Blown Diffuser??

[forty-two]

i doubt it, and if it is the case then Newey should certainly shut its mouth about the F-Duct safety.
If you stall the rear diffuser the air under the floor will not accelerate anymore, thus heap up under the floor making the car unstable, guess what happens then if you hit someones rear wheel with your front wheel. You will simply take off due to the instability of the whole floor

I have to say Wesley, your premonition is more than a litte bit chilling!

Could you perhaps give me tonight's winning lottery numbers?

[manchild]

Blown diffuser pioneered by Newey? No.

Got this info from a friend of mine:

http://translate.google.com/translate?j ... l=it&tl=en

[speedsense]

Blown diffuser pioneered by Newey? No.

Got this info from a friend of mine:

http://translate.google.com/translate?j ... l=it&tl=en

Racing is so cyclic, isn't it? JCM got it from airplane technology and applied it to the Renault and it's turbo exhaust, then it gets rehasted by Newey at Mclaren and onward to Red Bull.
...though the only other team that has "current" experience with the technology outside of Newey, is Newey's former employer, Mclaren. Guess we'll get to see how much they remember at Silverstone....

[speedsense]

it possible that all the time we spend on the mclaren's rear wing
that red bull actually had a blown diffuser that stalls at high speeds?
the difference is that it uses exhaust gas which varies with rpm not air speed
that could explain why red bull didn't have a ride height system and yet it is able to be low enough to scrape the ground at quali and do fine in the race
i mean there must be a point where the air speed at the bottom is so high compared to the air at the back that it essentially starts to stall. and since diffuser has little drag it doesnt really increase top speed that much but increase the L/D ratio and since it only works at higher rpm it basically become like an aero traction control (quote by lewis they have twice as much downforce)

the L/D ratio which i think is boosted....applies to mclaren too. when you introduce high speed air to the bottom of the wing it will increase downforce and when the wing comes to a stage where it creates too much drag it starts to stall.

the ride height issue is what i thought supported this idea. since diffuser has the highest L/D ratio you will reduce more downforce per drag when stalled, so increasing ride height with very little top speed gained.
what are your thoughts??? possible?

Two things,
A) a diffuser does not function or have the same properties (or drag penalty) of down ward forces as a wing does. Though a semantic statement, the diffuser does not "produce" downforce, but rather "allows" "downforce" (wings) or "downward force producing" devices (spoilers,body panels) to have a greater effect by increasing those devices effectiveness by lowering under body pressures.

B) stalling this device (diffuser) causes greater drag by introduction and "restoring" of higher pressures underneath the car. The downforce on top has not changed but the acting force of these devices has. The overall negative (as in negative lift) L/D changes to a higher ratio due to a reduction or removal of the anti lift properties that the diffuser provides.

End result, less downforce creation resulting in higher ride height with no change in L/D (on top of the car) = greater frontal area and lower top speed...IMHO

[wesley123]

i doubt it, and if it is the case then Newey should certainly shut its mouth about the F-Duct safety.
If you stall the rear diffuser the air under the floor will not accelerate anymore, thus heap up under the floor making the car unstable, guess what happens then if you hit someones rear wheel with your front wheel. You will simply take off due to the instability of the whole floor

I have to say Wesley, your premonition is more than a litte bit chilling!

Could you perhaps give me tonight's winning lottery numbers?

I know 3 of them, i dont know if i am too late.

the numbers 8, 9 and 3 are correct at least.

But now back on topic, i said such an thing as an diffuser sucks air away under the floor, causing it to get sucked to the ground, all due to the large floor exit(the diffuser), if you staal this that area will essentially be gone, the flow would detach at a point there, wich reduces this vacuum effect, the air wich was essentially speed up will slow down causing more and more pressure under the floor, the air then has nowhere to go causing unstable aerodynamics. Dont know if it is correct but it is just how i think it goes

[BreezyRacer]

Wesley's statement of a stalled diffuser is correct. It's just a bad idea because diffuser downforce is NEARLY free. There is nothing to be gained and lots to be lost in this move. It's hard enough to stall the wings, which BTW, have massive amounts of drag associated with their downforce.

Guys the real reason that Red Bull placed these exhausts where they did was to isolate the diffuser from the rear tire turbulence. It's that simple. In fact, if in doubt, look at the diffuser box .. it's narrower than the regs allow. Why did they do that? Because volume alone doesn't make an effective diffuser. Isolation from turbulence in the floor area and the diffuser exit are critical. BTW, look at the new Ferrari diffuser .. it's even a bit narrower than the Red Bull, for the same reason.

