A question for any Aerodynamicists

[sknguy]

I had posed this question to someone on line a while back but they didn't deem to think it would be efficient enough. But... I was wondering if putting dimples, like the dimples on a golf ball, into the carbon fibre body of an F1 car would generate enough benefits to be useful?

Here's a quote from an australian radio show transcripts about new swimsuit technology.

Tim Lees: "Fastskin is a fabric that’s unique to Speedo.. ...Basically, in layman’s language, what it’s doing is creating a very, very small separation between the surface of the fabric and the water that’s flowing over it, and thereby reducing drag."

Buick is using dimples on the undercarriage of one of their cars to reduce cabin/road noise. Grant it the dimples would be blemishes for regular car owners if used on the bodies of production vehicles.

[Monstrobolaxa]

I other previous topics we have already talked about this aspect...here is the link...

http://www.f1technical.net/forum/viewtopic.php?t=881

I think we looked at all the aspects of this topic....if you have any other questions....just post them....

[Monstrobolaxa]

Here are some more posts where we talk about it:

http://www.f1technical.net/forum/viewtopic.php?t=541&highlight=dimples

http://www.f1technical.net/forum/viewtopic.php?t=671&highlight=dimples

http://www.f1technical.net/forum/viewtopic.php?t=414&highlight=dimples

[Tomba]

seems like we do a lot of talking about swimming suits :p

[Guest]

Thanks... checking the posts!

[sknguy]

Wow... those are some great discussions. I've been looking for an answer to that curiosity for a long time know. But I'll wager there are a lot of nooks, crannies and airbox interiors where microturbulence could be applied.

Thanks again guys.

[Guest]

you see, the difference is a golfball is completely round, with the dimples there is a smaller vortex behind it. a f1 car is a totally different shape and the dimples would only slow it down because of added resistance, and due to particularly the diffuser it would be of no help

[Monstrobolaxa]

And besides that it would upset the airflow to the major downforce "creators".

[CFDruss]

dimples could work very effectively in F1, but at the moment there is no need. Dimples are used in aerospace at the moment with significant effects

[kluxorious]

Actually the dimple wouldn't do much good for an F1 car. It would mess up the airstream.

[CFDruss]

not at all, its depends where they are placed.

[Guest]

prove it

[Asphodel]

For a smooth sphere from Re=1e3 to 3e5, the drag is relativlty constant. however, at Re>3e5 there is a sudden change in drag from from Cd=0.4 to about Cd=0.15. This is because the BL changes from a laminar BL to a turbulent BL which delays separation and reduces pressure drag. The dimples on a golf ball trip the BL at lower Re and this lower drag can be experienced at lower Re.
I am not sure what Re of a Formula 1 car is. It will depend on what length scale is used for different areas. However, if the BL is already turbulent, then dimples are not going to improve anything considerably. I imagine the cars are not driving through nice laminar air so I doubt a laminar BL will form. If this is the case, it is better to have a surface that is smooth to try and reduce viscous forces on the car.

[CFDruss]

There is no point in me proving it cause there are far more educated people out there that have already proved it.

There is much much discussion on this subject. let start with the golf ball, the dimples are infact added no to increase lift (although they do offer an improvement) they are infact added to reduce drag. This is achived my "triping" the laminar boundary layer in to a turbulent state, thus energizing the BL. If you plot the flow of fluid over a ball, you will find the boundary layer seperates just before the centre, cause a large wake behind the ball and hefty drag penalties. The dimples, by tripping the Laminar BL into a turbulent form helps to keep the BL attached for a longer period and reducing the drag during flight. The fact that the ball is also spinning obviously improves their use far more.

Now with an F1 vehicle. the boundary layer will always attach to a surface as a laminar form and the point of transition will occur dependant on the flow conditions. This postion can be roughly calculated using the reynold formula of Re = pVL / u and using a Re critical value of around 10^6. Now, if seperation of the flow is occuring early and cause a part stalled wing, then a method of energizing the boundary layer can be used, such as vortex generator. Because dimples trip the boundary layer into a turbulent state, the boundary layer has more energy and a later seperation will result. This does increase skin friction drag but this is neglagible compared to the benifits from reducing the wake.

A number of different reasons that they are not used on vehicle may arise through engineers, but maybe one is that there are simply more effcient methods of engergizing the BL, such as williams serated gurney flap that promotes downstream vorticies. Dimples may help reduce drag on a car if very carefully placed, but golf balls are only dimpled like they are to keep the pattern fairly uniform regardless of orientation. On an aerodynamic body that has a fixed orientation to the airstream, a well-placed trip strip or vortex generator would likely yield even more benefit.

[Scuderia-Russ]

prove it

Tut,it's his job idiot.