naca-rm-e51g30
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National Advisory Committee for Aeronautics, Research Memorandum - Performance of a Cascade in an Annular Vortex Generating Tunnel Over Range of Reynolds Numbers
As part of an.investigation of the nature and distribution of
losses in a compressor, the Reynolds number effect on the performance
of a cascade of compressor blades was examined in an annular vortexs
generating tunnel over a range of Reynolds number from 50,000 to
250,000 and at angles of attack of 15° and 25°. The mean radius
section of the cascade showed a total-pressure deficiency, which could
be expected from two-dimensional boundary-layer considerations, while
the hub and tip sections showed no evidence of a critical Reynolds
number within the range investigated.
The turning angle showed no appreciable variation.with change in
Reynolds number for either of the angles of attack regardless of the
spanwise position of the measuring station.
The low pressures attained at high altitudes are known to have a
detrimental effect on engine operation and to decrease the efficiency
of the axial-flow compressdr by a few percent (reference 1). This
effect has been attributed chiefly to the fact that at high altitudes
the initial compressor stages operate at very low Reynolds numbers.
Although some investigations of the effect of Reynolds number on
compressor performance have been carried out, they are limited either
to the two-dimensional type (reference 2) or to the investigation of
the compressor as a whole (reference 1). Recent investigations of
secondary flow (references 3 to 5), however, have shown that this type
of flow may have considerable influence in blade passages. The viscous
origin of the secondary flow makes it important to investigate the
effects of Reynolds number in a three—dimensional configuration in a
somewhat more detailed manner than has hitherto been done.
In order to determine the effect of Reynolds number in regions
where secondary flows are likely to occur, an investigation was con-
ducted at the NASA Lewis laboratory to determined the distribution of
losses downstream of a cascade of 65-(12)10 compressor blades
(reference 6) over a range of Reynolds numbers. The tests were made at
two angles of attack in an annular vortex—generating tunnel. In order
to isolate the Reynolds number effects, Mach number limits were
maintained between 0. 2 and O. 35.
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