U.S. patent application number 09/853472 was filed with the patent office on 2002-01-24 for shaft bearing for a turbomachine, turbomachine, and method of operating a turbomachine.
Invention is credited to Becker, Bernard, Reichert, Arnd.
Application Number | 20020009361 09/853472 |
Document ID | / |
Family ID | 7887449 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020009361 |
Kind Code |
A1 |
Reichert, Arnd ; et
al. |
January 24, 2002 |
Shaft bearing for a turbomachine, turbomachine, and method of
operating a turbomachine
Abstract
The shaft bearing supports the rotor of a turbo-machine which
extends along a rotor axis. The shaft bearing has a bearing element
with a bearing surface. The bearing surface supports an associated
rotor surface and the bearing element can be axially displaced. The
invention further relates to a turbo-machine and to a method for
operating said turbo-machine.
Inventors: |
Reichert, Arnd; (Duisburg,
DE) ; Becker, Bernard; (Muhlheim A.D. Ruhr,
DE) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
Post office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
7887449 |
Appl. No.: |
09/853472 |
Filed: |
May 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09853472 |
May 11, 2001 |
|
|
|
PCT/DE99/03488 |
Nov 2, 1999 |
|
|
|
Current U.S.
Class: |
415/110 |
Current CPC
Class: |
F16C 17/04 20130101;
F16C 32/0696 20130101; F01D 25/166 20130101; F16C 32/067 20130101;
F16C 2360/23 20130101; F05D 2240/53 20130101; F16C 32/0692
20130101; F16C 25/02 20130101; F01D 11/22 20130101 |
Class at
Publication: |
415/110 |
International
Class: |
F01D 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 1998 |
DE |
198 52 047.6 |
Claims
We claim:
1. A turbomachine, comprising: a casing with a conical inner wall;
a rotor extending through said casing along a rotor center line
through said casing, said rotor carrying a plurality of rotor
blades each having a blade tip facing towards said inner wall and
having a conicity substantially corresponding to said inner wall,
whereby a radial gap is formed between each said blade tip and said
inner wall; a shaft bearing having at least one axially
displaceable bearing element formed with a bearing surface
immediately adjacent a rotor surface and being capable of axially
displacing said rotor surface; and a mechanical displacement device
connected to said bearing element and configured to displace said
bearing element and said rotor, and to compensate for an increase
in said radial gap upon heating during an operation of the
turbomachine.
2. The turbomachine according to claim 1, wherein said axially
displaceable bearing element is an axially displaceable annular
piston.
3. The turbomachine according to claim 1, wherein said mechanical
displacement device comprises a displacement element and a
displacement drive.
4. The turbomachine according to claim 3, wherein said displacement
drive includes an electric motor.
5. The turbomachine according to claim 1, wherein said bearing
surfaces are displaceably disposed for displacement by between 0.5
mm and 5 mm.
6. The turbomachine according to claim 1, wherein said bearing is a
rotor bearing for stationary operation.
7. The turbomachine according to claim 1, wherein said rotor blades
are disposed in at least two rows of rotor blades at an axial
distance from one another, and wherein said casing and said blade
tips are configured such that an axial displacement of said rotor
provides an equal radial gap for each of said rows.
8. A method of operating a turbomachine, which comprises: providing
a turbomachine with a casing having a conical inner wall and a
rotor in the casing, the rotor carrying a plurality of rotor blades
each having a blade tip facing towards the inner wall and having a
conicity substantially corresponding to a conicity of the inner
wall and forming a radial gap between each blade tip and the inner
wall; supporting the rotor in a shaft bearing having at least one
axially displaceable bearing element formed with a bearing surface
immediately adjacent a rotor surface; and displacing the rotor
relative to the casing by displacing the axially displaceable
bearing element, and thereby adjusting the radial gap between the
blade tip and the inner wall to suit a given operating condition of
the turbomachine.
9. The method according to claim 8, which comprises setting the
radial gap on reaching a powered operation condition of the
turbomachine.
10. The method according to claim 9, which comprises determining
that the powered operation condition of the turbomachine has been
achieved during a specified time period.
