turbof1 wrote:With flow heavily disrupted above the diffuser, the high pressure area above the diffuser als dissapears or is severely weakened. A difuser works by having low pressure beneath it and high pressure above it, but air volume has been hugely reduced and so there is less air to "press" on the diffuser.
Actually a diffuser's job is to slow air down so that it exits the volume between the floor and ground as efficiently as possible. The whole point of getting air to flow around the sidepods and over the diffuser's top surface is to ensure that the velocity of the air above and below the diffuser at the trailing edge of the diffuser is similar. The diffuser doesn't create downforce, it helps other parts of the car create downforce (noteably the leading edge of the floor and the kink line where the diffuser joins the floor).
Whilst there will be some "Newtonian downforce" from the air above the diffuser hitting the diffuser's upper surface, the main downforce isn't produced by the diffuser itself.
In extremis, if the pressure above the diffuser is a lot higher than the pressure below (as you suggest), the air will want to turn around the diffuser trailing edge and flow back in to the low pressure region below. This is not good. By making the pressure above and below the trailing edge equal (or even slightly lower above), the flow will just carry on behind the trailing edge and then interact with the flow from the beam wing etc.
If you are more fortunate than others, build a larger table not a taller fence.
