Macroscopic Lattice Boltzmann Method (MacLAB).

The birth of the lattice Boltzmann method (LBM) fulfils a dream that simple arithmetic calculations can simulate complex fluid flows without solving complicated partial differential flow equations. Its power and potential of resolving more and more challenging physical problems have been and are being demonstrated in science and engineering covering a wide range of disciplines such as physics, chemistry, biology, material science and image analysis. The method is a highly simplified model for fluid flows using a few limited fictitious particles that move one grid at a constant time interval and collide each other at a grid point on uniform lattices, which are the two routine steps for implementation of the method to simulate fluid flows. As such, a real complex particle dynamics is approximated as a regular particle model using three parameters of lattice size, particle speed and collision operator. A fundamental question is "Are the two steps integral to the method or can the three parameters be reduced to one for a minimal lattice Boltzmann method?". Here, I show that the collision step can be removed and the standard LBM can be reformulated into a simple macroscopic lattice Boltzmann method (MacLAB). This model relies on macroscopic physical variables only and is completely defined by one basic parameter of lattice size dx, bringing the LBM into a precise "Lattice" Boltzmann method. The viscous effect on flows is naturally embedded through the particle speed, making it an ideal automatic simulator for fluid flows. The findings have been demonstrated and confirmed with numerical tests including flows that are independent of and dependent on fluid viscosity, 2D and 3D cavity flows, and an unsteady Taylor-Green vortex flow. This provides an efficient and powerful model for resolving physical problems in various disciplines of science and engineering.