what are these stuck on Aero thingies?
 

I've seen this guy on the way to work for a couple years.
kinda curious what these things are and if/how they work?

You somehow missed all the conversations about air tabs? :confused:

yes,
mr 11,xxx posts, I have missed all the OLD conversations about something that I have never seen or known what to call them :thumbup:

thanks FRANK LEE
even though you were being a condescending ass, you did help me by providing a term to look up

Airtab | Aerodynamic Fuel Savers | How Airtabs Work


they claim that they can help with more than just fuel

I am always here to help. Remember that you ungrateful snot.

They're vortex generators. It is considered by some, myself included, to be a fad device. The most effective aspect of the design is to make money for the people selling them. They have legitimate uses on aircraft, but on ground transport no one has really shown them to have a great effect, if any.

They are purported to help maintain attached flow longer to help reduce drag, or to allow the air to fill in the void behind a vehicle faster thus reducing drag.

2 basic things working against them are:

They are purported to create a turbulent boundary layer which helps to create attached flow...well, all ground vehicles have a continuous turbulent boundary layer, there really isn't laminar flow on ground vehicles. And that's OK.

There is a huge volume of air that is affected by the passing of a vehicle through it, it is NOT just the air rushing over the 2 inches above the surface of the vehicle that is moved about but several 10's of feet of air around it and many hundreds of feet behind that all matter. The VG's are essentially blades of grass in a hurricane breeze and really cannot alter enough of the flow of air in such a way as to make a difference.

Search "vortex generators" here in ecomodder, the subject has been thoroughly hashed out several times.

Like HHO, this is a subject of often contentious debate. I only hope it leads you to further try and learn the basics of aerodynamics so you can understand that these are kazoos trying to be in the Philharmonic.

Well I see the contentiousness is faster than my lousy ability to type. I thought I was going to be the first to answer.

Come on guys. Be nice.

That is Frank Lee being nice.

Lolz!

The only time they are going to help is if they are placed on the vehicle and studied in a wind tunnel. Or placed by someone who specializes in automotive aerodynamics and has spent a lot of time hanging out at the local wind tunnel.
These little things actually increase drag and what you are trying to do is place these drag increasing structures ahead of a very large drag increasing design feature, to try and reduce drag.

unofficial guide to frank lee posts....

1 sentence - (regardless of words used) is nice

2 sentences - he's warm in up!

3 sentences - rember the duck and cover drills in elementary school?

(love ya Frank Lee!!:thumbup:

Those air tabs can be helpful, but it takes testing to know whether how they are being deployed is helpful.

I 100% guarantee that there is a lot more to be gained on that truck without spending one red cent on VGs. For what the guy spent on VGs, he could have bought or made an air dam that likely does a lot better than what he has there.

Just the fact that his wide-open wheel well is still uncovered proves there's more gain to be had.

Don't take Frank Lee seriously, he is a Ford man. Apparently, there have not been enough kids trespassing on his lawn lately.

Frank, I hope you do not mind my kidding too much.

I see air tabs on semis. That industry has the money and motivation to pursue new technology, but I would not expect them to waste money on fads.

I see them all the time on semis.

AutoSpeed - Blowing the Vortex, Part 4

The aerodynamics of a 40ft long box van are different to a hatchback. There is a lot of length for reattachment of that kerfluffle that happens at the front.

I tried them six years ago on the back of the topper on my pickup truck. I didn't notice any difference good or bad. I took them off after about six months because I got sick of people asking about them and they made it harder to wash and wax the truck.

The A&P book I read said
VGs (Vortex Generator) are for maintaining attached airflow at excessive angle of attack preventing a stall.
Also that a VG should be placed 1/3 cord for of the point of separation. At 15° off of the direction of airflow (as apposed to direction of travel this could be 90°to the direction of travel.
The other day I saw a 53' reafer with a VG kit (1 pice per side with ~ 12 VG each) placed ~12-18 forward of the door hinges. The oddity was the VG s were orientated wide side leading like a NACA duct intake.(>--).. I think someone didn't read the instructions and installed the left pice on th right side .

