The Coupled Energy model is an extension of the Coupled Flow model. Together they solve the conservation equations for mass, momentum and energy simultaneously using a time- (or pseudo-time-) marching approach. This formulation is particularly robust for solving compressible flows and flows with dominant source terms, such as buoyancy.
Furthermore, due to the preconditioned form of the governing equations used by the Coupled Flow and Coupled Energy models, convergence rate is effectively independent of Mach number, ranging from incompressible through to supersonic regimes.