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Re: [ESPResSo-users] Espresso/Espresso++ and multiphase fluids


From: Ulf Schiller
Subject: Re: [ESPResSo-users] Espresso/Espresso++ and multiphase fluids
Date: Thu, 13 Feb 2014 18:18:05 +0100
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On 02/13/2014 06:07 PM, Axel Arnold wrote:
Hi Markus,

finally also something regarding your question about multiphase fluids :-).

First note that the Shan-Chen was developed for simulating embedded
particles, not so much plain fluids. For the ltatter, one often needs
larger grids, and wir currently limited to one GPU and something like
150^3 lattice nodes on 4GB GPUs. Also, walls for Shan-Chen probably
should have different wetting properties for the different liquids, not
just our current bounce-back walls. Marcello and Mauro, who actually
wrote the code, are currently thinking about how and what to do.

Hi!

With respect to multiphase fluids, my personal opinion is that the Shan-Chen model is a mixed blessing. I dare to say that the first and foremost reason for its popularity is simply that it is simple. However, there are a number of limitations: the interaction parameter connects the equation of state and the surface tension, so they cannot be separated. Moreover, the Maxwell reconstruction fails, i.e., the model is thermodynamically inconsistent. There is a considerable body of publications addressing these shortcomings in one way or the other, and there are alternative multiphase models out there, too. The bottom line is that you will have to find out whether the Shan-Chen algorithm is suited for your application.

Regarding flow-focusing, I think you would want to get at least the hydrodynamic quadrupoles right (which may be tricky with Shan-Chen because it generates spurious currents that have a quadrupolar structure as well). Since the quadrupoles depend on the shape of droplets, the first thing to check might be the shape and Laplace pressure of droplets.

Best,
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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