Abstract
Mechanical energy is isoentropically transmitted to fluid-flow only by means of unsteady pressure forces, but the flow may be steady with respect to the rotating coordinate system in cases of turbomachines. If it flows along a cylindrical surface, the relative flow field is independent of the angular velocity of the system, but the field is significantly modified by the Coriolis acceleration if it flows changing the radial distance from the axis.
The flow field in a turbomachine is a slightly skewed three-dimensional one even if it is invisid flow. The real flow is much more complicated including secondary flows induced by different kinds of causes. They are, skewed boundary layer due to relative motion of walls, secondary flow induced in the endwall boundary layer of a curved channel, horse shoe vortex generated around the blunt leading edge of a blade at the root, secondary flow in the boundary layers of a stationary blade and of a rotating blade, as well as leakage flow through the clearance between the blade tip and the casing. Furthermore, in cases of transonic compressors, the Mach number relative to the blade varies considerably from the root to the tip of blade and complicated three-dimensional shock waves are generated.
