Just saw a TV ad for the Lexus LS430 showing how they use dimpled panels underneath to reduce wind resistance and noise. How is that possible? I thought smoother surfaces were better.
-Jesda
Lexus Has Dimples!
Well, in theory, the dimple pattern could be designed to create a specific frequency when at road speeds and thus be a source of "white noise". The net effect would be less audible noise than if the surface was smooth.
Did you notice the rims on the car, don't they look like the 2000 AE Q45 5 spoke rims?
Did you notice the rims on the car, don't they look like the 2000 AE Q45 5 spoke rims?
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elwesso
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Well I can do that.....
There are different dimple patterns, like different bolt patterns... There are 392, 332, round dimples, egg shaped dimples... On some of the new callaway balls there are hexagonal dimples.....
Right now I play most of the time a titleist PROv1 or PROv1 X, the "X" has a 332 dimple pattern.. I can defintely tell the difference between the egg shaped dimples of the X vs the round ones of the regular Pro V.....
Dimple DEPTH as well as edgyness (for lack of a better term, how how much they angle from the higest point to the lowest)... The nike tour accuracy has a VERY high edgy dimple pattern (392 pattern IIRC) and they seem to fly faster and cut through the wind better, but they dont seem to go farther set aside..... They seem to be more stable in the air, but I think the increase of control creates more lift and thus drag, making it a wash at best.....
HOWEVER... The performance of the golf ball is mainly dependant on the material of the cover and the materials and construction of the core..... Thinner covers are the new magic now, coupled with a single solid core.....
So in essence, the dimples arent as important as the rest of the construction of the ball.....
There are different dimple patterns, like different bolt patterns... There are 392, 332, round dimples, egg shaped dimples... On some of the new callaway balls there are hexagonal dimples.....
Right now I play most of the time a titleist PROv1 or PROv1 X, the "X" has a 332 dimple pattern.. I can defintely tell the difference between the egg shaped dimples of the X vs the round ones of the regular Pro V.....
Dimple DEPTH as well as edgyness (for lack of a better term, how how much they angle from the higest point to the lowest)... The nike tour accuracy has a VERY high edgy dimple pattern (392 pattern IIRC) and they seem to fly faster and cut through the wind better, but they dont seem to go farther set aside..... They seem to be more stable in the air, but I think the increase of control creates more lift and thus drag, making it a wash at best.....
HOWEVER... The performance of the golf ball is mainly dependant on the material of the cover and the materials and construction of the core..... Thinner covers are the new magic now, coupled with a single solid core.....
So in essence, the dimples arent as important as the rest of the construction of the ball.....
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Jeff Williams
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Here is a long explanation about golf balls, also check out shark skin swimsuites, its the same principleThe Dimples
Why, then, does a golf ball have dimples? The answer to this question can be found by looking at the aerodynamic drag on a sphere. There are two types of drag experienced by a sphere. The first is the obvious drag due to friction. This only accounts for a small part of the drag experienced by a ball. The majority of the drag comes from the separation of the flow behind the ball and is known as pressure drag due to separation. For laminar flow past a sphere, the flow separates very early as shown in Figure 1. However, for a turbulent flow, separation is delayed as can be seen in Figure 2. Notice the difference in the size of the separation region behind the spheres. The separation region in the turbulent case is much smaller than in the laminar case. The larger separation region of the laminar case implies a larger pressure drag on the sphere. This is why the professor experienced a longer drive with the marked ball. The surface roughness caused the flow to transition from laminar to turbulent. The turbulent flow has more energy than the laminar flow and thus, the flow stays attached longer.
Figure 1: Laminar Flow Over a Sphere. Figure 2: Turbulent Flow Over a Sphere.
So, why dimples? Why not use another method to achieve the same affect? The critical Reynolds number, Recr, holds the answer to this question. As you recall, Recr is the Reynolds number at which the flow transitions from a laminar to a turbulent state. For a smooth sphere, Recr is much larger than the average Reynolds number experienced by a golf ball. For a sand roughened golf ball, the reduction in drag at Recr is greater than that of the dimpled golf ball. However, as the Reyn olds number continues to increase, the drag increases. The dimpled ball, on the other hand, has a lower Recr, and the drag is fairly constant for Reynolds numbers greater than Recr.
Therefore, the dimples cause Recr to decrease which implies that the flow becomes turbulent at a lower velocity than on a smooth sphere. This in turn causes the flow to remain attached longer on a dimpled golf ball which implies a reduction in drag. As the speed of the dimpled golf ball is increased, the drag doesn't change much. This is a good property in a sport like golf.
Although round dimples were accepted as the standard, a variety of other shapes were experimented with as well. Among these were squares, rectangles, and hexagons. The hexagons actually result in a lower drag than the round dimples. Perhaps in the future we will see golf balls with hexagonal dimples.
Figure 3: Golf Ball with Round Dimples. Figure 4: Turbulent Flow with Hexagonal Dimples.
How a Golf Ball Produces Lift Lift is another aerodynamic force which affects the flight of a golf ball. This idea might sound a little odd, but given the proper spin a golf ball can produce lift. Originally, golfers thought that all spin was detrimental. However, in 1877, British scientist P.G. Tait learned that a ball, driven with a spin about a horizontal axis with the top of the ball coming toward the golfer produces a lifting force. This type of spin is know as a backspin.