11. The method according to claim 9, which comprises determining
that the powered operation condition of the turbomachine has been
achieved by determining the axial gap occurring as a consequence of
thermal expansions.
12. The method according to claim 9, which comprises determining
that the powered operation condition of the turbomachine has been
achieved by determining a relative displacement between the casing
and the rotor.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending
International Application No. PCT/DE99/03488, filed Nov. 2, 1999,
which designated the United States.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0002] The invention lies in the mechanical arts. More
specifically, the invention relates to a shaft bearing for the
rotor of a turbomachine. The rotor extends along a rotor center
line. The shaft bearing has a first bearing element which has a
first bearing surface and a second bearing element which has a
second bearing surface. In addition, the invention relates to a
turbomachine with a rotor which extends along a rotor center line
through a casing and in which the casing has a conical inner wall.
Rotor blades are arranged on the rotor and these each have a blade
tip which faces toward the inner wall and which, in a manner
analogous to the inner wall; is conical. The turbomachine has a
shaft bearing of the type mentioned above. The invention relates,
furthermore, to a method of operating a turbomachine, in which
method a displacement of the rotor is carried out relative to the
casing.
[0003] Published international PCT application WO 93/20335
describes a method and a configuration for controlling a gap width
between the blade tip of a rotor blade and a stationary casing of a
rotating machine with a turbine part and a compressor part. There,
the control of the gap width takes place in such a way that, during
the startup phase of the gas turbine, the shutting down of the gas
turbine and load changes of the gas turbine, the gap width is
larger than it is during continuous operation of the gas turbine.
By this means, the danger of a turbine blade rubbing on the casing
during starting, shut-down and load change is reduced. For this
purpose, the rotors of the compressor and the turbine are
permanently connected together so that they form a single rotor.
The casings of the compressor and the turbine are separated from
one another and the compressor casing is arranged so that it can be
displaced relative to the turbine casing. Due to a displacement of
the compressor casing, a displacement of the complete rotor and,
therefore, a displacement between the turbine rotor blades and the
turbine casing, take place simultaneously.
[0004] U.S. Pat. No. 1,823,310 describes a turbine, in particular a
steam turbine, in which means are provided for an axial
displacement of the rotor, so that a gap width is provided between
the turbine rotor blades and the turbine casing which is greater
during the starting and shutting down of the turbine than during
the normal operating conditions of the turbine. By this means, a
rub or damage to the turbine rotor blades is prevented. The means
for displacing the rotor blades act on a thrust bearing. This is
connected to the rotor in such a way that when the thrust bearing
is displaced axially, the rotor is also displaced. In that
configuration, the means comprise a system consisting of gearwheels
and racks by means of which the thrust bearing, and therefore the
rotor also, are axially displaced. The same setting principle for
the gap width between the rotor blades of a turbine and a turbine
casing is employed in French published patent application FR 2 722
836 A1 for a gas turbine with a compressor. There, the gas turbine
is supported at a turbine end so that it can be axially moved in a
bearing. Further support to the gas turbine takes place at a
compressor end by means of a ball bearing, which fixes the complete
gas turbine axially. The ball bearing, which is permanently
connected to the rotor of the gas turbine, can be axially displaced
by means of an appliance so that axial mobility of the rotor
relative to the turbine casing is also provided. The ball bearing,
and therefore the rotor, can be displaced relative to the turbine
casing by a displacement of .+-.2 mm.
[0005] U.S. Pat. No. 5,263,817 specifies a centrifugal compressor
and a gas turbine with a device for an active gap width control
between the rotor blades and the stationary casing. A ball bearing,
whose outer race is clamped into the casing in such a way that
there is still a small amount of axial mobility, which is limited
by a stop, is attached to the rotor. In that configuration, the
outer race of the bearing is clamped between the stop and an
electromagnetic drive, each of which is permanently connected to
the casing. The electromagnetic drive has an electromagnet which is
axially adjacent to a radial ferromagnetic disk permanently
connected to the rotor. The disk is attracted to a greater or
lesser extent, depending on the strength of the magnetic field
generated by the electromagnets, so that the axial position of the
complete rotor can be varied. By this means, it is possible to
actively control the axial position of a rotor blade, and therefore
of the gap width between the rotor blade and the conical turbine
casing.
