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Engineering with Simulation

In our previous blogs we discussed some of the tools and programs that engineers use to solve thermal management issues relating to electronics cooling. One of the tools that engineers have available is computational fluid dynamics (CFD). Computational Fluid Dynamics is a concept of fluid mechanics that simulate the interactions of gases and liquids with surfaces by using various algorithms and numerical methods.The process begins by utilizing the CFD software on the computer, and depending on the intensity of the project, possibly a supercomputer, where the basic geometry of the shape is input. This step is not that different from what most computer modeling or CAD applications are capable of. This is followed by creating a mesh, which is the uniform or non-uniform volume occupied by the test fluid. This information is divided among the cells of the object. Once this is achieved, the physical realities are entered which are the equations such as motions, enthalpy and radiation as well as the boundary conditions within which the fluid can act in the simulation. As the runs the simulation, the repeated processes slowly form results that fit the unknowns of the equations. The data can then be analyzed used to create a visualization of the simulation.

A Brief origin of Computational Fluid Dynamics

The backbone of almost all CFD simulations and problems are the Navier-Stokes equations, which define any single phase flow. These equations show how velocity, pressure, temperature and density in moving fluids are related. These equations were first derived in the early 1800’s by G.G. Stokes and M. Navier as complex extensions of the Euler equation that included the effects of viscosity. In theory, these equations could be solved for any given flow problem using calculus, however in reality they are too difficult and would take too long to solve. As they were simplified over the years they began to lose accuracy. In order to create more definitive calculation, more powerful and faster computers were needed to do the calculations without as many approximations.  The first computer modeled flow was performed at Los Alamos National Labs in July 1963, and featured a two-dimensional model of swirling flow around an object.  Soon thereafter the first three dimensional model was published, this one by John Hess and A.M.O. Smith of Douglas Aircraft in 1967. This model had one major flaw however in that it was not able to account for the lifting flows so it was limited to the hulls of boats and the fuselages of a plane.

Benefits of CFD

Due to the complete simulations that CFD programs can present they have many advantages when used correctly. First, they eliminate the need for the “build and test” design approach. Instead of creating multiple prototypes and testing them, wasting not only money but time, CFD can return the information immediately and at a higher accuracy than most physical tests. Also, the tests that are simulated in CFD are normally fairly difficult experiments to run in full size prototypes. Examples of this would be full scale simulations, such as boats or planes to determine environmental effects such as wind and rain, dangerous hazards such as explosions or radiation and physics based inquiries such as tests involving the planetary boundary layer. CFD is used in an incredibly wide range of fields, including aerospace, automotive, biomedical and even sports.  While all of these advantages and uses of CFD are strong benefits, CFD can be a very expensive process based on the need. High powered computers are not cheap to begin with and the time and man power that it takes to write the more complex programs is most certainly not free. When looking for an engineering firm to help develop a product, finding one that can utilize CFD as well as the other simulation tools available, will be beneficial in keeping time and cost to a minimum.

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