MECHANICAL COMPONENT FOR THERMAL TURBO MACHINERY

Abstract

A mechanical component for thermal turbo machinery, such as a steam or gas turbine, includes a base part and at least one additional device being mechanically coupled to the base part in order to influence the vibration characteristic of the base part during operation of the turbo machine. High-Cycle Fatigue at part-load can be reduced by enabling the mechanical coupling between the base part and the at least one additional device to change with the temperature of the at least one additional device.

Claims

1. Mechanical component for thermal turbo machinery, comprising a base part, and at least one additional device being mechanically coupled to said part in order to influence a vibration characteristic of said part during operation of the turbo machine, wherein a mechanical coupling between said part and said at least one additional device changes with a temperature of said at least one additional device.

2. Component as claimed in claim 1, wherein said at least one additional device is a device, which changes with temperature its form and position relative to said base part in order to establish an additional mechanical contact between said part and said at least one additional device within a predetermined temperature range.

3. Component as claimed in claim 2, wherein said at least one additional device is a bi-metallic device.

4. Component as claimed in claim 2, wherein said at least one additional device is a shape-memory-alloy device.

5. Component as claimed in claim 2, wherein said additional mechanical contact is a stiffening contact, which mechanically stiffens said part.

6. Component as claimed in claim 2, wherein said additional mechanical contact is a friction contact, which dampens vibrations in said part.

7. Component as claimed in claim 2, wherein said at least one additional device has the form of a longitudinal beam or curved plate, which is fixedly connected at both ends to said part, such that it establishes said additional mechanical contact in an area between both ends, when it changes with temperature its form and position relative to said part.

8. Component as claimed in claim 2, wherein said at least one additional device has the form of a longitudinal cantilever or curved plate, which is fixedly connected at one end to said part, such that it establishes said additional mechanical contact with its other, free end, when it changes with temperature its form and position relative to said part.

9. Component as claimed in claim 2, wherein additional sub-parts are provided on said at least one additional device in an area of said additional mechanical contact in order to influence the character of said additional mechanical contact.

10. Component as claimed in claim 2, wherein a heating or cooling means is provided for actively changing the temperature of said at least one additional device.

11. Component as claimed in claim 1, wherein said part is a blade or vane of a gas turbine.

12. Component as claimed in claim 1, wherein said part is an exhaust gas housing of a gas turbine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

[0044] FIG. 1 shows a Campbell Diagram of a rotating blade B and non-rotating vane V, whose eigenfrequencies .sub.B,N,Tb and .sub.V,N,Tb depend on the stiffening effect of the centrifugal load growing from 0 to the nominal speed .sub.N and softening effect of temperature increasing from the ambient temperature T.sub.a to base-load temperature T.sub.b, where k (where k=1, 2, . . . , ) denotes the harmonic excitation due to non-uniform circumferential pressure distribution of a flow medium within the turbine;

[0045] FIG. 2 shows a Conventional Campbell Diagram of a rotating blade B and stationary vane V concerning their eigenfrequency increase to values .sub.B,N,Tb-T and .sub.V,N,Tb-T due to temperature reduction T under the part-load GT operation condition at the unchanged nominal rotational speed .sub.N of a turbine train;

[0046] FIG. 3 shows a part-load Resonance Diagram (right-hand side picture) for a rotating blade B and stationary vane V recording eigenfrequency change (T).sub.B,N and (T).sub.V,N with respect temperature reduction T from base-load temperature T.sub.b under the part-load GT operation condition at the nominal rotational speed .sub.N of a turbine train, where a darker zone corresponds to the allowable temperature range of interest regarding needs of minimal T.sub.TAT (turbine outlet temperature) for GTCC operation;

[0047] FIG. 4 illustrates four design strategies of a rotating shrouded turbine blade (as an arbitrary example) against HCF, namely (1) Mass Strategy (MS): Component Mass Variation, (2) Stiffness-Strategy (SS): Component Stiffness Increase, (3) Damping-Strategy (DS): Component Damping Enlargement, and (4) Mistuning-Strategy (MTS): Component mistuned in terms of Excitation;

[0048] FIG. 5 shows typical deformation curves of systems having a bi-metallic configuration (dashed curve) or made of a shape memory alloy (solid lines) with respect to temperature T, where T.sub.a, T.sub.TAT-min, T.sub.b denote the ambient, minimal Turbine Outlet Temperature for GTCC operation, and base-load temperature of a GT engine, respectively, and q.sub.C,min denotes the threshold deformation of the system for a contact with the GT component of interest above temperature T.sub.TAT-min;

