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-   -   Pump or fan characteristic curve (http://www.cfd-online.com/Forums/cfx/26950-pump-fan-characteristic-curve.html)

A Arvelo January 28, 2009 11:52

Pump or fan characteristic curve
 
How do I input the characteristic curve of a fan or pump in CFX and let the program solve for the operating point?

sa January 28, 2009 15:34

Re: Pump or fan characteristic curve
 
Dear; The points on charaterstic curve are the result of CFX simulation not the input. Nonthless you can make the entire char. curve by changing the back pressure. In this way basically you will get complete flow field for different operting points on char. curve.

Regards

A Arvelo January 28, 2009 21:57

Re: Pump or fan characteristic curve
 
Ok, Let me explain the problem better. I have an application that has 12 fans. I have the fan pressure vs flow curve. Each fan will be operating on a different point in the curve given the nature of the problem. My intention is to enter the characteristic fan curve as an inlet boundary for each fan. Somehow that boudary has to be linked to the system pressure curve. I try inputing the fan curve as a 1D interpolation function but didn't work or I am doing something wrong. My apporach was to set the outlet pressure to 0 Pa, calculate the avg pressure at each fan location and convert that pressure with the 1D interpolation function to its equivalent velocity. Any comments?

Georg January 29, 2009 03:09

Re: Pump or fan characteristic curve
 
You are on the right way. Set pressure vs. mass flow curve by User function. Create Expression using this user function. Assign BCs by this expression. Convergence of the problem could be not good enough. So I think you should first solve the problem with fixed mass flow values on fans inlets. Then use res file as initial conditions.

serezhkin June 25, 2010 17:57

Quote:

Originally Posted by Georg
;91696
You are on the right way. Set pressure vs. mass flow curve by User function. Create Expression using this user function. Assign BCs by this expression. Convergence of the problem could be not good enough. So I think you should first solve the problem with fixed mass flow values on fans inlets. Then use res file as initial conditions.

Hi Georg,

I am trying to follow your directions.
I have created a user function as interpolation (data input) and I entered several points from the Fan curve.

Then I used the user function in expression for the fan curve.

However, when I try to use the expression as mass flow rate BC, it says:

"Bad expression value 'Fancurve' detected in parameter 'Mass Flow Rate' in object '/FLOW:Flow Analysis 1/DOMAIN:Default Domain/BOUNDARY:Fan_out/BOUNDARY CONDITIONS/MASS AND MOMENTUM'.
CEL error:
In the expression assigned to 'Fancurve', the function 'FAN curve' is called with the wrong number of arguments (0 - expected 1)."

Any suggestions on what I did wrong would be appreciated.

ghorrocks June 26, 2010 07:32

You need to give the interpolation function an input variable. Have a look in the tutorials.


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