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-   -   Why Mass flow Ave doesn't work? (http://www.cfd-online.com/Forums/cfx/20999-why-mass-flow-ave-doesnt-work.html)

Pete February 17, 2005 23:59

Why Mass flow Ave doesn't work?
 
Hi all,

I've created a 2D inclined plane & wish to do a mass flow averaged pressure at this plane. However, I always get a "nan" etc while using mass flow average at the plane that I created. No problem using this at inlet/outlet plane. Anyone know how to solve this?

Robin February 18, 2005 22:01

Re: Why Mass flow Ave doesn't work?
 
What do you get if you calculate the mass flow on the plane?

Pete February 20, 2005 20:41

Re: Why Mass flow Ave doesn't work?
 
Hi Robin,

Great to hear from you again. I'm calculating mass flow averaged pressure differential between two planes, not the mass flow. Can CFX do that?

Regards, Pete

Robin March 16, 2005 10:43

Re: Why Mass flow Ave doesn't work?
 
Yes, but there are two ways to calculate the mass flow average. The function massFlowAve() will divide by the net mass flow rate, whereas massFlowAveAbs() will divide by the absolute mass flow. Basically:
massFlowAve(p)@Plane 1 = massFlowInt(p)@Plane 1/massFlow()@Plane 1Hence my original question, what is the mass flow you calculate.

To make a short story longer, try the following expressions:
Pdiff 1 = massFlowAve(p)@Plane 1 - massFlowAve(p)@Plane 2
Pdiff 2 = massFlowAveAbs(p)@Plane 1 - massFlowAveAbs(p)@Plane 2
You might also consider whether you should be mass flow or area averaging. The area averaged pressure differencial would be:Pdiff 3 = areaAve(p)@Plane 1 - areaAve(p)@Plane 2
Regards,
Robin


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