CFD therefore also rests on the less secure foundation of models of turbulence, radiation, and chemical reaction. These models are embodied in sets of mathematical equations, similar in form to those for the conservation of mass and momentum, which purport to describe the most significant aspects of the phenomena in question. The turbulence models now in use derive mainly from research projects performed at Imperial College in London in the 1970s. Additions with respect to combustion have come from the University of Trondheim in Trondheim, Norway. One is known as LVEL, which is derived from L, the distance from the nearest wall, and VEL, the local velocity.
Radiation is a complex process that is expensive to compute exactly.
The validation of this method is still in progress. At this stage, we can assert that it gives exactly correct results in simple circumstances and plausible results otherwise. Chemical reaction is another expensive process to compute exactly. It is far more important to represent the turbulence properly than to refine the chemical-kinetic description. This assumption leads to several questions.