[schwereherzen]

Hello, I am trying to analyze on a centrifugal compressor. I meshed with Turbogrid. I need to choose ideal gas for my fluid on the loading screen, but the application gives an error at step 7 in the solution section. If I make the gas 25 degrees air, there is no problem. But I need ideal gas. I tried everything and couldn't solve the problem.
Thanks..

[Opaque]

It would be great if you were a bit more precise in your description.

Which application are you using when "loading screen"? CFX-Pre? If so, which mode did you select when opening? General/Turbomachinery?

Which set of instructions are you using that refers to "step 7"? Is it a provided tutorial?, or video? or else?

[schwereherzen]

Thank you for your interest, I do not speak English. That's why I use translation.
My sentences may sound a little garbled or incomplete.Let me explain what I do in order. First, I designed the compressor from the application called CFTurbo, then I transferred this design with ansyse turbogrid. I connected the turbogrid with turbo mesh and connected it with cfx.
After the turbo mesh step, there is a setup step in the cfx section, I need to choose my fluid ideal gas in the setup, and my parameters are 288.15 kelvins, my inlet pressure is 0 atmosphere inlet temperature. My outlet flow is 0.6 kg/s and my initial pressure is 1 atmosphere. After confirming these, I save and move on to the solution section. The solution starts and after a little progress, all the variables suddenly increase excessively and I get an error. I will leave a picture of it here. When I do the same things with 25 degrees air, not ideal gas, I do not get an error.
When I said step 7, I didn't mean step 7 that I applied. 7th step of iteration. I do 300 iterations in total.

[zacko]

It would be helpful if you provide your .out file of your simulation. There, the error warning of the solver is written.

[schwereherzen]

where can i find out file?

[zacko]

If you are working in Workbench, your CFX Node should look like the attached image.
Click on "Solution" and you can see your residuals on the left and your .out-File Data on the right.
If you are working in stand-alone, an .out-File will be generated simultaneously with your result file.

[schwereherzen]

CFX_001.zip


this file is .out

[zacko]

Is your inlet total pressure correct ?
Is it correct, that your model is subsonic ?

[schwereherzen]

I'm not sure about these. I don't know what subsonic means, I haven't touched it. but the inlet pressure will be 0 atm

[zacko]

This is basic fluid mechanics and you should have a look at these basics before carring out a CFD simulation.
But, the solver shows a fast increase of the Mach Number in your setup, which results in an overflow error.
Your boundary conditions should be checked.

Do you have any real purpose for this simulation ?

[schwereherzen]

yes i have a purpose this is my design assignment. I just changed my rev count from 90000 RPM to 40000 RPM and it's analyzing now. Is the mistake here?


but my speed should be 90000rpm

[zacko]

Unclear. Your Mach number will probably go down.
Does the solver show a message after every iteration that the Mach number is at a speicfic value ?

Where did you get the 90'000 rpm ?
Your compressor will probably operate under transonic or supersonic conditions with this speed.

[schwereherzen]

First of all, my teacher gave me the necessary values about design. It gave a speed of 90000 RPM, a flow rate of 0.6 kg/s and a pressure ratio of 4.5. I'm trying to design accordingly. If it is as you say, if I am going to make it supersonic or transonic, what values should I enter in the parts there?

I need to make supersonic for both input and output, right?

[zacko]

Can you, please, go into your impeller Domain R1 and change the Heat Transfer from adiabatic to Total energy. Try the simulation again.

[schwereherzen]

total energy already selected


but there is an option just below. Should I leave the option on or turn it off?


I can try with supersonic or mixed but I don't know what values to enter

[schwereherzen]

can you help my problem? please

[zacko]

sadly, I'm not an expert carrying out transonic or supersonic simulations. But, there is an FAQ
which you should check out and compare with your setup.

https://www.cfd-online.com/Wiki/Ansy...do_about_it.3F

Also, do you have an inlet and outlet domain for your impeller ?

[schwereherzen]

According to the values I entered in the program I designed, I think I can take a photo of that part.


p.zip



What does the analysis with 70 rpm and not doing the analysis at 80 and above indicate?

[schwereherzen]

ı am impeller