Using golf ball dimples to decrease vaccuum drag on motor vehicles and aircraft.

In summary: A golf ball with dimples experiences less drag due to the dimples creating a turbulence that covers a larger surface area of the ball and decreases the size of the vacuum behind it. This same technique could potentially be used on the bodies of motor vehicles and aircraft to increase their range and speed. However, for these larger and more aerodynamic shapes, dimples are not effective and other methods such as vortex generators are used. Additionally, airplanes do not want turbulent flow as it can lead to stalls, but they also cannot completely avoid it. Dimples on a golf ball work to increase the Reynolds number and trigger the laminar to turbulent transition sooner, which reduces drag. However, in the case of an aerodynamic shape, dimp
  • #1
Bararontok
298
0
A golf ball without dimples experiences more drag because the deflection area of the airflow around the ball is larger which means that the pressure drop behind the golf ball is also higher. The increased drop in pressure creates a suction vacuum behind the golf ball which pulls it back and decreases its velocity and range. The dimpled golf ball on the other hand experiences less drag because the dimples create a turbulence that causes a larger surface area of the golf ball to be covered by the flowing air which decreases the size of the vacuum behind the golf ball and subsequently its drag. So if the drag reduction caused by the dimples can be used on golf balls, then why not use this technique on the bodies of motor vehicles and aircraft to increase their range and speed?

Sources: http://wings.avkids.com/Book/Sports/instructor/golf-01.html
http://www.youtube.com/watch?v=nufXpDBELdQ&feature=related
 
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  • #2
A lot of airplanes use vortex generators to do something similar: making a controlled transition from laminar to turbulent airflow, which is much less violent and delays flow separation. http://en.wikipedia.org/wiki/Vortex_generator

For cars, I suspect the answer is two-fold:
1. Aesthetics.
2. They aren't aerodynamic enough in the first place for it to matter.
 
  • #3
Actually, the youtube link included in my first post shows a Mythbusters experiment with a dimpled automobile and proves that the fuel economy of the automobile covered in a dimpled body rises from 26mpg to 29.65mpg which is a 14% increase in fuel economy. With such a substantial increase in fuel savings, why not modify the body of the car but using the easier to machine vortex generators since they produce the same effect as the dimples?
 
  • #4
Airplanes don't want turbulent flow, otherwise they can stall. The dimples on a gold ball work to increase the Reynolds number of a flow that will become turbulent, effectively triggering the laminar to turbulent transition sooner. For a golf ball, this leads to a smaller effective space where turbulent flow occurs behind the ball, reducing the drag. That's my understanding, at least.
 
  • #5
Bararontok said:
Actually, the youtube link included in my first post shows a Mythbusters experiment with a dimpled automobile and proves that the fuel economy of the automobile covered in a dimpled body rises from 26mpg to 29.65mpg which is a 14% increase in fuel economy.
Wow, I stand corrected. I would have thought the front end of a car was so bad aerodynamically that the air would be turbulent right away.
With such a substantial increase in fuel savings, why not modify the body of the car but using the easier to machine vortex generators since they produce the same effect as the dimples?
Aesthetics, I'm sure.
 
  • #6
Cvan said:
Airplanes don't want turbulent flow, otherwise they can stall.
Anything moving through the air is going to get turbulent flow whether it wants it or not, with only a few rare exceptions. So the key is controlling it.

The P-51 is one of the few that was designed to have completely laminar flow, but it is extrordinarily difficult to keep the surfaces smooth enough to actually keep it laminar. Plus, laminar flow is unstable, so stalls are very violent in such aircraft:
The P-51 Mustang was the first aircraft intentionally designed to use laminar flow airfoils. However, wartime NACA research data shows that Mustangs were not manufactured with a sufficient degree of surface quality to maintain much laminar flow on the wing. The RAF found that the Bell P-63, despite being designed with laminar airfoils, also was not manufactured with sufficient surface quality to have much laminar flow.
http://www.aviation-history.com/theory/lam-flow.htm
The dimples on a gold ball work to increase the Reynolds number of a flow that will become turbulent, effectively triggering the laminar to turbulent transition sooner. For a golf ball, this leads to a smaller effective space where turbulent flow occurs behind the ball, reducing the drag. That's my understanding, at least.
Well, partly right. Since the transition is sooner, there is more turbulent air in a dimpled ball than a smooth one. But tubulent air stays attached to the ball better, which makes the flow separation region behind the ball smaller.
 
