The Nonisothermal Flow, Laminar Flow and Turbulent Flow Interfaces
When a multiphysics interface is added from the Fluid Flow>Nonisothermal Flow branch  of the Model Wizard or Add Physics windows, one of the Single-Phase Flow interfaces (laminar or turbulent flow) and Heat Transfer are added to the Model Builder.
In addition, the Multiphysics node is added, which includes the multiphysics coupling feature Nonisothermal Flow.
The Multiphysics Branch in the COMSOL Multiphysics Reference Manual.
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The Laminar Flow interface () combines a Heat Transfer in Fluids interface with a Laminar Flow interface.
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The Turbulent Flow, Algebraic yPlus interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, Algebraic yPlus interface.
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The Turbulent Flow, L-VEL interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, L-VEL interface.
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The Turbulent Flow, k-ε interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, k-ε interface.
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The Turbulent Flow, k-ω interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, k-ω interface.
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The Turbulent Flow, Low Re k-ε interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, Low Re k-ε interface.
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The Turbulent Flow, SST interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, SST interface.
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The Turbulent Flow, Spalart-Allmaras interface () combines a Heat Transfer in Fluids interface with a Turbulent Flow, Spalart-Allmaras interface.