U.S. patent application number 09/729046 was filed with the patent office on 2002-06-06 for mistuned rotor blade array for passive flutter control.
Invention is credited to Block, Rachel J., Byrne, W. Kerry, Montgomery, Matthew, Silkowski, Peter D., Srinivasan, Sriram.
Application Number | 20020067991 09/729046 |
Document ID | / |
Family ID | 24929355 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067991 |
Kind Code |
A1 |
Montgomery, Matthew ; et
al. |
June 6, 2002 |
Mistuned rotor blade array for passive flutter control
Abstract
The present invention relates to an improved array of flow
directing elements for incorporation in turbomachinery. In
accordance with the present invention, an array of flow directing
elements comprises a plurality of flow directing elements mounted
to a rotor disk. The plurality of flow directing elements includes
a first set of first flow directing elements whose natural
vibration frequency has been modified by having material removed
from a leading edge tip region and a second set of second flow
directing elements whose natural vibration frequency has been
modified by having material removed from a midspan leading edge
region. The array may further comprise unmodified flow directing
elements arranged with the modified flow directing elements.
Inventors: |
Montgomery, Matthew;
(Jupiter, FL) ; Byrne, W. Kerry; (North Palm
Beach, FL) ; Block, Rachel J.; (Greer, SC) ;
Silkowski, Peter D.; (Middletown, CT) ; Srinivasan,
Sriram; (Hebron, CT) |
Correspondence
Address: |
Bachman & LaPointe, P.C.
Suite 1201
900 Chapel Street
New Haven
CT
06510-2802
US
|
Family ID: |
24929355 |
Appl. No.: |
09/729046 |
Filed: |
December 4, 2000 |
Current U.S.
Class: |
416/203 ;
416/500 |
Current CPC
Class: |
F05D 2260/961 20130101;
F01D 5/16 20130101; Y10S 416/50 20130101; F01D 5/10 20130101 |
Class at
Publication: |
416/203 ;
416/500 |
International
Class: |
F01D 005/16 |
Claims
What is claimed is:
1. An array of flow directing elements for use in turbomachinery
comprising: a plurality of flow directing elements mounted to a
rotor disk; said plurality of flow directing elements comprising a
first set of first flow directing elements whose natural vibration
frequency has been modified by having material removed from a
leading edge tip region; and said plurality of flow directing
elements further comprising a second set of second flow directing
elements whose natural vibration frequency has been modified by
having material removed from a midspan leading edge region.
2. An array according to claim 1, further comprising said first and
second sets of flow directing elements being arranged in an
alternating pattern so that adjacent flow directing elements do not
have the same vibration frequency.
3. An array according to claim 1, wherein said first set of flow
directing elements has frequencies of first bending, first torsion,
and second bending vibration modes different from the first
bending, first torsion, and second bending vibration mode
frequencies of said second flow directing elements.
4. An array according to claim 1, further comprising third
unmodified flow directing elements.
5. An array according to claim 4, wherein said flow directing
elements are arranged in an alternating pattern of one of said
first flow directing elements, one of said unmodified flow
directing elements, and one of said second flow directing elements
so that no adjacent flow directing elements have the same vibration
frequency.
6. An array according to claim 4, wherein said flow directing
elements are arranged in sequences of one of said first flow
directing elements, one of said unmodified flow directing elements,
one of said second flow directing elements, and one of said
unmodified flow directing elements.
7. An array according to claim 4, wherein sufficient material is
removed from each said first flow directing element so that the
difference in first torsion frequency between an unmodified flow
directing element and said first flow directing element exceeds
1.0% of the average first torsion frequency for the unmodified flow
directing element.
8. An array according to claim 4, wherein sufficient material is
removed from said second flow directing elements such that the
difference in first torsion frequency between said unmodified flow
directing element and said second flow directing element exceeds
1.0% of the average first torsion frequency of an unmodified flow
directing element.
9. An array according to claim 4, wherein said first, second, and
third flow directing elements are aligned in a row.
10. An array according to claim 1, wherein said first and second
flow directing elements are aligned in a row.
11. An array according to claim 1, wherein said array comprises a
rotor blade assembly for an engine.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an array of flow directing
elements for turbomachinery, in particular to an improved rotor
blade array having improved flutter resistance due to structural
mistuning.
[0002] Turbomachinery devices, such as gas turbine engines and
steam turbines, operate by exchanging energy with a working fluid
using alternating rows of rotating blades and non-rotating vanes.
Each blade and vane has an airfoil portion that interacts with the
working fluid.
