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 3d
turbulent flow with Re_tau = 180.
I mapped the result from a 2nd order mesh (Originally 0.23 million
cells 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 with
2nd order accerlater. The simulation ended at t = 40.95s. Tolerance is
quite low (attached)
In case 2, due to the GPU memory size limit, I couldnt use bdf2 or
higher solver or the multip accerlerator. Instead, backward-euler and
rk4 are applied.
For case 1, tol finally reached nearly 2e-3. Near wall region matches
with paper results, while centerline velocity is a bit of higher.
For case 2, I havent done any post processing yet. However, although
the tol is extremely high, the visualized result seems to be
reasonable. So, I am confusing the plausible tol threshold.
Best regards,
Will
--
You received this message because you are subscribed to the Google
Groups "PyFR Mailing List" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/pyfrmailinglist.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups "PyFR
Mailing List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send an email to [email protected].
Visit this group at https://groups.google.com/group/pyfrmailinglist.
For more options, visit https://groups.google.com/d/optout.
