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INTRODUCTION Computational Fluid Dynamics
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CFD is the process of solving the fluid flow equation of mass, moment and energy on a computer as applied to a particular geometry and flow conditions.The basic flow variables such as velocity, pressure and temperature are computed at thousands of location.The CFD solution is based on the first-principle of conservation of mass, moment and energy
A tool for solving PDE’s
3 fundamental principles:
Mass is conserved (Continuity equation);
Newton’s second law (Navier-Stokes Eqn);
Energy is conserved (Bernoulli’s Equation)
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The Approach of Fluid Dynamics
Pure Experimental
Pure Theory
Computational Fluid Dynamics
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“A theory is something nobody believes except the person proposing the theory and an experiment is something everybody believes except the person doing the experiment”
--Albert EinsteinExperimental Investigation• Involve full-scale equipment•Full scale test are, in most cases, prohibitively expensive and often impossible.•Perform experiment on small-scale models. Information must be extrapolated to full scale, and general rules for doing this are often unavailable.• Small scale models do not always simulate all the features of the full-scale equipment.• There are serious difficulties of measurement in many situations.Theoretical Calculation• Consequences of a mathematical model, rather than those of an actual physical model.• Consists of set of differential equations.• A tiny fraction of the range of practical problems can be solved.
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Advantage of Theoretical Calculations
Low cost
Ability to simulate realistic
conditions
Speed
Ability to simulate ideal conditions
Completeinformation
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Why CFD?Growth in complexity of unsolved engineering problemsNeed for quick solutions of moderate accuracyAbsence of analytical solutionsThe prohibitive costs involved in performing even scaled laboratory experimentsEfficient solution algorithmsDevelopments in computers in terms of speed and storageSophisticated pre and post processing facilities
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Complements actual engineering testingReduces engineering testing costsProvides comprehensive data not easily obtainable from experimental tests.Reduces the product-to-market time and costsHelps understand defects, problems and issues in product/process
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Advantages of CFDIt complements experimental and theoretical fluid dynamics by providing an alternative cost effective means of simulating real flows.InsightBetter visualization and enhanced understanding of designs.ForesightTesting many variations until you arrive at an optimal result before physical prototyping and testing. Practically unlimited level of detail of results at virtually no added expense.EfficiencyCompression of design and development cycle.
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The simulation results in prediction of the flow fields and engineering parameters, which are very useful in the Design and Optimization of processes and equipments.Substantial reduction of lead times and costs of new designsAbility to study systems where controlled experiments are difficult or impossible to perform (e.g. very large systems)Ability to study systems under hazardous conditions at and beyond their normal performance limits (e.g. safety studies and accident scenarios)CFD is slowly becoming part and parcel of Computer Aided Engineering(CAE)
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Applications of CFDAerodynamics of aircraft : lift and dragAutomotive : External flow over the body of a vehicle or internal flow through the engine, combustion, Engine coolingTurbo machinery: Turbines, pumps , compressorsetc.Flow and heat transfer in thermal power plants and nuclear power reactorsHVACManufacturing–Casting simulation, injection moulding of plasticsMarine engineering: loads on off-shore structuresHydrodynamics of ships, submarines, torpedo etc.
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Applications of CFDElectrical and electronic engineering: cooling of equipment like transformers, Computers, microcircuits, Semiconductor processing, Optical fibre manufacturingChemical process engineering: mixing and separation, chemical reactors, polymer moldingTransport of slurries in process industriesEnvironmental engineering: External and internal environment of buildings, wind loading, Investigating the effects of fire and smoke, distribution of pollutants and effluents in air or water,Hydrology and oceanography: flows in rivers, oceansMeteorology: weather predictionEnhanced oil recovery from rock formationsGeophysical flows: atmospheric convection and ground water movementBiomedical engineering: Flow in arteries, blood vessels, heart, nasal cavity, Inhalers
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Pressure distribution on a pickup van with path lines
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Streamlines on a Submarine with the surface colored with Pressure
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Aerospace Applications
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Aerospace Applications
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Automotive Applications
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Methodology in CFD
Pre processor
Solver
Post ProcessorS.K.VENU
Pre processorGeometry generationGeometry cleanupMeshing
SolverProblem specificationAdditional modelsNumerical computation
Post ProcessorLine and Contour dataAverage ValuesReport Generation
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Definition of the geometry of the region of interest: the computational domain
Creating regions of fluid flow, solid regions and surface boundary names
Grid generation–the sub-division of the domain in to a number of smaller, non-overlapping sub-domains: a grid(or mesh) of cells(or control volumes or elements)
Pre processor
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Accuracy of a solution, calculation time and cost in terms of necessary computer hardware are dependent on the fineness of the grid.
Over 50% of time spent in industry on a CFD project is devoted to the definition of domain geometry and grid generation.
Selection of the physical and chemical phenomena that need to be modeled.
Definition of fluid properties.
Specification of appropriate boundary conditions at cells which coincide with or touch the domain boundary
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SolverCFD is the art of replacing the differential equation governing the Fluid Flow, with a set of algebraic equations (the process is called discretization), which in turn can be solved with the aid of a digital computer to get an approximate solution
Finite difference method
Finite Element Method
Finite volume method
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Post-processorVersatile data visualization tools.Domain geometry and grid displayVector plots showing the direction and magnitude of the flow.Line and shaded contour plots2D and 3D surface plotsParticle trackingView manipulation(translation, rotation, scalingetc.)Visualization of the variation of scalar variables(variables which have only magnitude, not direction, such as temperature, pressure and speed) through the domain.Quantitative numerical calculations.Charts showing graphical plots of variablesHard copy out putAnimation for dynamic result displayData export facilities for further manipulation external to the code
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