# defining new expressions

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 April 3, 2009, 11:07 defining new expressions #1 New Member   Mattia Join Date: Mar 2009 Posts: 9 Rep Power: 8 Dear all, good morning. I am simulating the flow within the diffuser of a centrifugal compressor and I'd like to post-process some properties (static pressure recovery coefficient, total pressure loss coefficient, efficiencies...) which are not available by default. They are of course functions of variables which are available in CFX-Post (like pressures, temperatures, velocities...). Of course I know the formula to calculate them: how can I implement those formula in CFX-Post, in order to analyze them? Thank you. Kind regards, MAttia.

 April 3, 2009, 13:12 #2 Senior Member   Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 8 Yes, define expressions from available variables to form variables you want. Define a quantitative that include the expression first, and then a variable. Enjoy your work!

 April 3, 2009, 14:42 #3 New Member   Mattia Join Date: Mar 2009 Posts: 9 Rep Power: 8 Yes, I got that. But my problem is: how do I define those expressions?! Let's say I have 2 variables x and y and I want to calculate z=2*x+y: where do I write that formula?! Probably you are saying in the quantitative window: OK, but how?! I try to add something new, but I couldn't. Thank you. Kind regards.

 April 5, 2009, 04:21 #4 Senior Member   Rikio Join Date: Mar 2009 Location: SH, China Posts: 182 Blog Entries: 1 Rep Power: 8 For your example, just give a name for a quantitative, coorZ, for example. Then define the quan as 2*x+y. It is so simple. Then define a variable as cZ, select the quantity coorZ as the expression. Just give different names for the quantitative and variable. Or there will be conflicts of name convention. I think you did not have a good look at the documentation, right? Do this to fix your puzzle, it will help you much. ^_^

 April 6, 2009, 05:36 #5 New Member   Mattia Join Date: Mar 2009 Posts: 9 Rep Power: 8 Well, I had read the manual, but with your answer it was easier to understand. Thanks a bunch! Cheers, M.

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