in solving an internal flow problem, due to the complexity of the geometry for the given problem, i transformed the certesian NV equations into boundary fitted coordinate system. but the problem is the boundary fitted coordinate is not an ORTHOGONAL coordinate system. so, can i use taylor series (in the boundary fitted coordinate system) to approximate all those derivatives in the transformed NV equations, that's the normal finite difference method? please advise. thanks.

typing mistake==> NV is NS(navier stokes)

(1). Try to take a look at Joe Thompson's book fo "numerical grid generation" . (2). You can transform the boundary conditions in the way as you transform the governing equations. That is, define the boundary conditions in the original coordinate system, then use the coordinate transformation to express the condition in the new coordinate system. The new coordiante system does not have to be an orthorgoanl coordinate system.