Materials for Dimple Surfaces (reduced separation)

[chillsworld]

Originally Posted by aerohead

*Same for Mythbusters.They must be an embarrassment to whoever authorized an engineering diploma.

Not sure why everyone keeps bringing up Mythbusters, at no point have I referenced them I don't even have cable television

Originally Posted by aerohead

*There is only an inch or so of laminar boundary layer on a car.The rest is turbulent boundary layer.
*This TBL allows for attached flow as long as the body cross-section does not vary by much (area rule/sectional density).
*Once you have TBL there is no need of dimples,as they'd be superfluous and only increase drag.
*If you have contours on the car which are too 'fast',then a dimple might behave as a crude VG,but they are in no way as efficient as a true VG,as far as feeding momentum into a compromised TBL which is otherwise separating.
*It is the vortices created by VGs which feed momentum into the weak TBL,forestalling separation.
*Dimples cannot produce the quality of vortices as with VGs.They are very inefficient in this regard.
*The only reason golf balls have dimples instead of VGs is because the ball spins,and regardless of the balls orientation in the air,the dimples always present the same 'face' to the boundary layer,allowing predictable flight.
*If the ball could be oriented and struck with the driver or iron without imparting spin,then we could put VGs on them and extend a drive or chip shot.
*In water,the dimples would help the board or hull 'plane',as in a stepped hull.The curvature is too gentle to produce separation.
*I feel like Bez has not read Hucho or anyone else,and is clueless about boundary layer theory,otherwise he wouldn't have done what he's done.
*Same for Mythbusters.They must be an embarrassment to whoever authorized an engineering diploma.
*If any notchback car is going to be modified for boundary layer control,it should be done with VGs.It's just better science.

I understand that the TBL shouldn't need to be energized on streamlined surfaces to stay attached, but why are there studies and wind tunnel experiments that show a decrease in surface friction and an improvement of .cd values on already streamlined surfaces (passenger train cars for example, they have no curves or bluff characteristics along their sides). According to your statements, there shouldn't be any improvement upon an already perfect TBL/BL scenario via the use of dimples or any other such "fake vortex generator"?? I guess I'm just confused by the fact that everyone says it won't work, yet I'm the only one providing data/links to anything. So while vortex generators might be "better science", is that true because people simply won't look at new data that didn't exist when Hucho did all of his stuff? Or is it because these new studies are incorrect, or maybe they aren't actually as efficient as they would be if they used "real" vortex generators?

"As the layers of air move over a rough surface, the air particles in the layer closest to the surface collide with the surface. This makes the air particles slow right down (and right at the surface, they completely stop!). These particles then collide with air in layers a bit further out and make them slow down as well. As you move further away from the surface, the speed of the air particles is not affected. This boundary layer is laminar at the beginning of the flow, but it gets thicker as the air moves along the surface and becomes turbulent after a point."

So even on a super slippery, super streamlined surface, eventually friction/drag increases and separation occurs right? Vortex generators are used to mix things up and change the dynamic of this occurrence correct? And more often than not, they focus entirely on a point where separation will naturally occur right? Or on the leading edge of something at an attack angle. You wouldn't just put them down the length of the car, or all over the top of the car for no reason. The research I have been linking to, says it decreases surface friction and thus prevents the friction from increasing and the occurrence of separation (to some extent)... Which is similar but different from what Vortex generators do. I don't claim to know how, which is why I'm providing quotes, links, and statements from other places.

If I would have known it was such a hot button topic, and that I would need to look so much stuff up just to not seem like an idiot who watched some TV episode, I wouldn't have bothered posting in the first place Anywho, I guess it's not a big deal, I sure don't have the means to test any of it... So I guess I'll move on to something else

~C

[freebeard]

Not sure why everyone keeps bringing up Mythbusters, at no point have I referenced them I don't even have cable television

You don't need cable; all the high-lites are on Youtube. I recommend Adam Savages one-day builds and resin-kit painting tutorials.

I guess I'm just confused by the fact that everyone says it won't work, yet I'm the only one providing data/links to anything.

Once again, I don't get to be part of everyone. What I suggested was a low-cost testing technique. I think bubble-rap would be halfway between dimples and an omni-directional vortex generator. They all provide a small-scale, localized disturbance of the overall air flow.

If I would have known it was such a hot button topic, and that I would need to look so much stuff up just to not seem like an idiot who watched some TV episode, I wouldn't have bothered posting in the first place

Well, thanks for bringing it up so we could all, for better or worse, exercise our 'thinkers'.

[oldtamiyaphile]

You've clearly come on here with a better understanding of the effects dimples than the average poster on the subject. While the general consensus might be against them that doesn't mean they can't work.

Personally, I'd love to see someone re-run the Mythbusters test in more controlled conditions. Their gains were clearly far too massive to take seriously.