[0006] German published patent application DE 42 23 495 A1
describes a gas turbine in which a rotor displacement device is
provided for setting a small blade clearance. The rotor
displacement device consists of a two-part suspended casing for
accommodating a thrust bearing, two annular support plates, which
are fastened to the induction casing and to which pressure cells
are attached. By means of these, the complete bearing position, and
therefore the position of the rotor, can be set in such a way that
an increased clearance can be set in the conical blade duct during
the start-up and shut-down phases of the gas turbine.
[0007] A common feature of all the prior art devices for displacing
a rotor of a turbomachine is substantial structural complication
and the interference with the design of a casing or a rotor, as
well as the correspondingly increased fault susceptibility.
SUMMARY OF THE INVENTION
[0008] The object of the present invention is to provide a shaft
bearing for a turbomachine which overcomes the above-noted
deficiencies and disadvantages of the prior art devices and methods
of this general kind, and which permits simple axial displacement
of the rotor. Further objects of the invention are to provide a
turbomachine with an axially displaceable rotor and a method of
operating a turbomachine with an axially displaceable rotor.
[0009] With the above and other objects in view there is provided,
in accordance with the invention, a turbomachine, comprising:
[0010] a casing with a conical inner wall;
[0011] a rotor extending through the casing along a rotor center
line through the casing, the rotor carrying a plurality of rotor
blades each having a blade tip facing towards the inner wall and
having a conicity substantially corresponding to the inner wall,
whereby a radial gap is formed between each the blade tip and the
inner wall;
[0012] a shaft bearing having at least one axially displaceable
bearing element formed with a bearing surface immediately adjacent
a rotor surface and being capable of axially displacing the rotor
surface; and
[0013] a mechanical displacement device connected to the bearing
element and configured to displace the bearing element and the
rotor, and to compensate for an increase in the radial gap upon
heating during an operation of the turbomachine.
[0014] In other words, the objects are achieved with the shaft
bearing which has a bearing element with a bearing surface, the
bearing element with the bearing surface serving as bearing for a
rotor surface and being axially displaceable in order to displace
the rotor.
[0015] The invention is premised on the realization that a
structural redesign of a shaft bearing in such a way that the
displacement of a rotor takes place by means of the shaft bearing
can be achieved without an essential design change to the rotor or
to a casing of a turbomachine. According to the invention, this
takes place by a bearing element, which serves as bearing for a
rotor surface, being axially displaceable. In this case, axially
displaceable signifies displacement in the axial direction relative
to a fixed point so that, as a result of the bearing arrangement
for the rotor surface, the rotor itself can also be axially
displaced. In this arrangement, the shaft bearing is axially fixed.
A shaft bearing is then preferably arranged between two radial
rotor surfaces of the rotor, a displacement of the rotor by means
of the shaft bearing being possible without design changes to the
rotor and to the casing. For this purpose, at least one bearing
element and therefore one bearing surface is axially displaceable.
During an axial displacement of this bearing element, an axial
displacement of the rotor takes place simultaneously.
[0016] This is particularly advantageous in the case of
turbomachines such as compressors, gas turbines, and steam
turbines. In this way, flow losses in radial gaps of a turbine, in
particular a stationary gas turbine with a conical inner wall, can
be reduced. The radial gaps are then free spaces between the
radially outer edge of rotor blades attached to the rotor and the
opposite casing parts (inner wall). Because of the pressure
difference between the pressure side and the suction side of the
rotor blades, working fluid flows through these gaps during the
operation of the turbine; in the case of a gas turbine, the working
fluid is gas. The mass flow through the gaps does not take part in
the conversion to work in the rows of rotor blades at an axial
distance from one another and therefore reduces the efficiency of
the turbine. In a gas turbine, approximately 30% of the flow losses
can be caused by gap leakage. This implies a reduction in the
efficiency of the gas turbine by up to 4%. The magnitude of the
leakage mass flow, and therefore also the level of the flow losses
caused, is determined by the gap width of the radial gaps. In the
case of gas turbines operating in a steady-state manner, what then
matters is the gap widths which become set during operation in the
continuous powered operation condition, i.e. during the set powered
operation condition. In what follows, this gap width is designated
as the hot gap. The reasons for the presence of these hot gaps are,
for example, the deviations produced by manufacturing tolerances
and a safety reserve, for example for unusual operating conditions
in the case of earthquakes or the like. Approximately half of the
hot gap occurring appears due to time-dependent expansions of the
individual turbine components; a steady-state condition of the hot
gap appears after the turbine has heated through completely, it
being possible for the individual turbine components, such as
casing parts or rotor blades, to take up very different
temperatures in this operating condition of the turbine, which
different temperatures can inter alia also cause distortions of the
individual components. By means of the shaft bearing specified, it
is inter alia possible to carry out an axial displacement of the
rotor in a simple manner after a steady-state operating condition
has been reached, in particular a powered operation condition of a
turbomachine, so that the magnitude of the hot gap can be set to a
prescribed value which is as small as possible while taking
account, if necessary, of existing manufacturing deviations and
safety reserves.
