An equation describing the development of streamwise vorticity is derived. The fluid is assumed inviscid and incompressible and to have a gradient of rotating total pressure across the streamtube. The equation is used to calculate, by finite difference techniques, the streamwise vorticity development for bends, rotating straight pipes, rotating axial to radial bends and for a rotating duct representing Eckardt’s impeller passage. The development of secondary flows in centrifugal compressors is discussed. It is concluded that the secondary flows within the boundary layer determine the position of the wake at outlet and probably influence separation. It is also concluded that the wake can be moved by altering mass flow rate, rotational speed or by introducing an inlet distortion to the flow.