Dear Will,

`Thanks for your message. We have applied the ACM solver to any internal`

`flows, so it is interesting see your progress.`

`"What is the meaning of ma = 0.2? Do you mean the max velocity/ac-zeta?`

`I think for ideal incompressible flow, ma = 0."`

`I meant the Mach number of the real life application that your are`

`trying to simulate. The pressure residual (div u), which is more stiff`

`to converge than velocity residuals, is kind of an indicator how far the`

`pseudo waves which distribute the pressure have travelled. For truly`

`incompressible flows (elliptic p, residual = 0), the information from an`

`arbitrary point would have to propagate everywhere in the domain within`

`every physical time-step. However, since the physical problems are never`

`incompressible, but low-Mach, it may not be necessary to drive the`

`pressure residual all the way to zero as long as the information has`

`propagated over important length scales. I understand if you want to`

`reproduce an incompressible test case you want to be as incompressible`

`as possible, but for low-Mach industrial applications this is not`

`necessarily the case.`

`The residuals in your cases are still quite high and they would benefit`

`from multip and BDF2. Just to give you some tips, I tend to keep`

`constant number of iterations, set the dt/dtau ratio between 5 and 10,`

`and aim for u,v,w < 1e-4 pressure typically < 1e-3 . For example, for a`

`Taylor-Green vortex Re=1,600, the level of convergence after 3 multigrid`

`cycles`

[solver-dual-time-integrator-multip] pseudo-dt-fact = 1.7

`cycle = [(4, 1), (3, 1), (2, 1), (1, 1), (0, 2), (1, 1), (2, 1), (3, 1),`

`(4, 3)]`

is 1254,10.002000000000095,3,0.00244778059095,0.000476855091426,0.000476823492017,0.00043626471224.

`Using the same cycle and again 3 cycles per time step, the convergence`

`of turbulent Jet at Re=10,000 is`

`240000,1799.9950000010913,3,0.00204563896311,0.000209207025143,0.000196374204824,0.000183716409294.`

I used dt/dtau = ~7 in both cases.

`Please also note that it can take considerable amount of time to`

`dissipate initial transient waves. I'm expecting this phenomenon to be`

`highlighted with internal flows because the waves are trapped inside the`

`domain. I would suggest developing the flow with P=1 and restart with`

`higher P after the flow has transitioned to turbulent.`

Cheers, Niki On 12/02/18 05:01, Will wrote:

Dear Nikki,What is the meaning of ma = 0.2? Do you mean the max velocity/ac-zeta?I think for ideal incompressible flow, ma = 0.My pesudo convergence history is attached below. My case is 3dturbulent flow with Re_tau = 180.I mapped the result from a 2nd order mesh (Originally 0.23 millioncells already turbulent) case to the 1st order one (1.3 million cells)and started the simulation at 0.0s ended 1s.case 1 is 0.23 million cells 2nd order mesh (1.8 million in pyfrm) case 2 is 1.29 million cells 1st order mesh (1.29 million in pyfrm) dt = 0.0005 and pseudo dt = 0.00001 with l2 norm tolerance.Case 1 was run in backward-euler and euler psedo time stepping with2nd order accerlater. The simulation ended at t = 40.95s. Tolerance isquite low (attached)In case 2, due to the GPU memory size limit, I couldnt use bdf2 orhigher solver or the multip accerlerator. Instead, backward-euler andrk4 are applied.For case 1, tol finally reached nearly 2e-3. Near wall region matcheswith paper results, while centerline velocity is a bit of higher.For case 2, I havent done any post processing yet. However, althoughthe tol is extremely high, the visualized result seems to bereasonable. So, I am confusing the plausible tol threshold.Best regards, Will --You received this message because you are subscribed to the GoogleGroups "PyFR Mailing List" group.To unsubscribe from this group and stop receiving emails from it, sendan email to pyfrmailinglist+unsubscr...@googlegroups.com<mailto:pyfrmailinglist+unsubscr...@googlegroups.com>.To post to this group, send email to pyfrmailinglist@googlegroups.com<mailto:pyfrmailinglist@googlegroups.com>.Visit this group at https://groups.google.com/group/pyfrmailinglist. For more options, visit https://groups.google.com/d/optout.

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