Learning Forum

[Bart]

Hello,

In our transient calculation, the value of last continuity residual in every time step is greated than 1. I am not sure if this calculation is accurate. The models applied are VOF model, LES model, dynamic mesh and compressible flow (ideal gas). I hope someone can tell me the accuracy of this calculation. If this simualtion lacks accuracy, how can I solve it?

Otherwise, how to choose the time discrete scheme, first-order or second-order? When I choose second-order, the solution is instability. While I choose first-order, I am afraid of the precision of LES.

Best regards!

[Rahul Kumar]

Hello,
Just looking at the residuals, especially for a transient flow, it would be difficult to guess the convergence. You could setup a monitor of a particular variable and check to see if the behavior is appropriate. Also, check the flux balance, the error should be less than 3% (less than 1% would be ideal).

[Bart]

Hello Thanks for your reply!
You mean, if the mass flux differnece between inlet and outlet is very small (less than 3%) at the last iteration of each time step, I can ignore the fact than the continuity residual is greater than 1 at the same case´╝ƒ Whether the residual is greater or less than 1 does not affect the results.
Kind regards!

[Rahul Kumar]

Yes, this means the simulation is respecting the conservation principle (the small error is related to numerical).

[Milne Ando]

 

hello sir,

could you teach me how to monitor the mass flow rate difference between inlet and outflow? In Solution>Report Definitions, right click and it’ll pop up a window; I wonder how to set up correctly.

Looking forward to your reply. Thank you.

 

[Bart]

Thank you for your help!