There are three versions of the same predefined multiphysics interface (all with the name hmnf) that combine the heat equation with either the laminar or turbulent flow equations. The advantage of using the multiphysics interfaces—compared to adding the individual physics interfaces separately—is that a set of two-way couplings has been predefined. In particular, the physics interfaces use the same definition of the density, which can therefore be a function of both pressure and temperature. Solving this coupled system of equations usually requires numerical stabilization, which the predefined multiphysics interface also sets up.

These physics interfaces vary only by one or two default settings (see Table 5-1) or selections from check boxes or lists under the Physical Model and Turbulence sections for the physics interface.