[ramirofreile]

Hello Julius,

In page 178 of the Kruger book mentions the following:

Despite what their names might suggest, both the fullway and halfway
approaches assume that the boundary is located approximately midway
between solid and boundary nodes, not on the solid nodes themselves.

Then in page 177 there are two figures that show the difference between half way and fullway bounce back. For the halfway bb, it takes deltat to return to the fluid node at the boundary, and for the fullway it takes 2*deltat. But the wall boundary is at a distance deltax/2 from the closest fluid node to the wall. The Zou He velocity boundary conditions assume that the node is at the wall.

So I still do not know how the AD lattice and NS lattice cope with this.
Thank you,

Ramiro

[ramirofreile]

I appreciate your time and help. Thank you!

[ramirofreile]

Mathias,

In a sense, I could solve the issue.

I tried modifying the dynamics I was using for the case above (the one which failed to maintain the 1.5 temperature value). The dynamics of the case currently not working are ForcedPSMBGKDynamics+TotalEnthalpyAdvectionDiffusionTRTdynamics with TotalEnthalpyPhaseChangeCouplingGenerator3D.
What I noticed from the Stefan Melting and Gallium Melting example is that with the defineRho function, the temperature value is set, and not the enthalpy (which is the “rho” for this model). In the past, when I tried to impose the hot enthalpy at the inlet, the temperature values didn’t make sense. That is the reason why I am directly defining the temperature with a 1.5 value currently.

Now I tried with the combination of ForcedBGKDynamics+AdvectionDiffusionBGKdynamics with NavierStokesAdvectionDiffusionCouplingGenerator3D. The temperature value 1.5 at the inlet is maintained throughout the simulation.

From this I am suspecting that there is an issue associated with the previous two dynamics, used for solidification and melting.

• This reply was modified 3 years, 1 month ago by ramirofreile.

[ramirofreile]

I am using a hot temperature of 1.5 and a cold temperature of 0.5, such that the physical temperature is equivalent to the lattice temperature.

Something curious is that when I change the fluid relaxation time from 0.51 to 0.55, now the temperature decreases up to 1.2 instead of 1.4. After this I suspected something could be wrong with the bounce back, so I set the cylinder wall in all of its length as a cold wall. The issue is still there.

I will keep trying to explore where the issue is. I will let you know what I can find.
Thank you very much for your time and help.

[ramirofreile]

I looked at “thermalPorousPlate3d” example. The only difference I can find with this example is the fact that at the corners of the inlet I am imposing a bounce back condition. This will get clearer with the following geometry and bc’s figure.

https://ibb.co/Gs1PcXJ (Geometry and BC’s of the problem)

As you have requested, in the next 2 figures I show the temperature and x-velocity of a slice section of the pipe. As seen in the temperature contour figure, the maximum temperature is around 1.36, while the Dirichlet value imposed is 1.5.

https://ibb.co/rxDRzMz (Temperature Contour)

https://ibb.co/t4WbpNh (X-Velocity contour)

Thank you,

Ramiro

• This reply was modified 3 years, 1 month ago by ramirofreile.

[ramirofreile]

Dear Mathias,

At the inlet I define bulkdynamics, use setAdvectionDiffusionTemperatureBoundary and finally ADlattice.defineRho(superGeometry,inlet,T_hot); where T_hot is an AnalyticalConst3D. For the NS lattice, I set the velocity using setInterpolatedVelocityBoundary.

Following your suggestion of resetting the temperature, I added the following to the function setBoundaryValues:

void setBoundaryValues( ThermalUnitConverter<T, NSDESCRIPTOR, TDESCRIPTOR> const& converter,
                        SuperLattice3D<T, NSDESCRIPTOR>& NSlattice,
                        SuperLattice3D<T, TDESCRIPTOR>& ADlattice,
                        int iT, SuperGeometry3D<T>& superGeometry)
{

  int iTmaxStart = converter.getLatticeTime( maxPhysT*0.2 );
  int iTupdate = 100;

  if ( iT%iTupdate == 0 && iT<= iTmaxStart ) {
    AnalyticalConst3D<T,T> T_hot(Thot);
    ADlattice.defineRho(superGeometry, 3 , T_hot);
  }

}

With this routine I haven’t noticed any changes, I still see a decrease in temperature at the inlet from timestep 2 onwards. However, I may not be doing the reset appropriately.

Thank you for your time,

Ramiro

[ramirofreile]

Dear Max,

Thank you for your answer!

1) I just noticed that the setAdvectionDiffusionConvectionBoundary is only coded for 3D (correct me if I am wrong).

2) I am just wondering if you could help me understand what is the difference between the bounce back and the setAdvectionDiffusionConvectionBoundary. I am guessing that this comes from the fact that in the bounce back the equilibrium functions are set with a zero velocity. Could you guide me towards the answer maybe with a reference of the equations?

Thank you again for your time.

Ramiro

[Author]

Posts