Re: [ESPResSo-users] Simulation of fluid using LB-method

[Wink, Markus]

Hi everybody,

finally, I got the right maximum velocity (see attached file). The boundary 
setting of Stefan resulted in the right fluid behavior. But when reading the 
answer of him, a new question arose:

What is the matter with the skin depth. What for do we need it in a simple 
poiseuille-flow simulation? In the user guide it is not well explained. Can 
someone tell me what it is and probably suggest some literature to me? Thanks a 
lot.

Greetings

Markus Wink
________________________________________
Von: address@hidden address@hidden" im Auftrag von "Stefan Kesselheim 
address@hidden
Gesendet: Donnerstag, 30. Januar 2014 14:57
An: address@hidden List
Betreff: Re: [ESPResSo-users] Simulation of fluid using LB-method

Hi everybody,
please forgive me, but is it clear that the solution is converged? Markus, have 
you tried running for twice (or half) as many steps, and checked that you get 
exactly the same results?
Because near the boundary the curvature looks perfect and closer to the center 
I'm not sure.

Let me make one thing clear. With our staggered grid the position of the node 
(m,n,o) is at m+0.5, n+0.5, o+0.5. This means if you lbboundary is located at 
z=1, it means there is a layer of wall nodes at x=*, y=*, z=0.5. For not too 
high viscosities (should be in the He formula as well) no measurable slip 
should appear and the hydrodynamic boundary should be located mid-grid, thus at 
z=1.
If you place a boundary at - say - 0.8, the hydrodynamic boundary of course is 
still at 1.

I'm not sure, Markus, if you put these parameters correctly into you 
theoretical curve. We introduced the staggered grid some time after Georg's 
bachelor thesis to allow for using a nonzero skin with LB.

Cheers
Stefan

On Jan 30, 2014, at 2:47 PM, Ulf Schiller <address@hidden> wrote:

> On 01/30/2014 02:33 PM, Georg Rempfer wrote:
>> Hey all,
>>
>> I remember that we fixed the issue with the missing 0.5*h*F some years
>> ago. For a flat bounce-back wall aligned with the lattice axis, the
>> actual hydrodynamic no-slip wall is positioned in the middle between the
>> last fluid node and the first wall node.
>
> There is still a viscosity dependent slip velocity, cf. Eq. (20) in [He et 
> al. (1997), J. Stat. Phys. 87, 115].
>
> Cheers,
> Ulf
>
> --
> Dr. Ulf D. Schiller                        Building 04.16, Room 3006
> Institute of Complex Systems (ICS-2)       Phone:   +49 2461 61-6144
> Forschungszentrum Jülich, Germany          Fax:     +49 2461 61-3180
>

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