[0017] The shaft bearing preferably has a further bearing surface
which is at an axial distance from the other bearing surface. The
two bearing surfaces then serve as bearings for respectively
different rotor surfaces at an axial distance from one another.
Each of the bearing surfaces can then be formed by an individual,
in particular annular bearing element or by a plurality of bearing
elements. The two bearing surfaces are then respectively configured
to be axially displaceable by means of corresponding bearing
elements. The shaft bearing is then a thrust bearing, on which
there is a loaded side (bearing surface) which accepts the rotor
axial thrust, which occurs mainly in this direction, and an
unloaded side (the further bearing surface) which, for example,
briefly accepts load under transition conditions (starting) or in
the case of faults. During the operation of the bearing, both
bearing surfaces are then provided with a corresponding lubricant
film (oil film) so that they act as corresponding sliding surfaces.
A bearing clearance present due to the lubricant film is then
preferably of the order of value of some tenths of a millimeter.
The bearing clearance occurring can be maintained by a
displacement, in particular a unidirectional displacement, of the
two bearing surfaces. By this means, a one-sided, smaller bearing
clearance on one of the bearing surfaces is avoided so that no
additional losses occur. In addition, this avoids an excessively
large bearing clearance which, in the case of an alternating axial
thrust direction of the rotor, could lead to undesirable and
powerful motions of the rotor with high peak accelerations and
inertia forces.
[0018] It is likewise conceivable for one bearing surface to be
axially displaceable by an axial displacement of one bearing
element or a plurality of bearing elements and for the other
bearing surface to be axially fixed. In this case, a displacement
of the rotor takes place by means of only one bearing surface, by
which means an embodiment of the shaft bearing can be achieved with
low design and technical supply complication.
[0019] In accordance with an added feature of the invention, the
axially displaceable bearing element is an axially displaceable
annular piston. A particularly uniform loading of the shaft bearing
and of the rotor surfaces can be achieved by this means. This is,
furthermore, particularly favorable if the axially displaceable
bearing element can be displaced by hydraulic means because a
uniform pressure distribution over the complete periphery of the
annular piston is then ensured by this means. It is, however,
likewise possible to provide a plurality of axially displaceable
bearing elements (bearing pads), which are, in particular, arranged
on a circle concentrically surrounding the rotor.
[0020] In an exemplary embodiment described in the following text,
the displaceable bearing element is displaceable by a hydraulic
system. In that configuration, the bearing element is acted on by a
hydraulic fluid, in particular by an oil, so that a displacement of
the rotor is ensured even in the case of full-load operation of the
turbomachine. The oil volume necessary for the displacement is then
preferably kept constant after a certain axial position has been
reached. Because, as is known, oil is an essentially incompressible
fluid, the axial position of the bearing surfaces, and therefore of
the rotor, never changes to any substantial extent, even in the
case of fluctuating forces (actual thrust), provided the oil
quantity is kept constant. The use of elastic supply lines (hoses)
can be avoided and correspondingly rigid line systems can be
employed in order to keep the oil volume correspondingly constant.