Originally Posted by chillsworld

. But none of them have figured out how to implement the idea...

You can buy little stainless mixing bowls for artists paint that measure about 1-1.5" diameter, all you need then is a hole saw and some bonding agent For bigger dimples you could cut up baking trays.

All you need now is a beater and a couple of afternoons.

[oldtamiyaphile]

Originally Posted by chillsworld

Not sure why everyone keeps bringing up Mythbusters, at no point have I referenced them I don't even have cable television

Here you go:

VIDEO: Mythbusters test golf ball-like dimpling effect on fuel economy (*Spoiler Alert!*)

[freebeard]

The simple truth is that when you say "dimples" 'everyone' says "Mythbusters".

It's like on Mystery Science Theatre 3000 whenever someone in a movie turns a flashlight on and swings it back and forth, the 'bots say "NBC Mystery Hour". They can't help themselves.

[Xist]

Oh ye of little Google-fu:
Dimpled Car MiniMyth | MythBusters | Discovery
http://ecomodder.com/forum/showthrea...les-10718.html
http://ecomodder.com/forum/showthrea...ars-29311.html (look at #4)
http://ecomodder.com/forum/showthrea...und-20548.html
http://ecomodder.com/forum/showthrea...wrap-6807.html
http://ecomodder.com/forum/showthrea...ank-12691.html
http://ecomodder.com/forum/showthrea...mics-6263.html

Those are unique results from the first of fourteen pages putting "Mythbusters golfball dimples" into the search box.

Edit: Old Tami beat me to it. I loaded the page and others responded before I could.

[chillsworld]

Originally Posted by freebeard

You don't need cable; all the high-lites are on Youtube. I recommend Adam Savages one-day builds and resin-kit painting tutorials.

Once again, I don't get to be part of everyone. What I suggested was a low-cost testing technique. I think bubble-rap would be halfway between dimples and an omni-directional vortex generator. They all provide a small-scale, localized disturbance of the overall air flow.

Well, thanks for bringing it up so we could all, for better or worse, exercise our 'thinkers'.

It's no fun if you're like everyone else, not being one of them is what makes you special man And I guess I could do the bubble wrap, I'm just not knowledgeable enough to know if the results would even be relevant for the theory behind dimples/pits/etc?? I'd hate to test it, have it do nothing, and then wrongfully provide empirical data that says dimples don't do anything. Does that make sense? If dimples truly are inefficient vortex generators like Aerohead said, then bumps would be relevant... But if dimples act in a manner which is different than a true vortex generator, then bumps wouldn't be a proper test right? I guess I can make a plan for testing it sometime soon, might hit you up for help with it since it's your idea

~C

[chillsworld]

Originally Posted by oldtamiyaphile

Here you go:

VIDEO: Mythbusters test golf ball-like dimpling effect on fuel economy (*Spoiler Alert!*)

Originally Posted by Xist

Oh ye of little Google-fu:
Dimpled Car MiniMyth | MythBusters | Discovery
http://ecomodder.com/forum/showthrea...les-10718.html
http://ecomodder.com/forum/showthrea...ars-29311.html (look at #4)
http://ecomodder.com/forum/showthrea...und-20548.html
http://ecomodder.com/forum/showthrea...wrap-6807.html
http://ecomodder.com/forum/showthrea...ank-12691.html
http://ecomodder.com/forum/showthrea...mics-6263.html

Those are unique results from the first of fourteen pages putting "Mythbusters golfball dimples" into the search box.

Edit: Old Tami beat me to it. I loaded the page and others responded before I could.

Oh I know what it is, haven't watched it yet. The first time it was mentioned I googled it... Doesn't change the fact that at no point have I referenced it in my posts, and there for would seem irrelevant for people to judge me and assume that I'm posting because of it Nor does it seem logical to keep referencing it, when I have linked to studies and articles that DO have controlled environments and aren't some TV show But thanks for the links, I guess I'll try to watch that episode at work today


~C

[chillsworld]

Originally Posted by oldtamiyaphile

You've clearly come on here with a better understanding of the effects dimples than the average poster on the subject. While the general consensus might be against them that doesn't mean they can't work.

Personally, I'd love to see someone re-run the Mythbusters test in more controlled conditions. Their gains were clearly far too massive to take seriously.

You can buy little stainless mixing bowls for artists paint that measure about 1-1.5" diameter, all you need then is a hole saw and some bonding agent For bigger dimples you could cut up baking trays.

All you need now is a beater and a couple of afternoons.

I wouldn't say I have a better understanding. I just don't have a pre-established aversion to the idea, like it would seem most people here have

I did the math based on boundary layer thickness and the design of the vortex generators used on the EVO, and the two studeis which listed dimesnions for their dimples/pits... And those *could* be perfect dimples/pits, the ratio of the width to depth is supposed to be important though. Now if only I felt comfortable doing that to my daily driver beater hahaha.

