The Rotating Machinery, Mixture Model, Spalart-Allmaras Interface
The Rotating Machinery, Mixture Model, Spalart-Allmaras (mm) interface () is used to model high Reynolds number flow of a multiphase mixture in equipment containing one or more rotating parts. The mixture consists of a liquid with dispersed particles, bubbles, liquid droplets, or solid particles, which are assumed to always travel with terminal velocity.
The interface solves one set of Navier–Stokes equations for the momentum of the mixture. The pressure distribution is calculated from a mixture-averaged continuity equation and the velocity of the dispersed phase is described by a slip model. The dispersed particles are tracked by solving a transport equation for the volume fraction of the dispersed phase. 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.
The physics interface can also model the distribution of the number density, which in turn can be used to calculate the interfacial area, useful when simulating chemical reactions in the mixture.
There are two study types available for this physics interface. Using the Time Dependent with Initialization study type, the rotation is achieved through moving mesh functionality, also known as sliding mesh. Using 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. All study types include an initial Wall Distance Initialization step in order to compute the wall distance. See Theory for the Rotating Machinery Interfaces in the CFD Module User’s Guide.
When this physics interface is added, the following default nodes are also added in the Model Builder, under Mixture Model, Spalart-Allmaras — Mixture Properties, Wall, and Initial Values. A Moving Mesh interface with a Rotating Domain node is added automatically in the Model Builder under the Definitions node. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Mixture Model, Spalart-Allmaras to select physics features from the context menu.
The physics interface settings are the same as described for The Rotating Machinery, Mixture Model, Laminar Flow Interface, for Moving Mesh, and for The Mixture Model, Spalart–Allmaras Interface in the CFD Module User’s Guide.