Feeding the Diffuser

[SiLo]

I was just thinking the other day that along with the Exhaust gases, do teams feed the diffuser air that has passed through the radiators? Would it be possible to have openings and tubes flowing into the second deck of the diffusers? A bit like the exhausts but from further forward.

[BreezyRacer]

No, you need charged airflow, not slow turbulent airflow likes comes on the backside of the radiators. Having said that, Sauber have introduced ducts that seem to "share" underbody airflow with the upper sides of the diffuser box, similar to what RB does with exhausts. How well does it work? Not sure but Sauber have been in the mid field mix lately. Check out the Sauber car thread for pics, etc.

[mep]

The diffusors task is to suck air from the floor.
If you fill the diff. with air from somewhere else it stops working.
Never forget that.

The exhaust gases are a different story because they have high kinetic energy and can accelerate the flow.

[SiLo]

Surely that could be created by having the latter part of the tube opening up to create a venturi? Therefore sucking the air through the hole. Wouldn't that be very beneficial if is was sucking air from infront of the rear wheels, creating a loss of pressure and a loss of drag.

[747heavy]

Surely that could be created by having the latter part of the tube opening up to create a venturi? Therefore sucking the air through the hole. Wouldn't that be very beneficial if is was sucking air from infront of the rear wheels, creating a loss of pressure and a loss of drag.

Please keep in mind how the underbody/floor of the car creates downforce - in a nutshell it´s the same principle then a wing.

You need a pressure difference above (higher) and below (lower) the floor, then you have a higher pressure left on top of the floor/car. Now you multiply the pressure with the area of the floor and you have the downforce the floor/underbody generates.
p=F/A --> F=p*A

F= (down)Force
p= Pressure
A= Area
So the downforce you can create is direct poportional to the pressue difference and the floor area - more = better.
The diffusor is "only" used to evacuate air from under the floor/car, as more air it can evacuate as lower the pressure will be under the floor -> higher pressure difference = more downforce. So bleeding air from above the floor is not a good idea in general, as it will reduced said pressure difference.

Now having said all that, we need to keep another aspect in mind.
There is a limit as how steep you can make your diffusor, it´s very similar to the angle of atack for a wing. At one point, the air will simply not being able to follow the contour of the diffusor, and slow down, seperate and killing of the low pressure. The diffusor will stall, in the same way a wing will stall at too high angles of attack.
To avoid this flow separation you need to re-energize the flow (speed it up) at one point.
This is where the exhaust comes into play, or you can bleed air with a higher speed from
above. It´s similar to what they do on the rear wings (blown rear wing/F-duct).
If you bleed air, you lose a bit of downforce in theory, but if your diffusor works better now, it will compensate for the loss by higher overall downforce. It´s a trade off.

Remember the discussion about the rake of the cars.
If some/one team is not able to keep the flow attached in their diffusor, they can´t run higher rake, as it will make their diffusor stall --> losing downforce.
Diffusor stall is critical under braking, if your diffusor is allready on the limit, the additional pitch/rake in braking can make it stall --> loosing (rear)downforce when you need it the most.
I´m sure some teams, can´t get the optimum out of flexi wings (wing in gound effect WiG), because their diffusor is not working at high pitch angles(rake).
But that´s just my opinion, I could be wrong

[SiLo]

Ok I see now. Changing it slightly, what about more channels underneath the car? To channel MORE of the air through the diffuser, obviously the channel would have to be inset, but instead of having one, maybe two or three feeding it? Or would that then create venturis inbetween the channels where they meet because the air would be going at different speeds?

[mep]

I´m sure some teams, can´t get the optimum out of flexi wings (wing in gound effect WiG), because their diffusor is not working at high pitch angles(rake).
But that´s just my opinion, I could be wrong

Sounds very plausible to me.
With the possibility to build double and triple diffusors teams try to get the diff. as big as possible and on the same time reduce the amount of downforce form the rear wing. Like McLaren with their blown rear wing.
Seems like especially they stretched things to far and suffer on the front now.

[747heavy]

Ok I see now. Changing it slightly, what about more channels underneath the car? To channel MORE of the air through the diffuser, obviously the channel would have to be inset, but instead of having one, maybe two or three feeding it? Or would that then create venturis inbetween the channels where they meet because the air would be going at different speeds?

