numerical ... algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. ... The fundamental basis of almost all CFD problems are the Navier Stokes equations, which define any single-phase fluid flow. These equations can be simplified by removing terms describing viscosity to yield the Euler equations. Further simplification, by removing terms describing vorticity yields the full potential equations. Finally, these equations can be linearized to yield the linearized potential equations. ... In all of these approaches the same basic procedure is followed. * During preprocessing o The geometry (physical bounds) of the problem is defined. o The volume occupied by the fluid is divided into discrete cells (the mesh). The mesh may be uniform or non uniform. o The physical modeling is defined for example, the equations of motions + enthalpy + radiation + species conservation o Boundary conditions are defined. This involves specifying the fluid behaviour and properties at the boundaries of the problem. For transient problems, the initial conditions are also defined. * The simulation is started and the equations are solved iteratively as a steady-state or transient. * Finally a postprocessor is used for the analysis and visualization of the resulting solution. source: http://en.wikipedia.org/wiki/Computational_fluid_dynamics