As an interdisciplinary science, CFD is now applied in the elds of aerospace, automotive, biomedical, civil, chemical, environmental, mechanical, and even electrical engineering, as well as in physics, chemistry, and biology. As Anderson (1995) stated, modern CFD cuts across all disciplines where the ow of a uid is playing a signicant role. CFD is essentially a science of replacing the governing equations describing the fundamental physical principles with discretized algebraic forms, which in turn are solved to obtain numerical values for the ow eld at discrete points in space and/or in time. is book is focused on the numerical methods to discretize the governing equations. However, it is necessary to introduce the governing equation before discussing the numerical methods.