The Rotating Machinery, Reacting Flow, Turbulent Flow, SST Interface
The Turbulent Flow, SST version of the Rotating Machinery, Reacting Flow interface (), found under the Rotating Machinery, Reacting Flow > Turbulent Flow branch () when adding a physics interface, is used to simulate the turbulent flow and mixing of chemical species in equipment containing one or more rotating parts. Reactions between the participating species can also be studied.
The physics interface combines the functionality of the Rotating Machinery, Turbulent Flow, SST and the Transport of Concentrated Species interface. The Reacting Flow multiphysics coupling, which is added automatically, couples fluid flow and mass transport. The averaged velocity and pressure fields are solved together with an arbitrary number of averaged mass fractions. The momentum balance is governed by the averaged Navier–Stokes equations, and the total mass conservation is governed by the continuity equation. The fluid-flow turbulence is modeled using the SST two-equation model with realizability constraints. The SST model is a so-called low-Reynolds number model, which means that it can resolve the velocity, pressure, and mass fractions all the way down to the wall. For this reason the physics interface can be used to study mass transfer at high Schmidt numbers. The SST model depends on the distance to the closest wall, and the physics interface therefore includes a wall distance equation. For the chemical species, the governing transport equations include convection, diffusion and, optionally, migration in an electric field. Turbulent reactions are modeled using the eddy dissipation model.
There are two study types available for this physics interface. For the Time Dependent with Initialization study type the rotation is achieved by moving mesh functionality, also known as sliding mesh. For the Frozen Rotor with Initialization study type the rotating parts are kept frozen in position, and the rotation is accounted for by the inclusion of centrifugal and Coriolis forces. In both study types initialization is performed by first solving for the distance to the closest wall.
When adding the multiphysics interface, the Turbulent Flow, SST and Transport of Concentrated Species interfaces are added to the Model Builder. A Moving Mesh interface with a Rotating Domain node is added automatically in the Model Builder under the Definitions node. In addition, the Multiphysics node is added, which automatically includes the multiphysics coupling feature Reacting Flow. The following default nodes are also added in the Model Builder under Turbulent Flow, SST — Fluid Properties, Wall, and Initial Values; and under Transport of Concentrated Species — Transport Properties, No Flux, and Initial Values.
See The Rotating Machinery, Reacting Flow, Laminar Flow Interface for details.
In earlier versions of COMSOL Multiphysics (prior to version 5.4), a specific physics interface called Rotating Machinery, Reacting Flow (rmrf) was added to the Model Builder. Now, a predefined multiphysics coupling approach is used, improving the flexibility and design options for your modeling. For specific details, see The Multiphysics Branch and Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.