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What is Computational Fluid Dynamics?

Computational fluid dynamics (CFD) is the use of computers and numerical techniques to

solve problems involving fluid flow.

Computational fluid dynamics (CFD) is the science of  predicting fluid flow, heat and mass

transfer , chemical reactions, and related phenomena by solving numerically the set of 

governing mathematical equations.

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Advantages 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 condition

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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 to

isolate specific phenomena for study.

Example: a heat transfer process can be idealized with adiabatic, constant heat

 flux, or constant temperature boundaries. 

Comprehensive Information

Experiments only permit data to be

extracted at a limited number of 

locations in the system (e.g. pressure

and temperature probes, heat flux

gauges, LDV, etc.) CFD allows the analyst to examine a

large number of locations in the region

of interest, and yields a comprehensive

set of flow parameters for

examination.

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Limitations of CFD

Physical Models 

CFD solutions rely upon physical models of  real world processes (e.g.

 turbulence, compressibility, chemistry, multiphase flow, etc.).

The solutions that are obtained through CFD can only be as accurate as

 the physical models on which they are based.

Numerical Errors

Solving equations on a computer invariably introduces numerical errors

Round-off error - errors due to finite word size available on the computer

Truncation error - error due to approximations in the numerical models

Round-off errors will always exist (though they should be small in mostcases)

Truncation errors will go to zero as the grid is refined - so mesh

refinement is one way to deal with truncation error.

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Limitations of CFD (2)

Boundary Conditions

As with physical models, the accuracy of the CFD solution is only as good

as the initial/boundary conditions provided to the numerical model.

Example: Flow in a duct with sudden expansion

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

poor better

Fully Developed

Inlet Profile

Computational

Domain

Computational

Domain

Uniform Inlet

Profile

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Summary

Computational Fluid Dynamics is a powerful way of modeling fluid

flow, heat transfer, and related processes for a wide range of important

scientific and engineering problems.

The cost of doing CFD has decreased dramatically in recent years, and

will continue to do so as computers become more and more powerful.