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high calculation time while obtaining RTD during two phase flow

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Old   February 9, 2022, 07:50
Default high calculation time while obtaining RTD during two phase flow
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Abhinav Maurya
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Unable to increase the time step size greater than 0.002s. Any greater time step leads to floating point exception error and once this error is obtained, irrespective of how smaller the time step size is kept, the error persists.

Steps and method being followed:
I. (Before tracer injection)

1. Setup: realizable K-e, standard wall functions; Multiphase - VOF; Species transport: OFF

2. Side Inlet: Air (Vol. frac 0); Top Inlet: Water (Vol. frac 1)

Ran the simulation in steady-state, obtained converged solution post 20000 iterations.



II. (During tracer injection) - Switched to Transient simulation

1. Setup: realizable K-e, standard wall functions; Multiphase - VOF; Species transport: ON

2. Side Inlet: Air (Vol. frac 0); Top Inlet: Water (Vol. frac 1 but tracer mass fraction = 1)

3. In the solution --> Controls --> Equation, Flow: Off, Volume Fraction: On, Turbulence: On, Tracer: On

Ran the simulation in the transient state, and ran the calculation for 0.16s with a time step size of 0.001.



III. (Post Tracer Injection)

1. Setup: realizable K-e, standard wall functions; Multiphase - VOF; Species transport: ON

2. Side Inlet: Air (Vol. frac 0); Top Inlet: Water (Vol. frac 1 but tracer mass fraction = 0)

3. In the solution --> Controls --> Equation, Flow: On, Volume Fraction: On, Turbulence: On, Tracer: Off

Started the simulation in the transient state with a time step size of 0.0001.

With the time step size of 0.0001s, solutions are converging for each time step and also up to the time step size of 0.002s.

However, further increasing the time step leads to the floating-point exception error and once this error is obtained, irrespective of how small the time-step size is, the error persists.

Simulation has to be run for 800s, so for the current time-step size calculation time is extremely high.

Please Help asap!

Last edited by Abhinavmaurya; February 19, 2022 at 11:16.
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calculation time, rtd, tundish

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