We show that an optical pulse inherently computes three-dimensional classical fluid dynamics. Taking optical diffraction, dispersion and nonlinearity into account, one can define the metaphoric fluid density, velocity and vorticity in the optical pulse. We propose the use of the group-velocity-delayed time to represent the third dimension of the fluid, and the "split-step" method to combine optical devices as a configurable system that simulates fluid flow. Optical systems, with the inherent speed, parallelism and configurability, may one day be utilized to assist the study of fluid dynamics.