And lastly, this approach cannot be compared to earlier blown diffusers where they used high speed exhaust gases to speed the airflow in the diffuser box. They are two totally separate approaches to using exhaust flow for aiding the diffuser.

[PlatinumZealot]

Very much so Breezyracer and speedsense. We can see this by observing the the Ferrari, Mercedez and ranault where the exhaust stream does not enter the diffuser as in the RedBull (which only a small portion of it does anyway).

[sknguy]

BreezyRacer's description is probably the correct one. There seems an awful lot of turbulence creating parts within which the diffuser is nestled. The more stable the air the more efficient the diffuser should be.

I really have to apologize for being off topic but I have to thank ringo for his response and his exercise. It hadn't occurred to me that the top surface shape of the car (downward force) would effect the location of the net force. Doh! I was completely ignoring that aspect. The shape of the side pods may have mainly a two-fold effect then. Thanks ringo, that is really cool.

here's a little exercise i did with a flat bottom evolution.

[speedsense]

Wesley's statement of a stalled diffuser is correct. It's just a bad idea because diffuser downforce is NEARLY free. There is nothing to be gained and lots to be lost in this move. It's hard enough to stall the wings, which BTW, have massive amounts of drag associated with their downforce.

Guys the real reason that Red Bull placed these exhausts where they did was to isolate the diffuser from the rear tire turbulence. It's that simple. In fact, if in doubt, look at the diffuser box .. it's narrower than the regs allow. Why did they do that? Because volume alone doesn't make an effective diffuser. Isolation from turbulence in the floor area and the diffuser exit are critical. BTW, look at the new Ferrari diffuser .. it's even a bit narrower than the Red Bull, for the same reason.

And lastly, this approach cannot be compared to earlier blown diffusers where they used high speed exhaust gases to speed the airflow in the diffuser box. They are two totally separate approaches to using exhaust flow for aiding the diffuser.

Consider a rotating wheel, in aero terms as a " rotary air pump". The wheel pumps air in both directions, outboard and inboard. The air is turbulent and literally a tornado.
A few millimeters away is the side gap of the diffuser and the ground and this pumped air tornado is "aimed" directly at this gap.
With the rules the sides of the diffuser cannot be "sealed" to the ground, so the tornado of air can freely enter the side of the diffuser, reducing it's effectiveness. The only way to reduce this is and to effect this tornado is with another "controlled" tornado or simply "vortex generation" with purpose built generators. Adding heat to this vortex accelerates it and intensifies it's energy causing less air to get "forced" into the bottom of the diffuser. IMHO

[Richard]

With the rules the sides of the diffuser cannot be "sealed" to the ground, so the tornado of air can freely enter the side of the diffuser, reducing it's effectiveness. The only way to reduce this is and to effect this tornado is with another "controlled" tornado or simply "vortex generation" with purpose built generators. Adding heat to this vortex accelerates it and intensifies it's energy causing less air to get "forced" into the bottom of the diffuser. IMHO

Thats what you can see on the RB pics. The exhausts discharges next to the diffusers creating a fast stream that aids the diffuser exit flow.


http://f1.gpupdate.net/en/photolarge.ph ... =1103-4460

I think the effect is two fold. Firstly, the exhaust flow could shield the DDD flow from turbulence. Secondly, the exhaust jet might create a low pressure zone that draws (pulls) the flow out of the diffuser.

I’d appreciate it is an aero person could explain how the temperature of the exhaust contributes to the enhanced flow compared to cold air. Is this because the hot air fro the exhaust is less dense than the cooler air from the DDD? This would create an even lower pressure zone which would result in suction from the DDD flow into the exhaust flow?

---

Thanks to breezyracer for posting the pic on the RB6 thread ...

viewtopic.php?p=167410#p167410

In this great pic you can clearly see some very large VGs on the sides of the diffuser, between the tire and the diffuser. Note that these VGs dump directly into the diffuser area instead of being kept outside the diffuser. They had to give away some diffuser isolation to do this , meaning the sides of the diffuser don't go all the way down to the maximum legal plane. But that's OK because the VG creates such a strong force that it isolates the diffuser flow better than extending the diffuser wall all the way down. This has to aid diffuser flow significantly!

[speedsense]

Thats what you can see on the RB pics. The exhausts discharges next to the diffusers creating a fast stream that aids the diffuser exit flow.


I think the effect is two fold. Firstly, the exhaust flow could shield the DDD flow from turbulence. Secondly, the exhaust jet might create a low pressure zone that draws (pulls) the flow out of the diffuser.