This avoids the axial position of the rotor alternating between the
left-hand stop point and the right-hand stop point in the case of
alternating thrust forces and constant oil pressure. If the
hydraulic fluid, in particular the oil, is enclosed within a
spatial region of constant volume, then, should the thrust force
change, the opposing force on the bearing surface will also change
so that the force equilibrium is maintained. In the case where no
active control of the axial position of the rotor is being carried
out, a stop is preferably present in both axial directions so that,
by means of a corresponding oil pressure, a pressure is present
which acts against the axial thrust of the rotor and clearly
overcomes the latter. The displacement then preferably takes place
by means of two bearing surfaces which can be displaced in the
axial direction, the volume of the hydraulic fluid (oil) pressing
on the bearing surfaces being changed in such a way that a desired
axial position of the rotor is set and the respective volumes of
the hydraulic fluid are then kept constant. The constant volumes
achieve the effect that the force caused by the oil pressure and
acting on the bearing surface is precisely opposite to and equal to
the axial thrust of the rotor. For the supply of the hydraulic
fluid, use is preferably made of an already available hydraulic
supply arrangement in the case of a shaft bearing which provides a
sliding bearing by means of a lubricant (hydraulic fluid). For this
purpose, a hydraulic system already employed for lifting the shaft
at low rotational speeds can, for example, be used, which system is
capable of generating correspondingly high pressures. Such a system
could therefore also be additionally selected, if required, in the
case of normal operation of a turbomachine in order to effect an
axial displacement of the rotor. For this purpose, an additional
high-pressure line can be led to the shaft bearing. With this
supply arrangement, a hydraulic fluid pressure, in particular an
oil pressure, of up to 160 bar is available.
[0021] In accordance with a preferred feature of the invention,
there is provided a mechanical displacement device for displacing
at least one bearing element. This mechanical displacement device
preferably has a displacement element, such as a spindle or the
like, and a displacement drive. The displacement drive is
preferably an electric motor. Other possibilities for designing the
displacement drive can be mechanical displacement drives which, for
example, use the rotation of the rotor during operation of the
turbomachine or the flow of the working fluid flowing through the
turbomachine.
[0022] The shaft bearing is preferably embodied as a sliding
bearing in which a film of a lubricant, in particular hydraulic
oil, forms between the bearing surface and the rotor surface. Such
a bearing is particularly advantageous for the support of a heavy
rotor such, for example, as that employed in stationary gas
turbines for the generation of electrical current.
[0023] The bearing surfaces, and therefore the rotor, can
preferably be displaced by between 0.5 mm and 5 mm. This
displacement is preferably provided in one direction so that the
gap width between rotor blades of the turbomachine and the inner
wall of the casing of the turbomachine is reduced during normal
operation of the turbomachine.
[0024] The shaft bearing preferably has a distance element, for
example a stop, by means of which the maintenance of a specified
minimum distance between the bearing surfaces is ensured. This is
particularly advantageous when a displacement of the rotor against
the resultant force acting on the rotor, caused for example by the
working fluid flowing through the turbomachine, takes place due to
the bearing element. In such a case, the distance element ensures
that the rotor takes up an axial position which it would have taken
up even without an axial displacement due to the bearing element
even in the case of a failure of the hydraulic supply or of the
displacement drive. This ensures the operational safety of the
turbomachine even in the case of a failure of the axial
displacement of the bearing element. Due to the axial thrust
occurring in a gas turbine, the rotor is pressed back into its
initial position by the gas forces in this case.
[0025] The object directed toward a turbomachine is achieved by one
which has a casing with an inner wall which extends conically in
the axial direction and in which the rotor guided through the
casing has rotor blades whose blade tips facing toward the inner
wall extend conically in a manner analogous to the inner wall. The
turbomachine then has a shaft bearing which is adjacent to a radial
rotor surface, is preferably arranged between two radial rotor
surfaces and has at least one axially displaceable bearing element
for the displacement of the rotor.