The biggest problem with your idea is, that the rules require the floor to be flat, and a step in the floor, to prevent exactly what you would like to do.
If the rules would permit it, the the underside of a F1 car could look like this:


here you see the tunnels you where talking about (I think, if I don´t understood you wrong)

maybe also of interest: (sorry is not new,and not the best quality)

http://fast1.onesite.com/my.speedtv.com/user/brawnista/08f84705e24102c33da1a6e7af4e475b.jpg?v=124313

and some basics explaint here:
http://www.racecar-engineering.com/arti ... ained.html

[wesley123]

look at the renault, wich got such underbody tunnels to grab air. If it was disallowed renault woudnt have it. The Renault also uses it as side protection.

[747heavy]

look at the renault, wich got such underbody tunnels to grab air. If it was disallowed renault woudnt have it. The Renault also uses it as side protection.

Hi Wesley,
Do you have a pic or link to this?
I would be interested to have a look.
Thanks

[Shrek]

I was wondering what happens if you don't have a diffuser? Other than drag would increase

[747heavy]

I was wondering what happens if you don't have a diffuser? Other than drag would increase

all things being equal (which is difficult), you would lose the downforce which is produced by the floor/underbody of the car. Because you won´t be able to generate the low pressure under the car.
I don´t think that the drag would increase significantly, as drag is more a function of the wings/upper body shape.
But it´s not so straight forward, to make a clear cut.
Nevertheless, I think it´s safe to say, that you would lose a fair amount of downforce from the cars.
If you try to recover this amount of downforce with more/larger wings, then your drag will increase.
Your aero efficiency (L/D ratio) will be worse.
The floor together with the diffusor is very efficient in the way it produces downforce.
It does not produce a lot of drag for the amount of downforce it generates.

[SiLo]

Yeah I think if they want to increase overtaking they should decrease wing size but increase the size/flexibility of the diffuser. Flexibility as in, with the rules, I don't think F1 could cope with flexing diffusers....

[747heavy]

Yeah I think if they want to increase overtaking they should decrease wing size but increase the size/flexibility of the diffuser. Flexibility as in, with the rules, I don't think F1 could cope with flexing diffusers....

Yes, if you would go back to a car which generates it´s downforce mainly by tunnels/underbody, and put some decent tyres (size) on the car, you could have this kind of close racing again.



The problem is, that with todays technology and knowledge about aerodynamics and groundeffect, you would end up with cars cornering at +6g´s in no time.
So it´s a bit dangerous to "let the dog´s lose" in this area.
To prevent an escalation of this, the FIA would maybe need to define a common/mandatory floor/diffusor package for everybody.
It´s doable, the question is, does they (FIA) want this to happen.

P.S.: I know, that the cars in the video are before the heydays of groundeffect, just chose the video, because it shows good and close racing IMHO.
In the heydays of groundeffect, you can see some cars running without a front wing, producing their downforce mainly from the underbody.
Part of the current dilema is, that todays car´s rely on there front wings so much, to make the overall aero package work.
And the front wing needs "clean" air to work best, making racing in traffic difficult.

[mep]

Do you really think only changing wing downforce to diffuser downforce will solve the problem?


I think they must find the right balance between different parameters.

Its hard to judge from the video you posted why they actually where able to run side by side that easily but take a look at this video.


I think the key here is that the following car gets a big advantage from running in slipstream. The leading car has almost no change to defend its position. During cornering their distance is similar to the one we have today. I would say even bigger. So the attempt to let the cars run closer to help overtaking will not pay of. The cars will just run close but this alone doesn’t help you to overtake.
How about DTM? They can run super close almost touching but is overtaking really easier?

They must focus more on the slipstream effect.
You need a got balance between relatively high drag and low engine power.
When a car runs on a straight it should get close to its top speed (limited by the high drag and the engine power) soon. When a car is running in slipstream drag should significantly drop so the weak engine can increase the cars speed. So the following car gets a massive speed overrun. Similar to the McLarens when they use their f-duct today.

Btw. Higher distance between cars will allow you to run longer in slipstream getting higher speed difference.

To get higher drag the cars should get their downforce from wings. The wing should be mounted higher. The cars and the tires should be wider.
Usingn diffusors would increase the efficiency between drag and downforce. Thats not what we need.

Another thing I noticed is that during the last corner the cars seems to rely on tire grip. Today downforce is the most important aspect there.
I think a downforce dominated car is easier to drive. When you go with such a car slightly faster trough a corner downforce will increase so it helps with grip. The limit of the car will be more transient.
A car relying on tires (weight, stickiness) will significant lose grip when you push to hard. A driver mistake will be punished harder and the limit is smaller.
So what you need is less downforce, more tire grip, and maybe heavier cars.

To sum up we need a balance between:

Drag (more) vs engine power (less)

Downforce (less) vs tire grip (more), and maybe weight (more)

Basically aerodynamic efficiency should get reduced.