[Marc]

Hey Tobit,

I can recommend you either the interpolated Boundaries or the offLattice Bounadries (aka Bouzidi) for turbulent flows. Every local boundary formulation will get instable. For the outlet (pressure) boundary, we don’t have a working offLattice Boundary. (I never get anti bounce back stable for higher Reynolds numbers). So I would recommend you to use the Interpolation boundary for the outlet and the offLattice boundary for the inlet.

Best Marc

[Marc]

Hey rffan78,

i am sorry for that annoying bug. Please change in openlb/src/io/gnuplotHeatMapWriter.hh line 155:
fout << “}”;
to
fout << “}” << “\n”;

Best,
Marc

[Marc]

Hey tobit,

this is a good question! I think you are familar with the TRT papers and you know the common TRT magic parameters (lambda=0,25 or lambda=0,375). These values are proposed as universal values. They are calibrated for poiseuille flow or laminar shear flows. In the case of turbulence you have to go magnitudes lower to reach the same stability as BGK and lamda gets a function of your Reynolds number. What you have to do is a lambda recalibration for your cannonical flow type. Your derivation for Smagorinsky TRT seems to be correct, but don’t expect an advantage in comparison for Smagorinsky BGK. If you get other results or see an increased stability, please let me know. I am interested in this topic.

Best Marc

[Marc]

Dear Laurent,

a short example for your problem:
// write output as JPEG and changing properties
heatmap::plotParam<T> jpeg_Param;
jpeg_Param.minValue = 0.;
jpeg_Param.maxValue = 5.;
heatmap::write(planeReduction, iT, jpeg_Param);

For additional modification of the heatmap writer, see the venturi example in the code.

Best,
Marc

[Marc]

Dear kolotinsky,
this is an bug under mac. It will be fixed in version 1.3. Please see the following code snipple what you have to change:
— a/src/io/gnuplotHeatMapWriter.hh
+++ b/src/io/gnuplotHeatMapWriter.hh
@@ -152,7 +152,7 @@ void writeHeatMapPlotFile(detailParam<T>& param) {
fout << “} else {“;
fout << “set terminal png ” << “size ” << 1920 << “,” << 1080 << “font \”,25\”” << “\n”;
fout << “set output ‘”<< param.pngPath << “‘”<< “\n”;
– fout << “}”;
+ fout << “}” << “\n”;
fout << “set pm3d map” << “\n”;
fout << “unset key” << “\n”;
fout << “set size ratio -1” << “\n”;

Best Marc

[Marc]

Dear Laurent,

I think you are are more intereseted in the pressure gradient then the absolute pressure. It is possible to set a certain pressure level (pressure level, see the converter) if you are really interested in the absolute pressure. Try to set the inlet on 200Pa and the outlet to 0Pa should be easier for the beginning. There is also one converter function for the conversion from pressure to density that will help you. I really recommend you our annular Spring School. There we have enough time to discuss about your individual problems.

Best Marc

[Marc]

Dear Laurent,

It is possible to change the inflow pressure. You can set a second pressure boundary at the inflow. The value of the density equals 1 is mostly related to a pressure of 0 Pa. The converter of OpenLB uses the SI System for physical quantities.

Best Marc

[Marc]

Hey Eric,

bounce back have to work in your simulation. If bounce back doesn’t work, your material number configuration is maybe not correct. There is no physical reason for this kind of stripes. The reason for the uptstream vortices could be a reflection of the pressure waves from the cylinder at the inlet. You can try to increase the space between your inlet and your cylinder and to change the boundary condition to velocity bounce back at the inlet.

Best Marc

[Marc]

Hey Eric,

try to use instead of the bouzidi boundary condition the bounce back condition. Furthermore you can use a LES turbulence model SmagorinskyBGK or SmagorinskyMRT to avoid very high resolutions.

Best Marc

[Marc]

Hey Eric,

first guess: 100 is not a really fine resolution for a Reynoldys number of 4000.
I need some additional information to evaluate possible error sources:
– boundary condition at the cylinder
– used turbulence modell
– max Mach number

Best Marc

[Marc]

Hey, it looks like you have problems with your geometry setup (material number config). Why you want to use uniform velocity at the inflow (plug flow). See the cylinder3d example and use it as a starting Point.
Best Marc

[Marc]

Hey,
I don’t know your duct geometry. If you have to set a special pertubated flow at the inflow, you can’t deal with periodic boundaries. You can test the channel flow with inlet and outlet conditions, but I think it will be a hard task and you will be not able to compare any achieved statistics in the channel flow.

[Marc]

Hey,
in the channel flow you have three directions: streamwise, spanwise and lateral. The idea is to set streamwise and spanwise to periodic boundaries. In lateral direction you should set a no slip condition (bounce back or derivates). If you want to check how to set periodic boundaries see the poiseuille example. In the case of periodic boundaries we have to add a force (see also the poiseuille example).

[Marc]

Hey,
it is hard to stabilize three pressure outlets by this high Reynoldsnumber. You should use periodic boundaries in span and streamwise direction and a body force to drive the flow.
Best Marc

[Marc]

Hey Ishann,

in the case of this high Reynoldsnumber, you are not able to do LES simulation without a performant cluster system. You can check your gridspacing in a y+ calculator for duct flows with a y+ between 2-3 and you will get an idea about the mesh size for your case.

Best Marc

[Author]

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