# slip boundary

Hi, I am simulating a 2-D pressure driven problem which is similar as poiseuille flow in the microchannel, the boundaries condition in the upper and lower are slip boundaries. I try to modify from bounceback to specular boundary condition which is used to simulate slip velocity on the plate, is it possible to make it by modify the swapAndStreamCell() and swapAndStream2D() functions in lbHelpers2D.h , thanks!

Hello,

if I were you I would not modify the swapAndStream method. I would rather write a new class based the BounceBack class in dynamics.h. You have an example of the use of that class in the cylinder2d.cpp.

Hi Malaspin

Thanks for helping the beginner!

I don’t know if there is difference of the calculation steps (in bouceback class)between bounceback and specular boundary conditions .

What do you mean exactly by that? The bounce back is replacing the standard collision step. The dynamics of your slip cells will be specular reflection.

Thanks for you patience! It helps a lot !
I rewrite the collide function in dynamics.hh but still couldn’t catch the slip velocity.

void BounceBack<T,Lattice>::collide (
Cell<T,Lattice>& cell,
LatticeStatistics& statistics )
{
for (int iPop=1; iPop <= Lattice::q/2; ++iPop) {

``````    if ( iPop==1)   std::swap(cell[iPop], cell[iPop+Lattice<T>::q/2]);
else                 std::swap(cell[iPop], cell[10-iPop]);

}
``````

}

By the way, when the bounceback is used at upper and lower plate, why there are always thin layers (dark blue) in pressure.gif , it is like the plate is thick, do you have idea about that?

It is better to combine the bounce back and specular reflection to capture the slip velocity at the wall. You can refer to: PRE, 2005, 72: 056301.

Hello tony99,

Which model do u use in simulating microflow? He’s thermal model or Guo Zhaoli’s TD2G9? I am working at this, too.
Maybe we can discuss further.

Best wishes,
Edward

Hello Edward,

As a beginner I try to simulate adiabatic liquid in microchannle now using the model here, I am glad to discuss with you.

Hello,