## A Multispeed Model for Lattice Gas Hydrodynamics

**Gerald Fahner***Physics Department, Bergische Universitat, Gesamthochschule Wuppertal,**Gauss-Strasse 20, Postfach 100127, 5600 Wuppertal, Germany*

#### Abstract

A discrete model for two-dimensional hydrodynamics is presented. Compared to previous cellular-automata constructions, it has a richer spectrum of states and is thus closer to molecular dynamics. First, the model is tested regarding equilibrium isotropy. Next, thermal effects in equilibrium are discussed. Then the lattice gas is used to model the two-dimensional incompressible Navier-Stokes equation by performing a Poiseuille flow experiment. The expected effect of the system size on viscosity is found. For the shear flow we observe a breakdown of isotropy---much stronger than that of the equilibrium distribution---appearing as a direction-dependent viscosity. The viscosity is computed from the nonequilibrium distributions, and agreement with the simulation results is found.