Blown Diffuser: How does it work actually and why it's there

[Just_a_fan]

1) "the lower component (of the exhaust flow) is used to seal the outer edges of the diffuser."

How is this done, air screen or vortex formation?

2) Why are the winglets on the hubs not movable aero devices and thus restricted?

Brian

Q1 vortex I would think - the edge of the floor plate is shaped which suggests they're trying to encourage a vortex

Q2 the cascades are, bizzarely, considered to be part of the brake duct. Yes, really. Another one of those "it's a hole but not a hole" type interpretations apparently.

[JohnsonsEvilTwin]

How is the starter-motor hole being blown of any benefit?

[Just_a_fan]

Presumably it helps to keep the flow in that region attached. Whether it improves downforce or drag, I don't know.

It must be a useful gain based on the steps the FIA went to to limit the size of the hole last year (or was it the year before?)

[JohnsonsEvilTwin]

As I understand it all the top teams bar Mercedes are doing this.

Would this go some way to explain why Mercedes have rear tyre wear issues?
Their side exit exhaust blows over the top of the diffuser with none of the energised flow being directed towards this hole.

[horse]

As I understand it all the top teams bar Mercedes are doing this.

I think part of that might come from the fact that the Meredes diffuser appears very convex in the central section. This may be to aid the work of the diffuser Gurney as the flow will not require as significant a direction change (speculative) than for a diffuser with a concave section.

Regarding the hole (or apparent lack), it may be that blowing on the convex surface would be too outward (or normal) from the surface and therefore do more harm than good (cause separation). Another possibility is that there still is a blowing hole, but that it's further towards the diffuser throat now that it's not required to start the engine.

[hardingfv32]

If we ASSUME that the exhaust is being routed into the inside of the diffuser, how does the effect the pressure drop in the diffuser area ONLY?

I appreciate that the exhaust flow/energy will increase the velocity of the flow in the diffuser and thus the flow under the floor. But countering this effect is the fact that the pressure differential between the diffuser inlet and exit is reduced, or is the an incorrect assumption?

Brian

[PlatinumZealot]

How is the starter-motor hole being blown of any benefit?

I think it helps the flow both on top and inside the diffuser. It prevents too much air from backing up under the gearbox and at the same time it acts a nozzle to help entrain air from under the diffuser.

But I don't think it is a night and day thing though.

@ Dave, yeah I think 3D expansion is the aim of those outward curling diffuser walls. I was interested in cone diffusers on turbines before I got interested in ones one cars. So in my head a diffuser is already something that can expand in all directions.


The slotted flaps atop the diffuser, I think this is a Torro Rosso Idea originally. I think it serves as a sloted gurney flap. Good Downforce to drag ratio. + The upward sweep of air exiting it gives a virtual extension to the diffuser IMO.

[godlameroso]

http://www.sciencedaily.com/videos/2008 ... strike.htm

According to this compressing or confining the energy of the airstream increases the vorticity of the system. I wonder if this applies to aerodynamics, and if so, how can this concept be exploited by F1 teams?

[PlatinumZealot]

Ok my 2 cents..

I think present day blown diffusers have two generations (types).

1. 2010 blown diffusers.. these work by adding energy to the diffuser as described by Dave above. It seems teams prefered to blow the diffusers from the top and sides. I think they might have some gasses curling under from the sides.

2. 2011 RedBull blown "vortex" difffusers.. work by creating a large vortex using a strake that is placed before the throat of the diffuser. The strake is placed infront of the exhaust and it causes the exhaust gases to curl under and into the diffuser while creating a huge side sealing vortex. This vortex is extrememly faster than a regular free stream air vortex because it is at the speed of the exhaust. Way over 100m/s faster than the free stream air. So a super vortex is created.RedBull has mastered this.
I call these second generation of diffusers exhaust vortex diffusers.

