Landracing Forum
Tech Information => Aerodynamics => Topic started by: Rex Schimmer on December 11, 2016, 03:10:44 PM
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Excellent paper by some engineers at Mitsubishi Motors on the sizing and application of Vortex Generators (VG) to reduce drag. Very applicable to Bonneville cars. I can think of several streamliners and lakesters that could use this technology.
http://www.4g63.de/facts/vortexgenerator-evo-mitsu.pdf
Rex
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Several are.
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Where they are allowed I hope!!!!
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In 1991 the Herbert Steen liner had them on the back to help the air transition to solve a chute deployment issue. There was a lot of people asking "what the hell are those things?".
Sid.
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A few streamliners & a few others run 'em
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I could be completely wrong... but the posted paper has the delta turned the other way (180 degree rotation) than the pictures that are posted. ??
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The Nish family has used and promoted the generators for years. Have 'em on the van, the race cars (as allowed, I presume) and so on. I'd say they'd be a reasonable source for information - maybe even data.
I wonder if Layne and Tom*, at Darko wind tunnel, have ever tried to quantify the things?
*Or anyone at any wind tunnel, or even you, Woody.
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Putting vortex generators at the trailing edge of a surface, as shown in the above photos, is pointless.
To be functional they need to be in a region where the flow has not already detached, and their purpose is to enhance attachment to the downstream surface. In the photos, they are probably in a region of detached flow and there is essentially no downstream surface. Wrong on both accounts.
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Putting vortex generators at the trailing edge of a surface, as shown in the above photos, is pointless.
To be functional they need to be in a region where the flow has not already detached, and their purpose is to enhance attachment to the downstream surface. In the photos, they are probably in a region of detached flow and there is essentially no downstream surface. Wrong on both accounts.
IO is correct. Look at the aviation industries use of VG. They are almost always before the recovery area of the foil. Their intended use is to promote attachment of the flow in areas of separation. Having no place to reattach the air means they are simply creating drag or aiding in moving the CP aft.
They also do cause separation drag in the upper areas of their outflows. One of the other benefits of VGs in aircraft is that the air behind them can become "excited" which provided more energy for lift. That energy is in the form of vortexes (hence the name - Vortex Generators) which is not laminar flow. The use of VG in aircraft can lower the stall speed of a wing as well as increase the lift so they do serve a purpose.
You never see the use of VG in production aircraft. VG are typically applied in the post-production phase of the aircraft and usually to adjust characteristics or tune a poor design shape. Most modern aircraft do not come with them from the factory and not all aircraft are certified for their use. If they were the utopia that were sold to the aviation industry in the late 80's and early 90's you would see them employed more widespread.
On cars, they have their use but like IO stated if there isn't anyplace for air to reattach to their employment provides limited benefit.
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Putting vortex generators at the trailing edge of a surface, as shown in the above photos, is pointless.
To be functional they need to be in a region where the flow has not already detached, and their purpose is to enhance attachment to the downstream surface. In the photos, they are probably in a region of detached flow and there is essentially no downstream surface. Wrong on both accounts.
They may not reattach the airflow at the end of the vehicle, but perhaps numerous small vortexes have less drag than one big one. I could see them working like the trailer tails on semi trucks.
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They may not reattach the airflow at the end of the vehicle, but perhaps numerous small vortexes have less drag than one big one.
As long as we're talking perhapses, the benefit in preventing the big vortices could be stability. Them big 'uns can grow slowly, collapse suddenly, and are asymmetrical.
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Putting vortex generators at the trailing edge of a surface, as shown in the above photos, is pointless.
To be functional they need to be in a region where the flow has not already detached, and their purpose is to enhance attachment to the downstream surface. In the photos, they are probably in a region of detached flow and there is essentially no downstream surface. Wrong on both accounts.
They may not reattach the airflow at the end of the vehicle, but perhaps numerous small vortexes have less drag than one big one. I could see them working like the trailer tails on semi trucks.
Having been involved in transportation and logistics for over 30 years I'll provide a simple observation. If you don't see the likes of Schneider, JB Hunt, UPS, FedEx, Ryder... adopting it onto their fleet vehicles there is a reason. I've been part of many a study on how to make tractor/trailer combos more efficient. After payroll, fuel is the number one expense. Anything you can do to cut it even by single digit percentages is adopted immediately by these organizations.
A simple cost benefit analysis done by these organizations will tell them if it is worth it or not. These guys aren't looking to go faster, they are looking for more fuel efficient. Coincidentally, MPG vs MPH have a common thread - aerodynamics. Trust me, these large carriers have annual fuel spends in the hundreds of millions of dollars. If they could save 1% with the bolt-on devices they would outfit their fleets overnight.
