Golf Ball Fluid Dynamics

OK, Let me give the Dimple Heads their due. In about the 1960's, the,USAF did a NASA drag reduction project on fighter jets. Basically air was pumped out of thousands or holes in the planes surfaces. It reduced drag by about 30%. Problem was outrageous cost of keeping the holes open to specifications. --------Most of the cheap obvious ideas are done in a lot of fields.

 

There is some qualitative discussion on this exact topic "Principles of Yacht Design"- Larsson & Eliasson.

 

The "shark skin" used on Conners A-cup boat had little riblets (1/10 mm) in a herring-bone pattern. The idea was that any flow trying to organize next to the surface would channel along a riblet and crash squarely into the next one, and thus be broken up.

I believe the appropriate view in this case is that of L F Richardson:

"Big swirls have little swirls that feed on their velocity,

little swirls have lesser swirls, and so on to viscosity"

Yoke.

 

What's the Reynolds Number of the golf ball?

What Reynolds Number would predict the boundary layer to be Laminar?

What Reynolds Number would predict the boundary layer to be Turbulent?

 

Thanks Kach 221 and Inquisitor, The article was very informative.

Before, I had the notion that generated air bubbles acts as ball bearings that will lubricate the hull and make it slippery. I was wrong.

The boundary layer that follows the hull shape is viscous and cohesive. The water particles in contact with the hull stick with the next layer of particles. As it moves towards the stern, it drags another layer and so on and so forth until it reaches a discontinuity or an abrupt curvature where the water (laminar flow) can no longer follow.

As it separates, it forms a resistance, as it forms a turbulent layer it is another resistance. This resistance is small and is lumped together as “other form of resistance”.

Any imperfection on the surface however microscopic will cause a turbulent flow and increases the resistance.

So what gives? Others claim that waxing the surface will increase speed while others will go for “shark skin” effect. The answer is they have found the “sweet spot” between speed, length, and form. Note that the fluid formula needs velocity, viscosity, and length with length expressed in non dimensional Froude number.

Waxing the surface (to reduce surface imperfection) reduces viscous drag, introducing bubbles will delay the separation point thereby “lengthening the hull”. As we all know, a longer hull is more efficient.

I am attaching a diagram of a typical hull form which appeared in Principle of Naval Architecture, second revision. This is more attuned to boat design while consistent with fluid dynamics (air and water being fluids), only some of the terms are different.

Dimples on the golf ball? Well, it “lengthened the hull”. Then they applied chapstick to make it go faster. Confusing isn’t it.

 

If you generate a lot of air bubbles in the area around a hull it will sink,no more boyancy so air bubbles must act as a lubricant and reduce drag.This was scientificly proven to prove how boats have dissapeared at sea.A boat was floted in a area areated with air compressors and the boat quickly sank.Boats have dissapeared in the North Sea and it is believed gas from the ocean floor had the same effect.

 

Tom, this has been mentioned several times and leads to some interesting questions. Do you have a link to any direct information on this air bubble experiment?

 

The experiment was shown on a Science program on TV I have not been able to find other experiments relating to boat hulls and friction and drag.

 

air bubbles

You guys should ask Eric Sponberg about this. If I'm not mistaken his Project Amazon and Warren Luhrs Thursdays Child used similar systems to inject air over the aft part of the hull. Eric can commnt much more in detail....

 

Air injection is nothing new, Sea-plane floats and stepped power-boat hulls have been doing it for some time.

The origenal subject... Golf-balls would have laminar flow, but also lots of separation. the dimples turbulate the flow, thus reducing the separation behind the ball, hence increasing it's didtance travelled. There are fluid-dynamics books that discuss the subject.

Tim B.

 

Evolution has been designing longer than NA's, anybody tried scales.?

 

I don't think this tape is water proof, interesting idea just the same.

http://www.lessgasmoremiles.com/


You can also click on "Patented Since 1996" and download the PDF, some interesting examples of application including airplane wings.

 

The idea of using golf ball dimples to reduce drag on shapes, sizes and speeds different than those of a golf ball indicates no knowledge of drag due to shape, size, or speed.

 

I'm not a fan of the dimple tape, however they are showing it at the most likely intersection of planes which would have air ripping off the surface and causing turbulance.

I think the trailing edge (rear window) as in the golf ball example would be the place to look first. The leading edge (front wind shield) as in the propeller example makes me most skeptacle.

I want to say it's all BS, but have to have faith in some test numbers - which have not been provided.

I could not make sense of them if they were given to me raw form from the wind tunnel. I'll have to leave that to better minds.

 

Lets not get side tracked With a single, gigantic bubble that may be as big as NYC. Please. Tiny bubbles only. They are not related to a rough hull bottom at all.