As far as not taking mythbusters 11% seriously, I think most people outside this website don't take the % claims regarding 90% of the common modifications done my members of this site seriously... Everything is relative, and each of us is usually quick to judge something we don't understand haha Not saying I personally think the 11% is accurate, just making an observation.

~C

[aerohead]

Originally Posted by chillsworld

Not sure why everyone keeps bringing up Mythbusters, at no point have I referenced them I don't even have cable television




I understand that the TBL shouldn't need to be energized on streamlined surfaces to stay attached, but why are there studies and wind tunnel experiments that show a decrease in surface friction and an improvement of .cd values on already streamlined surfaces (passenger train cars for example, they have no curves or bluff characteristics along their sides). According to your statements, there shouldn't be any improvement upon an already perfect TBL/BL scenario via the use of dimples or any other such "fake vortex generator"?? I guess I'm just confused by the fact that everyone says it won't work, yet I'm the only one providing data/links to anything. So while vortex generators might be "better science", is that true because people simply won't look at new data that didn't exist when Hucho did all of his stuff? Or is it because these new studies are incorrect, or maybe they aren't actually as efficient as they would be if they used "real" vortex generators?

"As the layers of air move over a rough surface, the air particles in the layer closest to the surface collide with the surface. This makes the air particles slow right down (and right at the surface, they completely stop!). These particles then collide with air in layers a bit further out and make them slow down as well. As you move further away from the surface, the speed of the air particles is not affected. This boundary layer is laminar at the beginning of the flow, but it gets thicker as the air moves along the surface and becomes turbulent after a point."

So even on a super slippery, super streamlined surface, eventually friction/drag increases and separation occurs right? Vortex generators are used to mix things up and change the dynamic of this occurrence correct? And more often than not, they focus entirely on a point where separation will naturally occur right? Or on the leading edge of something at an attack angle. You wouldn't just put them down the length of the car, or all over the top of the car for no reason. The research I have been linking to, says it decreases surface friction and thus prevents the friction from increasing and the occurrence of separation (to some extent)... Which is similar but different from what Vortex generators do. I don't claim to know how, which is why I'm providing quotes, links, and statements from other places.

If I would have known it was such a hot button topic, and that I would need to look so much stuff up just to not seem like an idiot who watched some TV episode, I wouldn't have bothered posting in the first place Anywho, I guess it's not a big deal, I sure don't have the means to test any of it... So I guess I'll move on to something else

~C

*Chronologically,it seems like the Mythbusters episode was the catalyst for the concept of dimples and drag reduction entering into the public mind.
*Jamie,or whoever is the 'engineer' on Mythbusters,ought to already understand the difference in the relationship between the Reynolds number of a golf ball and an automobile.It would have been covered in Fluid Mechanics,which he'd have to pass in order to get a degree.
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*Boundary layer aerodynamics of railroad trains would not be germane to a discussion of automobile boundary layers.The volume of the BL of a railroad train can easily exceed its frontal area.
*If you have another research which addresses dimples and automobiles which is peer-reviewed,we could look at that.
*TBL is TBL.Once it's established it works its wonders.
*The only way a dimple could 'work' is if it was acting as a crude VG.
*The 'new' studies must be viewed within a particular context.We have almost 100-years of VG research already documented.I would be very surprised if any stone has gone unturned.Winning world wars have depended upon such information.
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*The layer of air against the smoothest surface is at rest.
*If the TBL is in a unfavorable pressure gradient,due to Bernoulli's Theorem,it must decelerate.
*It can't decelerate since it's already at rest.
*The only reason it can stay attached,is if the TBL is transferring momentum from the inviscid flow outside the TBL.
*If the contour is too 'fast' the TBL will separate.
*If there is a surface downstream within a proper profile,there can be reattachment.
*VGs can help insure reattachment.Their vorticity feeds kinetic energy into a feeble TBL,re-energizing it,holding it against the boundary wall as if it were being machine-gunned from above.
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*On a super-slippery surface there will be about 1-inch of laminar boundary layer,then the rest is TBL.
*Friction drag is a consequence of viscosity,and shear stresses within the fluid as the varying strata laminations,at different velocities shear against one another.
*Attached flow is a function of pressure gradients,which are a function of body geometry.
*If the body is 'streamlined' it cannot produce separation,by definition.
*If it is pseudo-streamlined,like a VW Beetle,or,like a Mitsubishi Lancer,then it will have separation.
*VGs increase surface friction,but reduce overall drag through pressure drag reduction.
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It's not a sin to look and find things and share.The spirit of the whole thing is admirable and it needs to be applauded.
Some research is done by people who haven't done their homework.And because they don't know what they don't know,they don't even realize that they are making contextual comments when they are making them.Then it becomes a matter of damage control,attempting to rebut what is being passed off as true science.It's too dangerous to pass without a test.