I’d appreciate it is an aero person could explain how the temperature of the exhaust contributes to the enhanced flow compared to cold air. Is this because the hot air fro the exhaust is less dense than the cooler air from the DDD? This would create an even lower pressure zone which would result in suction from the DDD flow into the exhaust flow?

---

Engine design for a Harrier Jet...IE..use of cold and exhaust (hot) driven streams

"The hot air stream will be directed out of the rear nozzles at a higher velocity caused by the HP/combustion system than the cold air stream from the front nozzles. Via Reynold’s Transport Equation for the Law of Conservation of Momentum, one can show the force due to the moving air stream equals the product of the area of the air stream, the density of the air, and the velocity of the air squared.

F(thrust) ~ Area(air stream) * Density(air) * Average Velocityair2

Therefore, the rear thrust will be greater than the front thrust because it has a much greater velocity. The area of the air stream remains the same at the front and rear nozzles. To eliminate imbalance along the horizontal plane of the aircraft, the rear thrust must be closer to the center of gravity of the aircraft and the front thrust farther from the center. This would balance the opposing moments

F(front thrust) * Xf = F(rear thrust) * Xr "

http://web.mit.edu/2.972/www/reports/ha ... ngine.html

In this case, as you can see the hot air (exhaust generated and heated) has higher velocity for the same Area. With a "heated" vortex generator it would follow that it enhances it strength (through velocity) over cooler air.

[autogyro]

Here is a guess that gets away from the direct blowing of exhaust gas over the diffuser.
On full throttle, the mass 'exhaust gas' flow increases from the engine due to burning fuel. This flow alters the direction of airflow into the rear 'coke bottle' area. The main airflow is directed outside of the diffuser and upwards.
The result is slightly reduced diffuser DF and reduced drag.
Under braking the 'exhaust gas' flow reduces in volume with less fuel burnt and the airlow redirects inboard over the diffuser and lower wing section increasing DF into corners.
On high speed 'throttle on corners' the flow is of much higher mass airflow and the result is a neutral DF effect.

[speedsense]

Here is a guess that gets away from the direct blowing of exhaust gas over the diffuser.
On full throttle, the mass 'exhaust gas' flow increases from the engine due to burning fuel. This flow alters the direction of airflow into the rear 'coke bottle' area. The main airflow is directed outside of the diffuser and upwards.
The result is slightly reduced diffuser DF and reduced drag.
Under braking the 'exhaust gas' flow reduces in volume with less fuel burnt and the airlow redirects inboard over the diffuser and lower wing section increasing DF into corners.
On high speed 'throttle on corners' the flow is of much higher mass airflow and the result is a neutral DF effect.

My apology but I don't get how the first statement matches the last. It would have to, for the car to stick in turn 8 at Turkey.

And the seoond statement doesn't make physical sense. As it's heat, not burnt fuel that the effect is being generated from. The vortex generation from the sides of the diffuser, at full throttle, creates a sealing effect, enhancing flow over the center section. The sealing would be less at off throttle, spreading out the air flow, making it less effective.

At Turkey,RB's performance compared (fastest in section 2) to Mclaren's non-blown performance (fastest in section 1 and 3) in the lower speed corners, would seem to contradict your theory..or I'm not understanding your theory.,

[autogyro]

Not sure that I fully understand any theory.
It is just a guess. I do not think it is any more or less valid a guess than what I have seen already.
I was not considering the heat effects, I was considering the extra gas volume created by burning fuel on throttle and the lower gas volume off throttle.
The high speed corners IMO benefit the RB because it is more streamlined and makes more use of the much higher mass flow at speed which would negate my gas volume idea at high speed anyway.

[speedsense]

Not sure that I fully understand any theory.
It is just a guess. I do not think it is any more or less valid a guess than what I have seen already.
I was not considering the heat effects, I was considering the extra gas volume created by burning fuel on throttle and the lower gas volume off throttle.
The high speed corners IMO benefit the RB because it is more streamlined and makes more use of the much higher mass flow at speed which would negate my gas volume idea at high speed anyway.

Mclaren was beating the RB down the straights, by quite a bit, won't that be an indication of streamlined (Including use of the F-duct)?

EGT's can swing 400-600 F or more (depending on engine type) from off throttle to full throttle, under load.(I have no experience with F1 engines) Depending on the length of the exhaust pipe and whether the pipe is coated with some type of cooling material, unburnt fuel may or may not be burnt by the time it exits the pipe. Don't tend to see much flame on off-throttle in F1 so either the pipe is cool enough or unburnt fuel isn't making it all the way out the end of the pipe. IMHO