Intake plenum and 911 throttle body

[blue2000s]

Originally Posted by KRAM36

Wow, you haven't posted here in over a year blue2000s. Thanks for the explanation. So what is it about the radius that makes it flow 30% better? Does the larger radius give the air more room to move inside the Distribution T because it's already making it's own natural wedge which would reduce the area for the air to flow?

Yeah, me thinking the engine was making the air pull to the radius looks really stupid, well at least to you guys lol. I never thought about the air creating it's own wedge and I'm trying to figure out why this air is following the path it does in your simulations.

Also what about the 997 T being so much larger then the Plenum opening? Is this a huge issue?

Since finding the truth in lightness , I haven't been back to Porsches, so I don't come around here anymore, but I saw the I was quoted so took the opportunity to chime in.

Air moves by means of a difference in pressure. That's the "voltage". It doesn't matter (mostly) if it's being driven by above atmospheric to atmospheric or atmospheric to below atmospheric. If the difference in pressure is the same, the air would act the same, again mostly.

Moving air has momentum but it's motion is also subject to the pressure (force) acting on it. As air goes around a corner, the air at the inner side of the corner is accelerated more than that at the outer side.

This sets up a pressure difference where the air at the outside pushes on the air at the inside which helps the airflow make a smooth turn around the bend despite the air's momentum trying to push it all straight against the outside of the wall.

There is a point where the effect of the momentum overcomes the pressure difference and the air with the highest momentum (inside of the turn) pulls away from the wall and heads toward the back of the turn. This is called flow separation, you can see it in my CFD pictures.

Separation effectively shrinks the size of the tube that the air is flowing through as the air is ignoring the inside of the turn and really only flowing through some % if the tube. The rest is stagnant air.

The more smooth and large the inner turn, the lower the momentum at the inner wall, and the more likely the airflow at the inner wall is to stay attached. This is why the shape of the inside of a turn has so much more influence on the airflow than the outer. There is some speed threshold at any turn where the flow at the inner wall will detach. That speed depends on the geometry and roughness of the walls. The goal is to design that inner turn so that the threshold is above any speed that the engine will produce.