A turbomachine is a device in which energy transfer occurs between a flowing fluid
and a rotating element due to dynamic action, and results in a change in pressure
and momentum of the fluid. Mechanical energy transfer occurs inside or outside of
the turbomachine, usually in a steady-flow process. Turbomachines include all
those machines that produce power, such as turbines, as well as those types that
produce a head or pressure, such as centrifugal pumps and compressors. The
turbomachine extracts energy from or imparts energy to a continuously moving
stream of fluid. However in a positive displacement machine, it is intermittent.
The turbomachine as described above covers a wide range of machines,
such as gas turbines, steam turbines, centrifugal pumps, centrifugal and axial flow
compressors, windmills, water wheels, and hydraulic turbines. In this text, we
shall deal with incompressible and compressible fluid flow machines.