ALFAGTV6.COM

[Mats]

Did som modeling the other night and this is the result:



Trumpets...


Section


Another section


Added a diffusor thingy from the TB...
Volume is about 5 liters.

This is modeled around a set of trumpets I can buy and a TS Throttle body (dimensions from memory) but mostly I doodled a plenum just to have something to discuss here.

So, any input/flames?

[Reale]

That looks really great-
Nice full radius on the trumpets, too.
The diffuser is important, since you want the airflow to smoothly attach.

But where are the sliding, variable length runners?-Ha ha!

-Al

[Mats]

Well, will the diffusor work as a diffusor? We are talking high airspeeds now, something like 50m/s (off the top of my head) and my gut feeling tells me "Yeah, right" about attached flow in that area. :/

Variable lenght? These runners are so short I would need to rev insane amounts to get any RAM effect. Not showing the complete lenght though.
Good thing it's a turbo engine.

[Reale]

Just joshing about the variable length-it is still a pet project for me.
As long as we are talking about subsonic speeds (anybody jump in here please), I think the main thing is a gentle ramp angle exiting the throttlebody. I know there is math to determine the divergence angle of the diffuser.
-Al

[Mats]

Well, a diffusor like that would be very much longer then the one I modeled, don't think you can get attached flow. Very turbulent flow in that area.

[4sfed]

Why not attach the trumpets to the wall? The flow coefficient is better unless the inlet radius is very large . . . and then it's equal. I've attached a table from the "Handbook of Hydraulic Resistance" by I. E. Idel'Chik.

The note . . . (not sharpened) . . . refers to the edge of the flared tube when it's not attached to the end wall. If the edge is sharpened it will encourage stream separation. The eddies formed in the region of separation will contribute to a smooth flow into the tube . . . much like the re-entrant radius Mat has drawn.

BTW the V6 throttle body is 70 mm.

[Mats]

Well, I can buy the trumpets I modeled in the CAD-renderings at a reasonable price, MUCH easier them making them myself which would probably cost me the same in the end.

The dimensions of the TS TB I mentioned was the base-plate, the throat is more or less the same as the V6 ones as far as I know.

Any thoughts on the shape of the plenum?
How much space around the sides of the trumpets are needed? how much height? Maybe a rule of thumb or something, I have ½ the outer diameter of the trumpet on the one above. Enough?

[Reale]

I think if you could make the ramp from the throttle body a little longer and more shallow it might help, if only because the first trumpet in line might suffer from the turbulent flow.
Have you seen this:
http://www.me.psu.edu/me415/SPRING02/intake/intake.html

Might be helpful?

-Al

[Mats]

Nice link but they primarily talk about lengths, something I have already decided on.
More shallow angle of the diffusor would probably bee good but to make it around 10-12 degrees would make it impossibly long. Remember that there is also a pipe on the other side of the TB that will be bent more and more if I use a longer diffusor and that pipe needs to grow from 60mm to ~80mm so I feel like I'm only moving the problem around by making the diffusor longer...

Also, there is the "diminishing return" factor...
From memory the std 75 TS plenum is worse in terms of sharp bends and sudden enlargements right before the first runner.

[Reale]

Believe me, I understand! Underhood space is always at a premium. All of this theory stuff is fun to talk about, though!

-Al

[Mats]

Yep, thats true.