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UI ME 5160 - Intermediate Mechanics of Fluids

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Introduction to Computational Fluid Dynamics (CFD)OutlineWhat is CFD?Why use CFD?Where is CFD used?Slide 6Slide 7ModelingModeling (geometry and domain)Modeling (coordinates)Modeling (governing equations)Modeling (flow conditions)Modeling (initial conditions)Modeling(boundary conditions)Modeling (selection of models)Modeling (Turbulence and free surface models)Examples of modeling (Turbulence and free surface models)Numerical methodsDiscretization methodsDiscretization methods (Cont’d)Discretization methods (example)Discretization methods (example)Solvers and numerical parametersNumerical methods (grid generation)Numerical methods (grid transformation)High performance computing and post-processingTypes of CFD codesCFD Educational InterfaceCFD processCFD ProcessGeometryPhysicsMeshSolveReportsPost-processingPost-processing (Uncertainty Assessment)Post-processing (UA, Verification)Post-processing (Verification: Iterative Convergence)Post-processing (Verification, RE)Slide 41Post-processing (UA, Verification, cont’d)Post-processing (Verification, Asymptotic Range)Slide 44Post-processing (UA, Validation)Example of CFD Process using CFD educational interface (Geometry)Example of CFD Process (Physics)Example of CFD Process (Mesh)Example of CFD Process (Solve)Example of CFD Process (Reports)Example of CFD Process (Post-processing)58:160 CFD LabsIntroduction to Computational Fluid Dynamics (CFD)Tao Xing and Fred SternIIHR—Hydroscience & EngineeringC. Maxwell Stanley Hydraulics LaboratoryThe University of Iowa58:160 Intermediate Mechanics of Fluidshttp://css.engineering.uiowa.edu/~me_160/August 30, 20062Outline1. What, why and where of CFD?2. Modeling3. Numerical methods4. Types of CFD codes5. CFD Educational Interface6. CFD Process7. Example of CFD Process8. 58:160 CFD Labs3What is CFD?•CFD is the simulation of fluids engineering systems using modeling (mathematical physical problem formulation) and numerical methods (discretization methods, solvers, numerical parameters, and grid generations, etc.)•Historically only Analytical Fluid Dynamics (AFD) and Experimental Fluid Dynamics (EFD).•CFD made possible by the advent of digital computer and advancing with improvements of computer resources (500 flops, 194720 teraflops, 2003)4Why use CFD?•Analysis and Design1. Simulation-based design instead of “build & test”More cost effective and more rapid than EFDCFD provides high-fidelity database for diagnosing flow field2. Simulation of physical fluid phenomena that are difficult for experimentsFull scale simulations (e.g., ships and airplanes)Environmental effects (wind, weather, etc.)Hazards (e.g., explosions, radiation, pollution)Physics (e.g., planetary boundary layer, stellar evolution)•Knowledge and exploration of flow physics5Where is CFD used?•Where is CFD used?•Aerospace•Automotive•Biomedical•Chemical Processing•HVAC•Hydraulics•Marine•Oil & Gas•Power Generation•SportsF18 Store Separation Temperature and natural convection currents in the eye following laser heating. AerospaceAutomotiveBiomedical6Where is CFD used?Polymerization reactor vessel - prediction of flow separation and residence time effects. Streamlines for workstation ventilation•Where is CFD used?•Aerospacee•Automotive•Biomedical•Chemical Processing•HVAC•Hydraulics•Marine•Oil & Gas•Power Generation•SportsHVACChemical ProcessingHydraulics7Where is CFD used?•Where is CFD used?•Aerospace•Automotive•Biomedical•Chemical Processing•HVAC•Hydraulics•Marine•Oil & Gas•Power Generation•SportsFlow of lubricating mud over drill bitFlow around cooling towersMarine (movie)Oil & GasSportsPower Generation8Modeling•Modeling is the mathematical physics problem formulation in terms of a continuous initial boundary value problem (IBVP)•IBVP is in the form of Partial Differential Equations (PDEs) with appropriate boundary conditions and initial conditions.•Modeling includes: 1. Geometry and domain 2. Coordinates 3. Governing equations 4. Flow conditions 5. Initial and boundary conditions 6. Selection of models for different applications9Modeling (geometry and domain)•Simple geometries can be easily created by few geometric parameters (e.g. circular pipe)•Complex geometries must be created by the partial differential equations or importing the database of the geometry(e.g. airfoil) into commercial software•Domain: size and shape •Typical approaches •Geometry approximation•CAD/CAE integration: use of industry standards such as Parasolid, ACIS, STEP, or IGES, etc.•The three coordinates: Cartesian system (x,y,z), cylindrical system (r, θ, z), and spherical system(r, θ, Φ) should be appropriately chosen for a better resolution of the geometry (e.g. cylindrical for circular pipe).10Modeling (coordinates)xyzxyzxyz(r,,z)zr(r,,)r(x,y,z)CartesianCylindrical SphericalGeneral Curvilinear Coordinates General orthogonal Coordinates11Modeling (governing equations)•Navier-Stokes equations (3D in Cartesian coordinates)222222ˆzuyuxuxpzuwyuvxuutu222222ˆzvyvxvypzvwyvvxvutv     0zwyvxutRTpLvppDtDRDtRDR222)(23ConvectionPiezometric pressure gradientViscous termsLocal accelerationContinuity equationEquation of stateRayleigh Equation222222ˆzwywxwzpzwwywvxwutw12Modeling (flow conditions)• Based on the physics of the fluids phenomena, CFD can be distinguished into different categories using different criteria• Viscous vs. inviscid (Re)• External flow or internal flow (wall bounded or not)• Turbulent vs. laminar (Re)• Incompressible vs. compressible (Ma)• Single- vs. multi-phase (Ca)• Thermal/density effects (Pr, , Gr, Ec)• Free-surface flow (Fr) and surface tension (We)• Chemical reactions and combustion (Pe, Da) • etc…13Modeling (initial conditions)•Initial conditions (ICS, steady/unsteady flows)•ICs should not affect final results and only affect convergence path, i.e. number of iterations (steady) or time steps (unsteady) need to reach converged solutions.•More


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