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Space variant boundary conditions

Posted Sep 9, 2014, 4:42 a.m. EDT Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD), Parameters, Variables, & Functions Version 4.4 5 Replies

Anoop Asranna
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Hello everyone,
I am modelling the combustion chamber of a biomass stove. For now, I aim to simulate just the fluid flows.
I am using the non isothermal flow interface to model this(axisymmetric). My fluid domain is continious and need to specify the heat source only in the interior of the combustion chamber.
I know this can be done using a step function. But how do you implement this step function on to a boundary condition? In my case, I am specifying a heat source and I want to implement the step function onto this. What is the syntax for the same?
Really need your help.Have been wasting too much time on this!

thanks,
Anoop
5 Replies Last Post Sep 10, 2014, 3:54 p.m. EDT
Pieter Westerik
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Posted: 1 decade ago Sep 10, 2014, 9:44 a.m. EDT
To the Definitions or Global Definitions node you can add a Functions -> Step function, which has the default name 'step1', but you can change it, and also its parameters. Then you can use it in your heat source, you can give it the value 'step1(r)' or 'step1(z)' or '100*(1-step1(r))' or however you want to use it. Does that help?
To the Definitions or Global Definitions node you can add a Functions -> Step function, which has the default name 'step1', but you can change it, and also its parameters. Then you can use it in your heat source, you can give it the value 'step1(r)' or 'step1(z)' or '100*(1-step1(r))' or however you want to use it. Does that help?
Anoop Asranna
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Posted: 1 decade ago Sep 10, 2014, 10:21 a.m. EDT
Thanks for the reply Pieter.
Not sure if it is working though. I defined a step function in global definitions. Then I added a heat source boundary condition(non isothermal flow). there in the Heat source section I put in 'step1(r)*2500' in the 'Total Power' space.(In my case, there is heat generation at every point inside the combustion chamber.I need to specify a step function because my domain is continuous )
When I run this there is an error message saying 'Strings are only allowed in function arguments'.
Am I missing something here?
Thanks in advance.
Thanks for the reply Pieter. Not sure if it is working though. I defined a step function in global definitions. Then I added a heat source boundary condition(non isothermal flow). there in the Heat source section I put in 'step1(r)*2500' in the 'Total Power' space.(In my case, there is heat generation at every point inside the combustion chamber.I need to specify a step function because my domain is continuous ) When I run this there is an error message saying 'Strings are only allowed in function arguments'. Am I missing something here? Thanks in advance.
Anoop Asranna
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Posted: 1 decade ago Sep 10, 2014, 10:42 a.m. EDT
I have attached the file .Might be helpful.
I have attached the file .Might be helpful.

Attachments:

Anoop Asranna
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Posted: 1 decade ago Sep 10, 2014, 10:42 a.m. EDT
I have attached the file .Might be helpful.
I have attached the file .Might be helpful.
Josh Thomas Certified Consultant
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Posted: 1 decade ago Sep 10, 2014, 3:54 p.m. EDT
Anoop-

You must call your step function in the Total power edit field as follows:

step1(r[1/m])*2500[W]

This will use the r-coordinate independent variable as the input to your step function. The [1/m] makes the call to the step function unitless. This is not crucial but it avoids the text from turning orange indicating a units inconsistency.

--
Best regards,
Josh Thomas
AltaSim Technologies
Anoop- You must call your step function in the Total power edit field as follows: step1(r[1/m])*2500[W] This will use the r-coordinate independent variable as the input to your step function. The [1/m] makes the call to the step function unitless. This is not crucial but it avoids the text from turning orange indicating a units inconsistency. -- Best regards, Josh Thomas AltaSim Technologies

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