CFD INTRO A MUST HAVE DOC

7/28/2019 CFD INTRO A MUST HAVE DOC

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Numerical Simulations

ystem- eve pro ems

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)


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CFD Codes

va a e commerc a co es uent, sta -c , xa, c -ace, c x etc.

Other structures codes with fluids capability ansys, algor, cosmosetc.

Supporting grid generation and post-processing codes

NASA and other government lab codes

Netlib, Lin ack routines for new code develo ment

Mathematica or Maple for difference equation generation

Use of spreadsheets (and vb-based macros) for simple solutions


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What is Computational Fluid Dynamics?

omputat ona u ynamcs s t e sc ence o pre ct ng

fluid flow, heat transfer, mass transfer, chemical reactions, and relatedphenomena by solving the mathematical equationswhich govern these

, .

The result of CFD analyses is relevant engineering data used in:

conceptual studies of new designs eta e pro uct eveopment

troubleshooting

redesign

CFD analysis complements testing and experimentation. Reduces the total effort required in the laboratory.

Courtesy: Fluent, Inc.


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Applications

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...



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CFD - How It Works

Fillin nayss egns w t a mat ematca mo e

of a physical problem. Conservation of matter, momentum, and

Nozzle

Bottle

region of interest.

Fluid properties are modeled empirically.

to make the problem tractable (e.g., steady-state, incompressible, inviscid, two-dimensional).

Provide appropriate initial and/or boundaryconditions for the problem.

Domain for bottle fillingpro em.



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CFD - How It Works (2)

CFD applies numerical methods (calledscret zat on to eveop approx mat ons o t e

governing equations of fluid mechanics and the fluidregion to be studied.

overnng eren a equa ons age rac

The collection of cells is called thegrid or mesh.

The set of approximating equations are solvednumer ca y on a compuer or e ow evariables at each node or cell.

System of equations are solved simultaneously to.

The solution is post-processedto extract quantities ofinterest (e.g. lift, drag, heat transfer, separation points, Mesh for bottle filling

, . . .



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An Example: Water flow over a tube bank

Goal

compute average pressure drop, heattransfer 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 negligiblePhysical System can be modeled

ow s transatona y per o c .e.geometry repeats itself)

with repeating geometry.



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Mesh Generation

preprocessor for meshing. Mesh is generated for the fluid region

(and/or solid re ion for conduction).

A fine structured mesh is placedaround cylinders to help resolve

boundary layer flow.

remaining fluid areas.

Identify interfaces to which boundaryconditions will be applied.

cylindrical walls inlet and outlets

symmetry and periodic facesSection of mesh for tube bank problem



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Post-processing

xtract reevant engneer ng

data from solution in theform of:

x-y po s

contour plots

vector plots sur acevo ume negra on

forces

fluxes

partc e traector es

Temperature contours within the fluid region.



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Advantages of CFD

ow ost

Using physical experiments and tests to get essential engineering data fordesign can be expensive.

ompua ona smua ons are rea vey nexpensve, an coss are eyto decrease as computers become more powerful.

Speed smua ons can e execue n a s or per o o me.

Quick turnaround means engineering data can be introduced early in thedesign process

Many flow and heat transfer processes can not be (easily) tested - e.g.

hypersonic flow at Mach 20



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Advantages of CFD (2)

Ability to Simulate Ideal Conditions

CFD allows great control over the physical process, and provides the ability toisolate specific phenomena for study.

Example: a heat transfer process can be idealized with adiabatic, constant heatflux, or constant temperature boundaries.

Comprehensive Information

Experiments only permit data to beextracted at a limited number oflocations in the system (e.g. pressureand temperature probes, heat flux

, , .

CFD allows the analyst to examine alarge number of locations in the regionof interest, and yields a comprehensiveset of flow parameters forexamination.



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Limitations of CFD (2)

oun ary on t ons

As with physical models, the accuracy of the CFD solution is only as goodas the initial/boundary conditions provided to the numerical model.

xampe: ow n a uc w su en expanson

If flow is supplied to domain by a pipe, you should use a fully-developedprofile for velocity rather than assume uniform conditions.

ComputationalDomain

ComputationalDomain

Fully DevelopedInlet Profile

Uniform InletProfile



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Summary

omputatona u ynamcs s a power u way o mo e ng u

flow, heat transfer, and related processes for a wide range of importantscientific and engineering problems.

e cost o o ng as ecrease ramat ca y n recent years, anwill continue to do so as computers become more and more powerful.



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Numerical solution methods

onssency an runca on errors

As h-> 0, error -> 0 (hn, tn) Stability

Convergence

Gets close to exact solution

Physical quantities are conserved

Boundedness (Lies within physical bounds)

Realizability (Be able to model the physics)

Accuracy (Modeling, Discretization and Iterative solver errors)


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CFD Methodologies

nte erence met o

Simple grids (rectangular)

Complex geometries -> Transform to simple geometry (coordinaterans orma on

Finite volume method

Complex geometries (conserve across faces) Finite element metho

Complex geometries (element level transformation)

Spectral element method

Higher order interpolations in elements Lattice-gas methods

Basic momentum rinci le-base

CFD INTRO A MUST HAVE DOC

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