Just_a_fan wrote: ↑04 Feb 2022, 17:19
Zynerji wrote: ↑04 Feb 2022, 16:53
Just_a_fan wrote: ↑04 Feb 2022, 16:50
From that view, it makes me wonder if the idea is to use the front of the sidepod to deflect air laterally and then the shape of the rear end encourages air flow down from above the car on to the rear floor. If you can't use big bargeboards to move air laterally, using the outermost strake and the sidepod front face to do it seems like the next best idea.
Wouldn't you want slow/stagnant air above the tunnels (top of floor) to create a pressure difference on both sides to create downforce? Or is that compromised to get fast air over the top of the diffuser exit to aide extraction?
They want fast air over the exit of the diffuser because this makes it more efficient - the diffuser's job is to slow the air down so if you can blow fast air across the edge of the diffuser, the speed difference it has to deal with is less. The beam wing helps here too because it accelerates the air immediately below it (and thus immediately above the diffuser lip) improving the situation further. The beam wing also helps with the expansion, of course, and results in an effectively extended upper diffuser surface. That's my "school boy understanding" of it, anyway.
The air that can't go through the tunnels and goes over the floor and under the sidepod undercut, will be much higher pressure than the diffuser in general(especially if we have a choked diffuser throat). The edge wing is there to prevent or delay the air over the floor from curling under the floor. It still will curl under the floor of course because high pressure goes to low, this will create two strong counter clockwise vortices. As we discussed in the aero thread, vortices can amplify each other if they interact properly.
The airflow that is accelerated by the throat of the diffuser's massive low pressure, and the expansion fans that follow the throat, all the way to the beam wing, help drive the two vortices, and those vortices will help pull air through the floor further accelerating it. This in turn will create a bigger pressure difference between the top and bottom of the car, in a positive feedback loop similar to the way a turbo creates pressure.
With subsonic flows, or incompressible flows, diffusion slows down air, with sonic or compressible flows, diffusion accelerates air. For a diffuser to accelerate air via expansion that air already is either sonic or suffering from compression effects. Have you ever wondered why we use diffusers and not nozzles at the back of the car?
