Clearance control system for a rotary machine and method of controlling a clearance

A clearance control system for a rotary machine includes an outer casing including an outer casing main portion having a first radial thickness, wherein the outer casing is configured to expand at a first time rate of thermal expansion. Also included is an inner casing disposed between the outer casing and a rotary portion, the inner casing including an inner casing main portion having a second radial thickness that is less than the first radial thickness, wherein the inner casing is configured to expand at a second time rate of thermal expansion that is greater than the first time rate of thermal expansion of the outer casing. Further included is an inner casing leg configured to separate from an outer casing leg during expansion of the inner casing and configured to engage the outer casing leg during contraction of the inner casing.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to rotary machines, and more particularly to a clearance control system for adjusting the clearance between a stationary component and a rotary component of the rotary machine, as well as a method of adjusting the clearance.

In certain applications, a clearance may exist between components that move relative to one another. For example, a clearance may exist between rotary and stationary components in a rotary machine, such as a compressor, a turbine, or the like. The clearance may increase or decrease during operation of the rotary machine due to temperature changes and other factors. A smaller clearance may improve performance and efficiency in a compressor or turbine, because less working fluid leaks between blades and a surrounding structure, such as a shroud, for example. However, a smaller clearance also increases the potential for a rub condition between the rotary and stationary components. For example, the potential for a rub condition may increase during transient conditions and decrease during steady state conditions. Unfortunately, existing systems do not adequately control clearance in rotary machines. Manipulating the response of surrounding structures include a fast response during startup to avoid rubbing, however, an associated fast response during shutdown may result in rubbing and/or pinching during shutdown or subsequent restart. Conversely, slow responses of the surrounding structures may lead to rubbing and/or pinching during a cold start transient.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a clearance control system for a rotary machine includes an outer casing including an outer casing main portion having a first radial thickness, wherein the outer casing is configured to expand at a first time rate of thermal expansion. Also included is an inner casing disposed between the outer casing and a rotary portion, the inner casing including an inner casing main portion having a second radial thickness that is less than the first radial thickness, wherein the inner casing is configured to expand at a second time rate of thermal expansion that is greater than the first time rate of thermal expansion of the outer casing. Further included is an inner casing leg configured to separate from an outer casing leg during expansion of the inner casing and configured to engage the outer casing leg during contraction of the inner casing.

According to another aspect of the invention, a clearance control system for a rotary machine includes an inner casing operatively coupled to an outer casing, the inner casing configured to move radially at a first time rate. Also included is a thermal mass operatively coupled to the outer casing and to the inner casing, wherein the thermal mass is configured to contact the inner casing, the inner casing configured to move radially at a second time rate that is slower than the first time rate upon contact with the thermal mass.

According to yet another aspect of the invention, a clearance control system for a turbine system includes an outer casing including an outer casing main portion configured to expand at a first time rate of expansion. Also included is an inner casing disposed between the outer casing and a rotary component of the turbine system, the inner casing configured to expand at a second time rate of expansion that is greater than the first time rate of thermal expansion of the outer casing. Further included is an inner casing leg configured to separate from an outer casing leg during expansion of the inner casing and configured to engage the outer casing leg during contraction of the inner casing.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, a rotary machine10constructed in accordance with an exemplary embodiment of the invention, is schematically illustrated. The disclosure herein relates to clearance control techniques that are implemented in the rotary machine. The rotary machine10illustrated comprises a turbine-based engine, such as those employed in an aircraft, locomotive, or power generation system. However, it is to be appreciated that alternative embodiments of the rotary machine10may benefit from the embodiments of the invention described herein. In particular, as will be understood from the description herein, the gas turbine engine comprises a compressor section12and a turbine section24, but the embodiments described below may be used with simply a standalone compressor, for example.

As used herein, the term “clearance” or the like shall be understood to refer to a spacing or gap that may exist between two or more components of the rotary machine10that move relative to one another during operation. The clearance may correspond to an annular gap, a linear gap, a rectangular gap, or any other geometry depending on the system, type of movement, and other various factors, as will be appreciated by those skilled in the art. In one application, the clearance refers to the radial gap or space between housing components surrounding one or more rotating blades of a compressor, a turbine, or the like. By controlling the clearance using the embodiments herein, the amount of leakage between the rotating blades and the housing may be actively reduced to increase operation efficiency, while simultaneously reducing the possibility of a rub (e.g., contact between housing components and the rotating blades). As will be appreciated, the leakage may correspond to any fluid, such as air, steam, combustion gases, and so forth. The terms “rate,” “rate of expansion,” “rate of contraction,” or the like, refer to a time rate of expansion or contraction.

