The software is based upon relationships known as the Navier-Stokes equation: highly complex, non-linear differential equations that represent the movement of fluid or gas through three-dimensional space. Although the Navier-Stokes equation is more than 100 years old, the technique did not become useful until the late 1960s when powerful computers made the application practical.
The CFD method works by dicing up a problem into imaginary cubes of fluid or gas, applying the Navier-Stokes equations to each of the cubes, balancing the mass, momentum, and energy between them, and then reassembling the collective behavior of all the cubes back into the original problem. In any given project, the number of imaginary cubes, or cells, is routinely between 50,000 to 200,000, but it often extends up to 600,000 to 800,000 cells. Each cell usually has seven degrees of freedom (DOF) associated with its behavior. The DOFs are typically pressure, temperature, velocities in three dimensions, and two turbulence terms. The cells can also have additional terms such as secondary species concentrations, or kinetic reaction equations.