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CHAPTER
3 ɅNSYS Meshing
In this Chapter
3.1 Introduction to Discretization 3.3 Global Mesh Control
3.2 Introduction to ɅNSYS Meshing 3.4 Local Mesh Control
3.1 Introduction to Discretization
There are several methods of discretization that are programmed in commercial codes. ANSYS
FLUENT and ANSYS CFX both use FVM. This is because FVM has certain advantages and the scheme is
robust. The most popular methods are FDM and FVM, and we will discuss them next
3.1.1 Finite Difference Method
Of all methods, FDM is the simplest. It can be said that CFD started from FDM. Initially, mathematicians
derived simple formulas to calculate derivatives and then the methods improved and CFD advanced to
more advanced methods. Currently, computations such as DNS and LES are only theoretical. The
rationale of FDM can be understood from the concept of a derivative. The derivative of a function gives
the slope of the function. For a function of x-component of velocity u, the slope of u with respect to x can
be determined numerically as:
where the subscripts i and i þ 1 are the points for calculating the u values. Here, Dx denotes the grid
spacing. The method for calculating the first derivative is also called the forward difference method, as
we will soon observe.
3.1.2 Finite Volume Method
The FVM is widely used in CFD codes because of its various advantages over FDM. The FVM can be used
for any sort of grid, i.e., structured or unstructured, clustered or non-clustered, and so forth.
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