[0026] Due to the conical (tapered) contour, at least in some
regions, of the inner wall of the casing of the turbomachine, a
change in gap occurs when the rotor is displaced relative to the
casing. In the turbomachine specified, the relative position of
rotor and casing in the continuous condition (steady-state powered
operation condition) of the turbine can be changed in such a way
that the hot gap is reduced by the proportion which takes account
of the transient thermal expansions. Such transient thermal
expansions occur in the turbomachine during the period before all
the components of the turbomachine have permanently taken up their
steady-state operating temperatures characteristic of the operating
condition and have therefore taken up their corresponding thermal
expansions (distortions).
[0027] The turbomachine is preferably a gas turbine, an aircraft
engine turbine, or a stationary gas turbine for the generation of
electrical energy. A stationary gas turbine can then have an
electrical output of more than 60 MW.
[0028] The turbine of the turbomachine preferably has at least two
rows of rotor blades (blade rows) which are at an axial distance
from one another, the casing and/or the blade tips being designed
in such a way that an axial displacement of the rotor provides
approximately the same radial gap for each blade row. For this
purpose, the obliquity (conicity) is approximately the same in all
turbine stages, i.e. blade rows.
[0029] With the above and other objects in view there is also
provided, in accordance with the invention, a method of operating a
turbomachine, which comprises:
[0030] providing a turbomachine with a casing having a conical
inner wall and a rotor in the casing, the rotor carrying a
plurality of rotor blades each having a blade tip facing towards
the inner wall and having a conicity substantially corresponding to
a conicity of the inner wall and forming a radial gap between each
blade tip and the inner wall; supporting the rotor in a shaft
bearing having at least one axially displaceable bearing element
formed with a bearing surface immediately adjacent a rotor surface;
and
[0031] selectively displacing the rotor relative to the casing by
displacing the axially displaceable bearing element, and thereby
adjusting the radial gap between the blade tip and the inner wall
to suit a given operating condition of the turbomachine.
[0032] In other words, the displacement of the bearing element
effects a displacement of the rotor relative to the casing, so that
a specified radial gap is set between the blade tip and the inner
wall to suit the operating condition of the turbomachine. This can
take place in an essentially passive manner in such a way that an
active control of the gap width is avoided and a specified
displacement of the rotor is carried out corresponding to the
respective operating condition. Such a displacement can, for
example, be realized either by the bearing element being acted on
by a hydraulic fluid at a specified pressure, so that a specified
displacement value is set, or by the bearing element not being
acted upon by pressure. The passive setting of the gap width is
therefore based on carrying out either no displacement of the rotor
or only a specified displacement of the rotor. It is, of course,
also possible to carry out a variable displacement of the rotor by
means of corresponding appliances.
[0033] A displacement of the rotor is preferably only carried out
when a steady-state operating condition of the turbomachine has
been reached with a completely steady-state temperature
distribution of the individual components of the turbomachine
corresponding to the operating condition. The achievement of such
an operating condition, in particular of the normal powered
operation condition of the turbomachine, can be determined by
specifying a previously determined period, by the measurement of
temperatures in the casing, by the measurement of temperature
differences, by the measurement of a radial gap occurring as a
consequence of the thermal expansions, which radial gap is
preferably measured, and by a relative displacement between casing
and rotor. A relative expansion between rotor and casing is
preferably measured at the shaft bearing acting at least as thrust
bearing at opposite ends of the rotor.
[0034] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0035] Although the invention is illustrated and described herein
as embodied in a shaft bearing for a turbomachine, turbomachine and
method of operating a turbomachine, it is nevertheless not intended
to be limited to the details shown, since various modifications and
structural changes may be made therein without departing from the
spirit of the invention and within the scope and range of
equivalents of the claims.
