AN EVALUATION OF THE BOUNCE-BACK BOUNDARY-CONDITION FOR LATTICE BOLTZMANN SIMULATIONS

The bounce-back boundary condition for lattice Boltzmann simulations i s evaluated for flow about an infinite periodic array of cylinders. Th e solution is compared with results from a more accurate boundary cond ition formulation for the lattice Boltemann method and with finite dif ference solutions. The bounce-back boundary condition is used to simul ate boundaries of cylinders with both circular and octagonal cross-sec tions. The convergences of the velocity and total drag associated with this method are slightly sublinear with grid spacing. Error is also a function of relaxation time, increasing exponentially for large relax ation times. However, the accuracy does not exhibit a trend with Reyno lds number between 0.1 and 100. The square lattice Boltzmann grid conf orms to the octagonal cylinder but only approximates the circular cyli nder, and the resulting error associated with the octagonal cylinder i s half the error of the circular cylinder. The bounce-back boundary co ndition is shown to yield accurate lattice Boltzmann simulations with reduced computational requirements for computational grids of 170 x 17 0 or finer, a relaxation time less than 1.5 and any Reynolds number fr om 0.1 to 100. For this range of parameters the root mean square error in velocity and the relative error in drag coefficient are less than 1 per cent for the octagonal cylinder and 2 per cent for the circular cylinder. (C) 1997 by John Wiley & Sons, Ltd.