Always look at the big carriers and what they adopt, the little guys or the one-off guys are easily swayed...I've seen it a hundred times.
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Back in the mid 90s I postulated the skirts we now see on trailers. Dang it, shoulda patented the idea. But as for aero fuel savings -- on our straight trucks I spec'd Noze Cones over the objection of the dealer. Gee, I wonder why my fleet always got distinctly better gas mileage. . .
As for trailer tails -=- more and more of 'em out there, and yes, on the bigger fleets. Schneider doesn't yet -- but they've got faux moon discs on the drive wheels of the tractors. We drove back and forth to Indy this past week and saw dozens of tails deployed. Maybe it's a smaller percentage improvement and takes a big enough company to commit. Crete has some, Willis has lots, Covenant many. Over to you and back to racing aero...if you want.
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Hmmm?? I know that my neighbor, Toyota, has place several VGs on their new Prius near the rear of the vehicle. Several are integrated in the tail lights and several are underneath right before the rear bumper.
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Hmmm?? I know that my neighbor, Toyota, has place several VGs on their new Prius near the rear of the vehicle. Several are integrated in the tail lights and several are underneath right before the rear bumper.
Might have more to do with keeping the lights and body clean from accumulation of road dirt. At one time Mercedes made a reasonably big deal out of how the ribbed shapes on their tail lights tended to keep them cleaner than otherwise. (Didn’t make them easier to wash, though.)
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Some have said it gives clean air for the pilot chute to catch the air better and help pull out the main canopy.
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The Nish family has used and promoted the generators for years. Have 'em on the van, the race cars (as allowed, I presume) and so on. I'd say they'd be a reasonable source for information - maybe even data.
I wonder if Layne and Tom*, at Darko wind tunnel, have ever tried to quantify the things?
*Or anyone at any wind tunnel, or even you, Woody.
Twenty years ago, we tested patented vortex generator strips an inventor contacted us about. We let him guide the location on a couple of cars we had. Most of the trials were unsuccessful. Then we evaluated the vortex strips on a notch-back vehicle like the one shown in the Mitsubishi paper. They were located just below the back glass header. We measured a significant drop in drag in that application, more than double the small amount (CD=0.004) stated in this paper.
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Oh bbarn, if production aircraft don't use vortex generators, than B-52 A through E models never existed. There were long rows do v/g on the back of each wing ahead of the ailerons to promote better airflow to them. Boeing made around 500 or so of them. On the G and H models, ailerons were eliminated and roll control was done by spoiler action. I worked flight test for several of the large aircraft manufacturers and many of their aircraft used vortex generators. One funny thing we used to do to new airman just out of tech school was to send them to the tool crib for a special voltmeter to check the vortex generators. It never failed to amuse us and make the tool crib attendant unhappy when the kid went over there dutifully intending to get that special meter. In flight test we often tufted a surface to record laminar airflow. Depending on the camera results, we might add a row of vortex generators to see if airflow to the surface was improved and how much. If it worked out, than production was notified and a modification was authorized. Depending on the shape of a vehicle on the ground or in the air, vortex generators may be great or something to bang into tear up your body or really add to stability, but is all case by case as I see it?
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Oh bbarn, if production aircraft don't use vortex generators, than B-52 A through E models never existed. There were long rows do v/g on the back of each wing ahead of the ailerons to promote better airflow to them. Boeing made around 500 or so of them. On the G and H models, ailerons were eliminated and roll control was done by spoiler action. I worked flight test for several of the large aircraft manufacturers and many of their aircraft used vortex generators. One funny thing we used to do to new airman just out of tech school was to send them to the tool crib for a special voltmeter to check the vortex generators. It never failed to amuse us and make the tool crib attendant unhappy when the kid went over there dutifully intending to get that special meter. In flight test we often tufted a surface to record laminar airflow. Depending on the camera results, we might add a row of vortex generators to see if airflow to the surface was improved and how much. If it worked out, than production was notified and a modification was authorized. Depending on the shape of a vehicle on the ground or in the air, vortex generators may be great or something to bang into tear up your body or really add to stability, but is all case by case as I see it?
I would agree with your case by case assessment. VG's do exist on many aircraft, there are even aircraft that have been issued a certificate of waiver for their use. Back in the 90's we looked at putting them on our Navajo Chieftain. They did increase payload and reduce fuel burn so I would say they do work - of course I never said they didn't either.