[0036] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a longitudinal section taken through a gas
turbine;
[0038] FIG. 2 is a partial sectional view of a shaft bearing with
an hydraulically displaceable bearing element;
[0039] FIG. 3 is a partial sectional view of a shaft bearing with
an electromechanically displaceable bearing element;
[0040] FIG. 4 is a detail of a longitudinal section of a turbine
with a conical casing;
[0041] FIG. 5 is a diagrammatic sectional view of an axial shaft
bearing; and
[0042] FIG. 6 is a partial longitudinal section through a
turbomachine with a conical housing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Referring now to the figures of the drawing in detail and
first, particularly, to FIG. 1 thereof, there is seen a
longitudinal section through a turbomachine 19, which, in the
present case, is a gas turbine. The machine has a compressor 27 and
the actual turbine 18. A combustion chamber 28 with a plurality of
burners 29 is arranged between the compressor 27 and the turbine
18. The gas turbine 19 has a rotor 2, which is manufactured from
rotor disks on the tie-rod principle. At the compressor end, the
gas turbine 19 has a shaft bearing 1 (see FIG. 2 and FIG. 3). The
actual turbine 18 has, in a casing 20, an inner wall 21, which
expands conically in the axial direction and which is formed from
wall segments and guide vanes 30 with guide-vane platforms. The
guide-vane platforms and the wall segments can have, respectively,
a different inclination relative to the rotor center line 3 of the
rotor 2. Rotor blades 22 are connected to the rotor 2 and these
rotor blades 22 are arranged in a total of four rotor blade rows
24, 25, which are at an axial distance from one another. Each rotor
blade 22 has a blade tip 23, which faces toward the inner wall 21
and has an obliquity (slope relative to the rotor center line 3)
corresponding to the inner wall 21. A radial gap 26 (see FIG. 6) is
formed between each blade tip 23 and the associated region of the
inner wall 21. During normal operation, a hot gas flows through the
turbine 18. The hot gas reaches the turbine 18 from the combustion
chamber 28 and emerges from the turbine 18 at a turbine outlet
31.
[0044] A shaft bearing 1, which is configured as a stationary
sliding bearing, is shown in longitudinal section in FIG. 2. The
shaft bearing 1 encloses the rotor 2 in the peripheral direction
and is arranged axially between two radial rotor surfaces 6, 7. The
shaft bearing 1 has two bearing elements 4, 5, which are at an
axial distance from one another and have respective bearing
surfaces 14, 15. The bearing surface 15 of the bearing element 5 is
immediately adjacent to the rotor surface 7 and is separated from
the latter by a film of a hydraulic fluid (hydraulic oil) 8.
Similarly, the bearing surface 14 is separated from the rotor
surface 6 by hydraulic fluid 8. In addition, a film of hydraulic
fluid 8 is present in the peripheral direction between the rotor 2
and the shaft bearing 1. The shaft bearing 1 is, in this
arrangement, a thrust bearing and a journal bearing. The shaft
bearing 1 can, of course, be configured as a thrust bearing, in
which case a separate journal bearing can be provided. The bearing
element 5 can be displaced axially, an oil space 17, into which
hydraulic oil can be fed under high pressure, being arranged in the
shaft bearing 1 for axial displacement, so that an axial
displacement of the bearing element 5 is achieved. The bearing
element 5 has, toward the oil space 17, respective sealing rings 32
on an internal periphery (inner diameter) and on an external
periphery (outer diameter). The bearing element 5 is preferably
configured as an annular piston. The bearing element 4 is
preferably likewise configured to be axially displaceable.
Respective supply lines 16 for the hydraulic fluid 8, which are
connected to a hydraulic supply system 12, lead to the oil space
17, to the bearing element 4, and to the external periphery of the
rotor 2. The hydraulic supply system 12 has a non-illustrated
reservoir for hydraulic fluid 8 and corresponding, non-illustrated
hydraulic pumps for generating a high pressure and for supplying
hydraulic fluid to the bearing surfaces 6, 7 and to the external
periphery of the rotor 2.
[0045] In this configuration, the hydraulic supply system 12 is
preferably configured in such a way that hydraulic fluid can be fed
at a corresponding pressure to the bearing elements 4 and 5 so that
an axial displacement of the rotor 3 is achieved. After achievement
of the axial displacement of the rotor 2, it is possible to keep
the volume of the hydraulic fluid acting on the bearing elements 4
and 5 constant in each case by means of the hydraulic supply system
12 or, if appropriate, by means of a different device, for example
by means of one or more shut-off valves. This achieves the effect
that, due to the incompressibility of the hydraulic fluid, a
respectively opposite and equally large counterforce is generated
in the shaft bearing 1 even when there are changes to the axial
thrust of the rotor 2; the rotor 2 therefore remains in the desired
axial position.
