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ERCOFTAC Special Interest Group onQuality and Trust in Industrial CFD

Best Practice Guidelines

Editors:

Michael Casey and Torsten WintergersteFluid Dynamics Laboratory

Sulzer [email protected]

[email protected]

Version 1.0 January 2000


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Contents1. Introduction 51.1. Purposes of this document 51.2. Scope 51.3. Background to the problems of CFD 5

1.4. Background to this document 61.5. Structure of this document 62. Source of errors and uncertainties in CFD simulations 82.1. Overview of CFD simulations 82.2. Importance of errors and uncertainties in engineering applications 82.3. Errors and uncertainties 92.4. Categorisation of errors and uncertainties 92.5. Definitions of verification, validation and calibration 103. Numerical errors, convergence and round-off errors 113.1. Global solution algorithm 113.2. Convergence errors 123.3. Round-off errors 133.4. Grids and grid design 143.5. Spatial discretisation errors 163.6. Temporal discretisation errors for time-dependent simulations 173.7. Types of implementation of boundary conditions 183.8. Special remarks on the finite-element method 194. Turbulence modelling 204.1. RANS equations and turbulence models 204.2. Classes of turbulence models 214.3. Near-wall modelling 244.4. Weaknesses of the standard k- model with wall functions 274.5. Inflow boundary conditions 28

4.6. Unsteady flows 284.7. Laminar and transitional flows 285. Application uncertainties 285.1. Geometrical uncertainties 285.2. Boundary conditions 295.3. Initial condition and initial guess 315.4. Uncertainties with regard to steady flow, symmetry, and periodicity 325.5. Physical properties 326. User errors 336.1. General comments 336.2. Control of the working process 336.3. Training requirements for CFD users 35

7. Code errors 377.1. Guidelines for the code developer and vendor 377.2. Guidelines for the code user 378. Validation and sensitivity tests of CFD models 398.1. Selection of test cases for validation 398.2. Design and use of sensitivity tests 409. Examples of application of best practice guidelines 419.1. Introduction to the test cases 419.2. Test case A : 2-D transient scalar bubble convecting at 45 degrees 41


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9.3. Test case B : T-Junction between main and auxiliary pipe 439.4. Test case C : Natural convection flow in a square cavity 479.5. Test case D : Sudden Pipe Expansion 519.6. Test case E : Transonic airfoil RAE2822 569.7. Test Case F : Engine Valve 599.8. Test case G : Low speed centrifugal compressor (LSCC) 65

9.9. Test Case H : Turbulent flow in a model outlet plenum 7110. Suggestions and need for further work 7710.1. Revision of best practice guidelines 7710.2. Extension of the best practice guidelines 7710.3. Application procedures 7711. Checklist of best practice advice for industrial CFD 7811.1. Guidelines on the training of CFD users 7811.2. Guidelines on problem definition 7811.3. Guidelines on solution strategy 7811.4. Guidelines on global solution algorithm 7911.5. Guidelines on validation of models 7911.6. Guidelines on turbulence modelling 8011.7. Guidelines on definition of geometry 8211.8. Guidelines on grids and grid design 8211.9. Guidelines on boundary conditions 8311.10. Guidelines on the solution of discretised equations using a CFD code 8611.11. Guidelines on assessment of errors 8811.12. Guidelines on interpretation 8911.13. Guidelines on documentation 8911.14. Guidelines on communication with code developer 8912. Acknowledgements 9113. References 92

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