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National Advisory Committee for Aeronautics, Technical Notes - Turning Angle Design Rules for Constant Thickness Circular Arc Inlet Guide Vanes in Axial Annular Flow

A survey of data from investigations of axial-flow-compressor
inlet guide vanes with circular-arc, constant-thickness sections and
axial air inlet was conducted to establish a relation between vane '
camber and air turning angle for use in the design of this type of
vane. Two design rules were obtained for vanes set at zero angle of
incidence, solidities from 1.4 to 1.7, and inlet Mach numbers of
approximately 0.5.

From the data as measured, a linear relation between air turning
a and vane-camber angle was deduced for turning angles from 10° to
41 for vanes with greater amounts of turning at the tip than at the
hub and with annulus area ratios across the vane of from 0.86 to 0.95.
The relation was then generalized to take into account the varying
axial velocity across the vanes by correcting the measured data to
constant axial velocity on the basis of the inlet velocity and the
assumption of constant circulation. A corrected turning-angle design
rule applicable over a. wide range of axial-velocity ratios was thus
obtained for turning angles from 12° to 40°. A correction for vane
settings other than zero incidence was also deduced from the data for
camber angles from 25° to 40°. The turning-angle relations were com-
pared with existing design rules and data based on two-dimensional
cascade and potential flow available in the literature. Design con-
siderations and limitations involved in the use of circular-arc inlet
guide vanes are discussed.

In the many types of turbine power plant that involve flow
through annular passages, the designs frequently require the use of
vanes to deflect or to turn the air circumferential: through some
prescribed angle. Turning vanes are principally used as the inlet
guide vanes (prerotation vanes) of current steady-flow compressors.
For compressor application in particular, inasmuch as the rotor design
is based on the attainment of the required. variations in Velocity
direction and magnitude at the outlet from the prerotation vanes,
the proper design of guide vanes is an important step in the devel-
opment of a successful unit.

Methods of design of guide vanes for annular passages are based
primarily on considerations of vane air-turning—angle characteristics.
The required variation of turning angle along the radial height of
the vane is determined from the radial variations of the velocity com-
ponents desired at the outlet of the blade row. The desired velocity
distributions are usually calculated from the variation of tangential
velocity required by the type of velocity diagram used in compressor-
design theory.