  • #7
Bararontok said:
A golf ball without dimples experiences more drag because the deflection area of the airflow around the ball is larger which means that the pressure drop behind the golf ball is also higher. The increased drop in pressure creates a suction vacuum behind the golf ball which pulls it back and decreases its velocity and range. The dimpled golf ball on the other hand experiences less drag because the dimples create a turbulence that causes a larger surface area of the golf ball to be covered by the flowing air which decreases the size of the vacuum behind the golf ball and subsequently its drag. So if the drag reduction caused by the dimples can be used on golf balls, then why not use this technique on the bodies of motor vehicles and aircraft to increase their range and speed?

Sources: http://wings.avkids.com/Book/Sports/instructor/golf-01.html
http://www.youtube.com/watch?v=nufXpDBELdQ&feature=related

In the case of a sphere, there is a sudden and dramatic drop in drag with the use of dimples for a certain Reynolds number. For low Re, dimples are worse, for high speed, dimples are better. In the case of an aerodynamic shape such as an aircraft or car, dimples do you no good - hence why they are not employed.
 
  • #8
Cvan said:
Airplanes don't want turbulent flow, otherwise they can stall.

Im afraid this just isn't quite right - turbulence and separation (stall) are not one in the same.
 
  • #9
Cyrus said:
In the case of a sphere, there is a sudden and dramatic drop in drag with the use of dimples for a certain Reynolds number. For low Re, dimples are worse, for high speed, dimples are better. In the case of an aerodynamic shape such as an aircraft or car, dimples do you no good - hence why they are not employed.

Actually, the youtube link included in my first post shows a Mythbusters experiment with a dimpled automobile and proves that the fuel economy of the automobile covered in a dimpled body rises from 26mpg to 29.65mpg which is a 14% increase in fuel economy. With such a substantial increase in fuel savings, why not modify the body of the car but using the easier to machine vortex generators since they produce the same effect as the dimples?
 
  • #10
Bararontok said:
Actually, the youtube link included in my first post shows a Mythbusters experiment with a dimpled automobile and proves that the fuel economy of the automobile covered in a dimpled body rises from 26mpg to 29.65mpg which is a 14% increase in fuel economy. With such a substantial increase in fuel savings, why not modify the body of the car but using the easier to machine vortex generators since they produce the same effect as the dimples?

Again, this is generally not true and does not work on cars. They got lucky with a freak case, I'll check out your link to see their setup better and report back.
 
  • #11
On a related note, plasma fields for reducing drag, seems to be an active area of interest.
https://www.physicsforums.com/showthread.php?t=116408
http://defensetech.org/2006/03/30/stealths-radioactive-secret/

I haven't read up on this in quite awhile, but, IIRC, it was dismissed for stealth applications because of the associated optical effects - early testing of this concept may account for some UFO reports. But what about commercial applications? Is that still a possibility? Anyway, another thread perhaps, but it came to mind.
 
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  • #12
I just watched the clip they did with the car, wow. Are you kidding me? That is not a valid test by any stretch of the imagination. They have so much crap that the basic aerodynamic shape of the car is altered to a significant degree. All they had to do was make a two models of a car with and without dimples and stick it into a wind tunnel. Bogus test, sorry.
 
  • #13
Cyrus said:
I just watched the clip they did with the car, wow. Are you kidding me? That is not a valid test by any stretch of the imagination. They have so much crap that the basic aerodynamic shape of the car is altered to a significant degree. All they had to do was make a two models of a car with and without dimples and stick it into a wind tunnel. Bogus test, sorry.

