21 replies to this topic

[mistareno]

I know it's been tried before on the Brabham BT46 (where it failed miserably), but I'm wondering if the flat floors of todays f1 may make it viable?

If you used something dimpled like this -

<IMG>http://www.heseco.co...ed-assembly.jpg</IMG>

- covering the underfloor area and the flat area infront of the rear wheels, would you be able to reduce the sidepod size and therefore the associated drag?

Is surface cooling so ineffective that its a pointless excercise?

I would've thought the high airspeed under the car would be ideal?

Edited by mistareno, 17 February 2014 - 23:10.

[Bloggsworth]

No, it wouldn't work without the under-body being the size of a football pitch. To cool effectively you need turbulence as the air needs to hang around long enough for heat transfer to take place and turbulence generates drag - It's a balancing act which it looks as if Red Bull got wrong, even in power station cooling towers the water is trickled down ribbed surfaces for maximum cooling.

[mistareno]

Yeah, the pic of the panel in the link has dimples embossed into it. I assume to promote localised turbulence.

[saudoso]

It's been tried by Gordon Murray in 1975, dind't work, not enough cooling.

Not sure if it could work today. I'd guess not.

[tomspar]

i think it is easier to route the media being cooled thru a compact radiator, which works well because finned area and turbulent air. getting the media out to less efficient body panels not easy. surface cooling may be practical for electronic power devices, though. even bolting them to the ballast would help.

[KingTiger]

It would ruin the underbody downforce, which is the most important area of the whole car. 

[mistareno]

It would ruin the underbody downforce, which is the most important area of the whole car. 

 

The underbody downforce would remain largely unchanged, possibly better.

 

The floor on the whole would still be flat but dimpled and with a diffuser at the rear.

 

The dimples create a turbulent boundary layer which would make them far more efficient than the ones tried on the BT46.

 

 

FWIW, I'm not saying that the car would have no radiators at all, just that the radiators could be reduced in size (along with their drag) if you could multi-task the large plan area of the floor as a flat panel radiator.

 

 

 

By heating the air as it passes under the car, it may also energise the air, effectively adding thrust and further increasing downforce.

 

I just wonder if it's worth revisiting the idea in this era of flat floor cars.

[PayasYouRace]

The underbody downforce would remain largely unchanged, possibly better.

 

The floor on the whole would still be flat but dimpled and with a diffuser at the rear.

 

The dimples create a turbulent boundary layer which would make them far more efficient than the ones tried on the BT46.

 

FWIW, I'm not saying that the car would have no radiators at all, just that the radiators could be reduced in size (along with their drag) if you could multi-task the large plan area of the floor as a flat panel radiator.

 

By heating the air as it passes under the car, it may also energise the air, effectively adding thrust and further increasing downforce.

 

I just wonder if it's worth revisiting the idea in this era of flat floor cars.

 

 

 

Dimpling only reduces drag on bodies like balls because it trips the boundary layer into turbulence (which means it sticks to the surface better and reduces the wake). It wouldn't really have much effect on a flat floor leading to a diffuser. Anyway, the dimpling would break the flat floor regulation by definition. (Seems obvious, no?)

 

You'd not be able to energise the air under the floor via turbulence to any useful extent. It's not like pumping exhaust in there, which is putting a lot of energy in there and can overcome the disadvantage of the turbulence created. Diffusers work better with laminar flow.

[AlexS]

Yeah that is mixing a ball rotational plus almost linear movement to a linear one. Also the air under the car is at high speed compressed with nowhere to go while the reason the ball with dimples works is because it decreases the air pressure around it.

[mistareno]

Anyway, the dimpling would break the flat floor regulation by definition. (Seems obvious, no?)

 

You'd not be able to energise the air under the floor via turbulence to any useful extent. It's not like pumping exhaust in there, which is putting a lot of energy in there and can overcome the disadvantage of the turbulence created. Diffusers work better with laminar flow.

 

IIRC the regulations allow 3mm of variation. If you made the dimples 3mm deep, it would still pass.

 

The P51 Mustang gained enough energy from heat added to that air passing through cooling system that the thrust produced negated the drag from the cooling system and actually resulted in positive thrust in some circumstances.

 

Yeah that is mixing a ball rotational plus almost linear movement to a linear one. Also the air under the car is at high speed compressed with nowhere to go while the reason the ball with dimples works is because it decreases the air pressure around it.

 

There have been wind tunnel tests conducted on stationary golf balls with the same effect. If a ball is hit without top spin or back spin, it won't rotate.

Edited by mistareno, 18 February 2014 - 10:24.

