CFD is a discipline that studies how simulate the behaviour of fluids with modern computing machines.
The acronym CFD stands for "Computational Fluid Dynamics", that implies the use of a numerical approach to investigate the dynamics of the fluid of interest. Born in early '60 with the emergence of digital computers, it has since come with a variety of different approaches, with models more or less complicated, able to solve flows more or less complex.
Today, the variety of the numerical schemes adopted is still present and a full discussion on them can be found at the official site of Flow Science (CFD101). Contrast to the analytic approach, this method permits to reach almost always to a solution, and in extremely short times. Compared to the analytic approach, CFD also has an additional economical advantage: in fact, it is not necessary to build a physical model of the problem, and to use complex machines to reproduce the fluid flow.
The geometrical 2/3D model is generated with the CAD system. In the simulation software the model is then assigned all the necessary physical characteristics of the material. Finally the necessary boundary conditions are added in order to reproduce the correct fluid behaviour.
All the information about the fluid flow - that can be very difficult to extrapolate in an experimental approach, are easily obtained. In fact, once executed the simulation, it is possible to have the values of every variable of interest, in every point of the domain, and at every time step.
With all these observations, CFD can be reasonably considered as the "third dimension" of fluid dynamics, equivalent at the analytical and experimental approach. In the past, due to the high complexity and cost needed to reach solution, the CFD was used especially in specialized academic research centres with self-written codes, or in the aeronautical/military industries, where they could afford high costs and highly reliable prototypes were needed.
Today, nevertheless, with the huge growth of computational power of personal computers and with the continuous development of the numerical codes the access barrier to these codes has fallen down.
In fact today it is possible to execute simulations with high precision and short solution times even with a common laptop computer! The CFD represents then a future more accessible day by day, and it is quickly overrunning all
scientific research fields, from hydraulic/environmental to micro-electromechanical systems, going through foundries, maritime industry and consumer products.