Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

254 Fluid Mechanics, Thermodynamics of Turbomachinery
(8.12)
EXAMPLE 8.2. Performance data from the CAV type 01 radial turbine (Benson et al.
1968) operating at a pressure ratio p01/p3 of 1.5 with zero incidence relative flow onto
the rotor is presented in the following form:
where t is the torque, corrected for bearing friction loss. The principal dimensions and
angles, etc. are given as follows:
Rotor inlet diameter, 72.5mm
Rotor inlet width, 7.14mm
Rotor mean outlet diameter, 34.4mm
Rotor outlet annulus width, 20.1mm
Rotor inlet angle, 0deg
Rotor outlet angle, 53deg
Number of rotor blades, 10
Nozzle outlet diameter, 74.1mm
Nozzle outlet angle, 80deg
Nozzle blade number, 15
The turbine is “cold tested” with air heated to 400K (to prevent condensation erosion
of the blades). At nozzle outlet an estimate of the flow angle is given as 71deg and the
corresponding enthalpy loss coefficient is stated to be 0.065. Assuming that the absolute
flow at rotor exit is without swirl and uniform, and the relative flow leaves the rotor
without any deviation, determine the total-to-static and overall efficiencies of the
turbine, the rotor enthalpy loss coefficient and the rotor relative velocity ratio.
Solution. The data given are obtained from an actual turbine test and, even though
the bearing friction loss has been corrected, there is an additional reduction in the specific
work delivered due to disk friction and tip leakage losses, etc. The rotor speed N
= 2410÷400 = 48,200rev/min, the rotor tip speed U2 = pND2/60 = 183m/s and hence
the specific work done by the rotor DW = U 2 2 = 33.48kJ/kg. The corresponding isentropic
total-to-static enthalpy drop is