Quote:
Originally Posted by ACEV
@aerohead,
Thank you, but you failed to prove that "boundary layers" have any bearing on the topic. Perhaps you'd like to explain for the benefit of all. 
@ChazInMT,
Now you're just being mean. You make all sorts of statements based upon assumption, but you fail to show proof for your position. It is too bad you cannot be courteous with your opinion. 
Here are a few of your assumptions:
1 You stated, "Apparently I wasn't direct enough for you, so I'll say it all here in plain English.". Evidently, you thought you were needing to be direct. Instead, you should have been plain and clear and non-confrontational.
2. "stymies the imagination" Really? Could it be that your imagination is weak?
3. "even a bunch of morons understand that, without attached flow, an aerodynamically low drag Cd cannot be achieved.". Wow! You just alienated all astronautical engineers everywhere.
4. Your fourth paragraph is a straw-man argument. It is meaningless, in this context, that many have doubts. It is also weird that you would point out that no one else has tried to test it. How ironic. The fact is that if something has been tested and shown, then others must prove it wrong, not the other way around. Since you state that no one else has tested it, then what is your point? You take a very unscientific position.
5. I appreciate your statement of "that's all I need to hear". That may indeed be good enough for you. It isn't for me. I want to see practical proof of someone's position, not theoretical assumptions. Theories are not, and never will be, facts.
6. You need to let Eakers and aerohead speak for themselves. I don't believe they need you to be their apologist.
Need I go on?
It is amazing how people make the worst assumptions about others. Can't you just assume the best? After all, that is what common courtesy is all about. Why do you think you need to "slam" someone?
For everyone's benefit let me state that the cornerstone of scientific research has always been, and will always be, observation. One of the correct assumptions about that fact is that it should be easy to make clear to even a grade-school-educated person what one is trying to get across. When a person who claims to know scientific fact cannot do that, they are a failure and are ignorant of the facts; as Albert Einstein said.
It was never my intention to offend anyone, but rather try to nudge people into being able to prove what they say with observable and easily duplicated facts. That some feel they are being attacked only shows their inability to prove their points to the benefits of all those reading these posts.
This is a place to share one's knowledge and questions and experiences. Those who do not want to take part in a polite manner should not be involved. Please go troll somewhere else. 
Thank you. |
1. a smooth golf ball is subjected to a laminar boundary layer and suffers flow separation ahead of it's maximum cross-section,ending up with a large wake of low base pressure, high profile drag,and low range on the fairway.
2. dimples incorporated into the golf balls surface provide an artificial roughness which forces the laminar boundary layer to transition immediately over to a turbulent boundary layer which can remain attached to 115-degrees aft of the balls forward stagnation point.The added flow attachment allows for some static pressure regain before the flow does separate into a smaller wake of higher base pressure,allowing reduced profile drag and greater range on a fairway drive.(if the ball didn't spin,a small patch of sand glued to the front of the ball would provide the same necessary roughness as the dimples do).
3. in this context,the dimples are soley responsible for altering the boundary layer.That's all they do.
4. from the research of Osborne Reynolds it was discovered that at some 'critical' velocity,for a given object,the boundary layer will naturally transition from a laminar,to a turbulent type.
5. since Reynolds number is a function of a bodies length,as compared to it's velocity in a specific fluid,when calculated for automobiles it is found that all production motor vehicles will achieve critical Reynolds number near 20 mph,and from there on,their drag coefficient will be constant up to transonic flow velocities,where compression effects begin to enter the picture.
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6. the un-modified Ford Taurus in the MythBusters episode would have a fully turbulent boundary.
7. dimples,as a turblulent boundary layer-forcing technology would be superflous.Once the candle is lit you can put away the matches!
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8.if MythBusters measured a drag reduction it cannot be attributed to the effect dimples render to golf balls.
9. the axisymmetric jet pumping action of free flight which aids the golf ball is not present in ground-effect.
9.a reasonable explanation would be that the dimples acted as turbulators (as Mitsubishi's vortex-generators on their Lancer notch-back) which fed vortical kinetic energy into an aft-body flow field,allowing sustained attachment where the flow would have otherwise been lost.The drag of the dimples was overshadowed enough by the overall profile drag reduction to show a net benefit (as the VGs do with the Lancer).