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Link between flow time and "experimental" time

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Old   July 17, 2022, 23:35
Post Link between flow time and "experimental" time
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Elliott
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Hello everyone.

I am currently carrying out a project for an internship where I have to simulate the flow of a gas through a system (close to a 6-meter long tube). I need to get the time it took for the gas to reach the outlet. I run my simulations in transient and my question is: how are linked the flow-time and the "real" time in Ansys Fluent (if there is any kind of connection)? The geometry I made is in scale of the real system in the laboratory. I thought maybe if I set Time step size at 1s and max iteration/time step at 1 it would give me the "real" time but I'm not sure about that.

Hope I was clear enough and you will be able to help me out, thank you!
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Old   July 18, 2022, 00:47
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Alexander
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flow time, which shows in fluent is "real time" in case you are using SI for all units in your case

to check flow time you may use following command, copy-paste it in console of fluent and press enter
Code:
(rpgetvar 'flow-time)
10 time steps with 1 second time step size gives you 10 seconds of "real time" as well as 100 time steps with 0.1 second time step size
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Old   July 31, 2022, 23:04
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Hello AlexanderZ, thank you for your reply.

Ok I understand what you told me. But actually I still have a problem with that, let me explain.

Through experimentation, I measured 3s for the gas to reach the end of the pipe.
When I set up Fluent Run Calculation Parameters as following:
  • Number of time steps: 4000
  • Time step size: 0.01s
  • Max iterations/Time step: 5
it takes 7.3s for the gas to reach the end of the pipe.

When I set up as following:
  • Number of time steps: 4000
  • Time step size: 0.01s
  • Max iterations/Time step: 10
then it takes 5.6s for the gas to reach the end of the pipe.

I tried to "calibrate" Fluent by changing the time step size and the max iteration/time step, but no can do, I cannot reach 3s. I have tried to find a function for changing these parameters but it is not satisfying.

I am running out of ideas, do you think I should keep trying searching or is there a way to understand how the parameters really impact the simulation?

Thank you for your time!
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