Importance of the diffuser?

[kilcoo316]

Downforce or lift only comes as a result of a differential in pressure.

You cannot consider the local diffuser without considering the pressure conditions on the upper surface as well.


As for the pressure conditions under the diffuser, local boundary layer effects cause the low pressure zones downstream of the ramp point. The effective area change doesn't kick in until the boundary layer is following the shape of the diffuser, and not in a small separation bubble at the ramp itself.

In an inviscid case, they wouldn't occur, flow would start to decelerate instantly as a function of the conservation of mass relationship.

(Assuming density is fixed, velocity will reduce linearly with increased area)


At the trailing edge of the diffuser, Kutta condition is enforced - there will be no downforce created at the trailing edge. The flow pressures will be equal top & bottom at the diffuser trailing edge.

There may be a shear layer between top and bottom flows, infact, it is probably advantageous to have one to try and entrain (drag/pull by momentum exchanges) more air out from under the floor.


The rake angle roger44 refers to is simply to increase the difference between the effective front area of the floor, and the effective rear area of the floor = more massflow rate under the car = more downforce.

[Gecko]

I think the above is generally correct, there are a few issues I have with some of the reasoning, however.

In an inviscid case, they wouldn't occur, flow would start to decelerate instantly as a function of the conservation of mass relationship.

(Assuming density is fixed, velocity will reduce linearly with increased area)

That is not entirely correct. Around any kink, the inviscid flow will be accelerated before and also after the kink. The drop in pressure after the beginning of the ramp is therefore (usually) not down to separation bubbles but due to simple inviscid flow around a kink. The flow is just not uniform in the vertical direction, even in the inviscid case

At the trailing edge of the diffuser, Kutta condition is enforced - there will be no downforce created at the trailing edge. The flow pressures will be equal top & bottom at the diffuser trailing edge.

With usual F1 diffuser designs, that is also not entirely true. Most diffusers have a sort of a Gurney flap element on them, which actually create a pressure difference between the top and bottom surfaces all the way to the trailing edge.

[xpensive]

Obviously only first China practice, but I am bold enough to say that McLaren's change in form from Malaysia clearly demonstrates the subject of this very thread?

As I said this morning on another thread, how difficult could it be to Oatley, bell, Byrne/Costa and Newey?

By the end of the year, hundreds om millions of EUR will have been spent by the BigDogs, cornering speeds off the clock and Brawn without money just making up the numbers at the back again.

This is something MrM should have considered before he inluded the diffuser in his political scheme.

[timbo]

Obviously only first China practice, but I am bold enough to say that McLaren's change in form from Malaysia clearly demonstrates the subject of this very thread?

Well, I think they have to test it, so they treat first practice differently to others.
Let's wait until Q2.

[kilcoo316]

That is not entirely correct. Around any kink, the inviscid flow will be accelerated before and also after the kink.

And the physical mechanism for that would be...?

(its an expanding duct here)

With usual F1 diffuser designs, that is also not entirely true.

Correct, and the Kutta condition is the exact reason why the gurney flap exists.

[donskar]

Obviously only first China practice, but I am bold enough to say that McLaren's change in form from Malaysia clearly demonstrates the subject of this very thread?

As I said this morning on another thread, how difficult could it be to Oatley, bell, Byrne/Costa and Newey?

By the end of the year, hundreds om millions of EUR will have been spent by the BigDogs, cornering speeds off the clock and Brawn without money just making up the numbers at the back again.

This is something MrM should have considered before he inluded the diffuser in his political scheme.

Interesting perspective. My 2 pence: it's quite conceivable that catching Brawn could take more than simply kludging up a Brawn DDD copy. It is possible that (as many others have already said) implementing DDD could require changes to the transmission casing, nose, and even rear suspension.

I worry about the longer term consequences: will this be the last straw for Renault? Will Toyota cut Williams off now that they (Toyota) are competitive themselves? Will the average fan care as much about "no-name" teams?

