A choking device to cause a sonic barrier to be formed which reduces the transmission of noise in a direction opposed to the direction of air flow in a compressor that may be part of an aircraft gas turbine engine is described. The noise reduction is accomplished by proper shaping and movement of inlet guide vanes, and an actuator is connected to selected guide vanes to effect movement by programmed amounts as required to choke or partially choke within the design range of the axial-flow-air compressor

Chestnutt, D.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
AUG 2 l 1974
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Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740023157 2020-03-17T15:11:10+00:00Z
United States Patent
Chestnutt
[in 3,829,237
[45] Aug. 13, 1974
[54] VARIABLY POSITIONED GUIDE VANES
FOR AERODYNAMIC CHOKING
[75] Inventor: David Chestnutt, Newport News,
Va.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: June 27, 1972
[21] Appl. No.: 266,820
[52] U.S. Cl 415/181, 137/15.1
[51] Int. Cl F02k 11/00, FOld 1/02, FOld 9/00
[58] Field of Search 137/15.1, 15.2; 181/33 HA;
415/181; 60/39.29
[56] References Cited
UNITED STATES PATENTS
2,805,818 9/1957 Ferri 415/181
2,806,350 9/1957 Hoffmann 60/39.29
3,583,417 6/1971 Clark 137/15.1
3,610,262 10/1971 Wise 137/15.1
Primary Examiner—Carlton R. Croyle
Assistant Examiner—Louis J. Casaregola
Attorney, Agent, or Firm—Howard J. Osborn; John R.
Mannin
[57] ABSTRACT
A choking device to cause a sonic barrier to be
formed which reduces the transmission of noise in a
direction opposed to the direction of air flow in a
compressor that may be part of an aircraft gas turbine
engine. The noise reduction is accomplished by proper
shaping and movement of inlet guide vanes, and an ac-
tuator is connected to selected guide vanes to effect
movement thereof by programmed amounts as re-
quired to choke or partially choke within the design
range of the axial-flow-air compressor.
7 Claims, 6 Drawing Figures
SECTION A-A
(NASA-Case-LAB-106U2-1) VARIABLY
POSITIONED GUIDE VANES FOB AEBODYNAMIC
CHOKING Patent (NASA) 8 p CSCL 21E
N74-3127(A
Unclas
00/28 U5938
PATENTED AUG 131374 3,829,237
SHEET 1 OF 4
FIG. 2
FIG. 1
14
PATENIEDWG13BH
SHEET H Of 4
3,829,237
PATENTED AOE131374 3,829.237
SHEET 3 OF 4
SECTION A-A
FIG. 4a
SECTION A-A
FIG. 41
PATENTEOAOG131974 3.829,237
SHEET * OF 4
FIG. 5
1 3,829,237
VARIABLY POSITIONED GUIDE VANES FOR
AERODYNAMIC CHOKING
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to inlet guide vanes of an axial-
flow-air compressor which are shaped and selectively
movable to cause either aerodynamic choking or par-
tial choking to occur, to reduce the transmission of
noise. It has particular utility for use on inlets of aircraft
engines although it could be used in any duct to attenu-
ate noise being transmitted upstream through the air
and the duct.
2. Description of the Prior Art
The prior art includes devices by which noise reduc-
tion in systems such as an aircraft gas turbine engine
having axial-flow compressors may be obtained by inlet
choking. Inlet choking in the past has been accom-
plished through reduction of the inlet area by (1) caus-
ing the outside diameter of the inlet to contract, (2)
axial movement of a variable diameter centerbody and
(3) installation of different thickness inlet guides.
These prior art techniques however have disadvan-
tages. For example, technique (1) above requires the
use of relatively complex and heavy equipment. Fur-
ther, the aerodynamic losses in the unchoked configu-
rations are excessive. Technique (2) above comprises
a somewhat simpler procedure, but requires the use of
relatively long centerbodies for the diffusion losses to
be acceptable. Further, the noise reduction is less than
that normally obtained by other choking means. Tech-
nique (3) above does not provide for variation of inlet
guide vane thickness and therefore has limited practi-
cal value.
Another prior art device is shown in the Jerie et al.
U.S. Pat. No. 3,270,953, which discloses a fixed blade
arrangement to reduce the operating noise of axial-flow
compressors by using a specific ratio of the number of
rotor blades to the number of stator blades, and by se-
lecting angular relationships of the edges of the rotor
and stator blades. It is also known that vanes may be
used to provide a variable area turbine entrance nozzle,
wherein the vanes are pivotable to vary the flow area
(Paetz U.S. Pat. No. 2,819,732), and that blades may
be adjustable in an turbo-compressor type gas engine
to control air flow where the sound frequencies are in-
dicative of operational characteristics of the device
(Warden et al. U.S. Pat. No. 3,245,219).