The illustrated embodiment of the rotary machine10includes the compressor section12and a plurality of combustor assemblies arranged in a can annular array, one of which is indicated at14. It should be appreciated that this invention is independent of the details of the combustion system, and the can annular system is referenced for purposes of discussion. The fuel and compressed air are passed into a combustion section18and ignited to form a high temperature, high pressure combustion product or air stream that is used to drive the turbine section24. The compressor section12and the turbine section24each include a rotary portion26surrounded by a casing structure32. The turbine section24is operationally connected to the compressor section12through a compressor/turbine shaft30(also referred to as a rotor). The rotary portion26comprises a plurality of rotor blades operatively coupled to the compressor/turbine shaft30.

Referring toFIGS. 2 and 3, the casing structure32is illustrated in greater detail. The casing structure32generally refers to a structure that surrounds and at least partially defines an internal region of the turbine section24and/or the compressor section12. The casing structure32may be a unitary structure or may be formed of multiple segments. In either event, the casing structure32comprises an outer casing34and an inner casing36. Although not illustrated, it is to be appreciated that a shroud structure may be operatively coupled to the inner casing36and positioned circumferentially around the rotary portion26. A clearance control system is employed to avoid potential rubs and excessive radial gaps between the rotor blades and the shroud during operation of the rotary machine10. In the absence of the clearance control system, the radial gap between the rotor blades and the shroud may increase or decrease due to temperature changes or other factors. For example, as the rotary portion26heats up during operation, thermal expansion of the outer casing34and the inner casing36may cause the shroud to move radially away from the rotational axis of the rotary portion26, thus increasing the clearance between the rotor blades and the shroud. Such a condition is generally undesirable because combustion gases that bypass the rotor blades via the radial gap are not captured by the blades and are, therefore, not translated into rotational energy. This reduces the efficiency and power output of the rotary machine10.

A clearance control system40according to a first embodiment includes the outer casing34and the inner casing36and relates to the interaction therebetween, as will be appreciated from the description below. The outer casing34comprises an outer casing main portion42and at least one outer casing leg44extending radially inwardly from the outer casing main portion42. Similarly, the inner casing36comprises an inner casing main portion46and at least one inner casing leg48extending radially outwardly from the inner casing main portion46. The outer casing34and the inner casing36are shown in an engaged condition50(FIG. 2) and a separated, or disengaged condition52(FIG. 3). The disengaged condition52is facilitated by the fact that the outer casing34and the inner casing36are not fixedly coupled, thereby allowing relative radial motion therebetween. The engaged condition50is defined by contact of the at least one outer casing leg44and the at least one inner casing leg48.

As noted above, the outer casing34and the inner casing36are susceptible to thermal expansion and contraction in response to thermal conditions of the rotary machine10. Specifically, upon an increase in temperature, the components expand and move radially outwardly, and upon a decrease in temperature, the components contract and move radially inwardly. While it is desirable for the casing structure32, and particularly the inner casing36, to move radially outwardly relatively fast during a startup time duration to avoid a rub condition with the rotor blades, a fast contraction response during a shutdown time duration may result in a rub during shutdown or “pinch” upon a subsequent restart of the rotary machine10. The decoupled configuration of the outer casing34and the inner casing36, wherein the outer casing leg and the inner casing leg are separated for at least a portion of the startup time duration, overcomes the aforementioned issue by providing a relatively fast startup response and a relatively slow shutdown response, as will be appreciated from the description herein.

Referring toFIGS. 4 and 5, with continued reference toFIGS. 2 and 3, respective responses of the outer casing34and the inner casing36are illustrated. It is to be appreciated that the radial position of each component is not represented, merely the radial responses of each component as a function of time. The outer casing34moves radially between a first outer casing position74and a second outer casing position76, while the inner casing36moves radially between a first inner casing position78and a second inner casing position80. During a startup time duration54(FIG. 4), the inner casing36expands and therefore moves radially outwardly at a more rapid time rate than the outer casing34. This faster time rate of expansion is a result of a thinner inner casing, relative to the outer casing34. Specifically, the outer casing main portion42comprises a first radial thickness56that is greater than a second radial thickness58of the inner casing main portion46. The thinner inner casing responds more rapidly to temperature changes of the rotary machine10, thereby leading to faster responses. This faster time rate of expansion leads to the disengaged condition52illustrated inFIG. 3. The time rate of expansion and radial movement of the outer casing34is referenced with numeral60, while the time rate of expansion and radial movement of the inner casing36is referenced with numeral62. The disengaged condition52exists for all or a portion of the startup time duration54. While not necessary, it is contemplated that the outer casing34and the inner casing36engage one another during a portion of the startup time duration54and/or during steady state operation of the rotary machine10.

