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Do I need Convergence Monitor for Unsteady Simulations? |
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August 31, 2012, 16:57 |
Do I need Convergence Monitor for Unsteady Simulations?
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#1 |
Member
dw
Join Date: Jul 2012
Posts: 32
Rep Power: 13 |
Dear All,
I saw a few posts on this forum that those people are monitoring the residuals or what for their unsteady simulations to see it converging or not. My question is: is it necessary? What are they monitoring? How to judge it converges or not? My case is an unsteady RANS simulation around a bluff body with vortex shedding and moderate to high Re. Once my boundary condition is right, the seatdy simulation results are good. Do I still need to monitor the convergence? Thanks for the help. 1/153 dw |
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August 31, 2012, 17:29 |
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#2 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,764
Rep Power: 71 |
Quote:
In my opinion, controlling the unsteady simulation by monitoring the time derivatives can be useful. - If the case is steady (laminar or RANS) that simply controls the residual you want to achieve. - For unsteady solutions (DNS/LES/URANS) that makes sense only in statistical sense. For example controlling kinetic energy in time for a flow in equilibrium or to check if something is going wrong (a rapid increasing in the kinetic energy can be the start of a numerical instability). In your case I suppose that the monitor of the time evolution can supply the evidence of the correct fundamental frequency of the vortex shedding |
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September 2, 2012, 09:50 |
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#3 | |
Senior Member
Join Date: Aug 2011
Posts: 272
Rep Power: 15 |
Quote:
if you compute incompressible flows then I would also monitor the continuity constraint div(U)=0 to check if is satisfied.... But keep in mind too that each time you ask your program to display something on screen it delays your computation. Some people loose 1/3 of the overall computational time in writing stuffs on screen that they never check.... |
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September 2, 2012, 11:00 |
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#4 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,764
Rep Power: 71 |
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