Hi Will,
If you look at the pressure field early in the simulation you can
clearly see that there is a periodicity issue. The source term you
impose is perfectly fine, but it does work for the gradient between the
periodic back face and the front face.
p(x) = 0 - 4x,
p'(x)= -4
but derivative at the discontinuity reads p'(0) = [p(0) - p(8)]/dx = [0
- (-32)]/dx.
Currently, we do not have a functionality to force the constant pressure
gradient in a periodic domain. However, for this case you can add the
following line to pyfr/solvers/baseadvec/kernels/negdivconf.mako, which
adds a "pressure derivative" source term (-4.0) to the x-momentum
equation (index [1]).
% for i, ex in enumerate(srcex):
tdivtconf[${i}] = -rcpdjac*tdivtconf[${i}] + ${ex};
% endfor
+ tdivtconf[1] = tdivtconf[1] - 4.0;
</%pyfr:kernel>
I did not properly test it, but I have attached a picture what I got
after running for a minute. Please note that the pressure looks constant
if you add the source term this way, because p = du/dx + dv/dx = 0 + 0.
I also suggest using BDF2, rk4 or tvd-rk4 and multigrid.
Regards,
Niki
On 21/11/17 11:30, Will wrote:
Dear Niki,
Thanks for your advice. I have got good alignment on cavity flow now.
I am now trying to simulate pressure driven laminar 2d pipe flow with
periodic inlet/outlet BC. The velocity profile at roughly 50 seconds
is still not parabolic. Instead, the flow generates some vortex at
ReD less than 200 when ac-zeta = 20. The result is attached also the
.pyfrm and .ini.
The pressure gradient is constant 4 and nu = 0.01.
Best regards,
Will
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