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The relative circumferential location of stator rows (stator indexing)
is an aspect of multistage compressor design that has not yet
been explored for its potential impact on compressor aerodynamic
performance. Although the inlet stages of multistage compressors
usually have differing stator blade counts, the aft stages of
core compressors can often have stage blocks with equal stator
blade counts in successive stages. The potential impact of stator
indexing is likely greatest in these stages. To assess the performance
impact of stator indexing, researchers at the NASA Lewis Research
Center used the 4-ft-diameter, four-stage NASA Low Speed Axial
Compressor for detailed experiments. This compressor has geometrically
identical stages that can circumferentially index stator rows
relative to each other in a controlled manner; thus it is an ideal
test rig for such investigations.
Measurements were made to first determine the indexing pattern
that would result in the wakes of each stator impacting the leading
edge of the adjacent downstream stators. This pattern served as
the initial indexing configuration from which detailed performance
measurements were then acquired as a function of stator indexing
at peak efficiency and peak pressure operating conditions. These
performance measurements showed that stator indexing had a small
but measurable effect on performance. For the stator indexing
configurations corresponding to the maximum and minimum performance
at each operating condition, areas upstream and downstream of
the third-stage blade rows were traversed in detail to assess
the effects of stator indexing on blade element performance parameters.
Finally, for a given stator indexing configuration, blade element
performance was measured across two different stator blade passages
to assess the level of passage-to-passage performance differences.
Results indicate that the measured performance differences due
to manufacturing and assembly tolerances are of the same order
as those due to stator indexing, which further indicates that
stator indexing has a small impact on performance.
Previous articleLast updated April 29, 1997
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