----
VGs could be used to allow a steeper angle >12° on a camback/ aerocap (as in a short bed) with out requiring the cap to be truncated . The reasons given by other builders of aerocaps for a truncated cap was . To get down to the tailgate ment an angle too steep and would cause a loss of attached air flow . With some $500/hr wind tunnel time a 3' aerocap with VG is possable . As it stands now without VG s an 8'+ bed is needed to maintain the templates <12° change of surface angle for attached flow.
Gumby Stay Flexible

How I understand a VG to work
 

Attachment 20291
AutoSpeed - Blowing the Vortex, Part 4
VG as i understand them. Running backwards as the article suggest seems counter productive as in this format it takes 2 VG each at opposite15°to air flow to achieve a single pair of counter rotating vortices ... 2 pucks =1 pair of vortices . And causes an increase of non aerodynamic frontal area. May as well glue bricks to the car ,there cheaper.
Turn them 180° and now you have 1 puck and 1pair of counter rotating vortices , and a streemlined additional frontal area. Much less math and drawing pictures on your car to figure out the proper orientation. based on tuft testing to determinethe befor during and after points of separation at various speeds to align the skinny end with the Wind(forward) . My choice after researching points to using a type2 skinny end with the Wind. With the skinny end aligned with the tuft ,putting the 2 tailes at +&- 15° to the air flow.

Their example of VG it the belly pan the vG action is more a saw tooth air dam . Showing a positive impact on aerodynamic efficiency. A better result wou have beenfrom a full air dam.
Their only use of tuft tested VG was on thire only non instant mpg . Making the visible improvement un measurable.

The CRX looking hatchbacks looks like the VG is located at the point of reattachment disturbing this reattachment. With no place for the vortex to stableize (hence the 1/3 forward its gota land and stableize before it can help). It appears as though this car could have shown improvement it the VG had been applied in a similar positions as the Insight and determined with tuft testing.

Found this while googling:

Aerodynamic Effects of Rear Spoiler and Vortex Generators on Passenger Cars

https://www.researchgate.net/profile...Passenger_Cars

researchgate
 

We'd want to look at:
* the blockage ratio of their model/wind tunnel test section
*buoyancy effects
* the Reynolds number based upon model scale and air velocity

I want to look at

https://www.researchgate.net/publication/290024199_The_COANDA_Flow_Control_and_Newtonian_Co ncept_Approach_to_Achieve_Drag_Reduction_of_Passen ger_Vehicle

But the Read More link starts off down a garden path instead of offering the PDF. This doesn't happen with the previously linked article. I guess I could use TOR to request it. :)

If the kick up effects are as I imagine it .the air circulating at the rear of the hatch is allowed to meet the air off the deck lid traveling in the same general angle, instead of at almost right angles. I clicked the "full text " link.they asked for an E-mail to notify me when 1 of the authors release it. This as I understand them from the abstract ,this smoth directional convergence, is what I was trying to promote with the duck bill sticking out behind my tail gate.

researchgate
 

Not to slam their research,but here's some considerations.
*at 1/15-scale,the test section flow velocity would need to be a minimum of 300-mph in order to achieve critical Reynolds number.
*The model's frontal area should not exceed 5% of the test section cross-sectional area.Clearly not the case.
*at 300-mph,transonic flow would be present with shockwaves forming on parts of the body,blocking airflow in those areas.
*at 300-mph,the boundary layer would be thick enough on the walls,ceiling ,and floor of the test section as to choke off the flow,creating a velocity acceleration discontinuity over the length of the model,compounding the blockage effects and supersonic jets.
*at 300-mph,the wheels and lower body of the model could be immersed in the boundary layer,which would never happen at 1:1 - scale.
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If the authors had actually read Hucho's book,they'd know these things before they ever began,and never proceeded.
Another thing,these sorts of body details cannot be examined at this sort of scale level.Maybe 1:2 scale,then 1:1 scale verification later.
I think it's one of those Donald Rumsfeld moments in science,where the investigators didn't know the known knowns.

They either had an air tunnel and picked an inappropriate scale; or picked a scale and chose air over a water tunnel. Then it's all downhill from there.

Donald Rumsfeld's contributions to scientific thought are greatly misunderstood, and I think incorrectly attributed here.

A true Donald Rumsfeld moment would be deciding that you do aero testing with the scale model you have, not the scale model you might want or wish to have at a later time.

Or perhaps it would be phrased Absurd. We don’t need nearly 1:1. Not that large. Certainly no more than 1/15.

Whichever way you apply him, the result is an abject failure, but the exact reasons why can be fascinating.