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CFX-Pre Efficiency Monitor

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Old   October 19, 2022, 05:48
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Amre
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Hello,


I'm relatively new to CFD work and this forum has been great help just reading the discussions on similar issues. But, I can't seem to find any mention of this specific problem.


I'm simulating a steady-state centrifugal compressor case. The case runs fine and I don't see any glaring issues but I'm trying to add an efficiency monitor to my solver. As I've found in the CFX Reference Guide, this option should be in "Output Control > Monitor" but it simply isn't. I've attached a screenshot of the monitor tab. As far as I've seen in the manual, the efficiency option should come in just below "Monitor Particles"



For more details, I'm using Ansys Workbench. I imported my mesh from TurboGrid where I specified that the machine is a Centrifugal Compressor. I then started with "Turbo Mode" to setup the simulation then I would go through and make more edits in the regular "General Mode".



I hope this is enough information. Thank you.
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Old   October 19, 2022, 15:55
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Unfortunately, there are no pre-defined expression for efficeincy. Therefore, you should create an CEL-expresssion yourself that calculates the efficiency. Then in the Monitor menu, create a monitor that refers to your efficiency-espression. Just like you do for expression betaTT.
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Old   October 19, 2022, 16:53
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Hello Gert-Jan,


Thank you for responding. I did find mention of this efficiency checkbox in the CFX Reference Guide. So, I do believe it's there or at least should be. I'm using Ansys 2021 R2 if that might make a difference. The reference guide I'm using is for the same version of course.

Your suggestion is a good one, but one I unfortunately tried already. Any expression with the variable (Isentropic Compression Efficiency) or (Isentropic Total Enthalpy) unfortunately errors out with an "Illegal callback" error as soon as the solver run starts. So, that leaves me kind of stumped at the moment. How would you write an Isentropic Efficiency expression for a centrifugal compressor? Because the ones I've tried have not really worked.

This also leads me to believe that there might be some other issue that's causing this sort of error.
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Old   October 19, 2022, 17:04
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Load the results in Post and use the calculator. It contains predefined setups for pumps, turbines, probably compressors as well.
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Old   October 20, 2022, 10:20
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Thank you very much. I was able to find expressions for total-to-total isentropic efficiency in the expressions tab of CFD-Post. And these ones didn't error out this time.
Much appreciated
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