Why did they allow this to air on discovery channel if it is bogus? Should they not get sued for misinformation?
 
  • #14
Mythbusters is designed for entertainment; not scientific rigor. None the less, their experiments are often designed well providing both goals can be met.

Popular Mechanics conducted a similar test with different results and explained some of the problems with the entire idea of dimples: http://www.popularmechanics.com/cars/news/4316702
 
  • #15
Bararontok said:
Why did they allow this to air on discovery channel if it is bogus? Should they not get sued for misinformation?

It's a TV show - it's fun to watch. Based on their personalities on the show, I don't doubt their results are accuate; however, the problem is correlation does not eqaul causation (It is a poorly designed experiment with no definitive result that it was the dimples that reduced the gas milage, and not due to some other phenonemnon).

As an aside, you can't sue someone for 'misinformation.'
 
  • #16
Another factor that I feel was over looked is body shape. A gold ball is a sphere and an airplane/car is not. The "dimple effect" ultimately comes from flow separation and where the flow separates. On a golf ball, you want flow separation as late as possible due to its circular cross section in order to reduce drag created from a difference in pressure. However, aircraft don't really much flow separation except maybe cases with large angles of attack. So the only real effect dimple will have is if they reduce the influence of surface friction which as far as I know, they don't.
 
  • #17
Topher925 said:
Another factor that I feel was over looked is body shape. A gold ball is a sphere and an airplane/car is not. The "dimple effect" ultimately comes from flow separation and where the flow separates. On a golf ball, you want flow separation as late as possible due to its circular cross section in order to reduce drag created from a difference in pressure. However, aircraft don't really much flow separation except maybe cases with large angles of attack. So the only real effect dimple will have is if they reduce the influence of surface friction which as far as I know, they don't.

Precisely.
 
  • #18
BobG said:
Mythbusters is designed for entertainment; not scientific rigor. None the less, their experiments are often designed well providing both goals can be met.

Popular Mechanics conducted a similar test with different results and explained some of the problems with the entire idea of dimples: http://www.popularmechanics.com/cars/news/4316702

Incidentally the study by Popular Mechanics looks at dimples that are ~5mm, while the Myth Busters looked at dimples ~75mm (just guessing, estimating 3 inches as approximately the the size of the tennis ball they used). I googled a picture of what the Fastskin's dimples look like and found this. http://www.google.com/imgres?imgurl...tx=64&ty=88&page=1&ndsp=20&ved=1t:429,r:2,s:0

I'm not saying the MythBusters got it right, although it looked reasonably convincing, but its not clear to me that the Popular Mechanics example disproves MythBusters results.
 
  • #19
On a side note, I've seen at least one production car with vortex generators very similar to ones used on airplanes; the Mitsubishi Lancer Evolution VIII. Whether they're helpful in terms of mileage, no idea.

mitsubishi-lancer-evolution-viii-mr-fq-400-top-3_124.jpg

2005-Lancer-Evolution-VIII-MR-FQ-400-RA-1024x768.jpg


turp_0901_09_z+project_mitsubishi_lancer_evolution_ix_interior_exterior+vortex_generators.jpg
 
  • #20
It is a good start.
 
  • #21
Bararontok said:
It is a good start.

I have no idea what this is supposed to mean or imply. :confused:
 
  • #22
Vortex generators on cars? :) Cool idea as an aero enthusiast. As to it's usefulness in reducing drag to improve top speed performance and gas mileage? Hmmmm :).

Here's a scholarly report from Mitsubishi on the topic:
http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf

They estimated for the Lancer that it reduced CD by .006. Given that car CD that I've seen listed between .30 to .25 a .006 improvement is roughly a 2% improvement. Given the velocities we drive our cars at I doubt that it could amount to much!
 
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  • #23
Cyrus said:
In the case of a sphere, there is a sudden and dramatic drop in drag with the use of dimples for a certain Reynolds number. For low Re, dimples are worse, for high speed, dimples are better. In the case of an aerodynamic shape such as an aircraft or car, dimples do you no good - hence why they are not employed.

