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National Advisory Committee for Aeronautics, Technical Notes - Two Dimensional Compressible Flow in Centrifugal Compressors with Straight Blades

Six mmerical examples are presented for steady, two-dimensional,
cmpressible, nonvisoous flow in centrifugal conrpressors with straight
blades, the center lines of which generate a right circular cone
when rotated about the axis of the compressor. A seventh example is
presented for incompressible flow. The solutions were obtained in a
region of the compressors, including the impeller tip, that was con-
sidered to be unaffected. by diffuser vanes or by the inlet configur-
ation of the impellers. Each solution applies to redial- and conical-
flow compressors with various cone angles but with the same included
passage angle between blades. (The solutions also apply to radial-
ani conical-flow turbines with the rotation and. flow direction
reversed.) The effects of variations in the following pmters
were investigated: (1) flow rate, (2) ller-tip speed, (5) vari-
ation of passage height with radius, and 4-) number of blades. The
mmerical results are presented in plots of the streamlines, constant
Mach number lines, and constant pressure-ratio lines.

Correlation equations are developed whereby the flow conditions
in any impeller with straight blades can be determined. (in the
region investigated. by this analysis) for all operating conditions.
As examples of the- information provided by the correlation equations,
the velocities along the blade surfaces are presented. for a wide
range of impeller-tip Mach number, flow coefficient, and. included
passage angle.

At the present time, the design. of centrifugal canpressors is
primarily an art, rather than a science. Little detailed knowledge
of flow conditions within the compressor is available upon which to
base a rational design. If these flow conditions could be determined,
design methods might be developed for centrifuyl compressors with
higher aerodynamic efficiency and. better over-all perfoumnce. For
example, the compressor efficiency would be improved if favorable
velocity distributions (fr-an the standpoint of boundary-layer
growth and separation) could be obtained along the flow surfaces
by proper desigr of the compressor.