RhieChowMassFlux

Computes H/A and 1/A together with face mass fluxes for segregated momentum-pressure equations using linear systems.

Overview

This object is responsible for generating the following fields for a SIMPLE-type segregated solver:

  • (inverse of the matrix diagonal) which is used as a diffusivity for the pressure equation. This field is stored in a face-based functor, so face values are easy to access but cell values need to be reconstructed. This is mainly used in the pressure Poisson equation where only face values are queried.

  • whose divergence is used as a source in the pressure Poisson equation. This field is also stored in a face-based functor, so face values are easy to access, but cell-center values need to be reconstructed.

  • which is the Rhie-Chow corrected face mass flux. This is also stored in a face-based functor, so face values are easy to access, but cell-center values need to be reconstructed.

Besides these capabilities, this user object is also responsible for reconstructing cell velocities at the end of the pressure corrector step. For more information on these fields and processes, we suggest visiting SIMPLE.

The object enables the computation of the standard (SIMPLE) or consistent (SIMPLEC) momentum projection matrix () and neighbour face flux () vector via "pressure_projection_method". In general, SIMPLEC will be stable with higher relaxation factors for pressure than SIMPLE. This is particularly useful in problems with slow-converging pressure fields, such as those with high Reynolds numbers, complex geometries, viscous flows in narrow channels, multiphase flows, problems with rapidly varying thermophysical properties, and, in general, when using high-resolution grids.

Reconstructed Pressure Gradient

The reconstructed pressure-gradient option uses the Aguerre reconstruction (Aguerre et al. (2018)) implemented by FVReconstructedPressureGradient. It is useful when the conservative Rhie-Chow face flux is smooth, but the cell-centered velocity still exhibits oscillations because its pressure gradient is not fully consistent with that face flux.

After a pressure correction, the method reconstructs a cell velocity that is compatible with the corrected conservative face flux and then determines the pressure gradient required by the cell momentum balance. The newly reconstructed gradient corrects the velocity immediately so that the cell velocity and continuity-preserving face flux remain consistent. A relaxed version of that gradient is used by the next momentum predictor to avoid introducing an abrupt change into the pressure-velocity coupling. The accepted gradient is carried between time steps and is preserved through time-step retries and restarts.

The following options control the reconstruction:

  • "gradient_relaxation" controls how strongly the newly reconstructed gradient changes the gradient used by the next momentum solve. The default value of 0.1 is deliberately conservative. Smaller values provide more damping and can improve robustness, but usually require more outer iterations. Values closer to 1 respond more quickly to the latest pressure correction, but can strengthen pressure-velocity oscillations.

  • "base_gradient_method" selects the ordinary pressure-gradient method used before the first reconstructed gradient is available. The default is green-gauss.

For example, the following tested input selects the reconstructed method through an input-file variable and uses that selection for the pressure variable:

    gradient_method = ${pressure_gradient_method}
(modules/navier_stokes/test/tests/finite_volume/ins/channel-flow/linear-segregated/2d/reconstructed-force-channel.i)
[Variables<<<{"href": "../../syntax/Variables/index.html"}>>>]
  [pressure]
    type = MooseLinearVariableFVReal<<<{"description": "Base class for Moose variables. This should never be the terminal object type", "href": "../variables/MooseLinearVariableFV.html"}>>>
    initial_condition<<<{"description": "Specifies a constant initial condition for this variable"}>>> = 0
    solver_sys<<<{"description": "If this variable is a solver variable, this is the solver system to which it should be added."}>>> = pressure_system
    gradient_method<<<{"description": "Default gradient computation method to register when a consumer requests gradients from this variable. This may be a built-in method name like 'green-gauss' or 'green-gauss-venkatakrishnan', or the name of an object in [FVGradientMethods]."}>>> = ${pressure_gradient_method}
  []
[]
[FVGradientMethods<<<{"href": "../../syntax/FVGradientMethods/index.html"}>>>]
  [reconstructed]
    type = FVReconstructedPressureGradient<<<{"description": "Reconstructs and relaxes the pressure gradient used for Rhie-Chow momentum coupling.", "href": "../fvgradientmethods/FVReconstructedPressureGradient.html"}>>>
    base_gradient_method<<<{"description": "Gradient method used before Rhie-Chow has computed reconstructed gradients."}>>> = green-gauss
    # This is the relaxation used by the reconstructed-gradient channel regression tests.
    gradient_relaxation<<<{"description": "Relaxation factor applied when updating the reconstructed pressure-coupling gradient."}>>> = 0.1
  []
[]
(modules/navier_stokes/test/tests/finite_volume/ins/channel-flow/linear-segregated/2d/reconstructed-force-channel.i)

Use the same reconstructed pressure-gradient definition for every LinearFVMomentumPressure component coupled to this pressure equation. Mixing gradient definitions among velocity components would make the reconstructed cell velocity inconsistent with the coupled momentum balance. Other equations and diagnostic quantities should continue to use an ordinary gradient method.

