Introduction to Computational Fluid Dynamics
What is fluid flow?
Fluid flow is:
- breathing, drinking, digesting, washing, swimming, smoking;
- laundering clothes, and hanging them out to dry;
- heating or ventilating a room; extinguishing a fire with water;
- burning gasoline in an automobile engine to create power and (unfortunately) pollution;
- making soup, creating plastics from petroleum;
- flying an airplane, parachuting, surfing, sailing;
- soldering, making steel, electrolysing water;.... and so on ....
What is CFD?
CFD is predicting what will happen, quantitatively, when
fluids flow, often with the complications of:
- simultaneous flow of heat,
- mass transfer (eg perspiration, dissolution),
- phase change (eg melting, freezing, boiling),
- chemical reaction (eg combustion, rusting),
- mechanical movement (eg of pistons, fans, rudders),
- stresses in and displacement of immersed or surrounding solids.
Click here to see some examples of CFD predictions
How old is CFD?
Its early beginnings were in the 1960's.
- Its first successes came to prominence in the 1970's.
- The creation of the CFD-service industry started in the 1980's.
- The industry expanded significantly in the 1990's.
- Expansion continued in the Second Millennium as CFD packages devloped easier
connexions with those for CAD and solid-stress analysis.
- A significant change of the near future is likely to involve the
use of pay-as-you go remote computing, via Internet.
What use is CFD?
Knowing how fluids will flow, and what will be their quantitative effects on the solids
with which they are in contact, assists:-
- building-services engineers and architects to provide comfortable and safe human
- power-plant designers to attain maximum efficiency, and reduce release of pollutants;
- chemical engineers to maximize the yields from their reactors and processing equipment;
- land-, air- and marine-vehicle designers to achieve maximum performance, at least cost;
- risk-and-hazard analysts, and safety engineers, to predict how much damage to
structures, equipment, human beings, animals and vegetation will be caused by fires,
explosions and blast waves.
CFD-based flow simulations enable:-
- metropolitan authorities need to determine where pollutant-emitting industrial plant may be
safely located, and under what conditions motor-vehicle access must be restricted so as to
preserve air quality;
- meteorologists and oceanographers to foretell winds and water currents; - hydrologists
and others concerned with ground-water to forecast the effects of changes to
ground-surface cover, of the creation of dams and aquaducts on the quantity and quality of
- petroleum engineers to design optimum oil-recovery strategies, and the equipment for
putting them into practice;
Within a few years, it is to be expected, surgeons will conduct
operations which may affect the flow of fluids within the human body (blood, urine, air,
the fluid within the brain) only after their probable effects have been predicted by CFD
How does CFD make predictions?
CFD uses a computer to solve the relevant science-based mathematical equations,
using information about the circumstances in question.
Its components are therefore:
- the human being who states the problem,
- scientific knowledge expressed mathematically,
- the computer code (ie software) which embodies this knowledge and expresses the
stated problem in scientific terms,
- the computer hardware which performs the calculations dictated by the software,
- the human being who inspects and interprets their results.
Can CFD be trusted?
Click here to read a more
extended discussion of validation
CFD-based predictions are never 100%-reliable, because:
- the input data may involve too much guess-work or imprecision;
- the available computer power may be too small for high numerical accuracy (this is often
- the scientific knowledge base may be inadequate (so is this).
The reliability is greater:
- for laminar flows rather than turbulent ones
- for single-phase flows rather than multi-phase flows;
- for chemically-inert rather than chemically-reactive materials;
- for single chemical reactions rather than multiple ones;
- for simple fluids rather than those of complex composition.
Therefore, coal-fired furnaces represent an extreme of uncertainty; but
CFD is nevertheless used increasingly in their design because the uncertainties resulting
from its non-use is even greater.
Click here to
see some "validation" results
Click here for a more extended account of what CFD
can and cannot do
How does one become a CFD User?
In the past, there have been three methods for obtaining the benefits of CFD:
- Purchase (or rent) a suitable computer code, and learn how to use it for yourself.
- Hire a consultant to use the code for you and to provide you with the results of the
- Avail yourself of remote computing power, and expertise, via
However, nowadays there are intermediate methods also.
Click here to see the spectrum of services offered
Where do CHAM, and PHOENICS, fit in?
- CHAM was the first provider of general-purpose CFD software. The original PHOENICS
appeared in 1981.
- CHAM has also originated many of the mathematical techniques and physical models which
have become generally adopted by the industry, especially in connexion with turbulence,
multi-phase flow and chemical reaction.
- The innovating tradition continues, with the result that today's PHOENICS contains many
unique features, eg:
- simultaneous stresses in solids;
- multi-fluid turbulence models;
- the LVEL and IMMERSOL models for interspersed solids and fluids;
- the virtual-reality user interface;
- use via Internet ; etc.
However, CHAM also includes public-domain models and features which it has not
invented, if its users appear to want them. This is why PHOENICS has more models of
turbulence and two-phase flow than any other code on the market.
The PHOENICS computer-code family.
- Few CFD users require the full power of PHOENICS; for most are concerned with only
narrow sectors of engineering or science, in which only a restricted number of types of
phenomena play a part.
- For this reason, the general-purpose PHOENICS can be packaged and accessed in
special-purpose form, so that its user is not distracted (or daunted) by features which
are of no concern.
- Currently available special-purpose versions of PHOENICS include:
- FLAIR for heating and ventilating of buildings;
- HOTBOX for electronics-cooling applications;
- CVD for chemical-vapour-deposition reactors;
- ROSA for river-oil-spill analysis;
- SCONES for steam-condenser simulation;
- TACT for natural-draught cooling-tower design.
Click here for more information
- Because each has the same "CFD-engine" inside, users can call on more power,
and rely on more quality assurance, than any one-purpose-only code can provide; and at a