Microsoft PowerPoint - Fluent’s solve

Microsoft PowerPoint - Fluent’s solve - S O...

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Unformatted text preview: S O L U T I O N S O L U T I O N S O L U T I O N S O L U T I O N S O L U T I O N S O L U T I O N S O L U T I O N S O L U T I O N T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T T E C H N I Q U E S I N F L U E N T p r e p a r e d b y : S . M . p r e p a r e d b y : S . M . r a f i g h r a f i g h 2 1 1 2 1 1 C o u r s e B y : P r o f . C o u r s e B y : P r o f . H o s s e i n i H o s s e i n i Solver Options • As discussed in the last lecture Fluent has an unsteady solver and steady solver options • The unsteady solver is used for dynamic mulations where you are integrating in time simulations where you are integrating in time • The steady solver is designed to get to get a steady flow or time averaged steady flow solution Solver Options • Both steady and unsteady can be used with the segregated solver or the coupled solver. • The segregated solver solves the equation set quentially sequentially • The coupled solver solves the equation set in one go. This is the more “modern” solver but consumes more memory My experiences • The segregated solver is the default option. For most purposes this is good enough. Ive never had to use the coupled solver m of the view that you should think more • I am of the view that you should think more about the possible transient aspects of the problem and worry about steady vs unsteady rather than segregated vs coupled Convergence r Inevitably any iterative/numerical solution procedure will only give a solution which is “converged” relative to some criteria r The solution may be converged if: ll discretized transport equations are obeyed to a – All discretized transport equations are obeyed to a specified tolerance defined by Fluent’s residuals (but these may be too large) – The solution no longer changes with more iterations (but the problem may be stuck) – Overall balances close (for a steady flow simulation) Convergence • Convergence is not the same as accuracy. The solution is accurate if it matches experimental data (which you obviously need to make the dgement) judgement) • Thus there are qualitative and quantitative aspects to convergence. Convergence - Residual Plots r Fluent keeps track of the residuals throughout the iteration. The default value of these is 1.0e-3.(except for enthalpy - 1.0e-6 and species transport 1.0e-5) You should plot these. lve Monitors Residuals Plot – Solve-> Monitors -> Residuals -> Plot r The residual plots show when the residuals have reached a specified tolerance r They can show which equations are having convergence problems, though this is sometimes difficult and there are other ways finding this out - see multigrid verbose r The residuals measure the imbalance on conservation equations Convergence - Residual Plots...
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This note was uploaded on 06/21/2011 for the course ME 20345 taught by Professor Prof. hosseini during the Fall '10 term at Sharif University of Technology.

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Microsoft PowerPoint - Fluent’s solve - S O...

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