fluent培训内部资料(海基科技5)
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The Coupled-Explicit solver should only be used for unsteady flows when the characteristic time scale of problem is on same order as that of the acoustics.
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Outline
Using the Solver
Setting Solver Parameters Convergence
Definition Monitoring Stability Accelerating Convergence
Time required: Implicit solver runs roughly twice as fast. Memory required: Implicit solver requires roughly twice as much memory as coupledexplicit or segregated-implicit solvers!
Enable the solution monitors of interest
Setting Under-relaxation Setting Courant number
Yes
Calculate a solution
Modify solution parameters or grid
Accelerating Convergence
Interpolation Methods for Pressure
Additional interpolation options are available for calculating face pressure when using the segregated solver. FLUENT interpolation schemes for Face Pressure: Standard default scheme; reduced accuracy for flows exhibiting large surface-normal pressure gradients near boundaries. Linear use when other options result in convergence difficulties or unphysical behavior. Second-Order use for compressible flows; not to be used with porous media, jump, fans, etc. or VOF/Mixture multiphase models. Body Force Weighted use when body forces are large, e.g., high Ra natural convection or highly swirling flows. PRESTO! use for highly swirling flows, flows involving steep pressure gradients (porous media, fan model, etc.), or in strongly curved domains.
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Choosing a Solver
Choices are Coupled-Implicit, Coupled-Explicit, or Segregated (Implicit) The Coupled solvers are recommended if a strong inter-dependence exists between density, energy, momentum, and/or species.
faces
( )
f
, f
Af S V
User can choose either the cell (centroid) or node-value based algorithm for the gradient on cell faces in v6.1
Interpolation schemes for the convection term:
Field variables (stored at cell centers) must be interpolated to the faces of the control volumes in the FVM:
( )t t ( )t V f f V f Af t faces
Grid Independence Adaption
Accuracy
Appendix: Background
Finite Volume Method Explicit vs. Implicit Segregated vs. Coupled Transient Solutions
SIMPLEC
PISO
5-7
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Initialization
e.g., high speed compressible flow or finite-rate reaction modeled flows. In general, the Coupled-Implicit solver is recommended over the coupled-explicit solver.
e.g., tracking transient shock wave
The Segregated (implicit) solver is preferred in all other cases.
Lower memory requirements than coupled-implicit solver. Segregated approach provides flexibility in solution procedure.
5-5 © Fluent Inc. 6/29/2015
Second-Order Upwind Scheme
Quadratic Upwind Interpolation (QUICK)
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Iterative procedure requires that all solution variables be initialized before calculating a solution. Solve Initialize Initialize...
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Solver Settings
5-1
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
5-2 © Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Solution Procedure Overview
Solution Parameters
SIMPLE
default scheme, robust
Allows faster convergence for simple problems (e.g., laminar flows with no physical models employed). useful for unsteady flow problems or for meshes containing cells with higher than average skew.
5-6 © Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Pressure-Velocity Coupling
Pressure-Velocity Coupling refers to the numerical algorithm which uses a combination of continuity and momentum equations to derive an equation for pressure (or pressure correction) when using the segregated solver. Three algorithms available in FLUENT:
First-Order Upwind Scheme
easiest to converge, only first order accurate.
Power Law Scheme
more accurate than first-order for flows when Recell< 5 (typ. low Re flows). uses larger „stencils‟ for 2nd order accuracy, essential with tri/tet mesh or when flow is not aligned with grid; convergence may be slower applies to quad/hex and hybrid meshes (not applied to tri mesh), useful for rotating/swirling flows, 3rd order accurate on uniform mesh.
Set the solution parameters
Choosing the Solver Discretization Schemes
Initialization Convergence
Initialize the solution
Monitoring Convergence Stability
Grid Independence Adaption
Check for convergence No Check for accuracy Yes Stop No
Accuracy
5-3
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
5-4
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Discretization (Interpolation Methods)
The Coupled-Explicit solver should only be used for unsteady flows when the characteristic time scale of problem is on same order as that of the acoustics.