[0003] Airfoils have natural vibration modes of increasing
frequency and complexity of the mode shape. The simplest and lowest
frequency modes are typically referred to as first bending, second
bending, and first torsion. First bending is a motion normal to the
flat surface of an airfoil in which the entire span of the airfoil
moves in the same direction. Second bending is similar to first
bending, but with a change in the sense of the motion somewhere
along the span of the airfoil, so that the upper and lower portions
of the airfoil move in opposite directions. First torsion is a
twisting motion around an elastic axis, which is parallel to the
span of the airfoil, in which the entire span of the airfoil, on
each side of the elastic axis, moves in the same direction.
[0004] It is known that turbomachinery blades are subject to
destructive vibrations due to unsteady interaction of the blades
with the working fluid. One type of vibration is known as flutter,
which is an aero-elastic instability resulting from the interaction
of the flow over the blades and the blades'natural vibration
tendencies. The lowest frequency vibration modes, first bending and
first torsion, are typically the vibration modes that are
susceptible to flutter. When flutter occurs, the unsteady
aerodynamic forces on the blade, due to its vibration, add energy
to the vibration, causing the vibration amplitude to increase. The
vibration amplitude can become large enough to cause structural
failure of the blade. The operable range, in terms of pressure rise
and flow rate, of turbomachinery is restricted by various flutter
phenomena.
[0005] It is also known that the blades' susceptibility to flutter
is increased if all blades on a disk are identical in terms of
their vibration frequencies. Advances in manufacturing techniques
have resulted in the production of blades that have nearly uniform
properties. This uniformity is desirable to ensure consistent
aerodynamic performance, but undesirable in that it increases
susceptibility to flutter. Therefore, it has become desirable to
introduce intentional variation in the blades during the
manufacturing process to achieve flutter resistance. These
variations should significantly affect the vibration
characteristics of the blade, thus introducing structural
mistuning, without compromising aerodynamic performance or
introducing undue complexity to the manufacturing process.
[0006] The use of nonuniformity in vibration frequency to avoid
flutter instability for a row of attached blades is addressed in
U.S. Pat. No. 5,286,168 to Smith. The approach discussed in this
patent uses frequency nonuniformity for flutter avoidance, but
requires the manufacture of two distinct blade types.
[0007] The use of nonuniformity in shroud angle to avoid flutter
instability for a blade row of attached, shrouded blades is
addressed in U.S. Pat. No. 5,667,361 to Yaeger et al. This approach
is unattractive for modern gas turbine engines since the use of
shrouds imposes an aerodynamic performance penalty.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to
provide an improved array of flow directing elements for use in
turbomachinery, which array provides passive flutter control.
[0009] It is a further object of the present invention to provide
an improved array as above which does not require two distinct
types of flow directing elements.
[0010] The foregoing objects are attained by the improved array of
the present invention.
[0011] In accordance with the present invention, an array of flow
directing elements for use in turbomachinery for providing passive
flutter control is provided. The array broadly comprises a
plurality of flow directing elements mounted to a rotor disk with
said plurality of flow directing elements comprising a first set of
first flow directing elements whose natural vibration frequency has
been modified by having material removed from a leading edge tip
region and a second set of second flow directing elements whose
natural vibration frequency has been modified by having material
removed from a midspan leading edge region.
[0012] Other details of the structurally mistuned array of the
present invention, as well as other objects and advantages
attendant thereto, are set forth in the following detailed
description and the accompanying drawings wherein like reference
numerals depict like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1a and 1b are side views of flow directing elements to
be used in the array of the present invention;
[0014] FIG. 2 is a perspective view of a first embodiment of an
array of flow directing elements in accordance with the present
invention;
[0015] FIG. 3 is a perspective view of an alternative embodiment of
an array of flow directing elements in accordance with the present
invention; and
[0016] FIG. 4 is a perspective view of yet another alternative
embodiment of an array of flow directing elements in accordance
with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0017] The intent of the present invention is passive flutter
control by constructing an array of flow directing elements from
structurally mistuned elements or blades with different natural
vibration frequencies. The structural mistuning could be
accomplished by manufacturing flow directing elements or blades
with different geometric parameters that include, but are not
limited to, blade thickness, chord length, camber, and profile
shape. Since the manufacture of multiple flow directing element or
blade types is undesirable, structural mistuning can be
accomplished by manufacturing a single flow directing element or
blade type and machining features into the flow directing element
or blade that alter the natural vibration frequencies of the flow
directing elements or blades. Such features include, but are not
limited to, chord blending, as shown in FIGS. 1a and 1b, or
squealer cuts along the tip of the flow directing element or
blade.
