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Evaluating expression at a specific location in CFX Pre

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Old   August 17, 2017, 08:08
Default Evaluating expression at a specific location in CFX Pre
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Brian
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I am running a large transient simulation with a time-dependent, spatially varying source term in CFX. In order to verify that this source term is doing what I actually expect it to while the solution is in progress, I would like to set up a monitor to evaluate the source term expression (at a specific point) so that it is plotted in the Solver Manager/output to the monitors file. Could anyone help me with how to set this up please?

So far, the things I have tried that do not work are:
  • Output Control>Monitor>Monitor Points>Cartesian Coordinates does not work as it is an expression that I want to evaluate, not a variable
  • Output Control>Monitor>Monitor Points>Expression does not work as the expression varies at different locations
  • Creating the following expression (SparkLocation is a monitor point created at the correct location) does not work as the CFX solver will only accept a variable and not an expression as the argument for probe
    Code:
    probe(expression)@SparkLocation

I'm sure that there must be a very simple way to do this, but it still evades me despite trawling through the manuals and extensive use of Google. Any suggestions would be very much appreciated!

Last edited by gotang; August 17, 2017 at 10:13. Reason: Clarification in the question.
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Old   August 17, 2017, 10:56
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That is a documented limitation with a known workaround.

Create an Additional Variable/Option = Algebraic Expression, say MyProbeExpression.

Then, probe(MyProbeExpression)@SparkLocation..
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Old   August 17, 2017, 11:23
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Thank you, I think that is exactly what I am looking for. To ask a stupid question though: How do I assign a variable to the expression? I have used "Insert Additional Variable", set "Variable Type" to "Unspecified", but cannot for the life of me figure out how to specify to CFX that it should be defined by the algebraic expression. The closest to instructions that I can find in the documentation is in the CFX Solver Modelling Guide:

Quote:
For example, you could create an Additional Variable for a pressure coefficient by creating an unspecified Additional Variable with dimensionless units and assigning it to an expression
But I cannot figure out how to assign the Additional Variable to an expression. Apologies for the dumb question - I am still converting to CFX from Fluent, and I haven't quite got my head around how cases are set up yet!
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Old   August 17, 2017, 11:29
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Go to the domain where the Spark Location is, and activate the Additional Variable.

Additional variables require two steps: definition, and activation.
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Old   August 17, 2017, 11:33
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Thank you! That fixes my issue entirely. Much obliged.
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