Pressure Diffusion Interpolation

The "pressure_diffusion_interpolation" parameter selects whether average or harmonic interpolation is used when computing the face values of Ainv, the diffusion tensor in the pressure correction diffusion term. When using Navier Stokes Flow Segregated / WCNSLinearFVFlowPhysics, select this through the pressure_diffusion_interpolation parameter in the Physics block.

Input Parameters

  • p_diffusion_kernelThe LinearFVPressureCorrectionDiffusion kernel acting on the pressure.

    C++ Type:std::string

    Controllable:No

    Description:The LinearFVPressureCorrectionDiffusion kernel acting on the pressure.

  • pressureThe pressure variable.

    C++ Type:VariableName

    Unit:(no unit assumed)

    Controllable:No

    Description:The pressure variable.

  • rhoDensity functor. A functor is any of the following: a variable, a functor material property, a function, a postprocessor or a number.

    C++ Type:MooseFunctorName

    Unit:(no unit assumed)

    Controllable:No

    Description:Density functor. A functor is any of the following: a variable, a functor material property, a function, a postprocessor or a number.

  • uThe x-component of velocity

    C++ Type:VariableName

    Unit:(no unit assumed)

    Controllable:No

    Description:The x-component of velocity

Required Parameters

  • blockThe list of blocks (ids or names) that this object will be applied

    C++ Type:std::vector<SubdomainName>

    Controllable:No

    Description:The list of blocks (ids or names) that this object will be applied

  • pressure_diffusion_interpolationaverageThe face interpolation method for Ainv in the pressure correction diffusion term.

    Default:average

    C++ Type:MooseEnum

    Options:average, harmonic

    Controllable:No

    Description:The face interpolation method for Ainv in the pressure correction diffusion term.

  • pressure_projection_methodstandardThe method to use in the pressure projection for Ainv - standard (SIMPLE) or consistent (SIMPLEC)

    Default:standard

    C++ Type:MooseEnum

    Options:standard, consistent

    Controllable:No

    Description:The method to use in the pressure projection for Ainv - standard (SIMPLE) or consistent (SIMPLEC)

  • vThe y-component of velocity

    C++ Type:VariableName

    Unit:(no unit assumed)

    Controllable:No

    Description:The y-component of velocity

  • wThe z-component of velocity

    C++ Type:VariableName

    Unit:(no unit assumed)

    Controllable:No

    Description:The z-component of velocity

Optional Parameters

  • allow_duplicate_execution_on_initialFalseIn the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).

    Default:False

    C++ Type:bool

    Controllable:No

    Description:In the case where this UserObject is depended upon by an initial condition, allow it to be executed twice during the initial setup (once before the IC and again after mesh adaptivity (if applicable).

  • execution_order_group0Execution order groups are executed in increasing order (e.g., the lowest number is executed first). Note that negative group numbers may be used to execute groups before the default (0) group. Please refer to the user object documentation for ordering of user object execution within a group.

    Default:0

    C++ Type:int

    Controllable:No

    Description:Execution order groups are executed in increasing order (e.g., the lowest number is executed first). Note that negative group numbers may be used to execute groups before the default (0) group. Please refer to the user object documentation for ordering of user object execution within a group.

  • force_postauxFalseForces the UserObject to be executed in POSTAUX

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Forces the UserObject to be executed in POSTAUX

  • force_preauxFalseForces the UserObject to be executed in PREAUX

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Forces the UserObject to be executed in PREAUX

  • force_preicFalseForces the UserObject to be executed in PREIC during initial setup

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Forces the UserObject to be executed in PREIC during initial setup

Execution Scheduling Parameters

  • control_tagsAdds user-defined labels for accessing object parameters via control logic.

    C++ Type:std::vector<std::string>

    Controllable:No

    Description:Adds user-defined labels for accessing object parameters via control logic.

  • enableTrueSet the enabled status of the MooseObject.

    Default:True

    C++ Type:bool

    Controllable:Yes

    Description:Set the enabled status of the MooseObject.

  • use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

    Default:False

    C++ Type:bool

    Controllable:No

    Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.

Advanced Parameters

  • prop_getter_suffixAn optional suffix parameter that can be appended to any attempt to retrieve/get material properties. The suffix will be prepended with a '_' character.

    C++ Type:MaterialPropertyName

    Unit:(no unit assumed)

    Controllable:No

    Description:An optional suffix parameter that can be appended to any attempt to retrieve/get material properties. The suffix will be prepended with a '_' character.

  • use_interpolated_stateFalseFor the old and older state use projected material properties interpolated at the quadrature points. To set up projection use the ProjectedStatefulMaterialStorageAction.

    Default:False

    C++ Type:bool

    Controllable:No

    Description:For the old and older state use projected material properties interpolated at the quadrature points. To set up projection use the ProjectedStatefulMaterialStorageAction.

Material Property Retrieval Parameters

Input Files

References

  1. Horacio J Aguerre, Cesar I Pairetti, Cesar M Venier, Santiago Márquez Damián, and Norberto M Nigro. An oscillation-free flow solver based on flux reconstruction. Journal of Computational Physics, 365:135–148, 2018.[Export]