Question for aerodynamics experts
Discussion
intrepid44 said:
Because the golf ball is trying to create lift, and the car is not. .
OK, then turn it upside down and you have downforce. I guess there is no part of a car which is like a spinning airborne sphere, but surely there must be some area of the car's body that would benefit?
If only Adrian Newey was a PH poster
Edited by garycat on Wednesday 26th December 14:15
Only creates lift when the golf ball is spun.
Wikipedia said:
When a golf ball is hit, the impact which lasts less than a millisecond, determines the ball’s velocity, launch angle and spin rate, all of which influence its trajectory (and its behavior when it hits the ground).
A ball moving through air experiences two major aerodynamic forces, lift and drag. Dimpled balls fly farther than non-dimpled balls due to the combination of two effects:
Firstly, the dimples delay separation of the boundary layer from the ball. Early separation, as seen on a smooth sphere, causes significant wake turbulence, the principal cause of drag. The separation delay caused by the dimples therefore reduces this wake turbulence, and hence the drag.
Secondly, backspin generates lift by deforming the airflow around the ball, in a similar manner to an airplane wing. This is called the Magnus effect. Backspin is imparted in almost every shot due to the golf club's loft (i.e. angle between the clubface and a vertical plane). A backspinning ball experiences an upward lift force which makes it fly higher and longer than a ball without spin.[1] Sidespin occurs when the clubface is not aligned perpendicularly to the direction of swing, leading to a lift force that makes the ball curve to one side or the other. Unfortunately the dimples magnify this effect as well as the more desirable upward lift derived from pure backspin. (Some dimple designs are claimed to reduce sidespin effects.)
In order to keep the aerodynamics optimal, the ball needs to be clean. Golfers can wash their balls manually, but there are also mechanical ball washers available.
http://en.wikipedia.org/wiki/Golf_ball A ball moving through air experiences two major aerodynamic forces, lift and drag. Dimpled balls fly farther than non-dimpled balls due to the combination of two effects:
Firstly, the dimples delay separation of the boundary layer from the ball. Early separation, as seen on a smooth sphere, causes significant wake turbulence, the principal cause of drag. The separation delay caused by the dimples therefore reduces this wake turbulence, and hence the drag.
Secondly, backspin generates lift by deforming the airflow around the ball, in a similar manner to an airplane wing. This is called the Magnus effect. Backspin is imparted in almost every shot due to the golf club's loft (i.e. angle between the clubface and a vertical plane). A backspinning ball experiences an upward lift force which makes it fly higher and longer than a ball without spin.[1] Sidespin occurs when the clubface is not aligned perpendicularly to the direction of swing, leading to a lift force that makes the ball curve to one side or the other. Unfortunately the dimples magnify this effect as well as the more desirable upward lift derived from pure backspin. (Some dimple designs are claimed to reduce sidespin effects.)
In order to keep the aerodynamics optimal, the ball needs to be clean. Golfers can wash their balls manually, but there are also mechanical ball washers available.
A dimpled golf ball doesnt create lift. Unless it is spun (
Cheers Wiki) The dimples have the effect of moving the separation point of the air from the ball further back. I can't remember exactly why. This means the area of low pressure (and turbulence) behind the ball is smaller therefore drag is reduced.
[Speculation]As for cars being covered in dimples I guess for most shapes it would only serve to create turbulence and therefore drag. For any ball/cylindrical like shapes it would presumably be easier and more aero efficient to redesign the shape rather than make it dimply.[/Speculation]
Cheers Wiki) The dimples have the effect of moving the separation point of the air from the ball further back. I can't remember exactly why. This means the area of low pressure (and turbulence) behind the ball is smaller therefore drag is reduced. [Speculation]As for cars being covered in dimples I guess for most shapes it would only serve to create turbulence and therefore drag. For any ball/cylindrical like shapes it would presumably be easier and more aero efficient to redesign the shape rather than make it dimply.[/Speculation]
Edited by RodentRacing on Wednesday 26th December 14:31
From what I've read in Autosport (Gary Anderson's great) the main problem with F1 aero is keeping the fast moving air attached to your car, so you can direct it to the wings and produce downforce. The sprouty bits and mini wings around the cars are more like flow conditioners, to ensure that the fast moving air doesn't detach before it gets to the rear wing. I think that having the bodywork dimpled would increase the possibility of this detached air, thereby reducing the effect of the wings and decreasing downforce.
The dimples do reduce drag, but in the case of an F1 car, downforce production is more 'important' than drag reduction as the engines are comparatively powerful whereas grip is limited.
This is, of course, only my opinion and could be completely wrong.
The dimples do reduce drag, but in the case of an F1 car, downforce production is more 'important' than drag reduction as the engines are comparatively powerful whereas grip is limited.
This is, of course, only my opinion and could be completely wrong.