[0018] Constructing an array such that the natural vibration
frequency of each flow directing element or blade differs from that
of immediately adjacent flow directing elements or blades increases
the flutter resistance of the flow directing elements or blades.
The frequency separation criterion is that adjacent flow directing
elements or blades differ by at least 1.0% of the average
frequency. The foregoing separation criterion is imposed on each of
the structural modes that pose a flutter threat, typically first
bending and first torsion. The different structural modes of the
different flow directing elements or blades also preferably have
separate frequencies, e.g. the first bending frequency of a high
frequency flow directing element or blade should differ from the
first torsion frequency of a low frequency flow directing element
or blade by at least 1.0%.
[0019] Referring now to FIGS. 1a and 1b, two flow directing
elements or blades 10 and 12 are shown. Each flow directing element
or blade 10 and 12 has an airfoil portion 14, a hub surface 16, a
tip surface 18, and a leading edge 20. Flow directing element or
blade 10 has a higher first torsion frequency due to material being
removed from the region 22 bordering the tip surface 18 and the
leading edge 20. Flow directing element or blade 12 has lower first
torsion frequency due to material being removed from the mid-span,
leading edge region 24. The material may be removed from the
regions 22 and 24 using any suitable technique known in the art.
Other than having material removed from respective regions 22 and
24, the flow directing elements or blades 10 and 12 are of the same
type.
[0020] The amount of material removed from the regions 22 and 24
should be such that (1) the difference in first torsion frequency
between an unmodified flow directing element or blade and each of
the flow directing elements or blades 10 and 12 exceeds 1.0% of the
average first torsion frequency; and (2) the difference in first
bending frequency between an unmodified flow directing element or
blade and each of the flow directing elements or blades 10 and 12
exceed 1.0% of the average first bending frequency.
[0021] FIG. 2 illustrates one embodiment of an array of flow
directing elements to be incorporated into turbomachinery device
such as a gas turbine engine or a steam turbine. Such devices
typically having a plurality of rows of flow directing elements,
such as rotor blades, which are alternated with rows of stationary
vanes or blades. The combination of a rotor row and vane row being
known as a stage. In the embodiment of FIG. 2, the flow directing
elements are aligned in a row of alternating high and low frequency
flow directing elements or blades 10 and 12. As can be seen from
this figure, the flow directing elements or blades 10 and 12 are
attached to a disk 32. The disk 32 may comprise any suitable rotor
disk known in the art. Further, the blades 10 and 12 may be
attached to the disk 32 using any suitable means known in the
art.
[0022] FIG. 3 illustrates an alternative embodiment of an array of
flow directing elements to be incorporated into a turbomachinery
device. As shown in this figure, the flow directing elements or
blades are aligned in a row and include alternating high frequency
flow directing elements 10, unmodified flow directing elements 36,
and low frequency flow directing elements 12 attached to a disk 32.
As before, the disk 32 may comprise any suitable rotor disk known
in the art. The flow directing elements or blades 10, 12, and 36
may be attached to the disk using any suitable means known in the
art.
[0023] FIG. 4 illustrates still another embodiment of an array of
flow directing elements to be incorporated into a turbomachinery
device. The array 40 has a plurality of flow directing elements or
blades in the following sequence: a high frequency flow directing
element or blade 10, an unmodified flow directing element or blade
36, a low frequency flow directing element or blade 12, and an
unmodified flow directing element or blade 36. The flow directing
elements or blades 10, 36, and 12 are arrayed in a circular
pattern. The flow directing elements or blades 10, 36 and 12 are
mounted to a disk 32. The disk 32 may comprise any suitable rotor
disk known in the art. The blades 10, 36, and 12 may be attached to
the disk 32 using any suitable means known in the art.
[0024] As previously discussed, the various embodiments of the flow
directing elements array of the present invention may be used in a
wide variety of turbomachinery to provide passive flutter
control.
[0025] It is apparent that there has been provided in accordance
with the present invention a mistuned rotor blade array for passive
flutter control which fully satisfies the means, objects, and
advantages set forth hereinbefore. While the present invention has
been described in the context of specific embodiments thereof,
other alternatives, modifications, and variations, will become
apparent to those skilled in the art have read the foregoing
description. Therefore, it is intended to embrace those
alternatives, modifications, and variations which fall within the
broad scope of the appended claims.
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