Patent Application
20110318162
The present invention generally relates to gas turbine engines, and more particularly relates to systems and methods for improving the rotor tip clearance and shaft dynamics of gas turbine engine rotors.
For gas turbine engines, it is generally known that the operational clearances between the tips of rotating blades and engine static structure impact the thermodynamic efficiency and fuel burn of the engine. Hence, gas turbine engine manufacturers continually seek ways to reduce these operational clearances. The value of even several thousandths of an inch improvement can be quite significant, especially in the high pressure turbine and high pressure compressor. As a result, many gas turbine engine manufacturers trade markedly higher manufacturing costs in exchange for small improvements in blade tip clearance. These costs can be embedded in complex design features, in high precision manufacturing tolerances, and exotic build processes as a means to achieve reduced blade tip clearance. Despite such efforts, typically two to five thousandths of an inch in tip clearance is needed to accommodate geometric uncertainty in the location of the rotor centerline with respect to key locations on the static structure.
In addition to the operational clearances described above, gas turbine engine rotor dynamics receive great attention during engine design. This includes the placement of shaft critical speed in the frequency domain, and the rotor response to imbalance and transient excursions through critical speeds. Critical speed placement is controlled primarily via stiffness in the rotor/bearing support, while rotor response to imbalance and transient critical speed operation is controlled via damping. Typically, damping and stiffness control are provided via hydraulic devices, such as “squeeze film dampers” (SFDs), at rotor bearing locations. As is generally known, SFDs achieve both stiffness and damping via the whirl motion of the shaft within a controlled oil film annulus. However, both the stiffness and the damping coefficient achieved are highly non-linear with respect to orbital (whirl) displacement of the shaft. Moreover, the stiffness and damping coefficients are inexorably linked, which means one cannot be modified without a large effect on the other. This results in an inability to precisely locate and control response to critical speeds, since stiffness and damping are varied along with whirl displacement. This variability and imprecision causes manufacturers to design gas turbine engines with substantial frequency margin above running speeds for shaft bending mode critical speeds, and with having to accept some uncertainty in the placement and response of rigid rotor modes, which are commonly traversed in transient speeds during start and shutdown.
The net effect of the tip clearance and shaft dynamics issues described above can result in reduced efficiency and increased product cost, with additional costs embedded in a reduced yield in the assembly/test process due to the incidences of engines failing to meet specifications for temperature or vibration.
Hence, there is a need for a rotor tip clearance and shaft dynamics system and methods for gas turbine engines that provides increased efficiency and reduced operational and manufacturing costs. The present invention addresses at least this need.
In one exemplary embodiment, a gas turbine engine rotor tip clearance and shaft dynamics system includes an engine case, a gas turbine engine, a rotor bearing assembly, and a plurality of vibration isolators. The gas turbine engine is disposed within the engine case and includes a rotor. The rotor bearing assembly is disposed within the engine case and rotationally mounts the gas turbine engine rotor therein. Each of the vibration isolators is mounted on the engine case and is coupled to the rotor bearing assembly, and each vibration isolator is configured to provide linear and independently tunable stiffness and damping.
In another embodiment, a gas turbine engine rotor tip clearance and shaft dynamics system includes an engine case, a gas turbine engine, a rotor bearing assembly, a plurality of vibration isolators, a plurality of actuators, and an actuator control. The gas turbine engine is disposed within the engine case and includes a rotor. The rotor bearing assembly is disposed within the engine case and rotationally mounts the gas turbine engine rotor therein. Each of the vibration isolators is mounted on the engine case and is coupled to the rotor bearing assembly, and each vibration isolator is configured to provide linear and independently tunable stiffness and damping. Each actuator is coupled to one of the vibration isolators and is coupled to receive actuation control signals. Each actuator is responsive to the actuation control signals it receives to actively control gas turbine engine rotor position and dynamics. The actuator control is operable to selectively supply the actuation control signals to each actuator.