As described above, it is also desirable to slow down the response of the casing structure32, and particularly the inner casing36, during a shutdown time duration64. As shown inFIG. 5, the response of the inner casing36is constrained by the outer casing34during the shutdown time duration64as a result of the distinct rates of expansion/contraction. Specifically, the time rate of expansions60,62merge into a single rate of expansion68(which is negative during the shutdown sequence) for at least a portion70of the shutdown time duration64. For illustration purposes, a hypothetical unrestrained response of the inner casing36is shown with dashed line72. Due to the distinct radial thickness, the thinner inner casing responds more rapidly to temperature changes of the rotary machine10, as well as a slower rate of contraction of the outer casing34. This leads to the engaged condition50illustrated inFIG. 2during the portion70of the shutdown time duration64discussed above. The engaged condition50constrains the contraction and movement radially inwardly of the inner casing36in both a mechanical and thermal aspect. Engagement of the at least one outer casing leg44and the at least one inner casing leg48provides a mechanical restraint that impedes the radial movement of the inner casing36. Additionally, heat transfer from the outer casing34to the inner casing36slows the cooling of the inner casing36, thereby reducing the rate of contraction of the inner casing36. Both the mechanical and thermal aspects of constraint reduce the inward radial movement of the inner casing36, which reduces the likelihood of a rub or pinch between the rotor blades of the rotary portion26and the surrounding structure, whether a shroud or the inner casing36, upon a restart of the rotary machine10.

Although the embodiments described above refer to controlling the time rates of expansion with distinct thicknesses, with respect to the outer casing34and the inner casing36, it is to be appreciated that the time rate of expansion may be controlled in various alternative manners. For example, one or both of the components may be coated or wrapped with a material or substance that manipulates the thermal time rates of expansion or surrounded by a thermal environment that controls the thermal time rates of expansion. However, any suitable control technique may be employed to establish distinct rates of expansion.

Referring toFIG. 6, a clearance control system100according to a second embodiment is illustrated. Like reference numerals associated with the first embodiment are employed with description of the second embodiment, where applicable. The clearance control system100relies on thermal constraint of the inner casing36during the shutdown time duration64. Specifically, a lever arrangement102is employed to operatively couple the inner casing36, the outer casing34and a thermal mass104. The thermal mass104comprises segmented thermal mass components which are actuated into contact with the inner casing36, as will be apparent from the description below. A first lever106is included to generate relative motion between the thermal mass104and the inner casing36. As shown, a first coupling109is located proximate a first end110of the first lever106and supports the thermal mass104. A second coupling112is located proximate a second end114of the first lever106and couples the first lever106to the outer casing34. A third coupling116is located along the first lever106at a location between the first coupling109and the second coupling112, but closer in proximity to the second coupling112. The above-described positioning of the couplings provides desired kinematics of the overall clearance control system100.

As described above in conjunction with the first embodiment, the inner casing36is thinner than the outer casing34and responds more rapidly to thermal conditions of the rotary machine10, wherein the lever is configured to engage the thermal mass and the inner casing during at least a portion of a shutdown time duration. As the temperature increases, the inner casing36moves radially outwardly at a more rapid rate than the outer casing34and the lever arrangement102is configured to impart outward radial movement of the thermal mass104during expansion of the inner casing36. Conversely, as the inner casing36contracts and moves radially inwardly at a more rapid rate, relative to the outer casing34, the inner casing36pulls on the first lever106and forces the thermal mass104into contact and thermal communication with the inner casing36. During the remainder of the shutdown time duration64, the thermal mass104would be held in contact with inner casing36as long as the inner casing36is colder than the outer casing34.

The lever arrangement102described above represents a passive actuation of the thermal mass104, but actuators may be included that are either passively or actively actuated. In an alternative embodiment, an active system actively actuates the thermal mass104into contact with the inner casing36. A controlled actuation device A, such as a solenoid or hydraulic piston—either ganged with a single actuator or with several actuators—around the circumference of the inner casing36may be employed.FIG. 7generally illustrates an embodiment having a plurality of thermal mass segments120each configured to communicate with the inner casing36.

As noted above,FIG. 6illustrates a passive actuation concept for placing thermal mass104into and out of contact with the inner casing36. Actuation of the thermal mass104could be accomplished by other passive or active means including electrical or hydraulic solenoids or other methods. Further, inner casing36could be a single wall casing (no separate outer casing). Significantly, the casing (i.e., forming or carrying components that form the flowpath outer wall) includes a heat storage element that it may be separated from or brought into thermal communication with (i.e., contact) to change the temperature and thermal growth of the casing for clearance control purposes.