Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

EXAMPLE 3.3. At the midspan of a proposed fan stator blade the inlet and outlet air
angles are to be a1 = 58° and a 2 = 44°. Using the data and correlation of McKenzie,
determine a suitable blade camber and space–chord ratio.
Solution. From eqn. (3.6) the vector mean flow angle is found,
From eqn. (3.42) we get the stagger angle,
Thus, am = 52.066° and x = 46.937°.
From eqn. (3.43), assuming that AVR = 1.0, we find
Using the optimum efficiency correlation, eqn. (3.44),
To determine the blade camber we combine
with eqn. (3.41) to get
Two-dimensional Cascades 83
According to McKenzie the correlation gives, for high stagger designs, peak efficiency
conditions well removed from stall and is in good agreement with earlier fan blade
design methods.
Turbine cascade correlation (Ainley and Mathieson)
Ainley and Mathieson (1951) reported a method of estimating the performance of
an axial flow turbine and the method has been widely used ever since. In essence the
total pressure loss and gas efflux angle for each row of a turbine stage is determined at
a single reference diameter and under a wide range of inlet conditions. This reference
diameter was taken as the arithmetic mean of the rotor and stator rows’ inner and outer
diameters. Dunham and Came (1970) gathered together details of several improvements
to the method of Ainley and Mathieson which gave better performance prediction for
small turbines than did the original method. When the blading is competently designed
the revised method appears to give reliable predictions of efficiency to within 2% over
a wide range of designs, sizes and operating conditions.