1. A computer program product tangibly embodied in a computer readable medium, the computer program product including instructions that, when executed, simulate fluid flow, the computer program product configured to cause a computer to: store, in a computer-accessible memory, parameters used by the computer to simulate fluid flow in a simulation space comprised of voxels according to a model, the parameters comprising a plurality of entries that correspond to elements having particular momentum states of possible momentum states at a voxel, and the voxels each corresponding, to a site within the simulation space; model interactions between elements of different momentum states according to the model; model movement of elements to new voxels according to the model; repeat the modeling of the interactions and the movement to produce a simulation result that describes fluid flow within the simulation space; and output the simulation result, wherein the model simulates a high-Knudsen number flow that has a Knudsen number greater than 0.1.