Question about Diffuser

[walkeriot]

When the air flow passes through the "diffuser", its velocity increases and pressure decreases. The lower pressure at the bottom versus the atmospheric pressure at the top of the car produces a suction force.

However, as shown in the picture below, the 'diffuser' actually has a nozzle shape, and as I mentioned above, the function that the “diffuser” has is same as a nozzle.

[/img][IMG:390:218]http://img505.imageshack.us/img505/8919/diffuserdq8.png[/img][img]

So, please anyone can tell me why the nozzle-like thing is called a diffuser? Or I’m theoretically wrong?

Thanks!

[walkeriot]

However, the rear part of the "diffuser" looks like a diffuser. Why it's designed like that?

[IMG:382:219]http://img70.imageshack.us/img70/1461/13732392qd4.png[/img]

[IMG:180:213]http://img472.imageshack.us/img472/3095 ... earfa6.png[/img]

[modbaraban]

Here's another pic. BAR007



can anybody explain how this works? How can it get sucked to the road while it has a 'floor' separating the airflow from the round.

[manchild]

Diffuser is fed by air that flows below the sidepods (left and right from the stepped floor and plank) while small amount of air that flows below the plank reaches diffuser "after" air that flows below sidepods has already entered it.






Top of the diffuser is just streamlined to fit as continuous part of engine cover.

[modbaraban]

...well the actual diffuser part is clear for me, but how that 'nozzle' in the middle helps?

[manchild]

...well the actual diffuser part is clear for me, but how that 'nozzle' in the middle helps?

Nozzle that can be seen here? That's just aperture for engine starter axle.



Yellow "dot"? Is that what you have in mind as "nozzle"?

[walkeriot]

yea, thanks alot, but i still can't understand it.

[IMG:395:221]http://img359.imageshack.us/img359/7141/untitleder5.jpg[/img]

the nozzle part is highlighted in red (as i think). if the "diffuser" acts like a nozzle, it provides the right funtion: lower the pressure.

but a real diffuser decreases the velocity and increases the pressure. so how does the fomula 1 'diffuser' work??

for the above statement, Ma<1 for sure.

Thx!

[modbaraban]

@ manchild

so there's no air coming through that hole? Why not then use that middle area as proper diffuser like on the sides? Also is there any sort of airflow going in the middle above the plank, and where it exits?

[manchild]

yea, thanks alot, but i still can't understand it.

[IMG:395:221]http://img359.imageshack.us/img359/7141/untitleder5.jpg[/img]

the nozzle part is highlighted in red (as i think). if the "diffuser" acts like a nozzle, it provides the right funtion: lower the pressure.

but a real diffuser decreases the velocity and increases the pressure. so how does the fomula 1 'diffuser' work??

for the above statement, Ma<1 for sure.

Thx!

That pic shows top of the diffuser and floor - not the bottom. Red zone you marked is exactly the space that gearbox/differential occupy. Looking from above gives you no insight about air conditioning shape of diffuser on the other side.

The top drawing shows you how it approximately looks from below:

[DaveKillens]

At the very rear of the undertray do we see the fences and tunnels that expand the airflow, and thus increase velocity, and decrease the pressure relative to the ambient pressure. Since the rear diffuser connects to the undertray without any protuberances, it applies Bernoulli's principle also to the underbody, high velocity, low pressure.......
So although just the very rear part of the underbody has the diffucer, it's influence bears on the entire underbody.

[walter]

the unique shape of the diffuser's central section(nozzle) is a great innovation that works around the mandated skid plate running down the center of the car and ending at the rear axle line. Just like dave said, it influences the entire underbody, grabbing most of the air not from underneath the central skidplate but from underneath the sidepods, if you notice the notches that allow its low pressure to take air from the sides, much further up the car than the end of the skid plate. This in turn multiplies the downforce created by the diffuser sections on each side, behind the sidepods.

I remember before the central skidplate was mandated Mclaren had some crazy diffusers back in the 90's(I believe it was Mp 4/6 but i may be wrong). It had a diffuser with a semi-circular cross section, rather than flat surfaces... anyone else remembers this?

[mahesh248]

the diffuser is used to produce a ventury effect ......? m guessing ..

[manchild]

I remember before the central skidplate was mandated Mclaren had some crazy diffusers back in the 90's(I believe it was Mp 4/6 but i may be wrong). It had a diffuser with a semi-circular cross section, rather than flat surfaces... anyone else remembers this?

Yes, it had a diffuser spanned as much as possible and it looked like a multiple arc bridge...

[scarbs]

Air does not flow through the nozzle shape (red) you’ve highlighted. Instead the flow passes outside the red lines in the side & central diffuser tunnels. The nozzle shape you’ve highlighted is only there to rejoin the flows split by the underbody step and fuselage of the car. In fact the area is actually full of gearbox, hydraulics and ballast when it’s installed on the race car.

There have some imaginative diffusers over the years. My favourites are:

The 1983 Ligier JS21, which has an almost sidepod-less design, the ducts around the radiators formed the upper surface of the diffuser, while a small floor to meet the flat bottom rules started the diffuser off.

The Jordan 191 with its two arched tunnels met by the curved sidepods walls.

Also the 2003 Sauber C23 diffuser did not have a tall central tunnel, but the floor at plank level swept up to form one diffuser and the side channel swept up to form their own.

[syguy]

Thought it might be useful to clarify the role of a diffuser.

Air enters a diffuser "...in a low-pressure, high-velocity state after accelerating under the car. By gradually increasing the cross-sectional area of the diffuser, the air gradually slows down [increasing its pressure] and returns to its original free-stream speed and pressure. The diffuser's aim is to decelerate the air without it separating from the tunnel walls, which would cause a stall, reducing the downforce and inducing a large drag force. By installing an inverted wing close to the diffuser exit it is possible to create a low-pressure area, which essentially sucks the air from the diffuser. The diffuser and wing combination permits a higher air-mass-flow rate through the diffuser, thus resulting in higher downforce [ahead of the diffuser]" from Secrets of Underbody Tunnels, Rear Diffusers and Venturis