LUDWIG: A parallel Lattice-Boltzmann code for complex fluids

This paper describes Ludwig, a versatile code for the simulation of Lattice -Boltzmann (LB) models in 3D on cubic lattices. In fact, Ludwig is not a si ngle code, but a set of codes that share certain common routines, such as I /O and communications. If Ludwig is used as intended, a variety of complex fluid models with different equilibrium free energies are simple to code, s o that the user may concentrate on the physics of the problem, rather than on parallel computing issues. Thus far, Ludwig's main application has been to symmetric binary fluid mixtures. We first explain the philosophy and str ucture of Ludwig which is argued to be a very effective way of developing l arge codes for academic consortia. Next we elaborate on some parallel imple mentation issues such as parallel I/O, and the use of MPI to achieve full p ortability and good efficiency on both MPP and SMP systems. Finally, we des cribe how to implement generic solid boundaries, and look in detail at the particular case of a symmetric binary fluid mixture near a solid wall. We p resent a novel scheme for the thermodynamically consistent simulation of we tting phenomena, in the presence of static and moving solid boundaries, and check its performance. (C) 2001 Elsevier Science B.V. All rights reserved.