[PayasYouRace]

IIRC the regulations allow 3mm of variation. If you made the dimples 3mm deep, it would still pass.

 

The P51 Mustang gained enough energy from heat added to that air passing through cooling system that it negated the drag from the cooling system in the first place and actually added gross thrust.

 

 

Fair enough it might pass the regulation, but then the fact that the teams aren't doing it now should be a clue. Simply, tripping the boundary layer into turbulent at the diffuser is not going to be benficial in that situation. It's beneficial when you have to get their air to move round a blunt rear surface, like on a ball.

 

I can actually think of one place where dimpling, might work, and that's on McLaren's rear suspension blockers.

 

The Mustang had it's radiator in a sort of basic ramjet configuration, adding a lot of energy to the air to produce a net thrust. However the important aspect is that was useful thrust for an aircraft which relies on aerodynamic thrust to move forward. If you start adding too much energy to the air passing under the car, you might add a slight amount of thrust, but it would be neglibigle compared to the mechanical traction from the tyres, and would produce a fair amount of lift under the car.

 

Up until this year the teams were using the exhaust to energise the air as it left the diffuser. If you start doing that under the entire car you're not gaining any advantage.

[mmmcurry]

Wouldn't all the dimples get clogged up with dirt from all the other cars adding weight and reducing any advantage?

[ExFlagMan]

It could possibly have a beneficial side effect in that it might deter the drivers from using the kerbs/run off areas as part of the race track in case it damaged the cooling.

[PayasYouRace]

Wouldn't all the dimples get clogged up with dirt from all the other cars adding weight and reducing any advantage?

 

I would think no more than a golf ball's dimples get clogged, and they operate in a much dirtier environment.

[AlexS]

Not at all, golf balls don't make 300km without being cleaned and trough so much dirt:dust,oil, rubber in air like an F1 car.

Edited by AlexS, 18 February 2014 - 13:04.

[PayasYouRace]

Having the dimples clogged with stuff would probably have a similar aerodynamic effect on a diffuser as the dimples themselves though. I doubt you'd collect that much dirt that the weight would be an issue. Still, you want your floor to be smooth.

[Jimisgod]

 

This is a plot of the drag coefficient versus Reynolds number for smooth and dimpled spheres. The Reynolds number is a non-dimensional parameter defined as UL/nu, where U is the velocity of interest (e.g. velocity of car or golf ball), L is a characteristic length scale (e.g. chord length of a wing or diameter of your golf ball) and nu is the kinematic viscosity of the fluid (around 1.5e-7 m2 /s for air).

 

Golf balls happen to have Reynolds numbers right around where that drop in drag is, and so they benefit from dimples. F1 cars probably have a Reynolds number orders of magnitude higher than balls, so dimples may not help.

[PayasYouRace]

Superb post Jimisgod!

 

Yes that is a factor. Essentially because the dimples are starting a turbulent boundary layer. The dominant factor of the Re in comparing these cases is the characteristic length (both are in air and at similar speeds, in terms of order of magnitute). On the golf ball, the Re is too low for full turbulence to develop from the boundary later. A car floor is much larger so the Re is much larger so full turbulent flow develops.

 

Finally, if you played golf with darts (a good aerodynamic shape) you wouldn't need dimples on them either. I would not recommend trying this at your local gold course.

Edited by PayasYouRace, 18 February 2014 - 13:29.

[tomspar]

Think the bottom of the car is mostly a wooden slab supplied/specified? by the FIA. Buzzkiller for lots of great underfloor ideas.

[PayasYouRace]

Think the bottom of the car is mostly a wooden slab supplied/specified? by the FIA. Buzzkiller for lots of great underfloor ideas.

 

There's the plank which is specified quite strictly, but it only takes up a narrow region on the centreline of the car. Then there's a specified height for a central "hull" and a slightly higher outer specified height.

Edited by PayasYouRace, 18 February 2014 - 16:54.

[Tenmantaylor]

I look at it this way, if somehow putting cooling plates/heatsinks or some other form of flat wide radiator on the underside of the body was legal and provided an aerodynamic advantage someone would have done it by now and tried to get rid of draggy sidepods.

[mistareno]

http://en.m.wikipedi...Supermarine_S.5

It appears that surface radiators can be made to work in high power applications.

The Supermarine S.5 was a single seater racing sea plane that had a 800+ hp engine that was cooled by surface radiators integrated into the top surface of the wings.

It actually held the air speed record back in the late 1930's.

That said, I did find reference to the plane being flown by the temperature gauge....

Edited by mistareno, 19 February 2014 - 05:48.