Nonisothermal Flow and Conjugate Heat Transfer trigger pseudo time stepping when Use pseudo time stepping for stationary equation form in the Fluid Flow interface is set to Automatic from physics.
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The multiphysics stabilizations (streamline diffusion and crosswind diffusion) are controlled by the Fluid Flow interface. For example, the multiphysics streamline diffusion can be disabled in a Laminar Flow physics node, in the Stabilization section. The stabilization selected in the Heat Transfer interface has no effect if the multiphysics coupling stabilization is active, but remains active if not. However, the isotropic diffusion is not a multiphysics stabilization and is controlled by each physics interface. The crosswind diffusion stabilization is turned off for the LES interfaces.
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The pressure, velocity, and temperature variables of the Nonisothermal Flow coupling node are set to the Common Model Input values of the Default Model Inputs node on its complementary selection, that is, all domains except those from the Selection list. It allows to couple multiple fluid flow interfaces with a single heat transfer interface. See Default Model Inputs in the COMSOL Multiphysics Reference Manual for details.
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The intersection of the Fluid or Moist Air feature’s selection with the Fluid Properties feature’s selection.
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The intersection of the Fluid feature’s selection within the Heat Transfer in Fluid interface and the Fluid Properties feature’s selection within the Viscoelastic Flow interface.
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The intersection of the Porous Medium feature’s selection within the Heat Transfer in Porous Media interface and the Porous Medium feature’s selection within the Brinkman Equations interface.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is chosen in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
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For From heat transfer interface: define the Density ρ in the Thermodynamics, Fluid section of the Fluid node, in the Heat Transfer coupled interface. Depending on the Fluid type option in this node, the density may bet taken from material, set directly, or computed by using the ideal gas law. The same value is automatically set in the Fluid Properties section of the Fluid Properties node, in the Fluid Flow coupled interface.
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For From fluid flow interface: define the Density ρ in the Fluid Properties section of the Fluid Properties node, in the Fluid Flow coupled interface. The same value is automatically set in the Thermodynamics, Fluid section of the Fluid node, in the Heat Transfer coupled interface.
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For Custom, linearized density, enter the Reference density ρref (SI unit: kg/m3) and the Coefficient of thermal expansion αp(SI unit:1/K), or select From material, or select a variable in the list if available. Regardless how the properties are defined they should be constant. If material properties are not constant you should consider using any of the other options to define the density. Also, if Custom, linearized density is used for incompressible flow, the density ρ is evaluated to ρref. In this case αp is not used unless Boussinesq approximation is selected. The same value is automatically set in the Fluid Properties section of the Fluid Properties node, in the Fluid Flow coupled interface, and in the Thermodynamics, Fluid section of the Fluid node, in the Heat Transfer coupled interface.
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For Custom, enter a Density ρ (SI unit: kg/m3), or select a density in the list if available. The same value is automatically set in the Fluid Properties section of the Fluid Properties node, in the Fluid Flow coupled interface, and in the Thermodynamics, Fluid section of the Fluid node, in the Heat Transfer coupled interface.
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When an interface is selected from the Heat transfer list, some of its model inputs are forced with values from the Nonisothermal Flow node. In addition, it defines how the turbulence has to be accounted for, depending on the Fluid flow interface’s turbulence settings.
Therefore, each fluid flow interface should be used in at most one Nonisothermal Flow node. In cases where multiple fluid flow interfaces are used, they can be coupled with a single heat transfer interface, using an equal number of Nonisothermal Flow nodes to define proper multiphysics couplings. In the Heat transfer interface, the inputs for pressure and velocity are then taken from the first Nonisothermal Flow node.
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If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the Fluid flow or Heat transfer lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.
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See also Theory for the Nonisothermal Flow and Conjugate Heat Transfer Interfaces in the CFD Module User’s Manual for more information.
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See also Theory for the Nonisothermal Viscoelastic Flow in the CFD Module User’s Manual for more information.
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