Application uncertainties result from insufficient knowledge to carry out the simulation. This is in most cases a lack of information on the boundary conditions or of the details of the geometry. A typical example is the lack of detailed information at the inlet. A complete set of inlet boundary conditions is composed of inflow profiles for all transported variables (momentum, energy, turbulence intensity, turbulence length scale, volume fractions, and so on). This information can be supplied from experiments or from a CFD simulation of the upstream flow. In most industrial applications, this information is not known and bulk values are given instead. In some cases, the detailed information can be obtained from a separate CFD simulation (for instance a fully developed pipe inlet flow). In other cases, the boundaries can be moved far enough away from the area of interest to minimize the influence of the required assumptions for the complete specification of the boundary conditions.

Typical application uncertainties are: