ABSTRACT
The governing equations of a mathematical model describe how the values of the unknown variables (i.e., the dependent variables) change when one or more of the known (i.e. independent) variables change. The starting point of any numerical simulation is the governing equations of the physics of the problem to be solved. An approximate form of the Navier–Stokes equations appropriate for low Mach number applications is used in the model. The approximation involves the filtering out of acoustic waves while allowing for large variations in temperature and density. Large eddy simulation does not adopt the conventional time- or ensemble-averaging Reynolds-averaged Navier–Stokes approach with additional modeled transport equations being solved to obtain the so-called Reynolds stresses resulting from the averaging process. The default combustion model in fire dynamics simulator uses the mixture fraction which is a quantity representing the fuel and the products of combustion.
