Diffuser functions

[marekk]

The real shocker is just how much the airflow to the beam wing and diffuser Gurney was top of the list in the design requirements of the RB5. It's like they had a 2 year head start on the rest of the field.

It's not very obvious, how important this gurney on top of diff is.
It creates small local area of low pressure behind, "sucking" boundary layer air at top inner wall of diffuser, preventing flow separation. Small changes in gurney's efficiency cause big changes in diffuser efficiency.

At the same time, to get some clean, powerfull, non turbulent flow to where diffuser gurneys are placed, is probably one of the hardest aerodynamical things to achive. For the central part of diffuser, responsible for most of the downforce, where the risk of diff stall (flow separation) is biggest, even more so.

IMO that's the source of Newey's obsession with rear packaging.

Once sure the diffuser will work 100%, one can try to squize from it a little extra power with the help of low pressure area generated by beam wing.

[PlatinumZealot]

Yes. But all of your devices (AC diff, turbine diff, rocket engine nozzle, even saxophone horn) work from high pressure at inlet to lower pressure at outlet.

We are discussing opposite scenario in this thread.

Your inlet and outlet is ambiguous. But if you talking about the diffuser you are wrong. The pressure just before the diffuser cone of those devices are lower than atmospheric. Why do you keep trying to break the laws of Physics?

OK.. back to the RedBull now

[PlatinumZealot]

+1

Quite simply, diffusors allow devices upstream to do the work. All a diffusor does it return gas to ambient pressure without shock....ideally.

Praise the lord! Hallelujah!!

[PlatinumZealot]

Thanks marekk, that makes sense. So running a diffuser indeed requires power, but significantly less than a wing-system of same DF. I forgot that what goes in - must go out too

No. Diffusers make it easier for the fluid to expand to atmospheric pressure, that if you had an abrupt end.

[hollowBallistix]

The real shocker is just how much the airflow to the beam wing and diffuser Gurney was top of the list in the design requirements of the RB5. It's like they had a 2 year head start on the rest of the field.

It's not very obvious, how important this gurney on top of diff is.
It creates small local area of low pressure behind, "sucking" boundary layer air at top inner wall of diffuser, preventing flow separation. Small changes in gurney's efficiency cause big changes in diffuser efficiency.

At the same time, to get some clean, powerfull, non turbulent flow to where diffuser gurneys are placed, is probably one of the hardest aerodynamical things to achive. For the central part of diffuser, responsible for most of the downforce, where the risk of diff stall (flow separation) is biggest, even more so.

IMO that's the source of Newey's obsession with rear packaging.

Once sure the diffuser will work 100%, one can try to squize from it a little extra power with the help of low pressure area generated by beam wing.

Wasn't the rear wing design on this Jaguar done to improve the flow out of the rear diffuser also ? same principle or the beam wing on F1 cars ?

[marekk]

Yes. But all of your devices (AC diff, turbine diff, rocket engine nozzle, even saxophone horn) work from high pressure at inlet to lower pressure at outlet.

We are discussing opposite scenario in this thread.

Your inlet and outlet is ambiguous. But if you talking about the diffuser you are wrong. The pressure just before the diffuser cone of those devices are lower than atmospheric. Why do you keep trying to break the laws of Physics?

OK.. back to the RedBull now

I see you have really hard time at understanding this simply device for years now.
Can you please explain, where this lower pressure just before the diffuser cone comes from ?

[marekk]

Wasn't the rear wing design on this Jaguar done to improve the flow out of the rear diffuser also ? same principle or the beam wing on F1 cars ?

Definitely. Hughe. With this one you need some real tyres to support the load.

[BreezyRacer]

Wasn't the rear wing design on this Jaguar done to improve the flow out of the rear diffuser also ? same principle or the beam wing on F1 cars ?

Definitely. Hughe. With this one you need some real tyres to support the load.

The key behind making this work is the placement of the wing in relation to the diffuser exit. F1 cars cannot place the wings behind the diffuser.

[bravefrog]

Yes. But all of your devices (AC diff, turbine diff, rocket engine nozzle, even saxophone horn) work from high pressure at inlet to lower pressure at outlet.

We are discussing opposite scenario in this thread.

Your inlet and outlet is ambiguous. But if you talking about the diffuser you are wrong. The pressure just before the diffuser cone of those devices are lower than atmospheric. Why do you keep trying to break the laws of Physics?

OK.. back to the RedBull now

I see you have really hard time at understanding this simply device for years now.
Can you please explain, where this lower pressure just before the diffuser cone comes from ?

Sure. Bernoulli's principle states that "for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy." http://en.wikipedia.org/wiki/Bernoulli's_principle

The air under an F1 car (or inside the saxophone) is travelling faster than the air outside it, therefore it is at a lower than atmospheric pressure. This lower pressure creates downforce -- under the whole floor -- not just under the rear axle.

As the low pressure air under the car (or inside the saxophone) flows through the diffuser it slow downs and returns to atmospheric pressure.

Seeing is believing; discover your inner Newey* by designing your own diffuser with this interactive demo: http://home.earthlink.net/~mmc1919/venturi.html

Robert

* obligatory Red Bull reference

[shelly]

[quote="bravefrog]The air under an F1 car (or inside the saxophone) is travelling faster than the air outside it, therefore it is at a lower than atmospheric pressure. This lower pressure creates downforce -- under the whole floor -- not just under the rear axle.
[/quote]

Pressure on the diffuser kink line is significantly lower than under the floor.
I a flat floor+diffuser you have two big suction peaks ate leading edge and kink line; pressure on the flat floor is lower than atmospheric, but much higher than those you have under thes two peak zones.

[noname]

Maybe you should start from defining what pressure you are talking about: static, dynamic, total... ? So far I am missing this in the discussion.

Anyway, just my thought.

[marekk]

The air under an F1 car (or inside the saxophone) is travelling faster than the air outside it, therefore it is at a lower than atmospheric pressure. This lower pressure creates downforce -- under the whole floor -- not just under the rear axle.

And what's the name of this magic force which do accelerate air from lower to higher pressure, creating downforce peak near diffuser kink ?

I know dark matter is supposed to have negative pressure, but it is also supposed to not interact with our "normal" matter by any means except gravity, so this will be not correct answer.

[shelly]

Maybe you should start from defining what pressure you are talking about: static, dynamic, total... ? So far I am missing this in the discussion.

Anyway, just my thought.

Usually when you just say "pressure" it is static pressure

[noname]

Usually when you just say "pressure" it is static pressure

Sure. I am just not sure if this knowledge is available to all involved in the discussion.

[Just_a_fan]

The air under an F1 car (or inside the saxophone) is travelling faster than the air outside it, therefore it is at a lower than atmospheric pressure. This lower pressure creates downforce -- under the whole floor -- not just under the rear axle.

And what's the name of this magic force which do accelerate air from lower to higher pressure, creating downforce peak near diffuser kink ?

Base suction.

But the diffuser doesn't really create base suction. The car does. The rear tyres, the sidepods and the rear wings do.

The car moving forwards also creates localised higher pressures on the the leading edges of the sidepods.

You have localised higher pressure in front and localised lower pressure at the rear. This makes air accelerate under the car. The diffuser helps to slow the air back down to ambient in order to reduce drag and aid downforce production. It doesn't suck the air through itself.

Bear in mind that the air is just minding its business until the car comes along. Then the localised pressure difference across the car (front to rear) makes the air move.