The Fluid-Particle Interaction Interface
The Fluid-Particle Interaction () multiphysics interface combines the Particle Tracing for Fluid Flow interface coupled with the Laminar Flow interface. The Fluid Particle Interaction multiphysics coupling feature is added automatically. The Fluid Particle Interaction interface is used to model the motion of particles in a fluid. As the particles are accelerated or decelerated by the drag force exerted by the fluid, the corresponding reaction force is applied to the fluid.
When a predefined Fluid-Particle Interaction interface is added from the Fluid Flow ()>Particle Tracing branch () of the Model Wizard or Add Physics windows, Laminar Flow and Particle Tracing for Fluid Flow interfaces are added to the Model Builder. A Multiphysics Couplings node is also added, which automatically includes the multiphysics coupling feature Fluid-Particle Interaction.
On the Constituent Physics Interfaces
The equations solved by the Laminar Flow interface are the Navier-Stokes equations for conservation of momentum and the continuity equation for conservation of mass. A Fluid Model is active by default on all the interface selection. The flow interface domain selection may be edited if the model contains solid domains.
The Particle Tracing for Fluid Flow interface is used to compute the motion of particles in a background fluid. Particle motion can be driven by drag, gravity, and electric, magnetic, and acoustophoretic forces. User-defined forces can be added. It is also possible to compute the particle mass and temperature.
Settings for Physics Interfaces and Coupling Features
When physics interfaces are added using the predefined couplings specific settings are included with the physics interfaces and the coupling features. However, if physics interfaces are added one at a time, followed by the coupling features, these modified settings are not automatically included.
For example, if single Laminar Flow and Particle Tracing for Fluid Flow interfaces are added, COMSOL Multiphysics adds an empty Multiphysics Couplings node. You can choose from the available coupling features but the modified settings are not included.
 
Coupling features are available from the context menu (right-click the Multiphysics Couplings node) or from the Physics toolbar, Multiphysics menu.
Table 6-3: Modified Settings for a Fluid-Particle Interaction Interface
Physics Interface or Coupling Feature
Modified Settings (if any)
Laminar Flow
No changes.
Particle Tracing for Fluid Flow
For the Particle Tracing for Fluid Flow interface, under Particle Release and Propagation, the Particle release specification is set to Specify mass flow rate.
The Drag Force node is added to the Particle Tracing for Fluid Flow interface. The Domain Selection is the same as that of the Particle Tracing for Fluid Flow interface.
Fluid-Particle Interaction
The Domain Selection is the same as that of the participating physics interfaces.
The corresponding Laminar Flow and Particle Tracing for Fluid Flow interfaces are preselected in the Fluid-Particle Interaction section.
Physics Interfaces and Coupling Features
Use the online help in COMSOL Multiphysics to locate and search all the documentation. All these links also work directly in COMSOL Multiphysics when using the Help system.
Coupling Features
The Fluid-Particle Interaction coupling feature node is described in this section.
Physics Interface Features
Physics nodes are available from the Physics ribbon toolbar (Windows users), Physics context menu (Mac or Linux users), or right-click to access the context menu (all users).
In general, to add a node, go to the Physics toolbar, no matter what operating system you are using. Subnodes are available by clicking the parent node and selecting it from the Attributes menu.
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The available physics features for The Particle Tracing for Fluid Flow Interface are listed in the section Domain, Boundary, Pair, and Global Nodes for the Particle Tracing for Fluid Flow Interface.
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The available physics features for The Single-Phase Flow, Laminar Flow Interface are listed in the section Domain, Boundary, Pair, and Point Nodes for Single-Phase Flow in the COMSOL Multiphysics Reference Manual.