Abstract
A simple and adaptable closure algorithm for the edge nodes of a lattice Boltzmann fluid simulation space is presented. Its rules are designed to be correct at every instant, to maintain local mass and to produce a specified fluid velocity and, crucially, the correct strain rate tensor at the resulting fluid boundary. Further, our algorithm models the fluid on boundary nodes to the same accuracy as on the bulk nodes and in a demonstrably equivalent manner, requiring only a specified boundary velocity, the fluid boundary pressure emerging. Illustrative results for steady and time-dependent flows, together with outline generalizations, are presented.