U.S. patent application number 09/735503 was filed with the patent office on 2002-06-20 for method using secondary orientation to tune bucket natural frequency.
Invention is credited to Wang, John Zhiqiang.
Application Number | 20020074102 09/735503 |
Document ID | / |
Family ID | 24956083 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020074102 |
Kind Code |
A1 |
Wang, John Zhiqiang |
June 20, 2002 |
Method using secondary orientation to tune bucket natural
frequency
Abstract
Tuning of turbine bucket torsional and stripe mode natural
frequencies can be effected without altering any turbine bucket
physical features, such as weight and/or shape, and without
affecting flexure frequencies. The tuning of certain turbine bucket
natural frequencies serves to avoid detrimental blade resonance,
thus improving the reliability of a gas turbine. The method
includes investment casting the turbine bucket with a single
crystal alloy, and tuning the natural frequency of the turbine
bucket without modifying physical features of the turbine bucket by
placing a crystal seed along a desired direction according to a
relative orientation of an engine axial direction.
Inventors: |
Wang, John Zhiqiang;
(Greenville, SC) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Road
Arlington
VA
22201
US
|
Family ID: |
24956083 |
Appl. No.: |
09/735503 |
Filed: |
December 14, 2000 |
Current U.S.
Class: |
164/122.2 ;
164/122; 164/122.1 |
Current CPC
Class: |
F05D 2300/607 20130101;
B22D 27/045 20130101; F01D 5/16 20130101; F05D 2230/21 20130101;
F01D 5/26 20130101 |
Class at
Publication: |
164/122.2 ;
164/122; 164/122.1 |
International
Class: |
B22D 027/04; B22D
007/10 |
Goverment Interests
[0001] This invention was made with Government support under
Contract No. DE-FC21-95MC-31176 awarded by the Department of
Energy. The Government has certain rights in this invention.
Claims
What is claimed is:
1. A method of manufacturing a turbine bucket comprising: (a)
investment casting the turbine bucket with a single crystal alloy;
and (b) tuning a natural frequency of the turbine bucket without
modifying physical features of the turbine bucket.
2. A method according to claim 1, wherein step (b) is practiced by
tuning the natural frequency of the turbine bucket without
affecting turbine bucket weight.
3. A method according to claim 1, wherein step (b) is practiced by
tuning the natural frequency of the turbine bucket without
affecting turbine bucket shape.
4. A method according to claim 1, wherein step (b) is practiced by
tuning torsional and stripe mode frequencies without affecting
flexure mode frequencies of the turbine bucket.
5. A method according to claim 1, wherein step (b) is practiced by,
prior to step (a), placing a crystal seed along a desired direction
according to an orientation relative to an engine axial
direction.
6. A method of tuning turbine bucket natural frequency comprising:
(a) placing a crystal seed along a desired orientation relative to
an engine axial direction; and (b) investment casting the turbine
bucket with a single crystal alloy, wherein the desired orientation
is selected to tune torsional frequencies without affecting flexure
frequencies.
7. A method according to claim 6, comprising tuning the natural
frequency of the turbine bucket without affecting turbine bucket
weight.
8. A method according to claim 6, comprising tuning the natural
frequency of the turbine bucket without affecting turbine bucket
shape.
Description
BACKGROUND OF THE INVENTION
[0002] This invention relates to gas turbine bucket construction
and, more particularly, to using secondary orientation to tune
turbine bucket natural frequencies.
[0003] As a rotational component in a gas turbine engine, the
turbine blade or turbine bucket experiences different dynamic
stimuli due to the aerodynamic disturbances from, for example, the
up- and down-stream nozzles, the combustor cans, the tip shrouds,
etc. When any of these stimulus frequencies is close enough to the
natural frequency of the rotational turbine bucket, resonance may
occur that will likely cause failures, usually catastrophic, to the
bucket due to high cycle fatigue. Indeed, a large number of engine
failures in the field can be traced back to the root cause of
vibration related failures. Thus, it is important in bucket design
to avoid resonance during operation by a sufficient margin.
[0004] Previously, tuning of bucket natural frequencies has been
accomplished using airfoil thickness to chord ratio, trailing edge
wedge angle, trailing edge mass, airfoil wall thickness, cooling
cavity size and number, tip shroud or cap, and camber. These
previous methods, however, typically require the alteration of some
physical feature of the bucket such as bucket weight or shape
and/or increased production costs or altering the flex modes when
only torsional or stripe modes are needed to be tuned. It is thus
desirable to effect tuning of bucket torsional and stripe mode
natural frequencies without altering any bucket physical features,
without increasing bucket manufacturing cost, and without affecting
the turbine bucket flexure frequencies.