SUMMARY OF THE DISCLOSURE
The disadvantages and limitations of the prior art are
solved by the instant invention which provides a simple
and reliable means of reducing the noise transmission
from the inlet of an axial-flow-air compressor, which
may be part of an aircraft gas turbine engine. This noise
reduction is accomplished by proper shaping and
movement of the inlet guide vanes to cause either aero-
dynamic choking or partial choking to occur, which-
ever is required. Aerodynamic choking causes a sonic
barrier to be formed which reduces the transmission of
noise in a direction opposed to the direction of air flow.
The invention comprises a plurality of inlet guide
vanes, alternate ones of which are movable to selec-
tively effect the choked and unchoked condition. Fur-
thermore, the guide vanes are contoured and shaped to
optimize their effectiveness.
The advantages of the invention over the prior art
are: (1) the device is capable of choking or partially
5 choking over the entire operating range of a compres-
sor during operation, (2) it is much simpler, (3) is re-
quires less weight, (4) it is more economical to install,
and (5) the unchoked configuration is capable of oper-
ating at smaller aerodynamic losses than other type
10 choking devices.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of an axial-air-flow compressor
inlet;
15 FIG. 2 is a perspective view of the configuration of
a guide vane according to the invention;
FIG. 3 shows a plurality of guide vanes in an air flow
path, alternate ones of which are movable, according
to the invention;
20 FIGS. 4(a) and 4(b) are taken along section lines
A—A of FIG. 1, and respectively show the unchoked
and choked positions of the guide vanes of the FIG. 3
configuration;
FIG. 5 shows another guide vane configuration ac-
25 cording to the invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a front view of inlet 10 of a conven-
tional axial-air-flow compressor having a plurality of
30 guide vanes 11 symetrically arranged about the longitu-
dinal axis thereof. The structure of an individual guide
vane 11 is shown in perspective view in FIG. 2. The
guide vanes are relatively thin and taper outwardly in
frontal dimension from their inner position 18 to their
35
 outer position 12, in inlet 10.
The operation of one embodiment of the guide vane
structure according to the invention, may be described
with respect to FIG. 3 which shows the side position of
a series of five guide vanes 11 arranged in the air flow
40
 path. Each guide vane 11 consists of an elongated and
relatively thin structure having a slight curve. With re-
spect to FIGS. 2 and 3, each guide vane 11 comprises
a substantially symmetrical elongated parabolic struc-
ture having substantially straight end sections 13 and
45
 14 and curved center section 15. The longitudinal axis
of ends 13 and 14 are located in the same plane. The
thickness of guide vanes 11 increases from the extremi-
ties of ends 13 and 14 towards the geometrical center
16 of the guide vanes, which is also the crest of curved
portion 15.
The thickness of guide vanes 11 at point 16 is desig-
nated T, and the length of the guide vanes 11 is desig-
nated L. The longitudinal distance between the points
at which ends 13 and 14 start to curve and the geomet-
rical center 16 of the guide vanes is designated M. The
lateral distance between the extremities of ends 13 and
14 and the midpoint 17 of the thickness dimension of
guide vanes at point 16, is designated R. Ends 13 and
60 14 are substantially straight for a distance L/7.
The dimensions R, T and L are determined depend-
ing upon the particular installation. The dimensions R
and M depend upon the minimum air flow at which
choking is required. The dimensions R and L depend
65 upon the maximum deflection of the airstream before
separation occurs. The dimension T depends upon the
maximum air flow at which choking is not required.
The guide vanes can be easily designed to allow for a
50
55
3,829,237
maximum air flow rate without choking during normal
operation and yet cause the choked condition, in a
manner described hereinafter, at a minimum air flow
rate whenever large noise reductions are required.
The manner in which the choked condition is ob-
tained in the guide vane embodiment shown in FIG. 3
may be described with respect to the guide vane posi-
tions indicated by the broken and solid lines. The solid
line positions of the guide vanes indicate the unchoked
condition. By moving alternate guide vanes 11 towards
the right a predetermined distance, the desired choked
condition can be obtained. Thus it is seen with refer-
ence to FIG. 3 that by moving two of the five guide
vanes a predetermined distance into the air flow path,
to the position designated by the broken line designa-
tion of the guide vanes so moved, the choked condition
is attained wherein the air flow is constricted. By so
moving alternate guide vanes to the choked condition,
a minimum air-flow rate will be provided whenever
large noise reductions are required. It should be under-
stood that the definition of alternate guide vanes in-
cludes other arrangements, such as every third or
fourth vane being movable.
An actuating mechanism that may be employed to
move the guide vanes between choked and unchoked
conditions is shown in FIGS. 4(a) and4(fc) of the draw-
ings. FIG. 4(a) shows the unchoked position, wherein
guide vanes 20 through 24 are aligned laterally. Guide
vanes 20, 22 and 24 are attached to centerbody 25
which is selectively movable to the right or left. In the
position shown in FIG. 4(b) the centerbody 25 has
been moved to the left thereby moving guide vanes 20,
22, 24 to the left to provide the choked condition,
which will minimize the air-flow rate by restricting the
air-flow area. The actuating mechanism 26 may com-
prise any device that will move alternate guide vanes
attached thereto programmed amounts as required to
choke or partially choke within the design range of the
compressor.
