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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
5.1.2 Overview of CFD 
The science of computational fluid dynamics is made up of many different disciplines from the 
fields of aeronautics, mathematics, and computer science. A scientist or engineer working in the 
CFD field is likely to be concerned with topics such as stability analysis, graphic design, and 
aerodynamic optimization. CFD may be structured into two parts: generating or creating a 
solution, and analyzing or visualizing the solution. Often the two parts overlap, and a solution is 
analyzed while it is in the process of being generated in order to ensure no mistakes have been 
made. This is often referred to as validating a CFD simulation. 
5.1.3 CFD Solutions 
When scientists or engineers try to solve problems using computational fluid dynamics, they 
usually have a specific outcome in mind. For instance, an engineer might want to find out the 
amount of lift a particular airfoil generates. In order to determine this lift, the engineer must 
create a CFD solution, or a simulation, for the space surrounding the airfoil. At every point in 
space around the airfoil, called the grid points, enough information must be known about the 
state of a fluid particle to determine exactly what direction it would travel and with what 
velocity. This information is called flow variables. 
5.1.4 Governing Equations of Fluid Dynamics 
The governing equations of fluid dynamics represent the conservation of mass, momentum, and 
energy for a fluid continuum. The conservation of mass states that mass cannot be created or 
destroyed, and the conservation of energy is similar. The conservation of momentum is simply 
Newton's Law of Motion (force = mass x acceleration) that is cast in a form suitable for fluid 
dynamics. Because the governing equations are the three conservation laws, they are also referred 
to as the conservation law equations. The governing equations receive their name because they 
determine the motion of a fluid particle under certain boundary conditions. 
The governing equations remain the same, however, the boundary conditions will change for 
each problem. For example, the shape of the object may be different, or the speed of the 
undisturbed air may change. These changes would be implemented through a different set of 
boundary conditions. In general, a boundary condition defines the physical problem at specific 
positions. Fundamental boundary conditions include the no-slip condition at the interface 
between solid and fluid that leads to the formation of a wall boundary layer. Another is the fixed 
mass outlet where it is ensured that a constant mass flow is extracted from the solution domain at 
a specified plane. 