I don't worry about Brawn staying competitive. (Williams is another matter.) Brawn will have the money, and the human resources to stay at least competitive. Sponsors are beginning to sign up.

Your comment about the financial cost of playing catch-up is right on. Between KERS and DDD, reducing costs in F1 is a total joke. But not funny.

[xpensive]

I believe the xpensive process of catching-up is really my point donskar.

The grandees are royally pissed-off by now, still have money to burn with the best brains in the business, and will stop at nothing to further explore and expand this novel interpretation of the rules.

As Domenicali already hinted, Ferrari will build a new car to the new rules, while any engineer will know that the second attempt at something is typically more successful than the first, in particular if you can start where the competition is now.

I think season of 1979 is a good example of what can happen, in 78 Lotus had a monopoly on venturi-underbodies and walked away with everything, but in 79 they were nowhere, even with Andretti and Reutemann driving.

Brawn best do their winning while given the chance. As for Toyota, if they can't win this year they're gone.

[ISLAMATRON]

Your comment about the financial cost of playing catch-up is right on. Between KERS and DDD, reducing costs in F1 is a total joke. But not funny.

The engine freeze(and longer life requirements) has already paid for KERS more than 3 times over... it was just silly teams that paid 50 Million to squeeze about 35hp out of the engines when they were supposed to be frozen(FIA fault for not closing that loophole) instead of putting that money towards KERS.

KERS is a great idea but has been implemented very poorly... and everybody, the teams & the FIA, are at fault.

I'm glad to hear that Mosley has already shot down standard KERS, and is hinting at increasing its power output and such. New technology is where the money should go, not into getting 20 more RPM out of an late 1990's era engine.

It would have been cheaper to ban the DDD's for a majority of the teams but was it the fair and just thing to do according to the letter of the rules?... silly me looking for fairness & justice from an FIA ruling!?!?!!?

[xpensive]

Any engineer with a little experience of power- and energy-relations, would realize in a heartbeat that the recoverable energy through KERS is miniscule compared to what is wasted by aerodynamic and thermal losses. Only political nonsense.

Back to thread,
What was intended to save money, a limited diffuser, backfired completely due to shady rules and shadier interpretations.

[ISLAMATRON]

Any engineer with a little experience of power- and energy-relations, would realize in a heartbeat that the recoverable energy through KERS is miniscule compared to what is wasted by aerodynamic and thermal losses. Only political nonsense.

Back to thread,
What was intended to save money, a limited diffuser, backfired completely due to shady rules and shadier interpretations.

Only when KERS is limited as it is... what if it were allowed on all 4 wheels? but yes huge amounts of energy are wasted in aero losses... we ll know your quest for a closed wheel formula in F1.... similarly I look towards more energy efficient drive/powertranes in all vehicles.

[Bob Brown]

more powerful KERS = larger batteries = more weight.

I doubt that will appease too many people because then fuel tanks will have to be smaller and balance would be all loopy

[Jersey Tom]

Brawn with no money? I'd say Virgin is a pretty good sponsor to have...

[xpensive]

Nice try Islam, but you're not going to lure me into that discussion again, not on this pet-thread of my own anyway. [-X

Instead, get the load of this, even if Alonso was running 20 kg light, the bolt-on solution of this morning made wonders to that dog of a car, imagine what things will be like come Barcelona? Ferrari, Mclaren and BMW in that bracket as well?

[czt]

more powerful KERS = larger batteries = more weight.

I doubt that will appease too many people because then fuel tanks will have to be smaller and balance would be all loopy

More powerful KERS could play into the hands of flywheel based systems like the Williams or Flybrid systems - I think the current regs are pretty pointless as they don't allow enough energy recovery. If there was more to play for and more options in how you could recover/deploy energy I think we could see some quite interesting solutions being used.

[xpensive]

What's the name of this thread anyway?