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Introduction to Computational Fluid Dynamics (CFD)



What is CFD?

• The equations governing fluid flows are a set of coupled, non-linear partial differential equations (i.e. a type of differential equation, involving an unknown function (or functions) of several independent variables and their partial derivatives with respect to those variables.)


Continuity

Momentum


• Many real problems include additional terms and/or equations, governing heat transfer, chemical species, turbulence models, etc.

• Analytic solutions are known only for a few very simple laminar flow cases.

• An alternative is to “solve” the governing equations numerically, on a computer.

• Computational Fluid Dynamics (CFD) is this process of obtaining numerical approximations to the solution of the governing fluid flow equations.

• Many modern engineering systems require a detailed knowledge of fluid flow behaviour.

• Experiments provide useful data, but are often costly and time-consuming. It can also be difficult to measure the details required:

  • Measurement probes may disturb the flow excessively, and/or optical access may not be convenient.

  • Obtaining the correct parameter scaling may be difficult.

  • Reproducing some flow conditions safely (eg. explosions) may be difficult.

• Empirical correlations can be useful for simple problems – or first estimates – but are usually not available or applicable for complex problems.

• Note the use of the word “approximations”: all CFD solutions have some error associated with them.

• CFD does not remove the need for experiments: numerical models need to be validated to ensure they produce reliable and accurate results.

• With the growth of available computing power it has become possible to apply CFD even to very complex flowfields, giving detailed information about the velocity field, pressure, temperature, etc.

• The key to successful use of CFD is an understanding of where the errors come from; their implications, and how to ensure they are small enough to be acceptable in a particular application.

• The main aims of this course are thus to:

  • Provide an overview of the processes involved in CFD

  • Give an understanding of some of the key concepts in CFD

  • Provide an understanding of how to carry out simple CFD simulations from the beginning to the end using practical sessions

CFD Applications

Power and energy: Nuclear Reactors, Wind Turbines, Marine Current Turbines

Environmental: Dispersion of pollutants in air or water, wind microclimate

Building services: Ventilation of buildings, atrium design

Automotive: Aerodynamics of cars, aeroplanes, trains

Health and safety: Investigating the effects of fire and smoke

Process industry: Mixing vessels, chemical reactors

Electronics: Heat transfer within and around circuit boards

and many more!