Time step independence in Transient simulation with RPI Wall boiling

marcusaurelius · October 25, 2023, 08:35

I am trying to simulate subcooled flow boiling in horizontal channel with Non-equilibrium RPI wall boiling model. It is transient simulation with Implicit scheme. Steady state simulation are not giving the true results so that scenario is already discarded. I have already performed grid independency and now trying to do time step converging/independence for transient simulation. Started with time step of 5E-02 and reduced upto 1E-05. But, the results keep changing every time. The results have shown to match when time step is around 5E-03. With smaller time step, The results keep changing significantly.

y+ is around 30. I am using ANSYS Fluent

So, please help me how time step independence can be achieved?

The models and schemes are listed in picture attached.

PierreLCV · January 21, 2024, 11:39

Dear MarcusAurelius,
Do you have some figures to introduce ? Is it changing a lot when decreasing your time step ?

Best regards,
Pierre

marcusaurelius · January 22, 2024, 07:22

I have found out the reason for that. Selecting interfacial area model "ia-symmetric" instead of "ia-particle" solved the problem of Time step convergence.

But, the results are now way different than expected. The wall temperature is increasing by 2-3 times than actual.

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January 21, 2024, 11:39		#2
PierreLCV Member Pierre LECHEVALIER Join Date: Mar 2023 Posts: 31 Rep Power: 3	Dear MarcusAurelius, Do you have some figures to introduce ? Is it changing a lot when decreasing your time step ? Best regards, Pierre

January 22, 2024, 07:22		#3
marcusaurelius New Member marcus aurelius Join Date: Sep 2023 Posts: 18 Rep Power: 3	I have found out the reason for that. Selecting interfacial area model "ia-symmetric" instead of "ia-particle" solved the problem of Time step convergence. But, the results are now way different than expected. The wall temperature is increasing by 2-3 times than actual.