This is the principle of operation.. inspired by strakes on a fighter jet. Notice you need an angle of attack for the vortices to get stronger.. couple this with a high speed exhaust and you have a total sealing off of the diffuser.. this means you can raise the diffuser higher of the ground and increase you expansion ration WHILE still having energy added from the exhaust to prevent turbulence.



Implementation on the Ferrari F-150..

SCORE!!!

[youtube]http://www.youtube.com/watch?v=PDWFaRVQ ... r_embedded[/youtube]

Ok.. Joy time over..

[Pierce89]

Ok my 2 cents..

I think present day blown diffusers have two generations (types).

1. 2010 blown diffusers.. these work by adding energy to the diffuser as described by Dave above. It seems teams prefered to blow the diffusers from the top and sides. I think they might have some gasses curling under from the sides.

2. 2011 RedBull blown "vortex" difffusers.. work by creating a large vortex using a strake that is placed before the throat of the diffuser. The strake is placed infront of the exhaust and it causes the exhaust gases to curl under and into the diffuser while creating a huge side sealing vortex. This vortex is extrememly faster than a regular free stream air vortex because it is at the speed of the exhaust. Way over 100m/s faster than the free stream air. So a super vortex is created.RedBull has mastered this.
I call these second generation of diffusers exhaust vortex diffusers.

This is the principle of operation.. inspired by strakes on a fighter jet. Notice you need an angle of attack for the vortices to get stronger.. couple this with a high speed exhaust and you have a total sealing off of the diffuser.. this means you can raise the diffuser higher of the ground and increase you expansion ration WHILE still having energy added from the exhaust to prevent turbulence.



Implementation on the Ferrari F-150..

SCORE!!!

[youtube]http://www.youtube.com/watch?v=PDWFaRVQ ... r_embedded[/youtube]

Ok.. Joy time over..

There is the part where he said the vortex created a low pressure zone under the floor and diffuser which means downforce, not quite used to seal the diffuser but you were still quite close. you could still be right about sealing the sides of the diffuser to raise it and increase volume, but i think it truly is mostly using the low pressure from the core of the vortex to reduce overall pressure under the floor.

[speedsense]

Vortex generated in free flow air has little or no compressibility and is not as tightly wound

Vortex generated from exhaust is essentially a gas that the vortex generator is acting on and has high compressibility, forms a more tightly wound vortex with the "tornado" effect able to compress the gasses within the vortex...

IMHO is the energy he's talking about...and resembles more closely how a skirt would act on the sides of the floor or the diffuser creating better sealing effect.

The "real" question is would a skirt to the ground be better than blowing the diffuser with the exhaust? I say it would....

They are replicating the effect with high energy gas...

[shelly]

Agree with nn smikle, as I wrote here

viewtopic.php?f=12&t=9178&start=2190

[rjsa]

http://www.dyson.com/fans/# Check the video there. Similar principle how the diffuser accelerates (pulls) the flow from under the floor upstream/

[Pierce89]

Vortex generated in free flow air has little or no compressibility and is not as tightly wound

Vortex generated from exhaust is essentially a gas that the vortex generator is acting on and has high compressibility, forms a more tightly wound vortex with the "tornado" effect able to compress the gasses within the vortex...

IMHO is the energy he's talking about...and resembles more closely how a skirt would act on the sides of the floor or the diffuser creating better sealing effect.

The "real" question is would a skirt to the ground be better than blowing the diffuser with the exhaust? I say it would....

They are replicating the effect with high energy gas...

You could be right, but in the videa James Allison says the RB style diffusers use the extreme low pressure in the vortex core to reduce pressure under the floor. These are two different principles obviously. I just know you can get EXTREMELY low pressures in a vortex core, and I believe this is a greater pressure reduction than you could get by using the vortex to "seal" the edges of the diffuser. i just don't like the "sealing the edges of the diffuser" theory because the extra turbulence might cancel out the slightly increased vloume.

[hardingfv32]

How do you gain access to the core of the vortex without incurring the effects (high pressure?) of the flow that surrounds it?

Brian