GENERALLY, they are not installed onto GA aircraft at the factory. Some of it is cost, some of it is paperwork, some of it is they aren't effective for a particular model. On a B52, I could see them as highly beneficial. A B52 has a specific mission and that has to do with carrying weight. A VG CAN lower the stall speed as well as increase lifting capacity. On the B52 I would imagine that the VG's installed on both the wing and the ailerons were never at the trailing edge of the structure but rather at or forward of the recovery point of the wing.
You will also find VG's on production aircraft in specific locations, not strewn out in a line on the wing. They are judiciously placed on various areas of the fuselage other areas to correct or control specific areas of concern.
Keep in mind when I see the term VG I immediately think of the early applications in the general aviation market. These devices were installed in-line on each wing at the point of recovery along the entire length of the wing. The purpose of those was to promote particular characteristics of a wing within a give flight envelope. I am not counting the ones installed on the nose of an Super MD-88 that control the airflow into the engines 100' behind them. That is a particular application designed to shape a small segment of airflow and not induce lift/drag properties on a wing shape.
I could certainly see them in the pictures earlier in the thread having some influence on the pilot chute. Would be interesting to see video of deployment both with and without them and how much effect they may have.
Here are two examples of their employment that I am referring to. Notice they are installed in a line and in front of the recovery point of the wing. Their purpose here is to promote laminar flow. By that definition if you install them on the trailing edge of the wing they cannot promote laminar flow as there is nothing to attach the air too.
(http://www.cap-ny153.org/Aircraft%20Controls%20-%20Vortex%20Generators%20On%20Wings.jpg)
(http://rockets2sprockets.com/wp-content/uploads/2016/11/6a4eabc2-1678-4a25-afc8-3feda38b05c0.jpg)
I'll add this picture too. This is a flap on a Malibu, you can see they installed them forward of the recovery point. Again, their intended/purported use is to promote laminar flow so location, location, location!! lol
(https://www.nasa.gov/centers/langley/images/content/69889main_Micro-VG-fig5.gif)
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Has anyone tried air injection into the separated airflow region to reduce drag? The air to inject could be redirected from the front of the vehicle to small holes in the skin where vortex generators would normally be installed.
I have been reading where large ships are now using a similar concept called micro-bubbles that are injected onto the hull surface underwater. The air reduces drag up to 20% in the case of Quantum of the Seas cruise ship.
Don
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The air reduces drag up to 20% in the case of Quantum of the Seas cruise ship.
Don
the oxygen contained in that air will nurture barnacles to grow up to 40% faster :-D
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The Nish family has used and promoted the generators for years. Have 'em on the van, the race cars (as allowed, I presume) and so on. I'd say they'd be a reasonable source for information - maybe even data.
I wonder if Layne and Tom*, at Darko wind tunnel, have ever tried to quantify the things?
*Or anyone at any wind tunnel, or even you, Woody.
I have. Mixed results, not what you might expect.
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FWIW
I installed some VGs on a past car I owned in attempt to help keep the back window clear during rain. Water droplets would totally obscure my rearward vision at speed when it rained.
After I "installed" the VGs...at speeds above 45mph...the water on the rear window will start to blow off...after 50-55mph the back window would begin to dry. After sustained highway speeds the window would be completely dry. IN THE RAIN. It always fascinated me.
(https://scontent-iad3-1.xx.fbcdn.net/v/t1.0-9/1469739_10152344611465278_406098756_n.jpg?_nc_cat=0&oh=3d1ed294b3268c6a13e01de9908a9bc8&oe=5C0E8DBE)
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My bone stock SAAB SPG did the same thing...Pouring rain and a clear back glass. Odd.
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Here are two examples of their employment that I am referring to. Notice they are installed in a line and in front of the recovery point of the wing. Their purpose here is to promote laminar flow. By that definition if you install them on the trailing edge of the wing they cannot promote laminar flow as there is nothing to attach the air too.
I'll add this picture too. This is a flap on a Malibu, you can see they installed them forward of the recovery point. Again, their intended/purported use is to promote laminar flow so location, location, location!! lol
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I would argue a little about the use of the term Laminar flow. The very name "vortex generator" tells you it won't be laminar flow. The purpose is to keep the flow from stalling and seperating. With my limited understanding of aerodynamics. VG's are used in areas where flow is already going turbulent and used to keep it attached by introducing energy (read turbulence) into the air stream. Turbulent air is not laminar.
Very few airplanes or cars have laminar air flow for more than front leading edge of wing or fuselage/body.
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Depends on the angle of incidence the VG is placed. If set parallel to the airflow it will not induce (major) vorticies. If set off of inline, it will, hence my agreement on the induction of energized airflow.
