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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 1.0e3.(except for enthalpy  1.0e6 and species transport 1.0e5) 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.
 Fall '10
 prof. hosseini

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