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, state vectors for voxels, the state vectors corresponding to a model and comprising a plurality of entries that correspond to particular momentum states of possible momentum states at a voxel, and the voxels each corresponding to a site within a simulation space in which fluid flow is being simulated; perform interaction operations on the state vectors, the interaction operations modeling interactions between elements of different momentum states according to the model; perform move operations on the state vectors to reflect movement of elements to new voxels according to the model; repeat the interaction operations and the move operations 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.