Step 2: Boundary conditions are specified on each edge of the computational domain (2-D flows) or on each face of the domain (3-D flows)

Step 3: The type of fluid (water, air, gasoline, etc.) is specified, along with fluid properties (temperature, density, viscosity, etc.

Step 4: Numerical parameters and solution algorithms are selected.

Step 5: Starting values for all flow field variables are specified for each cell. These are initial conditions, which may or may not be correct, but are necessary as a starting point, so that the iteration process may proceed. For proper unsteady-flow calculations, the initial conditions must be correct.

Step 6: Beginning with the initial guesses, discretized forms of the continuity equation and Navier–Stokes equation are solved iteratively, usually at the center of each cell. If one were to put all the terms of Navier–Stokes equation on one side of the equation, the solution would be “exact” when the sum of these terms, defined as the residual, is zero for every cell in the domain. In a CFD solution, however, the sum is never identically zero, but (hopefully) decreases with progressive iterations. A residual can be thought of as a measure of how much the solution to a given transport equation deviates from exact, and you monitor the average residual associated with each transport equation to help determine when the solution has converged. Sometimes hundreds or even thousands of iterations are required to converge on a final solution, and the residuals may decrease by several orders of magnitude.