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Originally Posted by ChazInMT
Apparently you've rather fixated on the layer of air within a few inches of the car, while not totally insignificant, it is really pretty insignificant compared to the huge volume of air that is being affected by our vehicles as we plow through it.
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I'm not fixated on anything. I have created threads on ducted radiators, off road friendly aero modding, contributed to conversations about down force generation vs drag reduction, etc. etc.
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Keep in mind that ideally, our cars are moving through through calm air....the air is not blowing on our cars. When not ideal we are moving along in 6 lanes of traffic with a 25 MPH crosswind....program that into your CFD calculator.
The ultimate goal of aerodynamic drag reduction is to move through the air and displace the least amount of energy into moving the air out of your way, and falling back to calm again after you've passed, as quickly as possible. The less energy expended on making air move about, the more energy you save.
When you consider the amount of energy it takes for a fan to run and blow a little breeze around your room, then relate this to a car that is dragging a fat column of air behind it for a few hundred yards and moving air out to 15 feet in front of and around the car, you realize we a driving in huge fan blades that are stirring up the air. The most efficient shapes allow the air to move back into place in the easiest way possible while not creating any trailing vortices.
The layer of air next to the car has a small impact on the big picture, but the overall shape of the car is really what matters. You can't wrap a pig in a mink and call it a mink. For the ultimate drag reduction, build a VW XL-1.
You want to reduce the drag of a pig? Good luck with trying to mess with less than 1% of the air that is being displaced by the car and hoping the other 99% will bend to your will.
In so many words Aerohead is trying to tell you computers still really suck at trying to figure out aerodynamics because a car is constantly affecting 140,000 cubic feet of air weighing 12,000 lbs as it drives down the road and it's really hard to say how this air will behave. Not to mention it's all numbers in and numbers out on the computer, the numbers in thing is very subjective and a few missed assumptions on the input can create large variations from reality on the output. GIGO. I don't even pretend to know a lot about it, I again just listen to experts that say these things.
By saying you're going to dimple a car, you are asking the 6 lbs of air at the surface of the car to change the behavior of 12,000 lbs of air. (That's not really 1% is it?)
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If a reduction in friction drag occurs on a pig, no matter how insignificant, does it not decrease the energy needed to push through said massive amount of air? If said friction reduction leads to a boundary layer that stays attached to the pig longer, there by reducing the pressure drag at the rear of the pig, would it not lead to an even larger reduction in the energy necessary to move through the air? Further more, if there was no validity in this, then why has "Lufthansa Technik AG participated in a multifunctional coating research project since mid-2011, along with its partners, Airbus Operations; the Fraunhofer Institute for Manufacturing Technology and Advanced Materials in Bremen, Germany; and coating manufacturer Mankiewicz in Hamburg."??? On a plane, which is already streamlined, and an object we try to use for inspiration, this texture should decrease fuel consumption by 1% (no results, study on going)... Not much huh? That's 94 million dollars a year in fuel savings across their fleet! I think I would trust people trying to save 94 million dollars, before I would trust auto manufacturers who don't stand to gain anything from said research. Now before we jump on me for comparing aerodynamics and surface friction with dissimilar shapes and vehicles used under vastly different circumstances... I'm simply providing information regarding the decrease in energy that would occur via nothing other than manipulating your "less than 1%" of the air, and I understand that implementation and results would obviously be different.
I get that computers suck, but this just seems kind of silly. So far this has been the gist of the this thread:
Response: Do you see it on planes cause that's proof it doesn't work.
ME: Actually here is an example of planes and trains and boats.
Response: Oh, well in that case they aren't like cars and so it doesn't count. Show me data to support this on cars
ME: I show research focused on cars.
Response: The data isn't good enough because computers suck, and there's no way manipulating 1% can impact anything.
ME: Well manipulating 1% is worth millions in research for some companies, and they are hoping to see a decrease in drag/decrease in consumption.
Response: ____________________________
His statement: "They do not work on cars, regardless of the scale of the dimples, unless your car is a 1.68-inch-diameter sphere spinning through the air with no ground plane." There is no reference to any testing, no reference to any modeling, no reference to any outcome of either. I find the opinion of an "expert" who provides no explanation for his very broad and absolute claim, to be somewhat irrelevant to this conversation. Especially when other companies are spending millions of dollars on objects other than golf balls. Industry experience is not to be ignored, education is to be respected, but an opinion is just an opinion.
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Anyway, fun stuff all of it! Keep learning!
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Couldn't agree more!