Issues with the permeability example

jesantos · January 18, 2020, 6:48pm

Hi Palabos community,

I’m trying to calculate the absolute permeability on my sample following the instructions on the permeability.cpp tutorial. Everything runs well at the beginning, but the simulation never converges (I even tried to set-up my own convergence criterion).
Taking a closer look at the .vtks I noticed that there is very high velocity ‘currents’ where the outlet of the boundary condition is placed (Figure 1). I tried reducing the pressure gradient but the results look the same:

This is after 1000 iterations.

If I calculate the permeability every 250 iterations, the relative difference with the previous one is around 10% every time (I tried 1M iterations).

Any suggestions are welcome. The code (cpp) can be found here:

github.com

je-santos/MultiphasePorousMediaPalabos/blob/master/src/1-phase_LBM/permeability.cpp

/* Modified from file by Wim Degruyter */

#include "palabos3D.h"
#include "palabos3D.hh"

#include <vector>
#include <cmath>
#include <cstdlib>
#include <string>
#include <sstream>
#include <iostream>
#include <fstream>
#include <iomanip>

using namespace plb;
using namespace std;

namespace patch
{
  template < typename T > std::string to_string( const T& n )

This file has been truncated. show original

And the example is this one:

Thanks!!

orestis · January 22, 2020, 2:33pm

Hello,

thank you for the great work!

Where is the in/outlet located? Does the in/outlet intersect with the bounceback nodes?

jesantos · January 22, 2020, 3:33pm

Hi @orestis,

Thanks for your reply. I noticed that I was placing the density boundary conditions on top of my bounce back nodes, this was probably causing those ‘spurious’ currents. By leaving some blank nodes and placing the boundaries there, the problem converges.

All the best,
Javier.

scout · May 7, 2021, 4:31am

hey,I also encuontered the same problem,I always thought I need reduce the pressure gradient to solve this problem.But it misconvergence until 20000 iterations.Could you tell me how to leave blank nodes in detail? My work is the soil pore.

jesantos · May 12, 2021, 4:10am

@scout feel free to check my example:

https://github.com/je-santos/MPLBM-UT/tree/master/examples/tortuosity_carbonate

ms123 · September 21, 2021, 5:53am

Hello, can Palabos measure absolute permeability values of order 10^-3?

jesantos · October 2, 2021, 9:36pm

It all depends how you scale your LB parameters.

ms123 · April 16, 2023, 8:24am

Can you please explain, how to scale LB parameters? Also if you could explain the conversion of GradP into physical units from lattice units.