Handbook of Turbomachinery Second Edition Revised - Ventech!

pressure, inlet losses are usually on the order of 1–3% of the inlet total
pressure. For turbines in engines, there is usually no real inlet, as they are
closely coupled to the combustor or the preceding turbine stage. In this case,
the duct losses are usually assessed to the upstream component.
Stator Losses
The stator losses arise primarily from friction within the vane row, the
secondary flows caused by the flow turning, and exit losses due to blockage
at the vane row trailing edge. The stator loss coefficient can be defined in
several ways. Two popular definitions are
or
Dp 0 stator ¼ Ystator
Dp 0 stator ¼ Ystator
1
2 rV2 1
1
2 r V2 0 þ V2 1
2
ð29Þ
ð30Þ
In either case, the loss coefficient is made up of the sum of coefficients for
each loss contributor:
Ystator ¼ Yprofile þ Ysecondary þ Ytrailing edge
ð31Þ
Profile refers to frictional losses. There can be additional loss contributions
due to incidence (the flow coming into the stator is not aligned with the
leading edge), shock losses (when the stator exit velocity is supersonic), and
others. Much work has been dedicated to determining the proper values for
the coefficients, and several very satisfactory loss model systems have been
developed. As loss models differ for axial-flow and radial-inflow turbines,
these models will be discussed in the individual sections that follow.
Rotor Losses
Rotor losses are modeled in a manner similar to that for stators. However,
the pressure loss is measured as a difference in relative total pressures and
the kinetic energy is based on relative velocities. As with stators, the rotor
loss is based on either the exit relative kinetic energy or the average of the
inlet and exit relative kinetic energies:
Dp 00
rotor ¼ Xrotor
Copyright © 2003 Marcel Dekker, Inc.
1
2 rW 2 2
ð32Þ