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May 20, 2020, 10:27 |
Pressure ratio calculation CFX
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#1 |
Member
Join Date: Mar 2020
Posts: 33
Rep Power: 6 |
Hello,
I am working on steady state simualtion of centrifugal compressor and I want to evaluate pressure ratio in CFD post. When I go to function calculator, I see average and massflowaverage values of pressure. Which one is right in this case? I checked one thread for transient simulation and he used massflowaverage of total pressure at inlet and oulet. However when I do this I get very high pressure ratio. When I use simple average of total pressure at inlet and outlet, I get more reasonable value of slightly greater than 3. which one is right? One more question is I have a converged solution for one mass flow rate, how can i use this one for other mass flow rates so that simulation converges faster? Thank you. |
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May 20, 2020, 11:35 |
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#2 |
Senior Member
Join Date: Jun 2009
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A few questions:
1 - are you using a non-zero Reference Pressure? 2 - is there any recirculation at the boundaries? Then, for the calculation: 1 - I would use massFlowAveAbs(Total Pressure in Stn Frame)@Boundary, 2 - I would include the Reference Pressure, just in case. Ratio = (Reference Pressure + massFlowAveAbs(Total Pressure in Stn Frame)@Boundary 1) / (Reference Pressure + massFlowAveAbs(Total Pressure in Stn Frame)@Boundary 2) If it does not match your expected value, there is something not accounted for: 1 - Well converged solution? 2 - Proper mesh independent solution? 3 - Relevant features included in the model? The averaging type should not be a knob to adjust to match to data. Hope the above helps
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May 20, 2020, 11:55 |
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#3 | |
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Quote:
and for the solution yes it is converged and the results are not changing with further refinement. I am using stage mixing model. |
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May 21, 2020, 11:10 |
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#4 | |
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Quote:
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May 29, 2020, 17:01 |
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#5 |
New Member
Sumanth
Join Date: Aug 2018
Location: Germany
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The streamlines usually have a starting point which you define and these are arbitrarily chosen in CFX based on number of elements on the starting surface and the number of streamlines you wanna visualize. They start at the cell center and since your meshes are not the same, the streamlines you will be visualizing are not gonna be the same as their starting points are gonna be different. I hope this helps.
Moving on to the pressure values, I am really not sure what is a practical solution in your case. You need to first do a mesh sensitivity study. May be that will give you some insight in this problem. Also, check literature and compare with these results. |
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