The backspin increases the speed on the upper surface of the ball while decreasing the speed on the lower surface. From the Bernoulli principle, when the velocity increases the pressure decreases. Therefore, the pressure on the upper surface is less than the pressure on the lower surface of the ball. This pressure differential results in a finite lift being applied to the ball.
Figure 5: Smoke Flow Patterns Over a Spinning Sphere.
The dimples also help in the generation of lift. By keeping the flow attached, the dimples help promote an asymmetry of the flow in the wake. This asymmetry can be seen in Figure 5. In this figure, the smoke shows the flow pattern about a spinning golf ball. The flow is moving from left to right and the ball is spinning in the counter-clockwise direction. The wake is being deflected downwards. This downward deflection of the wake implies that a lifting force is being applied to the golf ball.
Why, then, does a golf ball have dimples? The answer to this question can be found by looking at the aerodynamic drag on a sphere. There are two types of drag experienced by a sphere. The first is the obvious drag due to friction. This only accounts for a small part of the drag experienced by a ball. The majority of the drag comes from the separation of the flow behind the ball and is known as pressure drag due to separation. For laminar flow past a sphere, the flow separates very early as shown in Figure 1. However, for a turbulent flow, separation is delayed as can be seen in Figure 2. Notice the difference in the size of the separation region behind the spheres. The separation region in the turbulent case is much smaller than in the laminar case. The larger separation region of the laminar case implies a larger pressure drag on the sphere. This is why the professor experienced a longer drive with the marked ball. The surface roughness caused the flow to transition from laminar to turbulent. The turbulent flow has more energy than the laminar flow and thus, the flow stays attached longer.
Figure 1: Laminar Flow Over a Sphere. Figure 2: Turbulent Flow Over a Sphere.
So, why dimples? Why not use another method to achieve the same affect? The critical Reynolds number, Recr, holds the answer to this question. As you recall, Recr is the Reynolds number at which the flow transitions from a laminar to a turbulent state. For a smooth sphere, Recr is much larger than the average Reynolds number experienced by a golf ball. For a sand roughened golf ball, the reduction in drag at Recr is greater than that of the dimpled golf ball. However, as the Reyn olds number continues to increase, the drag increases. The dimpled ball, on the other hand, has a lower Recr, and the drag is fairly constant for Reynolds numbers greater than Recr.
Therefore, the dimples cause Recr to decrease which implies that the flow becomes turbulent at a lower velocity than on a smooth sphere. This in turn causes the flow to remain attached longer on a dimpled golf ball which implies a reduction in drag. As the speed of the dimpled golf ball is increased, the drag doesn't change much. This is a good property in a sport like golf.
Although round dimples were accepted as the standard, a variety of other shapes were experimented with as well. Among these were squares, rectangles, and hexagons. The hexagons actually result in a lower drag than the round dimples. Perhaps in the future we will see golf balls with hexagonal dimples.
Figure 3: Golf Ball with Round Dimples. Figure 4: Turbulent Flow with Hexagonal Dimples.
How a Golf Ball Produces Lift Lift is another aerodynamic force which affects the flight of a golf ball. This idea might sound a little odd, but given the proper spin a golf ball can produce lift. Originally, golfers thought that all spin was detrimental. However, in 1877, British scientist P.G. Tait learned that a ball, driven with a spin about a horizontal axis with the top of the ball coming toward the golfer produces a lifting force. This type of spin is know as a backspin.
The backspin increases the speed on the upper surface of the ball while decreasing the speed on the lower surface. From the Bernoulli principle, when the velocity increases the pressure decreases. Therefore, the pressure on the upper surface is less than the pressure on the lower surface of the ball. This pressure differential results in a finite lift being applied to the ball.
Figure 5: Smoke Flow Patterns Over a Spinning Sphere.
The dimples also help in the generation of lift. By keeping the flow attached, the dimples help promote an asymmetry of the flow in the wake. This asymmetry can be seen in Figure 5. In this figure, the smoke shows the flow pattern about a spinning golf ball. The flow is moving from left to right and the ball is spinning in the counter-clockwise direction. The wake is being deflected downwards. This downward deflection of the wake implies that a lifting force is being applied to the golf ball.
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Jeff Williams
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So, the Lexus will spin out easier? NO WAY, AM I GETTTING ONE, NOW!!!maxnix wrote:Yep, it's all about laminar flow, and in a golf balls case, spin - which increases the speed of the flow realtive to the velocity of the ball.
By the way, Golf Balls have dimples, the Lexus has bumps. I am sure, they react differently.
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one ton garage
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The dimples are usually only needed on a trailing edge.. such as the rear end on a car. Golf balls are dimpled all around because they're spherical, and they basically spin as they fly. Dimpled aero panels are not a gimmick though.. you will see some bonneville vehicles with them (most notably the Corbin bike is the best example I can think of), and what's great is, if you look under the new toyota prius, you will see the exact same dimpled panels as those on the new LS. They're just plastic, so they're super cheap and easy to make.. yet they do make a slight improvement in aerodynamics, and hey, every little bit helps...
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Jeff Williams
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