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Old   September 27, 2011, 11:42
Question Change BCs during simulation
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I need to change the type of BC I am using halfway through my simulation. I want to know the best way to do this.

I have considered using multiple configurations but I have some questions about that:
When I specify the total time under analysis type for the configuration after I have changed my BC's is it the total time of both configurations or it that the total time of just the second configuration?
Also when my time dependent expressions are evaluated will the variable t (time) be reset in the second configuration?

It would be nice to be able to do this without multiple configurations if possible. I specifically need to change my inlet with Cartesian velocity components specified to an outlet with Cartesian velocity components specified. I also need to change all of my outlets with specified mass flow rates (one per outlet) to inlets with specified mass flow rates.
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Old   September 27, 2011, 15:04
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Hello Tav

I have not worked to much with multiconfigurations so i cant be much help there but i know there is at least 1 good tutorial which explains how to work them, after this post i will look for it and edit it in.

I dont see why you need the multiconfiguration for what you are doing. Instead of using "Inlet" and "Outlet", simply use "Opening" BC. In the you can then change the mass and momentum option to Cartesian Velocity Components and specify you velocity there. You would then just need to define a velocity function that represents the change in direction you desire.
I'm sure something like that can be done for the Outlets to change them to Openings but i'm not 100% that you can specify mass flow rates with openings, something you would have to look up/try.

Thank You,


Edit: there is definitely a multiconfiguration tutorial in the ansys customer service portal if you have access, if not google it and i'm sure you can find a link.
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Old   September 27, 2011, 16:00
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Thanks for the response,

I looked at the multiple configuration tutorial. It is similar to the circular vent tutorial. It starts with a steady state analysis then uses the results of that to start a transient analysis. So those tutorials do not really answer any of my questions.

I do not want to use an opening because it is not recommended for LES which I am also using (I also checked mass flow rate is not a way to specify a BC for an opening). I could do this without multiple configurations if CFX will allow me to have all inlets with some having negative mass flow rates. Will CFX allow me to do that? I am also unsure if that will affect the numerics (i.e. I am not sure if an inlet is treated numerically different from an outlet if a mass flow rate is specified).
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