Why CFD?
Fluid dynamics is the science of fluid motion. Fluid flows are commonly studied in one of the 3 ways:
- theoretical fluid dynamics,
- experimental fluid dynamics,
- numerically: Computational Fluid Dynamics.
What is CFD?
Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. CFD is the science of predicting fluid flow, heat transfer, mass transfer, chemical reactions and related phenomena by solving the mathematical equations which govern these processes using numerical methods. CFD enables scientists and engineers to perform numerical experiments (i.e. computer simulations) in a virtual flow laboratory.
What is a fluid flow?
Fluid flows encountered in everyday life include:
- interaction of various objects with the surrounding air/water (aerospace, automotive and marine applications),
- complex flows in heat exchangers, chemical reactors and furnaces,
- combustion in automobile engines and other propulsion systems,
- heating, ventilation and air conditioning of buildings and vehicles,
- environmental hazards (air pollution, transport of contaminants),
- heating, ventilation and air conditioning of buildings, cars,
- film coating, thermoforming in material processing applications,
- processes in human body (blood flow, breathing).
CFD does not replace the measurements completely but the amount of experimentation and the overall cost can be significantly reduced. Equipment and personnel are expensive and difficult to transport. CFD simulations are relatively inexpensive, and costs are likely to decrease as computers become more powerful. CFD gives an insight into flow patterns that are difficult, expensive or impossible to study using traditional (experimental) techniques. CFD simulations can be executed in a short period of time. Quick turnaround means engineering data can be introduced early in the design process. CFD allows great control over the physical process, and provides the ability to isolate specific phenomena for study. Experiments only permit data to be extracted at a limited number of locations in the system (pressure and temperature probes, heat flux gauges). 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. CFD solutions rely upon physical models of real world processes (turbulence, compressibility, chemistry, multiphase flow). The CFD solutions can only be as accurate as the physical models on which they are based. The accuracy of the CFD solution is only as good as the initial/boundary conditions provided to the numerical model.
Why CFD in the design of bridges?
The spectacular engineering failure in the 20th century happened in Tacoma, Washington on 7th November, 1940. During morning hours the bridge began to roll very strangely in 35mph winds. The oscillation took the form of twisting motion that leads the main section of bridge to tilt in 45 degree angle from its original position. This cause the main span of bridge collapsed.
The disaster of this bridge illustrates two key points to be noted:
- the fluid mechanics can play a role in the critical occurrence outside the traditional spheres of aerospace and mechanical engineering,
- the study of this occurrence during the design phase of a project will surely save lot of time and money.