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Outline
Using the Solver
Setting Solver Parameters Convergence
Definition Monitoring Stability Accelerating Convergence
Time required: Implicit solver runs roughly twice as fast. Memory required: Implicit solver requires roughly twice as much memory as coupledexplicit or segregated-implicit solvers!
Enable the solution monitors of interest
Setting Under-relaxation Setting Courant number
Yes
Calculate a solution
Modify solution parameters or grid
Accelerating Convergence
Interpolation Methods for Pressure
Additional interpolation options are available for calculating face pressure when using the segregated solver. FLUENT interpolation schemes for Face Pressure: Standard default scheme; reduced accuracy for flows exhibiting large surface-normal pressure gradients near boundaries. Linear use when other options result in convergence difficulties or unphysical behavior. Second-Order use for compressible flows; not to be used with porous media, jump, fans, etc. or VOF/Mixture multiphase models. Body Force Weighted use when body forces are large, e.g., high Ra natural convection or highly swirling flows. PRESTO! use for highly swirling flows, flows involving steep pressure gradients (porous media, fan model, etc.), or in strongly curved domains.
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Choosing a Solver
Choices are Coupled-Implicit, Coupled-Explicit, or Segregated (Implicit) The Coupled solvers are recommended if a strong inter-dependence exists between density, energy, momentum, and/or species.
faces
( )
f
, f
Af S V
User can choose either the cell (centroid) or node-value based algorithm for the gradient on cell faces in v6.1
Interpolation schemes for the convection term:
Field variables (stored at cell centers) must be interpolated to the faces of the control volumes in the FVM:
( )t t ( )t V f f V f Af t faces
Grid Independence Adaption
Accuracy
Appendix: Background
Finite Volume Method Explicit vs. Implicit Segregated vs. Coupled Transient Solutions
SIMPLEC
PISO
5-7
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Initialization
e.g., high speed compressible flow or finite-rate reaction modeled flows. In general, the Coupled-Implicit solver is recommended over the coupled-explicit solver.
e.g., tracking transient shock wave
The Segregated (implicit) solver is preferred in all other cases.
Lower memory requirements than coupled-implicit solver. Segregated approach provides flexibility in solution procedure.
5-5 © Fluent Inc. 6/29/2015
Second-Order Upwind Scheme
Quadratic Upwind Interpolation (QUICK)
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Iterative procedure requires that all solution variables be initialized before calculating a solution. Solve Initialize Initialize...
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Solver Settings
5-1
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
5-2 © Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Solution Procedure Overview
Solution Parameters
SIMPLE
default scheme, robust
Allows faster convergence for simple problems (e.g., laminar flows with no physical models employed). useful for unsteady flow problems or for meshes containing cells with higher than average skew.
5-6 © Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Pressure-Velocity Coupling
Pressure-Velocity Coupling refers to the numerical algorithm which uses a combination of continuity and momentum equations to derive an equation for pressure (or pressure correction) when using the segregated solver. Three algorithms available in FLUENT:
First-Order Upwind Scheme
easiest to converge, only first order accurate.
Power Law Scheme
more accurate than first-order for flows when Recell< 5 (typ. low Re flows). uses larger „stencils‟ for 2nd order accuracy, essential with tri/tet mesh or when flow is not aligned with grid; convergence may be slower applies to quad/hex and hybrid meshes (not applied to tri mesh), useful for rotating/swirling flows, 3rd order accurate on uniform mesh.
Set the solution parameters
Choosing the Solver Discretization Schemes
Initialization Convergence
Initialize the solution
Monitoring Convergence Stability
Grid Independence Adaption
Check for convergence No Check for accuracy Yes Stop No
Accuracy
5-3
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
5-4
© Fluent Inc. 6/29/2015
Fluent User Services Center www.fluentusers.com
Introductory FLUENT Notes FLUENT v6.1 Feb 2003
Discretization (Interpolation Methods)