Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

There is a fundamental difference between the flows in turbine cascades and those
in compressor cascades which needs emphasising. A fluid flowing through a channel
in which the mean pressure is falling (mean flow is accelerating) experiences a relatively
small total pressure loss in contrast with the mean flow through a channel in
which the pressure is rising (diffusing flow) when losses may be high. This characteristic
difference in flow is reflected in turbine cascades by a wide range of low loss
performance and in compressor cascades by a rather narrow range.
Compressor cascade performance
Two-dimensional Cascades 69
FIG. 3.11. A sample plot of inlet and outlet stagnation pressures and fluid outlet angle
(adapted from Todd 1947).
A typical set of low-speed compressor cascade test results (Howell 1942) for a specific
geometry is shown in Fig. 3.12a. This type of data is derived from many pitchwise
traverses, over a range of incidences, using pressure probes such as those described
in the previous section. Traverse measurements are usually made in a plane parallel to
the blade exit plane at about a quarter chord downstream. The data from each traverse
are processed following a procedure described by several authors, e.g. Horlock (1966),
and the procedure is not repeated here.