CFD and FI intake manifold

[nuvola rossa]

This is a topic that usually on other forums don't have replies... :confused

I have a friend that have a legal version of SW2008 with COSMOSfloworks that I can use on his pc :)

I'm not an engineer, he is a civil engineer but he doesn't have a minute to help me with things of my car... and he doesn't like them so he don't know very well things like FI components :( (all bricks and no pistons:D )

I never used solidworks before ten days ago, but now I'm able to design something like a log manifold easily and trying learning models more complex everyday with tutorials...

Now to the fun part: cosmos and its boundary conditions;)

It has many options for the inlet of the manifold, like flow, volume or pressure, and the same for the outlet.

I made some "analysis", and printed flow lines and pressure to play a little with functions...

I need to know how to set and which boundaries in general for a turbocharged intake manifold...

tell me if it's correct what I'm doing:
- I set to the inlet (air from turbo) of the manifold a flow calculated with tools like turbo calc (or formulas) and as pressure "14.5psi+boost psi";
- at runners I set 14.5psi of enviroment pressure
and then I run the solver. It does the meshes and I chose to plot the flow patterns on the model, and it give me the flow colour matched to pressure or velocity.

Now I don't know really what pressure should be good, what velocity to not go over... I read that speed shouldn't go over mach1... but infos here are zero, maybe because they are $$$ softwares and not many engineers want headaches with custom parts...

who can give an input to this discussion to grown up?


and I know that I'm a n00b in physics, but that's not my job:D
Just trying to learn every detail of these cars :)
(don't flame me too much:D)

[ADVANT123]

Here is an excellent thread that was recently posted regarding intake manifold design for turbocharged applications and the use of CFD programs to improve designs:

http://forums.hybridz.org/showthread.php?t=127863&highlight=intake+manifold+design

[nuvola rossa]

I've read that thread days ago, very good infos. I'll read another time now to see if I can find the answer of my questions about cosmos...

PS: that guy made a jewel!

[wulfgang]

Nice software. Your boundary conditions will determine whether or not your flow calculation is even valid, so don't screw them up ;) This is especially true with incompressible flow, which most people screw up by default.

1. For the outflow, in my opinion, you need to set a velocity boundary. This is because an engine is like a positive displacement pump. At a given rpm, the velocity of the gas flowing past the intake manifold gasket can be assumed to be a constant, independent of boost pressure, the throttle setting, etc. DO NOT set a pressure condition on the outlet.

2. The inlet should just be a pressure/density/temperature (pick any two) condition, along the lines you were suggesting. I'd just assume WOT at full boost with no pressure drop at around 110-120 F to get things going.

3. The stock manifold is made from PEEK or polyamide-imide (or something similar) and is a good insulator. This would be a zero heat flux condition on the wall (Dirichlet condition). However, if you are making an aluminum manifold, you may want to set an exterior wall boundary condition on temperature (Neumann condition), say 150 F, just to see if the effect is significant in a hot engine bay.

Your intake manifold should never see flows even close to Mach 1. And if the Mach # even goes over 0.3, I'm pretty sure the solver you are using will be inaccurate, but that doesn't matter because like I said, you shouldn't be flowing that much air.

Your calculation will tell you what a flow bench would tell you, nothing more. The beauty of the OEM manifold is that it is designed for a dynamic flow rather than a steady one. For example, SW will not be able to tell you where the torque peak will occur, which is very important on a street car.