The High Mach Number Reacting Turbulent Flow, Spalart-Allmaras () multiphysics interface is used to simulate the transport and reaction of species in turbulent gas flows where the velocity magnitude is comparable to the speed of sound in the gas, that is, flows in the transonic and supersonic range.

It combines the High Mach Number Flow, Spalart-Allmaras interface, the Transport of Concentrated Species interface and, optionally, the Chemistry interface. The High Mach Number Reacting Flow multiphysics coupling, which is added automatically, couples fluid flow and mass transport with reactions. The multiphysics coupling takes into account the heat of reaction, enthalpy diffusion, and contributing mass fluxes, and applies turbulence modeling for the mass transport. In addition, the temperature dependency of the chemical properties and reactions are accounted for.

The Chemistry interface defines thermodynamic properties and transport properties of the fluid. Provided that properties of each species have been defined, composition dependent mixture properties such as the heat capacity, the density, and the heat conduction are defined. The Chemistry interface also defines reaction rates for species involved in the chemical reactions added to the system.

The Transport of Concentrated Species interface solves for an arbitrary number of mass fractions. The species equations include transport by convection, diffusion and, optionally, migration in an electric field. Mass transfer close to walls is modeled using wall functions. A Transport Properties feature is active by default on the entire interface selection

The equations solved by the High Mach Number Flow, Spalart-Allmaras interface are the Navier-Stokes equations for conservation of momentum, the continuity equation for conservation of mass and the equation for the conservation of energy. Turbulence effects are modeled using the Spalart-Allmaras one-equation model. The Spalart-Allmaras model is a so-called low-Reynolds number model, which means that it can resolve the flow all the way down to the wall. The Spalart-Allmaras model depends on the distance to the closest wall. The physics interface therefore includes a wall distance equation. A Fluid Properties feature is active by default on the entire interface selection.