Exhaust Blown Floor - Forward Exhaust Exit

[hardingfv32]

So then the RB rake setup is not about increasing the low pressure created by the diffuser?

Brian

[wesley123]

It is if I'm correct. The exhaust flow seals the floor from the rear wheels, this in turn allows for an effectively way larger diffuser.

[Sonic59]

So then the RB rake setup is not about increasing the low pressure created by the diffuser?

Brian

If u raise rear of the car - u increase car body angle of attack, which leads to higher downforce. If u raise both rear and front of the car - lose downforce, no change on drag:

[godlameroso]

Hi, the diffuser can be 1000mm wide by 100mm high,

I'm pretty sure maximum diffuser height is 125mm above the reference plane.

[hardingfv32]

1) But why is the diffuser effectively larger? The roof geometry is essentially the same but just high off the ground. How goes the diffuser create more low pressure by raising both the opening and exit?

2) On page 65 of this thread, in a video, James Allison clearly states that the exhaust is used to form a vortex. The low pressure generated by the vortex in then used to generate downforce. No mention of sealing the diffuser.

Brian

[wesley123]

1) But why is the diffuser effectively larger? The roof geometry is essentially the same but just high off the ground. How goes the diffuser create more low pressure by raising both the opening and exit?

Because the diffuser trailing edge is higher of the ground? Over the whole floor this would generate more downforce due to better low pressure, as well as the kink becoming more effective, this generates lower pressure, increasing downforce.

2) On page 65 of this thread, in a video, James Allison clearly states that the exhaust is used to form a vortex. The low pressure generated by the vortex in then used to generate downforce. No mention of sealing the diffuser.

Brian

And how does this low pressure vortex generates its dfownfore then? Right, by blowing it under the flow, it actually seals the floor. If that isnt the case, why actually placing the exhaust in this area? It is quite obvious by the metal in this area that the exhaust blows here and barely into the diffuser(Only this footplate is made of metal, the diffuser has not or barely any)

[Sonic59]

1) But why is the diffuser effectively larger? The roof geometry is essentially the same but just high off the ground. How goes the diffuser create more low pressure by raising both the opening and exit?

Diffuser is a part of a car body. Downforce is generated by the whole body:

Diffuser simply sucks air from the front. The larger diffuser - the more air it sucks.

2) On page 65 of this thread, in a video, James Allison clearly states that the exhaust is used to form a vortex. The low pressure generated by the vortex in then used to generate downforce. No mention of sealing the diffuser.

No. The vortex is working like a skirt. It prevents air from outside of the car to move under its body. If air moves under body it spoils low pressure zone:

[wesley123]

possibly reducing underbody sensitivity too due to it being less vulnerable to crosswinds?

[hardingfv32]

1) "Because the diffuser trailing edge is higher of the ground? Over the whole floor this would generate more downforce due to better low pressure, as well as the kink becoming more effective, this generates lower pressure, increasing downforce."

Why is this the case? The leading edge (or kink) is also higher. Does raising the whole diffuser increase downforce (ASSUMING a fixed air speed and equal quality of side sealing)? What scientific law or principle applies?

2) "No. The vortex is working like a skirt. It prevents air from outside of the car to move under its body. If air moves under body it spoils low pressure zone:"

James Allison is the Techincal Director of Lotus Renault. Are we to believe you or anyone on this forum have a better understanding of this subject than him?

Brian

[raymondu999]

To my understanding the kink is not considered the leading edge. The leading edge is the "tongue"like thing sticking out in the front; the bib. The changes in the height of this would be insignificant compared to the rear exit area. Raising the rake of the diffuser increases downforce; it can't just move vertical.

I'm pretty sure James Allison's FEE concept is different to Newey's rear exhaust concept. Newey blows the exhausts slightly off to the side of the diffuser and just creates basically two walls of air which then become fluidic skirts.

[hardingfv32]

1) The start of the diffuser, kink, does raise along with the exit of the diffuser but at a slope or angle related to the rake. Is the raising of the kink good or bad for the efforts of the diffuser to create low pressure? Is this a compromise where a net gain in height between the kink and exit represents an improvement?

2) James Allison clearly states the both FEE & EBD use the same principle of a vortex adding low pressure to the floor system.

Brian

[wesley123]

1) "Because the diffuser trailing edge is higher of the ground? Over the whole floor this would generate more downforce due to better low pressure, as well as the kink becoming more effective, this generates lower pressure, increasing downforce."

Why is this the case? The leading edge (or kink) is also higher. Does raising the whole diffuser increase downforce (ASSUMING a fixed air speed and equal quality of side sealing)? What scientific law or principle applies?

No scientific law or whatever applies here, it just is the case, the Red Bull car is built around this with the exhaust sealing the floor

2) "No. The vortex is working like a skirt. It prevents air from outside of the car to move under its body. If air moves under body it spoils low pressure zone:"

James Allison is the Techincal Director of Lotus Renault. Are we to believe you or anyone on this forum have a better understanding of this subject than him?

Brian

Of course Allison will reveal everything about the system. What has he actually said about the exhaust usage? Right that it generates a vortex which creates downforce. Where it does is not said, but with the footplate of the diffuser being covered i metal I find it quite clear this vortex goes under the floor, sealing the floor from the rear wheels.

[MIKEY_!]

If the exit is larger (provided sealing is good) then there will be more DF (so long as there is no flow separation of some kind) because even though the diffuser itself is not any larger the sealing effect creates an invisible wall on each side, extending towards the ground. The start of the diffuser will be higher but that won't matter much because the gap at the front of the floor is still roughly the same size. Think of the diffuser having real carbon skirts like the old days. It's the same effect.

[raymondu999]

1) The start of the diffuser, kink, does raise along with the exit of the diffuser but at a slope or angle related to the rake. Is the raising of the kink good or bad for the efforts of the diffuser to create low pressure? Is this a compromise where a net gain in height between the kink and exit represents an improvement?

I'm quite sure the kink is not the start. the "start" is all the way at the front of the floor.

[MIKEY_!]

Ok, figure 1 is a normal floor + diffuser with rake. Lots of blue leakage around the edges as it doesn't seal.

Figure 2 is the FEE. Sealing (red) along most of the floor but not in the crucial diffuser area as the rear tires get in the way.

Figure 3 is the EBD. The forward floor is not sealed but not as much potential there to create DF, while the diffuser is sealed giving a much larger diffuser exit than the other two.