Exactly! And this based not only on the Reynolds number, but also on the shape. For example, the Reynolds number for a bullet is quite low, but we're not dimpling bullets for a reason, and that reason isn't that bullets are supersonic, as nearly all handgun bullets are subsonic.

Golfballs are a fairly special case, falling into that rare regime of both Reynolds number and shape where dimpling actually improves flight performance.

Interestingly, I find it odd why the wings of most birds are covered by turbulent feathers, as opposed to the beatle's fairly smooth sheets...

Hmm... I feel a study coming on...
 
  • #24
mugaliens:

Insects versus birds: the great divide

http://www.citeulike.org/group/918/article/790560
 
  • #25
Yes, thanks, John, and you're absolutely correct with respect to the world of micro-UAVs. They simply fly based much more in the Reynolds numbers of the birds and the bees than of anything approaching a meter or beyond. And yes, sharp leading edges and laminar flow combined with capitalizing on turbulent after-effects is the order of the day!

I have a dynamically, self-learning and stabilized helo-toy I bought for $100. I occasionally demonstrate it for guests who are leading aerospace designers, and about half of them still bite off on my story that it's the latest model in the USAF arsenal and costs $200 thousand per copy. When I show them the sales ticket and they're agahst, I remind them the iPhone, iPad and iPod Touch have the same or better sensors, for less than $300, and that the rest is simply programming, at which point they start to realize this technology no longer costs millions.

Of course some of the spouses start fingering their jewels, as they become aware their corporate income-funded riches are about to dry up.

As for me? Well, heck, I'm making a mint helping corporations figure out ways to do the same job for thousands of dollars these days that they used to pay millions of dollars for in yesteryear.

These days we're at the point where we can re-create the flight of a http://en.wikipedia.org/wiki/Entomopter" [Broken].

The key is in advancements in inertial sensors and computational (computer programming) control. Aside from these two factors, we could have done this 50 years ago.
 
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  • #26
Cyrus said:
I just watched the clip they did with the car, wow. Are you kidding me? That is not a valid test by any stretch of the imagination. They have so much crap that the basic aerodynamic shape of the car is altered to a significant degree. All they had to do was make a two models of a car with and without dimples and stick it into a wind tunnel. Bogus test, sorry.

Watch the whole episode. They did test models, both in a wind tunnel and in a water tunnel with die to look at flow. Both tests conducted at NASA JPL so they're definitely reliable. Both with positive results. In addition, they covered the car in smooth clay and tested it first. Then created the dimples and put the carved out pieces inside the car to compensate weight. They did 5 60mph 1mile long runs each, not beginning data collection until 60mph was achieved each time and stopping data collection at exactly 1 mile. Sounds like they covered all the variables to me.
 
  • #27
If you scale up from a golf ball to a toyota prius, I'm curious how much the scale of the dimples would be to harness this...or it doesn't scale.
 
  • #28
claytonh4 said:
Watch the whole episode. They did test models, both in a wind tunnel and in a water tunnel with die to look at flow. Both tests conducted at NASA JPL so they're definitely reliable. Both with positive results. In addition, they covered the car in smooth clay and tested it first. Then created the dimples and put the carved out pieces inside the car to compensate weight. They did 5 60mph 1mile long runs each, not beginning data collection until 60mph was achieved each time and stopping data collection at exactly 1 mile. Sounds like they covered all the variables to me.

Are you familiar with Reynolds number and how to properly scale wind tunnel tests. It is more than likely that they didn't properly scale because the Mythbusters almost never properly scale anything.

That driving test they did with and without dimples was not even remotely close to a well controlled experiment. What if the temperature changed a little and effected the air properties, what if the wind was blowing a little faster during one test than the other, what if the driver accelerated differently or spent some of the time driving at 61mph. Are speedometers really that accurate? (I have no idea) The power required to overcome air resistance goes up with velocity cubed! So a small change in velocity from the wind or driving at a different speed can have an impact. So no, they did not cover all of the variables. They never cover all of the variables.
 
