Tracer analysis in CFX with non-Newtonian fluid

Isar.charmchi · December 17, 2021, 08:35

Hi CFXers,

I want to do the tracer test in ANSYS-CFX version 2021R2.

I implement my viscosity as CEL and the CFX-pre give me the following error:

Parameter 'Kinematic Diffusivity' in object '/FLOW:Flow Analysis 1/DOMAIN

efault Domain/FLUID MODELS/ADDITIONAL VARIABLE:Tracer' has been assigned an expression that references the following unavailable variables: sstrnr

I know that I have to insert my transient result in the CFX-pre as a user function and use them to initialize my velocity and pressure? Am I correct? If yes, I am not sure in transient stats I have to output which parameter? Also, I was thinking if I just output the shear strain rate in transient stats and then export it from postprocessing and input it as a user function in CFX-pre of NY tracer simulation is it not enough?
Would you please clarify for me the issue?

Thanks in advance for your help!

ghorrocks · December 18, 2021, 04:56

The error states you are setting the kinematic diffusivity of an additional variable. This is not the viscosity. Did you intend to do this? If you want to set the viscosity then you should set the viscosity (obviously).

I do not understand your paragraph starting with "I know that I have to ....". You do not need to use a transient result to set initial conditions for velocity and pressure, you can do it directly. This is covered in the CFX tutorial examples. Have you done the tutorial examples? That covers basic stuff like this.

Isar.charmchi · January 5, 2022, 07:17

Thanks Glenn.

Yes, I am trying to set kinematic viscosity for non-Newtonian fluid that is dependent on shear strain rate of fluid as kinematic viscosity is equal to (viscosity/density). Viscosity of the fluid is changing according to the shear strain rate and while I am trying to set the kinematic viscosity of my tracer I receive error that sstrnr that is the shear strain rate of each cell of the domain is unkown. I would like to know how can I solve the problem?

I am well aware that before running the case you can give the residual file as initial condition for your simulation. but I cannot proceed with this error. I have to give the initial condition or information regarding the sstrnr in CFX-pre.

Thank you in advance!

ghorrocks · January 5, 2022, 18:00

Please attach your CCL file.

December 17, 2021, 08:35	Tracer analysis in CFX with non-Newtonian fluid	#1
Isar.charmchi New Member Isar Charmchi Join Date: Aug 2021 Posts: 18 Rep Power: 5	Hi CFXers, I want to do the tracer test in ANSYS-CFX version 2021R2. I implement my viscosity as CEL and the CFX-pre give me the following error: Parameter 'Kinematic Diffusivity' in object '/FLOW:Flow Analysis 1/DOMAINefault Domain/FLUID MODELS/ADDITIONAL VARIABLE:Tracer' has been assigned an expression that references the following unavailable variables: sstrnr I know that I have to insert my transient result in the CFX-pre as a user function and use them to initialize my velocity and pressure? Am I correct? If yes, I am not sure in transient stats I have to output which parameter? Also, I was thinking if I just output the shear strain rate in transient stats and then export it from postprocessing and input it as a user function in CFX-pre of NY tracer simulation is it not enough? Would you please clarify for me the issue? Thanks in advance for your help!

December 18, 2021, 04:56		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The error states you are setting the kinematic diffusivity of an additional variable. This is not the viscosity. Did you intend to do this? If you want to set the viscosity then you should set the viscosity (obviously). I do not understand your paragraph starting with "I know that I have to ....". You do not need to use a transient result to set initial conditions for velocity and pressure, you can do it directly. This is covered in the CFX tutorial examples. Have you done the tutorial examples? That covers basic stuff like this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

January 5, 2022, 18:00		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Please attach your CCL file. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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January 5, 2022, 07:17		#3
Isar.charmchi New Member Isar Charmchi Join Date: Aug 2021 Posts: 18 Rep Power: 5	Thanks Glenn. Yes, I am trying to set kinematic viscosity for non-Newtonian fluid that is dependent on shear strain rate of fluid as kinematic viscosity is equal to (viscosity/density). Viscosity of the fluid is changing according to the shear strain rate and while I am trying to set the kinematic viscosity of my tracer I receive error that sstrnr that is the shear strain rate of each cell of the domain is unkown. I would like to know how can I solve the problem? I am well aware that before running the case you can give the residual file as initial condition for your simulation. but I cannot proceed with this error. I have to give the initial condition or information regarding the sstrnr in CFX-pre. Thank you in advance!