[0049] FIG. 6-8 show an embodiment of the invention by applying a bimetallic TMD to the stationary Exhaust Gas Housing of a GT for achieving a stiffening effect to shift the original system's eigenfrequency by due to the additional bending stiffness of the bi-metallic system, where T.sub.T means the threshold temperature of interest;

[0050] FIG. 9 shows TMD configuration for multi-contacts amplifying stiffening effect and/or frictional damping performance with respect to the mode shapes of the baseline part, with FIG. 9(a) showing examples of a thin-wall, thick-wall and solid sub-parts for generating different contact characteristics, and with FIG. 9(b) illustrating the results of the sub-parts arranged for stiffening and damping effects in the resonance response function;

[0051] FIG. 10 illustrates re-design degrees of freedom with TMD in mechanical contact with the base part, where and correspond to the stiffening or damping concept with one sub-part (see FIG. 9) depending on vibration magnitudes of the base part; and

[0052] FIG. 11 shows a part-load Resonance Diagram for a rotating blade B and stationary vane V equipped with the proposed TMD, which shifts the original eigenfrequency (T).sub.B,N and (T).sub.V,N by required values .sub.B(T) and .sub.V(T) (as illustrated with two long-dashed curves) to avoid the resonances that appear within the operation zone of the part-load condition, or which increases the damping performance of the overall system in terms of varying mass flow {dot over (m)}, which can generate asynchronous excitations of the baseline component.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

[0053] An overall idea of the present invention is to introduce an additional device into a new or existing design of a baseline component or part of a thermal turbo machine, especially a gas or steam turbine, which by mechanical coupling with the component passively changes the mechanical properties of the baseline component in terms of variation of the operation temperature of the engine.

[0054] This additional device, from now on called Thermal Memory Device (TMD), increases the reference stiffness of the baseline component and also enlarges the frictional damping onto mechanical contacts between the baseline component and the additional device. These additionally created mechanical properties of the baseline component with a TMD protect the engine from High-Cycle Fatigue under high temperature operations like in gas turbines. Through the created mechanical contacts onto the baseline component, the TMD does not cause any thermal stress during rapid variation of the thermal boundary conditions because the baseline component and additional device can slide relatively to each other without generating any thermal stress concentration during their thermal expansions. The aerodynamic performance of the engine is not impacted by applying the TMD inside the baseline component like for instance a cooled turbine blade or vane.

[0055] At the on-design point, each component of a GTCC system must be free of resonance in accordance with Campbell diagram (see FIGS. 1 and 2). The part load conditions of e.g. a GT engine generate two effects of (1) Metal Temperature Reduction of components, and/or (2) Generation of unexpected asynchronous excitations that are usually known from the test engine or field experiences.

[0056] In case of the unexpected resonance under the part-load operation, there are 4 standard resonance-mitigation strategies, such as Mass-Strategy (MS), Stiffness-Strategy (SS), Damping-Strategy (DS), and Mistuning-Strategy (MTS), as illustrated in FIG. 4.

[0057] According to the Mass-Strategy (MS), the mass of vibrating areas of the large component, e.g. an Exhaust Gas Housing, is locally changed. This is not an effective solution because frequency shifts of 2-3 Hz require a significant modification of the geometry of the large baseline component.

[0058] The Damping-Strategy (DS) is based on the friction or impact dissipation mechanism and does not relate to a straightforward engineering solution. Also, the Mistuning-Strategy (MTS) is an out-of-the-box solution of the engineering practice, which usually corresponds with too high costs for its validation.

[0059] Therefore, the Stiffness-Strategy (SS), which increases the overall stiffness of the component, is applied as the most simple and efficient mitigation. Often, an additional coupling like e.g. a bolt or stab is welded between the components or component parts, which increases the system's frequency of interest. However, this stiffening solution placed in the flow channel of a turbine generates aerodynamic losses or can easily lead toward new TMF (Thermal-Mechanical Fatigue) damages. For the components operating above evaluated temperature, an additional stiffness caused by the bolt does not allow for the thermal expansion of the overall system and TMF cracks can appear on the zones of thermal stresses driven by variable part-load operation conditions.

[0060] In GT technology, the thermally loaded components are usually designed for internal cooling and comprise thin-shell structures to avoid too high thermal stress concentrations during fast start-ups or shut-downs of an engine. In other words, a typical GT vane comprises a hollow space for internal cooling, which can be used for introducing an additional structural element which stiffens the baseline component for shifting its eigenfrequency above the resonance of interest.

