8 Replies Latest reply on Nov 11, 2009 9:03 PM by Bill McEachern

Flow setup question

Hi all,

I am rtying to setup a simulation to show air flowing through a bore, and interfacing with a throttle plate. i have attached an image to illustrate. Basically i need  floworks to show that a suction is being created due to the pressure drop, and give me a mass flow rate in lbs/hr. is this possible???? I have been trying for a while now with no luck. I know what the flow should be but when i run the simulation i get values no where near what they should be, so i have obviously missed something somewhere. i can provide any additional data if needed. Thanks in advance!

Tony

• Re: Flow setup question
HI Tony: Should be fairly simple. Use symmetry to help speed it up. Would you mind trying "pushing" the flow with the known mass flow rate (1/2 for the half model) and using env pressure on the opposite end? Set a surface goal on the inlet as the static pressure (then you can set an equation goal for graphing the 'suction' value and observe how it is, or is not converging). Make sure to turn-on the "manual specfication of minimum gap size" to be the gaps between the throttle plate and the bore minimum clearance, and of course set the "manual specification of the minimum wall thickness" to be the throttle plate thickness. Hopefully this will resolve the model geometry well.
• Re: Flow setup question

Symmetry? never used it. how do i invoke it? Getting ready to leave for te day, will have to try it in the morning. Thanks for the tips. i will give it a go, and post back tomorrow!

Tony

• Re: Flow setup question
Hi Tony. From your image, it appears that the ZY plane is a symmetry plane (the plane of the monitor for the image that you snapped). Therefore, a plane cut at the Cartesian coordinate system's X=0 value will work as a symmetry plane.
To do this, just right click on the "Computational Domain" icon in the analysis manager tree, and choose:
"Edit Definition".
Then, click on the "Boundary Condition" tab, and look at the drop-down adjacent to "At X min" or "At X max".
You can select either one of those and choose the item "Symmetry" in the drop-down. Click OK.
This action will re-set the computational domain appropriately (make sure to show the computational domain to verify it is now half-sized), and you will need to re-mesh. The benefit is a halving of the cell count and thus the computational requirements, too. The software will automatically locate a "slip-plane" type of boundary condition on that plane, so the flow will slip on it (no friction) and will not cross over or into the other half.
Hope this helps alot! - Tony
• Re: Flow setup question
SYMMETRY Note: Forgot one important thing! You must set the computational domain boundary to stop at either X min or X max! Cheese and Crackers, I totally forgot that! Sorry: Right click on Computational Domain and choose "Edit Definition", then, on the tab "Size", set the X min or X max field to 0 (zero). If you place your cursor in another field (without clicking OK, just yet) you should immediately see the Domain resize itself. To reset the size to default: press the "Reset" button at the bottom to instantly reset the domain size to its default size.
• Re: Flow setup question
You need to be careful using symmetry in flow problems. I would not use it until you confirm that it will work so you need to do it without it first so you have some idea of what it should look like.
• Re: Flow setup question

Forgive my ignorance, as i have zero Flow experience.....Would you mind publishing a revised version of my image showing you suggestions? As far as an equation goal???? no idea where to go with that. what kind of equation are you refering to? Thanks.

• Re: Flow setup question

27.5 inH2O (60°F)   =   0.9925 psi

I assume you are setting up for a .9925 psi pressure drop.

So if atmospheric is 14.7 psia (407.3 inH2O abs), then the other side of the throttle plate would be 13.71 psia (379.7 inH2O abs). Automotive manifold pressures are usually computed using absolute reference, although 28 inH2O is the standard pressure drop for flow testing.

If you want to use gauge reference terms, atmospheric is 0 psig (or 0 inH2O) and the other side of the throttle plate would be -0.9925 psig (or -27.5 inH2O).

• Re: Flow setup question
Forgot to mention you can directly set the flow units for pressure to inches of water instead of psi or Pascals. Menu: Flow Simulation/Units. Then find the tree item "Main/Pressure & Stress". You can click in the Units column and choose "Inch Water".  Very cool software. -Tony