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National Research Committee for Aeronautics, Research Memorandum - Performance of the Modified V-1710-93 Engine Stage Supercharger with a Constant-Area Vaneless Diffuser

As part of an investigation to increase the power output of
the V-1710-93 engine at altitude, the engine-stage supercharger
was combined with a constant-area vaneless diffuser designed to
improve the performance of the engine—stage supercharger at the
rated engine operating point. The performance of the modified
supercharger was investigated in a variable-component supercharger
test rig and compared with that of the standard supercharger with
an 8-vaned diffuser. A separate evaluation of the component effi-
ciencies and a study of the flow characteristics of the modified
supercharger were made possible by internal diffuser instrumentation.

At the volume flow required by the engine for rated operating
conditions, the modified supercharger increased the over-all adia-
batic efficiency 0.05 and the over-all pressure coefficient 0.035,
Furthermore, the capacity of the engine-stage supercharger was
increased by replacing the standard 8—vaned diffuser with the
vaneless diffuser. The peak over—all adiabatic efficiency for the
modified supercharger, however, was 0.05 to 0.07 lower than that
of the standard unit over the range of tip speeds investigated.
The improved performance of the modified supercharger at rated
engine operating conditions resulted from a shift of the point of
peak adiabatic efficiency and pressure coefficient of the standard
supercharger to a higher volume flow,

The energy loss through the vaneless diffuser was found to
be small. Because of the restricted diffuser diameter, however,
diffusion was inadequate, which resulted in a relatively small
static-pressure_rise through the diffuser, high diffuser-exit
velocities, and excessive collector-case losses.

An investigation to improve the altitude performance of the
V-1710-93 engine was conducted at the NASA Cleveland laboratory.
Full-scale tests of the engine (reference 1) and component tests of
3he engine- stage supercharger (reference 2) indicated that the
volume flow of charge air required at rated engine conditions was
greater than the volume flow at which peak supercharger adiabatic
efficiency and pressure ratio occurred. Because the performance
beyond the point 01 peak conditions rapidly decreased as the volume
flow increased, the engine- Stage supercharger usually operated at
less than peak efficiency'when in use with the V-1710-93 engine.