Introduction to Computational Fluid Dynamics Lecture 2: CFD IntroductionNumerical SimulationsCFD CodesWhat is Computational Fluid Dynamics?ApplicationsCFD - How It WorksCFD - How It Works (2)An Example: Water flow over a tube bankMesh GenerationUsing the SolverPost-processingAdvantages of CFDAdvantages of CFD (2)Limitations of CFDLimitations of CFD (2)SummaryNumerical solution methodsCFD Methodologies© Ram Ramanan 01/13/19CFD 1ME 5337/7337Notes-2005-002Introduction to Computational Fluid Dynamics Lecture 2: CFD Introduction© Ram Ramanan 01/13/19CFD 2ME 5337/7337Notes-2005-002Numerical SimulationsSystem-level CFD problemsIncludes all components in the productComponent or detail-level problemsIdentifies the issues in a specific component or a sub-componentDifferent tools for the level of analysisCoupled physics (fluid-structure interactions)© Ram Ramanan 01/13/19CFD 3ME 5337/7337Notes-2005-002CFD CodesAvailable commercial codes – fluent, star-cd, Exa, cfd-ace, cfx etc.Other structures codes with fluids capability – ansys, algor, cosmos etc.Supporting grid generation and post-processing codesNASA and other government lab codesNetlib, Linpack routines for new code developmentMathematica or Maple for difference equation generationUse of spreadsheets (and vb-based macros) for simple solutions© Ram Ramanan 01/13/19CFD 4ME 5337/7337Notes-2005-002What is Computational Fluid Dynamics?Computational Fluid Dynamics (CFD) is the science of predicting fluid flow, heat transfer, mass transfer, chemical reactions, and related phenomena by solving the mathematical equations which govern these processes using a numerical process (that is, on a computer).The result of CFD analyses is relevant engineering data used in:conceptual studies of new designsdetailed product developmenttroubleshootingredesignCFD analysis complements testing and experimentation.Reduces the total effort required in the laboratory.Courtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 5ME 5337/7337Notes-2005-002ApplicationsApplications of CFD are numerous!flow and heat transfer in industrial processes (boilers, heat exchangers, combustion equipment, pumps, blowers, piping, etc.)aerodynamics of ground vehicles, aircraft, missilesfilm coating, thermoforming in material processing applicationsflow and heat transfer in propulsion and power generation systemsventilation, heating, and cooling flows in buildingschemical vapor deposition (CVD) for integrated circuit manufacturingheat transfer for electronics packaging applicationsand many, many more...Courtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 6ME 5337/7337Notes-2005-002CFD - How It WorksAnalysis begins with a mathematical model of a physical problem.Conservation of matter, momentum, and energy must be satisfied throughout the region of interest.Fluid properties are modeled empirically.Simplifying assumptions are made in order to make the problem tractable (e.g., steady-state, incompressible, inviscid, two-dimensional).Provide appropriate initial and/or boundary conditions for the problem.Domain for bottle filling problem.Filling NozzleBottleCourtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 7ME 5337/7337Notes-2005-002CFD - How It Works (2)CFD applies numerical methods (called discretization) to develop approximations of the governing equations of fluid mechanics and the fluid region to be studied.Governing differential equations  algebraicThe collection of cells is called the grid or mesh.The set of approximating equations are solved numerically (on a computer) for the flow field variables at each node or cell.System of equations are solved simultaneously to provide solution.The solution is post-processed to extract quantities of interest (e.g. lift, drag, heat transfer, separation points, pressure loss, etc.). Mesh for bottle filling problem.Courtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 8ME 5337/7337Notes-2005-002An Example: Water flow over a tube bankGoalcompute average pressure drop, heat transfer per tube rowAssumptionsflow is two-dimensional, laminar, incompressibleflow approaching tube bank is steady with a known velocitybody forces due to gravity are negligibleflow is translationally periodic (i.e. geometry repeats itself)Physical System can be modeled with repeating geometry.Courtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 9ME 5337/7337Notes-2005-002Mesh GenerationGeometry created or imported into preprocessor for meshing.Mesh is generated for the fluid region (and/or solid region for conduction).A fine structured mesh is placed around cylinders to help resolve boundary layer flow.Unstructured mesh is used for remaining fluid areas.Identify interfaces to which boundary conditions will be applied.cylindrical wallsinlet and outletssymmetry and periodic facesSection of mesh for tube bank problemCourtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 10ME 5337/7337Notes-2005-002Using the SolverImport mesh.Select solver methodology.Define operating and boundary conditions.e.g., no-slip, qw or Tw at walls.Initialize field and iterate for solution.Adjust solver parameters and/or mesh for convergence problems.Courtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 11ME 5337/7337Notes-2005-002Post-processingExtract relevant engineering data from solution in the form of:x-y plotscontour plotsvector plotssurface/volume integrationforcesfluxesparticle trajectoriesTemperature contours within the fluid region.Courtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 12ME 5337/7337Notes-2005-002Advantages of CFDLow CostUsing physical experiments and tests to get essential engineering data for design can be expensive.Computational simulations are relatively inexpensive, and costs are likely to decrease as computers become more powerful.SpeedCFD simulations can be executed in a short period of time.Quick turnaround means engineering data can be introduced early in the design processAbility to Simulate Real ConditionsMany flow and heat transfer processes can not be (easily) tested - e.g. hypersonic flow at Mach 20CFD provides the ability to theoretically simulate any physical conditionCourtesy: Fluent, Inc.© Ram Ramanan 01/13/19CFD 13ME 5337/7337Notes-2005-002Advantages of CFD (2)Ability to Simulate Ideal Conditions CFD allows great control over the physical