BRIEF SUMMARY OF THE INVENTION
[0005] In an exemplary embodiment of the invention, a method of
manufacturing a turbine bucket includes (a) investment casting the
turbine bucket with a single crystal alloy, and (b) tuning a
natural frequency of the turbine bucket without modifying physical
features of the turbine bucket. Step (b) may be practiced by tuning
the natural frequency of the turbine bucket without affecting
turbine bucket weight or turbine bucket shape. Step (b) may also be
practiced by tuning torsional and stripe mode frequencies without
affecting flexure mode frequencies of the turbine bucket. In this
context, step (b) is preferably practiced by, prior to step (a),
placing the crystal seed along a desired direction according to an
orientation relative to the engine axial direction.
[0006] In another exemplary embodiment of the invention, a method
of tuning turbine bucket natural frequency includes (a) placing the
crystal seed along a desired orientation relative to the engine
axial direction, and (b) investment casting the turbine bucket with
a single crystal alloy, wherein the desired orientation is selected
to tune torsional frequencies without affecting flexure
frequencies.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates a crystal orientation relative to engine
orientations;
[0008] FIG. 2 is a graph showing the effect of secondary
orientation on 1T and 2T frequencies; and
[0009] FIG. 3 is a graph showing the effect of secondary
orientation on 1-2S and 1-3S frequencies.
DETAILED DESCRIPTION OF THE INVENTION
[0010] With reference to FIG. 1, in a single crystal alloy, the
material directions along the X' and Y' axes are termed secondary
orientation, while that along the Z' direction is termed as the
primary orientation. The secondary orientation is defined by the
angle .theta..sub.s between the engine axial direction X and the
material direction X', which is the same as the angle between the
engine tangential direction Y and the material direction Y'.
[0011] Operating frequencies of turbine buckets can be determined
in the design phase using engineering models and the like as would
be apparent to those of ordinary skill in the art. The data for
FIGS. 2 and 3 is based on known Finite Element (FE) Analyses (known
as ANSYS code) and is validated through engine tests. Similar
engineering models by FE analyses can be used to determine bucket
natural frequencies. As noted, it is important to avoid resonance
by a sufficient margin to improve operating efficiency, and it thus
may be necessary to "tune" the natural frequencies of a turbine
bucket.
[0012] In a bucket of single crystal alloy, the shear modulus that
determines the torsional frequencies is dependent on the secondary
orientation .theta..sub.s. The tensile modulus along the radial
direction that determines the flexure frequencies, on the other
hand, is insensitive to the secondary orientation. Thus, with the
method of the present invention, the secondary orientation can be
used to tune the torsional frequencies without affecting the
flexure frequencies. FIG. 2 shows the change of 1T and 2T
frequencies as a function of the secondary orientation. FIG. 3
shows the change of 1-2S and 1-3S frequencies as a function of the
secondary orientation. It is known that changes in the secondary
orientation will not affect the flexure frequencies (such as 1F,
2F, etc.). Moreover, the change in secondary orientation does not
entail changes in turbine bucket weight and shape. To implement
certain preferred secondary orientation in an investment casting
process is a relatively easy operation, thus the impact is minimal
on manufacturing cost.
[0013] As noted, the data for FIGS. 2 and 3 is derived from FE
analyses. First analyses are conducted by incorporating the
secondary orientation in the engineering model, then the results
are correlated with the engine test results. Subsequently, the
secondary orientation is varied, and the curves are completed.
[0014] Investment casting with a single crystal alloy is known, and
the details of the casting process will not be described herein. A
related investment casting process is described in commonly-owned
U.S. Pat. No. 5,713,722, the contents of which are herein
incorporated by reference.
[0015] In the investment casting process, the secondary orientation
is controlled by placing the crystal seed along a desired
direction. Placing of the crystal seed in the investment casting
process does not affect the physical features of the turbine
bucket, such as the bucket weight or shape, and does not entail any
additional manufacturing operation or cost. As shown in FIGS. 2 and
3, the desired direction of the crystal seed or secondary
orientation is selected to effect a desired percentage change in
turbine bucket natural frequencies.
[0016] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention is not to be
limited to the disclosed embodiments, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
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