where there is indicated as well.

plane of symmetry. typical cross section in Fig.(2) as well as the plane of symmetry of the duct. The cartesian system of reference the shape of the cross section of the duct, for the flow will calculated, looks like suitable to use ellipsoidal coordinates as curvilinear coordinates. of an ellipsoidal coordinate system used for ellipse in Fig. (3). Here the transformation from plane to plane x-y or vice- versa can be calculated by known analytical functions.