways.

However, I did not see any noticeable change in the 3 years driving the Gen 2 so I think the change is small enough to justify with improved handling.