As for laminar flow in a wing, it greatly depends on the airfoil. On a NACA66 series the laminar flow exists natively for a little more than 30% of the chord.
Sent from my Pixel 2 using Tapatalk
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It takes energy to move air and that is supplied by the vehicle. Less air movement = more speed. Sometimes creating a zone of micro turbulence prevents the formation of major and more power robbing macro turbulence. The vortex generators move air into micro turbulence that would otherwise be feeding into large power robbing eddy currents. Sort of turbulence management rather than turbulence elimination.
Those are my simplistic thoughts on the matter. I can be wrong, I am no expert.
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I am familiar with "eddy currents" in electrical engineering. Does this same term have a definition in fluid dynamics?
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Big whorls have little whorls
That feed on their velocity,
And little whorls have lesser whorls
And so on to viscosity.
-- Lewis F. Richardson 1920
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Depends on the angle of incidence the VG is placed. If set parallel to the airflow it will not induce (major) vorticies. If set off of inline, it will, hence my agreement on the induction of energized airflow.
Are you talking about how the VG is oriented or the VG itself? The picture you posted of v-shaped VG's are not parallel but are oriented in line.
John
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OK, now it is clearer. VG's have to angle in on one another for them to be effective (see image). I have seen some VG's that look like raised NACA ducts that I guess work the same way so long as you mount them with the bigger end pointed at airflow.
John
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The ones that I put on my car had a template that makes them gradually angle out from center. Progessing from 0 to 15 degress irrc (this was like 8 years ago)
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Prof. Joseph Katz recommended I use them on the truck I was building????.
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where :?
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where :?
South Africa. :mrgreen:
Mike
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The Ranchero I was building. Joe suggested putting Polycarbonate panels on the sides between the rear part of the roof and load box cover.
I wanted to keep the thing looking like I built it so he said Vortex generators would help to a degree.
You guys may not remember but Joe Katz's students built a quarter scale model of my truck at SDSU on their 3 axis milling machine
and wind tunnel tested it. I've still got all the photos and aero results from San Diego. The truck had a CD the same as a Porsche GT3.
The iffy area was between the rear window andload box.
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Prof. Joseph Katz recommended I use them on the truck I was building????.
Joseph Katz book on race car aero was one of the first I read. Packed with great aero information.
John
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I wish I could see Joe's car collection. He said he had a few. :wink:
A genuine guy and always helped and answered my emails.
What he did for me was unbelievable. 8-)
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I was thinking of putting these on my roof rack wind deflector to help break up the wind going over/to the trailer.
Thought I'd check in here first to see what you all thought of these.
Do they really help with the suction coming off the back of the trailer ?
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They need to be in clean (laminar)air to work, any turbulence there any you may as well forget it
I brought some to try and improve handling on an APS streamlined bike , but it seems my problems were bigger than the help these gave ;)
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The truck had a CD the same as a Porsche GT3.
Porsche GT3 doesn?t have a Cd you?d want for an LSR car... big dangly wings and massive open cooling. There?s at least 20 if not 25 counts (1 count is 0.001 Cd) of cooling drag on that car.
The thing I?m starting to notice is that not many people in the community know what they should be targeting for drag, lift or frontal area.
In the production industry we build databases of competitive products so we can try to predict trends etc.
If you guys are interested and want to share data I can put together something like that for each of the classes (that generate this sort of data). We?d have to account for differences in testing methodology but I think I might be able to do it with an uncertainty band.
Let me know if there?s interest, the more people on board the better the data will be. My intention would be to publish all of this for the community, may even be an SAE paper in it.
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They need to be in clean (laminar)air to work, any turbulence there any you may as well forget it
My roof rack is almost a foot back from the top of the windshield . I made the wind deflector (flat plastic) the same angle as the windshield. Which helped a lot.
So would my roof rack be considered in laminar air OR would the air going over the windshield be turbulent ?
I may order only 10 ($30) just to see if any......
My bug line on the trailer is the last 4" at the top.
It used to be lower , so improvements have helped.
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Vortex generators will work in turbulent air but it has to be "attached". All air flow past the point of the critical Reynolds number is turbulent but if the surface is smooth the air flow can remain attached. Although attached laminar air flow has much lower drag than attached turbulent flow, once the air flow becomes turbulent and unattached the drag is radically increased. There are a number of long cars with flat sides that have an abrupt transition to the cone of the tail section, which would be a perfect place for vortex generators, they may not be effective simply because the turbulent boundary layer is to thick.
Rex