Centrifugal Compressor Efficiency

albertotato · May 25, 2016, 11:44

Hello,

I am relatively new to ANSYS. At the moment I am trying to model a centrifugal compressor using carbon dioxide as my working fluid. The main issue I am encountering is that when I reach CFX Solver the modelling indicates a 100% Total to Total Isentropic and Polytropic efficiency.

I have used Tutorial #25 Aerodynamic and Structural Performance of a Centrifugal Compressor in ANSYS CFX Tutorial V16 as a guiding tool. I have also watched several ANSYS videos regarding Turbo mode.

I first started by creating the geometry in BladeGen and then transferring the geometry to TurboGrid. There, I have created a mesh and ensure the Mesh Analytics didn’t highlight any discrepancies or warning. I then moved to CFX Setup, I used Turbo Mode to set the boundaries and interfaces. I ensure all sections were properly selected i.e counter rotating walls, Inlet, Outlets etc. I also ensured to specify it was a centrifugal compressor. Here, I provided ANSYS with a new material “SCO2” and provided the RGP file. I also ensured that the efficiency was selected in the output tab.

For the Inlet conditions I provided the Total Inlet Pressure [MPa], Total Temperature [K] as well as the corresponding axial and tangential components.

For the Outlet I provided Mass Flow for entire Machine.

I have established the reference Pressure of the domain to be 0 atm (I have seen this several times in many of the videos I’ve watched online) Not sure if this is correct.

The current axis of rotation is Z and my rotation is -21,000 RPM

After, specifying all this parameters in CFX Setup I move to CFX Solver. In every simulation I have noticed that the efficiency is not changing and is always 100%. When doing the tutorial mentioned above they did not indicate anything regarding efficiency but still managed to have this as an output and you can clearly see it vary as the model is solved, and as expected the changes decrease closer to the convergence point.

Are there any steps I am missing or something I am doing wrong?

Thank you in advance for any help

maheshchamarti · May 21, 2019, 12:08

Hi I am facing a similar issue. The compressor total to total efficiency is at 100%. How did you solve this ?

ghorrocks · May 21, 2019, 17:31

Have you looked at the basic stuff? https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

waradevivek · May 2, 2020, 02:54

I am also getting similar problem. does anyone got any solution to above problem?

May 25, 2016, 11:44	Centrifugal Compressor Efficiency	#1
albertotato New Member Alberto M Join Date: Mar 2015 Posts: 1 Rep Power: 0	Hello, I am relatively new to ANSYS. At the moment I am trying to model a centrifugal compressor using carbon dioxide as my working fluid. The main issue I am encountering is that when I reach CFX Solver the modelling indicates a 100% Total to Total Isentropic and Polytropic efficiency. I have used Tutorial #25 Aerodynamic and Structural Performance of a Centrifugal Compressor in ANSYS CFX Tutorial V16 as a guiding tool. I have also watched several ANSYS videos regarding Turbo mode. I first started by creating the geometry in BladeGen and then transferring the geometry to TurboGrid. There, I have created a mesh and ensure the Mesh Analytics didn’t highlight any discrepancies or warning. I then moved to CFX Setup, I used Turbo Mode to set the boundaries and interfaces. I ensure all sections were properly selected i.e counter rotating walls, Inlet, Outlets etc. I also ensured to specify it was a centrifugal compressor. Here, I provided ANSYS with a new material “SCO2” and provided the RGP file. I also ensured that the efficiency was selected in the output tab. For the Inlet conditions I provided the Total Inlet Pressure [MPa], Total Temperature [K] as well as the corresponding axial and tangential components. For the Outlet I provided Mass Flow for entire Machine. I have established the reference Pressure of the domain to be 0 atm (I have seen this several times in many of the videos I’ve watched online) Not sure if this is correct. The current axis of rotation is Z and my rotation is -21,000 RPM After, specifying all this parameters in CFX Setup I move to CFX Solver. In every simulation I have noticed that the efficiency is not changing and is always 100%. When doing the tutorial mentioned above they did not indicate anything regarding efficiency but still managed to have this as an output and you can clearly see it vary as the model is solved, and as expected the changes decrease closer to the convergence point. Are there any steps I am missing or something I am doing wrong? Thank you in advance for any help

May 21, 2019, 17:31		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,752 Rep Power: 143	Have you looked at the basic stuff? https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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May 21, 2019, 12:08	Efficiency at 100%	#2
maheshchamarti New Member Mahesh Chamarti Join Date: Feb 2017 Posts: 17 Rep Power: 9	Hi I am facing a similar issue. The compressor total to total efficiency is at 100%. How did you solve this ?

May 2, 2020, 02:54		#4
waradevivek New Member vivek Join Date: Oct 2011 Location: Pune Maharashtra Posts: 7 Rep Power: 14	I am also getting similar problem. does anyone got any solution to above problem?