  • #29
RandomGuy88 said:
Are you familiar with Reynolds number and how to properly scale wind tunnel tests. It is more than likely that they didn't properly scale because the Mythbusters almost never properly scale anything.

That driving test they did with and without dimples was not even remotely close to a well controlled experiment. What if the temperature changed a little and effected the air properties, what if the wind was blowing a little faster during one test than the other, what if the driver accelerated differently or spent some of the time driving at 61mph. Are speedometers really that accurate? (I have no idea) The power required to overcome air resistance goes up with velocity cubed! So a small change in velocity from the wind or driving at a different speed can have an impact. So no, they did not cover all of the variables. They never cover all of the variables.

Well I can see your point about scale issues as well as temp. dif. and wind, etc., however the acceleration time was not included in the test. They accelerated on the reg. gas tank then switched over to their gas tank that was actually being measured when 60mph was achieved. The car was then put on cruise control for testing time. Yes there could be anomalies, but I was impressed in the testing of variable accountability. Again though, scale, wind, temp., humidity could all lead to false data... they should've used an indoor track!
 
  • #30
I have a lot of respect for the Mythbusters guys. They have done more to interest kids in this country in science and engineering than any government program has, that's for sure. That said, nothing they do in the show should be considered scientifically sound. They do sometimes get it right and they sometimes get some good results, but rarely do they take into account all variables or do a full analysis of anything. Take it for what it is: and entertainment program with a science bent.
 
  • #31
The best way to compare the performance of a car body with golf ball dimples or vortex generators with a regular car body is to calculate or research the drag coefficients and the force and power produced by the vacuum drag and produce a table that will list all of these values for the three aerodynamic profiles to perform an accurate comparison. Of course other variables such as the cross-sectional area of the body and the weight of the body will have to be standardized for the comparison of performance factors to be accurate.
 
  • #32
the paper...
http://www.4g63.de/facts/vortexgenerator-evo-mitsu.pdf

Mech_Engineer said:
On a side note, I've seen at least one production car with vortex generators very similar to ones used on airplanes; the Mitsubishi Lancer Evolution VIII. Whether they're helpful in terms of mileage, no idea.

mitsubishi-lancer-evolution-viii-mr-fq-400-top-3_124.jpg

2005-Lancer-Evolution-VIII-MR-FQ-400-RA-1024x768.jpg


turp_0901_09_z+project_mitsubishi_lancer_evolution_ix_interior_exterior+vortex_generators.jpg
 

What is the concept behind using golf ball dimples to decrease vaccuum drag on motor vehicles and aircraft?

The concept is based on the idea that the dimples on a golf ball create a turbulent boundary layer, which reduces drag by reducing the size of the wake behind the ball. This same principle can be applied to motor vehicles and aircraft to decrease drag and increase fuel efficiency.

Has this concept been tested and proven?

Yes, this concept has been extensively tested and proven in wind tunnel experiments and computer simulations. It has also been successfully implemented in the design of some vehicles and aircraft, resulting in significant reductions in drag and increased efficiency.

What are the potential benefits of using golf ball dimples for drag reduction?

The potential benefits include increased fuel efficiency, reduced emissions, and improved performance and handling of vehicles and aircraft. This can also lead to cost savings for consumers and businesses, as well as a positive impact on the environment.

Are there any potential drawbacks or limitations to using golf ball dimples for drag reduction?

One potential drawback is that the dimples may increase the weight of the vehicle or aircraft, which could offset some of the fuel efficiency gains. Additionally, the dimples may not be suitable for all types of vehicles and may require additional maintenance and cleaning.

What other applications could this concept have?

This concept could potentially be applied to other forms of transportation such as trains, boats, and even spacecraft. It could also be used in the design of buildings and structures to reduce wind resistance and improve energy efficiency.

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