Initial Values
The Initial Values feature adds initial values for the velocity field and the pressure that can serve as an initial condition for a transient simulation or as an initial guess for a nonlinear solver.
D O M A I N S E L E C T I O N
From the Selection list, choose the domains to define initial values.
I N I T I A L V A L U E S
Enter values or expressions for the initial value of the Velocity field u (SI unit: m/s) and for the Pressure p (SI unit: Pa). The default values are 0.
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In a turbulent flow interface, initial values for the turbulence variables are |
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also specified. By default these are specified using the predefined variables |
Note |
defined by the expressions in Initial Values. |
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T h e S i n g l e - P h a s e F l o w , T u r b u l e n t F l o w I n t e r f a c e s
The descriptions in this section are structured based on the order displayed in the Fluid Flow branch. Because many of the interfaces are integrated with each other, most of the features cross reference to other interfaces. For example, all nodes that can be added for the turbulent flow interfaces are described for The Laminar Flow Interface.
Click the links to go to these main section topics:
•The Turbulent Flow, k- Interface
•The Turbulent Flow, Low Re k- Interface
•The Turbulent Flow, k- Interface
•The Turbulent Flow, Spalart-Allmaras Interface
The Turbulent Flow, k- Interface
The Turbulent Flow, k- interface (
), found under the Single-Phase Flow>Turbulent Flow branch (
) in the Model Wizard, has the equations, boundary conditions, and volume forces for modeling turbulent flow using the Reynolds averaged Navier-Stokes (RANS) equations, solving for the mean velocity field, the pressure, and the standard k- model, solving for the turbulent kinetic energy k and the rate of dissipation of turbulent kinetic energy .
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• Airflow Over an Ahmed Body: Model Library path |
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CFD_Module>Single-Phase_Benchmarks>ahmed_body |
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Model |
• Turbulent Flow Over a Backward Facing Step: Model Library path |
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CFD_Module>Single-Phase_Benchmarks>turbulent_backstep |
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The main feature is Fluid Properties, which adds the Navier-Stokes equations and the transport equations for k and , and provides an interface for defining the fluid material and its properties. When this interface is added, these default nodes are also added to the Model Builder—Fluid Properties, Wall (the default boundary condition is Wall
functions), and Initial Values.
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Right-click the Turbulent Flow, k- node to add other features that implement, for example, boundary conditions and volume forces.
Except where noted below, see The Laminar Flow Interface for all the
other settings.
Note
P H Y S I C A L M O D E L
Turbulence Model Type
For the Turbulent Flow, k- interface, this defaults to a RANS Turbulence
model type. This enables the Turbulence Model Parameters section.
Note
For 2D models, it also disables the Shallow Channel Approximation check
box.
2D
Turbulence Model
The interface changes to The Turbulent Flow, Low Re k- Interface when
Low Reynolds number k- is selected, to The Turbulent Flow, k- Interface
when k- and to The Turbulent Flow, Spalart-Allmaras Interface when
Tip
Spalart-Allmaras is selected.
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• Model Builder Options for Physics Feature Node Settings Windows |
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Theory for the Turbulent Flow Interfaces |
See Also |
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For node descriptions, see Boundary Conditions for the Single-Phase |
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Flow Interfaces. |
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The Turbulent Flow, Low Re k- Interface
The Turbulent Flow, Low Re k- interface (
), found under the Single-Phase Flow>Turbulent Flow branch, has the equations, boundary conditions, and volume forces for modeling turbulent flow using the Reynolds averaged Navier-Stokes (RANS) equations, solving for the mean velocity field, the pressure, and the AKN low-Reynolds number k- model, solving for the turbulent kinetic energy k and the rate of dissipation of turbulent kinetic energy . The interface also includes a wall distance equation that solves for the reciprocal wall distance.
The interface is the same as The Turbulent Flow, k- Interface (
) except the
Turbulence model defaults to Low Reynolds number k- .
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The Low Reynolds number k- interface requires a Wall Distance |
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Initialization study step in the study previous to the stationary or time |
Important |
dependent study step. |
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• For study information, see Stationary with Initialization, Transient |
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with Initialization, and Wall Distance Initialization in the COMSOL |
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Multiphysics Reference Guide |
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• Model Builder Options for Physics Feature Node Settings Windows |
See Also |
• Theory for the Turbulent Flow Interfaces |
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• For node descriptions, see Boundary Conditions for the Single-Phase |
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Flow Interfaces |
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The Turbulent Flow, k- Interface
The Turbulent Flow, k- interface (
), found under the Single-Phase Flow>Turbulent Flow branch (
) in the Model Wizard, has the equations, boundary conditions, and volume forces for modeling turbulent flow using Wilcox revised k- model.
The interface is the same as The Turbulent Flow, k- Interface (
) except the
Turbulence model defaults to k- .
The main feature is Fluid Properties, which adds the Navier-Stokes equations and the transport equations for the turbulent kinetic energy k and the specific dissipation , and provides an interface for defining the fluid material and its properties. When this
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