Convergence of a thermodynamics cycle

vortex69 · June 9, 2016, 18:50

Hello,

I have a simulation in Ansys CFX, which is a thermodynamic cycle. I want to study convergence on this simulation. But my problem is, the temperatures and pressures do not converge, since it is a thermodynamic cycle. Could anoyone help me, how to study the convergence ?

ghorrocks · June 9, 2016, 19:23

When I think of a thermodynamic cycle I think of compressors, turbines, heat sources and heat sinks combining together to give a cycle like Carnot, Brayton, Otto, Diesel, Miller etc etc. Each one of these devices has a complex flow and thermal field, and each one would be a challenging CFD simulation in itself. I would not consider doing a CFD simulation of all of them in a single model to model the entire thermodynamic cycle.

Am I correctly thinking of what you are trying to do? Or have I misunderstood the cycle you are trying to model?

vortex69 · June 9, 2016, 19:43

thank you for your reply. It is a Brayton like cycle, with hot and cold sides. I have the simulaton already done in Ansys, but how do I study the convergence ?

ghorrocks · June 9, 2016, 19:52

You normally measure convergence using residuals and imbalances. This is discussed in the documentation and examples are shown in the tutorials.

Can you post an image of what you are modelling? As my last post stated it is very unusual to use CFD to model an entire thermodynamic cycle so I would like to have a look at what you are doing.

vortex69 · June 9, 2016, 20:06

I know how to use residual, but in my case , the values of temperature and pressure are repeating, since it is a cycle, so that I can not use residual since they do not converge to a specific values. I do not know how to attach image file here, may be I can send u by email.

ghorrocks · June 9, 2016, 20:16

I am very confused about what you are saying. I really need to see a picture of what you are modelling - and preferably the CCL or output file as well please.

To post images or attachments on the forum:
* Click "Go Advanced"
* Click "attachments" (button looks like a paper clip)
* Click "Choose File" to select the file, then "upload" to put it on the server.
* Close the attachment window.
* Click "attachments" again (that's the paper clip)
* Click on the attachment to add a link to.

vortex69 · June 9, 2016, 20:48

this is the image. I could not find a CCL file

Quote:

Originally Posted by ghorrocks

I am very confused about what you are saying. I really need to see a picture of what you are modelling - and preferably the CCL or output file as well please.

To post images or attachments on the forum:
* Click "Go Advanced"
* Click "attachments" (button looks like a paper clip)
* Click "Choose File" to select the file, then "upload" to put it on the server.
* Close the attachment window.
* Click "attachments" again (that's the paper clip)
* Click on the attachment to add a link to.

ghorrocks · June 9, 2016, 21:16

Thanks - can you explain what is happening on the image?

Also attach an out file, please.

vortex69 · June 14, 2016, 13:15

the flow is pushed from the left side(cold side) to the right side(hot side).

ghorrocks · June 14, 2016, 20:12

That is not what I meant. I have no idea what the image you showed is and what the boundaries are. Also I do not know what you are doing with it - so please attach a marked up image and your output file.

June 9, 2016, 18:50	Convergence of a thermodynamics cycle	#1
vortex69 New Member Ali Join Date: Apr 2016 Location: Germany Posts: 25 Rep Power: 10	Hello, I have a simulation in Ansys CFX, which is a thermodynamic cycle. I want to study convergence on this simulation. But my problem is, the temperatures and pressures do not converge, since it is a thermodynamic cycle. Could anoyone help me, how to study the convergence ?

June 9, 2016, 19:23		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	When I think of a thermodynamic cycle I think of compressors, turbines, heat sources and heat sinks combining together to give a cycle like Carnot, Brayton, Otto, Diesel, Miller etc etc. Each one of these devices has a complex flow and thermal field, and each one would be a challenging CFD simulation in itself. I would not consider doing a CFD simulation of all of them in a single model to model the entire thermodynamic cycle. Am I correctly thinking of what you are trying to do? Or have I misunderstood the cycle you are trying to model? vortex69 likes this.

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June 9, 2016, 19:43		#3
vortex69 New Member Ali Join Date: Apr 2016 Location: Germany Posts: 25 Rep Power: 10	thank you for your reply. It is a Brayton like cycle, with hot and cold sides. I have the simulaton already done in Ansys, but how do I study the convergence ?

June 9, 2016, 19:52		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You normally measure convergence using residuals and imbalances. This is discussed in the documentation and examples are shown in the tutorials. Can you post an image of what you are modelling? As my last post stated it is very unusual to use CFD to model an entire thermodynamic cycle so I would like to have a look at what you are doing.

June 9, 2016, 20:06		#5
vortex69 New Member Ali Join Date: Apr 2016 Location: Germany Posts: 25 Rep Power: 10	I know how to use residual, but in my case , the values of temperature and pressure are repeating, since it is a cycle, so that I can not use residual since they do not converge to a specific values. I do not know how to attach image file here, may be I can send u by email.

June 9, 2016, 20:16		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I am very confused about what you are saying. I really need to see a picture of what you are modelling - and preferably the CCL or output file as well please. To post images or attachments on the forum: * Click "Go Advanced" * Click "attachments" (button looks like a paper clip) * Click "Choose File" to select the file, then "upload" to put it on the server. * Close the attachment window. * Click "attachments" again (that's the paper clip) * Click on the attachment to add a link to.

June 9, 2016, 21:16		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Thanks - can you explain what is happening on the image? Also attach an out file, please.

June 14, 2016, 20:12		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	That is not what I meant. I have no idea what the image you showed is and what the boundaries are. Also I do not know what you are doing with it - so please attach a marked up image and your output file.