[0046] A further embodiment of a shaft bearing 1 is shown in FIG.
3, likewise in longitudinal section. As compared with the
embodiment of FIG. 2, this embodiment does not provide hydraulic
displacement of the bearing element 5 but, rather, a displacement
of the bearing element 5 by electromechanical means. With respect
to the remaining design of the shaft bearing 1 of FIG. 3, reference
is had to the description of FIG. 2. A displacement element 10, in
particular a spindle which can be moved in the axial direction by a
displacement drive 11, an electric motor in this case, acts on the
bearing element 5 within the shaft bearing 1. Together with further
non-illustrated components, such as an electrical supply with
corresponding electrical lines, the displacement element 10 and the
displacement drive 11 form a mechanical displacement device 9 for
the axial displacement of the bearing element 5.
[0047] A distance element 13 (see FIG. 2 or 3), here configured as
a stop, is provided in the shaft bearing 1. An axial displacement
of the bearing element 5 in the direction of the bearing element 4
is limited by the distance element 13. By this means, an axial
movement of the rotor 2 in the direction of the bearing element 4
is also limited. This ensures that no displacement (not caused by
pure thermal expansions) of the rotor 2 in the direction toward the
turbine outlet 31 occurs and leads to a widening of the radial gap
and therefore to higher efficiency losses. Even in the case of a
failure of the hydraulic supply system or of the displacement
device 9, therefore, the radial gap 26 is not larger than that in
the case of a gas turbine 19 which does not execute any
compensation of the radial gap 26 in consequence of thermal
expansions of the rotor 2.
[0048] A further embodiment of a shaft bearing 1, which is
configured as a sliding thrust bearing, is shown in FIG. 4. As
compared with the embodiments shown in FIGS. 2 and 3, the shaft
bearing 1 encloses an annular shaft region which extends in the
radial direction and forms the two rotor surfaces 6 and 7. The two
bearing surfaces 14 and 15 are respectively adjacent to the two
rotor surfaces 6 and 7 and are respectively kept at a distance from
the rotor surfaces 6 and 7 by a corresponding lubricant, in
particular hydraulic oil. With respect to the further mode of
operation and design configuration of the shaft bearing 1,
reference should be had to the statements with respect to the
embodiments of FIGS. 2 and 3.
[0049] A shaft bearing 1, which has an essentially annular bearing
surface 14, is shown in FIG. 5 as diagrammatic cross section. The
bearing surface 14 is formed by a plurality of bearing elements 4,
bearing pads. In this configuration, the bearing elements 4 can
each be displaced individually in the axial direction or can be
moved in the axial direction in groups or all together by means of
an annular force transmission element, which is not shown for
reasons of clarity. It is obviously possible for the bearing
surface 14 to be formed by a single annular bearing element.
[0050] A detail of a turbomachine 19 with conically expanding
casing 20 (i.e., a taper casing) is shown in FIG. 6 as a
longitudinal section. A rotor blade 22 is shown, as an example, on
a rotor 2. Its blade tip 23 is embodied with the same obliquity in
a manner analogous to the inner wall 21 of the casing. The rotor
blade 22 shown by a dotted line corresponds to an operating
condition of the turbomachine 19 in which a thermal expansion of
the rotor 2 has taken place. Due to the thermal expansion, a
relatively large radial gap 26A has appeared between the blade tip
23 and the inner wall 21, through which radial gap 26A, flow losses
occur in the turbomachine 19 and cause a reduction in the
efficiency. The rotor blade 22 shown by a full line represents an
operating condition of the turbomachine 19 in which a displacement
of the rotor 2 has been carried out by means of a shaft bearing 1
in order to reduce the radial gap 26, as shown in FIGS. 2 or 3. The
radial gap 26 is then distinctly narrower than the radial gap 26A
with the non-displaced rotor 2. A reduction in the flow losses in
the radial gaps 26 of the turbomachine 19 is achieved by the
displacement of the rotor 2 by means of the shaft bearing 1 with an
axially displaceable bearing element 5. This method is particularly
effective for reducing the flow losses in the case of stationary
gas turbines, which are operated in a powered operation condition
over a long period.
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