[0061] To control this stiffening process in terms of temperature, the internal (additional) component or element is made of bimetallic material (BM) or shape memory alloy (SMA) whose characteristics are shown in FIG. 5. Deformations of the bi-metallic system (BM) are a substantially linear function in terms of temperature T. The shape memory alloy (SMA) demonstrates binary behavior of the deformation with the typical pseudo elastic-plastic hysteresis, as illustrated in FIG. 5.

[0062] FIGS. 6-8 show an example of how a standard baseline component can be equipped with an internal system made of conventional bi-metallic system, according to an embodiment of the present invention. Baseline component in this case is a stationary exhaust gas housing 10 of a gas turbine (see for example document U.S. Pat. No. 8,915,707 B2). The exhaust gas housing 10 comprises two concentric rings, namely an outer ring 11 and an inner ring 12. Both rings 11 and 12 are connected by a plurality of radial struts 13. Each strut 13 has a wing-like aerodynamic cross-sectional profile and a hollow interior 14 (FIGS. 7, 8).

[0063] As can be seen in FIGS. 7, 8, which show a cross-section in the plane A-A, a bi-metallic thermal memory device (TMD) 15 is arranged within a strut parallel to the longitudinal axis 21 of said strut. Thermal memory device 15 is positioned near the wall of strut 13, extends through hollow interior 14 of strut 13, and is rigidly fixed at both ends to the outer ring 11 and inner ring 12 by means of suitable fixations 16a and 16b. Thermal memory device 15 itself is divided in longitudinal direction into two bounded metal parts or beams 15a and 15b, which consist of metals with different thermal behavior to establish the necessary bi-metallic effect.

[0064] For temperatures below a threshold value T.sub.T, there is no mechanical contact between the inner surface of the baseline component 10 and the external surface of the bi-metallic system 15, as illustrated in FIG. 7. Above the threshold temperature T.sub.T of interest, the bi-metallic component 15 comes in contact with the baseline part 10 (contact area 17 in FIG. 8), what increases the overall eigenfrequency of the coupled internally system 11, 12, 13, 15 by the required frequency range . The frequency shift can be enforced by applying additional components with thermal memory made of bi-metallic or shape memory materials. Also, instead of one simple beam 15 clamped at its both ends, two cantilevers 22, 23 (FIG. 8) with one free end each can be used for getting two contacts with the baseline part 10.

[0065] Cantilever beams 22, 23 of different lengths could be considered for arranging contacts at different locations with respect to vibration nodes and antinodes of mode shapes of the baseline part 10 (see FIG. 8).

[0066] Furthermore, as shown in FIG. 9(a), the external surface of the thermal memory device 15 can be equipped with additional sub-parts 18, 19, 20, whose shapes better match with the internal contour of the baseline part (in the example strut 13). Additionally, these shapes can be arranged for creating the best friction damping performance during vibrations of the entire system. In particular, sub-part 18 is a hollow thick-wall part, sub-part 19 is a hollow thin-wall part, and sub-part 20 is a fully solid part. These different sub-parts 18, 19 and 20 each generate a different contact normal and tangential stiffness.

[0067] Thus, the thermal memory device TMD being in contact with the baseline part has two functions: [0068] 1) Stiffening effect for shifting the eigenfrequency of interest, and [0069] 2) Damping of the forced vibration through the frictional dissipation onto the contact.

[0070] Accordingly, two S-Stiffness and D-Damping Design Strategies SS and DS are thus realized in the structure of FIG. 9(a), as illustrated in FIG. 9(b). As explained above, each sub-part can be designed as a thin-wall, thick-wall or/and solid structure for reaching the damping performance on the contacts at different radii r1, r2 and r3 in accordance with an elastic-friction dissipation mechanism or other approaches known in the open literature. Because the thermal memory device 15 always presses sub-parts 18, 19 and 20 against the baseline part 13, contact wear would not have an impact on the damping performance and the entire free-failure operation. Anyway, the wear at said contacts can be minimized with a specific coating.

[0071] For the stationary baseline components, even of large dimensions like an EGH (Exhaust Gas Housing), the stiffening effect or/and the damping performance could be validated in a typical annealing oven by using a standard system for measuring vibrations in evaluated temperatures.

[0072] Depending on needs of the design protection, either stiffening or damping performance of the system can be enforced as schematically illustrated in FIG. 10. The vibrations of the baseline component, known from the measurements or/and computations, are considered as the kick-off point of the re-design.

