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Non-Cartesian coordinates are often employed in fluid mechanics to exploit the symmetry of particular
fluid systems. For example, it is convenient to employ cylindrical coordinates to describe systems possessing
axial symmetry. In this appendix, we investigate a particularly useful class of
non-Cartesian coordinates known as *orthogonal curvilinear coordinates*. The two most commonly occurring examples of this class in fluid mechanics are
cylindrical
and spherical coordinates. (Incidentally, the Einstein summation convention is not used in this appendix.) For more information on
orthogonal curvilinear coordinates see Milne-Thomson 2011.

Richard Fitzpatrick
2016-01-22