Edited by Hobbit123 on Thursday 27th December 15:07
Speedo used something similar in their swimsuits IIRC. It was based on shark skin though in that case. The surface was finely textured i.e. not smooth.
Water creating more drag than air, meant that the dimples on the surface caused the passing water to seperate from the surface, passing straight past and dip, creating essentially a series of vacuums.
In the golf ball sense, rotation would mean this effect runs 360 degrees around the object, decreasing drag, meaning it could travel further. In terms of lift, it will reach a greater height due to the reduction of drag, but that shouldn't be confused with it working like a plane wing, where airflow can vary between top and bottom.
If you were to apply the dimple theory to a car, in some senses it would be ideal, however, most drag you'll get at high speed, tends to be used to good effect, by channeling it to a place where it can be used as useful drag i.e. downforce, rather than drag which acts against forward travel. Alternatively, the surface itself would be shaped so that any drag caused, has a positive effect.
Any surface which isn't critical to airflow going in a certain path, or requiring an amount of drag, would benefit from a dimpled surface. Something like the outlet of a diffuser, where you're essentially channeling air at an accelerated rate, from a closed space into an open space, may benefit from this.
My 2p worth
Water creating more drag than air, meant that the dimples on the surface caused the passing water to seperate from the surface, passing straight past and dip, creating essentially a series of vacuums.
In the golf ball sense, rotation would mean this effect runs 360 degrees around the object, decreasing drag, meaning it could travel further. In terms of lift, it will reach a greater height due to the reduction of drag, but that shouldn't be confused with it working like a plane wing, where airflow can vary between top and bottom.
If you were to apply the dimple theory to a car, in some senses it would be ideal, however, most drag you'll get at high speed, tends to be used to good effect, by channeling it to a place where it can be used as useful drag i.e. downforce, rather than drag which acts against forward travel. Alternatively, the surface itself would be shaped so that any drag caused, has a positive effect.
Any surface which isn't critical to airflow going in a certain path, or requiring an amount of drag, would benefit from a dimpled surface. Something like the outlet of a diffuser, where you're essentially channeling air at an accelerated rate, from a closed space into an open space, may benefit from this.
My 2p worth
A non-smooth surface can reduce drag. In particular whilst smooth laminar flow is the lowest drag type of flow, it is unstable and easily breaks down into the non-laminar flow which has a lot of drag.
Turbulent laminar flow is more stable and only slightly more drag than smooth laminar flow
Various things have been used to induce turbulent laminar flow in various environments over the years, caraway seeds on racing dinghy masts being on of the favourites I remember.
The size of the "roughness" that best induces turbulent laminar flow varies with speed, viscoity of the medium etc. I suspect that the natural roughness of the materials in a F1 car is sufficient already at the speeds it attains(although I am guessing on that one)
Turbulent laminar flow is more stable and only slightly more drag than smooth laminar flow
Various things have been used to induce turbulent laminar flow in various environments over the years, caraway seeds on racing dinghy masts being on of the favourites I remember.
The size of the "roughness" that best induces turbulent laminar flow varies with speed, viscoity of the medium etc. I suspect that the natural roughness of the materials in a F1 car is sufficient already at the speeds it attains(although I am guessing on that one)
Anyone remember those shark skin swimsuits olympic swimmers wear(wore)? Lots of tiny scales that acted in a way that increased speed through the water...I was expecting to see it used in motor racing somewhere, but now I know why not.
Aero design must be at the point where every glimmer of an idea has to be tried.
How soon before we hear Max banning Ferrari's Nano-wings?
Aero design must be at the point where every glimmer of an idea has to be tried.
How soon before we hear Max banning Ferrari's Nano-wings?
Hobbit123 said:
The dimples do reduce drag, but in the case of an F1 car, downforce production is more 'important' than drag reduction as the engines are comparatively powerful whereas grip is limited.
Yeah I'd say that is the most crucial point. A spherical object naturally creates a big hole in the air behind it as it moves through it, making drag a big problem. As I understand it, the dimples on a golf ball help stop the air 'grip' the ball and so stop it creating such a big hole in it's wake, reducing drag. 'Separating' the air from an F1 car's surface would be bad however, as you want these to create downforce via the wings.
The ideal situation would be to have dimples that appear at speed in a straight line or dimples right at the back of the car, after the air has been used. But part right at the back of the car is the rear wing and the diffuser, the main creators of downforce. You want the air to grip and wrap around the car so that as much of it as possible flows over these two parts.
So that is why F1 cars won't use golf ball dimples, unless either 1) somesort of intelligent active aero devices are used which allows dimples to form in the surface at will - only when travelling in a straight line. Of course using such tech would reduce the drafting effect on straights so it would reduce overtaking, and it would not get my vote for that reason alone. 2) a whole new means of generating the lift/dowforce effect is used (say, anti-gravity), then you can expect to see dimples on aeroplane surfaces too.
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