[0073] At the region of interest of the baseline component, the thermal memory device TMD comes in the required technical (flat) or Hertz contact within the baseline component. In terms of the cross-section of the device, the overall baseline component stiffness can be increased or reduced after being in contact at the operation temperature of interest. Then, the overall stiffness of the entire system increases by ratio from the reference stiffness of the baseline as illustrated with a dark region (stiffness increase) in FIG. 10.

[0074] With respect to magnitudes of the relative contact vibration of the baseline component, the damping performance can grow or reduce. These damping performances can be also influenced in the re-design by applying of the particular contact form, contact stress magnitude or contact area as well as with specific coating increasing or decreasing friction coefficient. The designer has an option of adding additional contact areas as explained schematically with solid or hollow sub-parts in FIG. 9(a). Then, in terms of the vibration of the baseline component, the damping performance of the overall system in contact can be controlled with rate by using one or more hollow and solid sub-parts (bright upper region damping increase in FIG. 10).

[0075] The final outcomes of the rotating blade or stationary vane equipped by the component with thermal memory are illustrated with long-dashed curves in FIG. 11 (upper right part of the Figure). The original eigenfrequencies of the blade (T).sub.B,N and the vane (T).sub.V,N are shifted by the required values .sub.B(T) and .sub.V(T) to avoid the resonances that appear within the operation zone of the part-load condition (see the two long-dashed curves in FIG. 11). By using the component with thermal memory as explained above in connection with FIGS. 6-9, there are options for softening the effect such that for instance the new eigenfrequencies of the part are lower than the original ones. This mechanism is within the scope of the present invention, too.

[0076] The technology of the adding and mounting a thermal memory device (TMD) for part-load operation, as described above, can be applied to rotating components or stationary parts of different dimensions. Thus, a complete exhaust gas housing as shown in FIG. 6 or single blades or vanes can be equipped with a suitable TMD.

[0077] The proposed bi-metallic systems (15 or 22, 23 in FIG. 8) may be made of arbitrary metals that are available on market or can be developed according to particular design reasons. Also, arbitrary shape memory alloys (SMAs) may be made of known elements or may be developed for achieving the desired purpose of the design. In other words, all known or newly developed bi-metallic or/and shape memory alloys of various shapes and fixations are part of the present invention. This applies also to arbitrary forms of the TMDs. Additionally, sub-parts of the TMD device (as shown for example in FIG. 9) for frictional damping can be made of different materials or are designed as brushes or others for arranging soft- or hard-contact stiffness.

[0078] Several TMDs can be arranged in series or parallel connection for weakening or enforcing overall stiffness and/or damping results of the entire system. Also, the bi-metallic and shape memory alloy can be combined together for defining bi-linear stiffness effect as the result of the linear and binary deformation, respectively. In addition, to vary the stiffness result continually or temporarily, local or overall cooling or heating effects of this system can be considered that can be arranged through different sources like electrical heaters (24 in FIG. 8), and others.

[0079] In general, the thermal memory device TMD can be also designed within the meaning of increasing stiffness of the baseline component, whose original frequency begins to get larger above the threshold temperature of interest. For this general design purpose, the generated mechanical contact between the device and baseline component does not generate any thermal stress concentration which appears in every conventional joining techniques of welding, brazing, mechanical joining and others in the operation of thermal engines. This type of the application corresponds mainly to the design concept based on Stiffness-Strategy (SS) as illustrated in FIG. 4 and can be used for arbitrary operation condition of a thermal engine. In other words, this invention is not only limited to flexible operation of the engine.

[0080] The present invention is descried with respect to needs of GTSC and GTCC systems. Indeed, the scope of this innovation can be applied to other engines and machines that are designed for the on-design point but need to operate additional under various part-load operation conditions. The TMD can be triggered by thermal and mechanical loading change or can be driven with an active-control system (e.g. a heater 24, as shown in FIG. 8). The invention can be used for engines operating with constant and variable rotational speeds.

LIST OF REFERENCE NUMERALS

[0081] 10 exhaust gas housing (stationary) [0082] 11 outer ring [0083] 12 inner ring [0084] 13 strut [0085] 14 hollow interior [0086] 15 thermal memory device (TMD) [0087] 15a,b metal part [0088] 16a,b fixation [0089] 17 contact area [0090] 18,19,20 sub-part [0091] 21 longitudinal axis (strut) [0092] 22,23 cantilever [0093] 24 heater (e.g. electrical)