FIG. 5 illustrates another embodiment of the inven-
tion showing guide vanes 30 in the air-flow path. The
solid line position of guide vanes 30 show their normal
or unchoked condition. The choked condition can be
obtained by pivoting alternate guide vanes 30 about
their own centers, to the positions thereof shown in
broken lines. The configuration of guide vanes 30
shown in FIG. 5 is somewhat different from the config-
uration of guide vanes 11 shown in FIG. 3. Thus
straight end portions 31 and 32 of guide vanes 30 of
FIG. 5 are not in the same longitudinal plane, but are
located in substantially parallel longitudinal planes.
The designations T, R and L correspond however to the
same designations explained with reference to FIG. 1,
and the designation angle 6 indicates the angular devia-
tion of alternate guide vanes 30 from their unchoked
position as shown by the solid line guide vane configu-
ration, to their choked position as shown by the broken
line configuration of guide vanes 30. As in the previous
embodiment alternate may mean an arrangement other
than every other vane. An actuator mechanism 27 to
actuate the guide vanes 30 of FIG. 5 between choked
and unchoked condition would also be utilized to ro-
tate alternate vanes 30 about their own centers a pro-
grammed amount as required to choke or partially
choke within the design range of the compressor. The
actuator mechanism 27 may be housed within the cen-
20
terbody, and would have additional linkage to cause
guide vane rotation.
The guide vane structures of FIGS. 3 and 5 do not
show any prewhirl being added to the air flow, but pre-
5 whirl could be easily added along the guide vanes or at
their trailing edges without affecting the choking prin-
ciple. It is to be understood that although this device is
primarily intended for use on inlets of aircraft engines,
it could also be used in any duct to attenuate noise
'0 being transmitted upstream through the air in the duct.
What is claimed is:
1. In an axial-flow-air compressor having air inlet
means and a plurality of similarly configured inlet guide
15
 vanes positioned symmetrically therein, the improve-
ment comprising:
a radially and symmetrically positioned plurality of
tapered inlet guide vanes in the inlet of an axial-
flow-air compressor, capable of adding prewhirl to
air flowing therein,
each of the plurality of guide vanes being relatively
elongated along its longitudinal cross-sectional di-
mension and defining a central raised portion in the
25 form of an underchambered hump along said di-
mension,
positioning means operable to position the plurality
of guide vanes in parallel cross-sectional alignment
with corresponding points on said humps being
30 substantially coplanar to provide an unchoked con-
dition for the air flow, said positioning means being
further selectively operable to simultaneously
move the selected ones of the plurality of guide
vanes out of said alignment wherein selected
35 humps of the plurality of guide vanes are mis-
aligned to constrict the flow of air to provide a
choked condition causing a sonic barrier to be
formed which reduced the transmission of noise in
a direction opposed to the direction of air flow.
40 2. The axial-flow-air compressor recited in claim 1
wherein each of the plurality of inlet guide vane cross-
sections comprises substantially straight end portions
joined together by said raised portion in the form of an
underchambered hump.
45 3. The axial-flow-air compressor recited in claim 2
wherein each of the plurality of inlet guide vane cross-
sections is tapered to increase in thickness from their
straight end portions toward the center of the raised
portion, the latter being the thickest dimension thereof.
4. The axial-flow-air compressor recited in claim 3
wherein the longitudinal axes of the inlet guide vane
cross-sections straight end portions are located in the
same plane.
55
 5. The axial-flow-air compressor recited in claim 3
wherein the longitudinal axes of the inlet guide vane
cross sections straight end portions are located in paral-
lel planes.
6. The axial-flow-air compressor recited in claim 1
wherein the positioning means move alternate ones of
the plurality of inlet guide vanes out of the said parallel
cross-section alignment by movement thereof in an
axial direction.
7. In an axial-flow-air compressor having air inlet
means and a plurality of similarly configured inlet guide
vanes positioned symmetrically therein, the improve-
ment comprising:
60
3,829,237
A radially and symmetrically positioned plurality of
tapered inlet guide vanes in the inlet of an axial-
flow-air compressor, capable of adding prewhirl to
air flowing therein,
each of the plurality of guide vanes being relatively
elongated along its longitudinal cross-sectional di-
mension and defining a central curved portion
along said dimension,
positioning means operable to position the plurality
of guide vanes in parallel cross-sectional alignment
to provide an unchoked condition for the air flow,
10
said positioning means being further selectively op-
erable to simultaneously move selected guide vanes
out of said alignment by pivoting said selected
guide vanes about their own longitudinal axes
wherein selected curved portions of the plurality of
guide vanes are misaligned to constrict the flow of
air to provide a choked condition causing a sonic
barrier to be formed which reduces the transmis-
sion of noise in a direction opposed to the direction
of air flow.
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Variably positioned guide vanes for aerodynamic choking

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