# Divergency problem by computing a steady base flow with SFD

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 May 30, 2018, 12:07 Divergency problem by computing a steady base flow with SFD #1 New Member   Siqi Yin Join Date: May 2018 Location: Stuttgart, Germany Posts: 2 Rep Power: 0 Hello, I am running a SFD-solver which is based on icoFoam. The SFD-solver (SFD: Selective Frequency Damping ) computes a steady laminar flow over a plate where a cylinder roughness is set on. The grid is very fine so I computed with very small time step (1.5e-5 s) so that the CFL-number would be never above 0.9 . For the system/fvSolution file I set up the pressure (for solving the pressure Poisson equation) as p { solver PCG; preconditioner DIC; tolerance 5e-09; relTol 0.005; } at the beginning, then I thought the tolerance could be chosen with a higher one, so I changed it to 1e-8. After some while, the CFL-number began to drop and then somehow increased over 1.0, the case exploded . Could someone tell me why the CFL-number first dropped and then increased? Can I save my case by changing the tolerance to 5e-9 again?

 May 30, 2018, 12:15 #2 New Member   Siqi Yin Join Date: May 2018 Location: Stuttgart, Germany Posts: 2 Rep Power: 0 The equation system is changed in the icoFoam to fvVectorMatrix UEqn ( fvm::ddt(U) + fvm::div(phi, U) - fvm::laplacian(nu, U) + fvm::Sp(chi, U) // added - fvc::Sp(chi, Ubar) // added ); which is the SFD method . It can compute a steady base flow field U for the perturbation computation in the transition analysis.

 January 30, 2024, 06:23 Help regarding SFD implementation #3 New Member   Orissa Join Date: Feb 2022 Posts: 15 Rep Power: 4 I want to implement Selective Frequency Damping (SFD) to icoFoam solver to get the steady state solution can you please help regarding this how can i achive this. Thanks !!

May 8, 2024, 10:06
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 Originally Posted by pratyush_6174 I want to implement Selective Frequency Damping (SFD) to icoFoam solver to get the steady state solution can you please help regarding this how can i achive this. Thanks !!
I also need to use it for combustion to get steady flames. Can you tell me how you managed to do so?

 Tags cfl number, icofoam, pressure tolerance