Similar to the Laminar Flow interface, compressibility (Mach<0.3) is selected by default. If required this can be deactivated to simplify the model. However, for the Turbulent Flow interface, non-Newtonian fluid models cannot be activated.

C R E E P I N G F L O W

The Creeping Flow Interface () models the Navier-Stokes equations without the contribution of the inertia term. This is often referred to as Stokes flow and is appropriate for use when viscous flow is dominant, such as in very small channels or microfluidic applications. Often you may want to simplify long, narrow channels by modeling them in 2D. The shallow channel approximation (2D models only) is a useful feature as it includes a drag term to approximate the added affects given by thinness of the gap between one set of boundaries in comparison to the others.

The Creeping Flow interface can also be activated by selecting a check box on the Laminar Flow interface. This interface can also model non-Newtonian fluids, including the Power Law and Carreau models, although not turbulence.

R O T A T I N G M A C H I N E R Y

The Single-Phase Flow, Rotating Machinery Interfaces () are used for the modeling of flow where one or more of the boundaries rotates in a constant and periodic fashion. This is used for mixers and propellers. A simplification to the equations is possible by assuming and activating swirl flow (for 2D axisymmetric models), which assumes that velocity in the azimuthal direction (that is, the direction of the rotating flow) is constant.

Unlike the previous physics interfaces under the Single-Phase Flow branch, the Rotating Machinery, Fluid Flow interface cannot be activated directly from the Laminar Flow or one of the other interfaces. On the other hand, it similarly supports compressibility and noncompressibility, non-Newtonian fluids and the power law and Carreau models, and even turbulence, although only the k- model. This interface also supports creeping flow, although the shallow channel approximation is redundant.

Coupling to Other Physics Interfaces

Often, you may want to simulate applications that couple fluid-flow to another type of phenomenon described in another physics interface. Although this is not often another type of flow, it can still involve physics interfaces supported in the CFD Module and COMSOL Multiphysics base package. This is especially the case for applications that include chemical reactions and mass transport (see Chemical Species Transport Branch), or energy transport, found in Heat Transfer Branch.

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More extensive descriptions of heat transfer, such as involving radiation, can be found in the Heat Transfer Module, while a more vigorous tool for modeling chemical reactions and mass transport is found in the Chemical Reaction Engineering Module. Fluid flow is an important component for cooling electromagnetic phenomena, such as heat created through induction and microwave heating, which are simulated in the AC/DC and RF Modules, respectively. While many applications involve the effect of fluid-imposed momentum on structural applications; fluid-structural interaction (FSI). The Structural Mechanics and MEMS Modules feature interfaces specifically for these multiphysics applications.

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