In yet another embodiment, a method of disposing a gas turbine engine rotor that has a rotational axis about which it rotates during operation in an engine case is provided. The method includes determining a location of the rotational axis of the gas turbine engine rotor within the engine case, and disposing the gas turbine engine rotor at the location of the rotational axis. A plurality of vibration isolators are mounted on the engine case, with each vibration isolator including a plurality of adjustment devices. Each of the vibration isolators is coupled to the gas turbine engine rotor, and the gas turbine engine rotor is locked at the location of the rotational axis using the plurality of adjustment devices.
Furthermore, other desirable features and characteristics of the gas turbine engine rotor tip clearance and shaft dynamics system and method will become apparent from the subsequent detailed description and appended claims, taken in conjunction with the accompanying drawings and the preceding background.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description. In this regard, although various embodiments are described herein, for convenience of depicting a specific embodiment, as being implemented in a multi-spool turbofan gas turbine engine, it will be appreciated that embodiments of the system and method may be implemented in any one of numerous other machines that have rotationally mounted rotors.
Turning now to
The compressor section 104 may include one or more compressors 124, which raise the pressure of the air directed into it from the intake fan 114, and direct the compressed air into the combustion section 106. In the depicted embodiment, only a single compressor 124 is shown, though it will be appreciated that one or more additional compressors could be used. In the combustion section 106, which includes a combustor assembly 126, the compressed air is mixed with fuel supplied from a non-illustrated fuel source. The fuel and air mixture is combusted, and the high energy combusted fuel/air mixture is then directed into the turbine section 108.
The turbine section 108 includes one or more turbines. In the depicted embodiment, the turbine section 108 includes two turbines, a high pressure turbine 128, and a low pressure turbine 132. However, it will be appreciated that the engine 100 could be configured with more or less than this number of turbines. No matter the particular number, the combusted fuel/air mixture from the combustion section 106 expands through each turbine 128, 132, causing it to rotate. As the turbines 128 and 132 rotate, each drives equipment in the engine 100 via concentrically disposed rotors or spools. Specifically, the high pressure turbine 128 drives the compressor 124 via a high pressure rotor 134, and the low pressure turbine 132 drives the intake fan 114 via a low pressure rotor 136. Though not visible in
The exhaust section 112 includes a mixer 138 and an exhaust nozzle 142. The mixer 138 includes a centerbody 144 and a mixer nozzle 146, and is configured to mix the bypass air flow with the exhaust gas from the turbine section 108. The bypass air/exhaust gas mixture is then expanded through the propulsion nozzle 142, providing forward thrust.
As
The vibration isolators 150, as just noted, are each coupled to one or more rotor bearing assemblies. In the depicted embodiment, the vibration isolators 150 are each coupled to the low pressure rotor aft bearing assembly 202 and the high pressure rotor aft bearing assembly 204 via support structure 206. The configuration and implementation of the support structure 206 may vary, but in the depicted embodiment the support structure includes a strut 208 that traverses the gas path between the high pressure turbine 128 and the low pressure turbine 132. More specifically, each of the struts 208 extends through a stationary blade 210 that is disposed between rotating turbine blades 214 and 216 of the high pressure turbine 128 and the low pressure turbine 132. The strut 208 is in turn coupled to the rotor bearing assemblies 202, 204 via bearing support structure 212. It will be appreciated that the bearing support structure 212 may be preexisting, conventional bearing support structure or bearing support structure designed, configured, and implemented for use with the vibration isolators 150. It will additionally be appreciated that the vibration isolators 150 may be used to additionally or instead support other gas turbine engine components, such as the compressor 124.
The vibration isolators 150 are preferably implemented using any one of the numerous three-parameter vibration isolator configurations that implement the functionality of the D-Strut™ vibration isolator, manufactured by Honeywell International, Inc. of Morristown, N.J. For completeness, a schematic representation of a D-Strut™ vibration isolator is depicted in
Turning now to
Referring now to
The configuration of the vibration isolator 150 depicted and described herein is such that at relatively low speeds, the first linear spring element 306 (e.g., the first and second flexural members 402, 404) is deflected by motion at the rotors 134, 136, and the hydraulic fluid 418 is readily forced through the orifice 406 between the fluid cavity 414 and the fluid reservoir 416, thereby decoupling the second linear spring element 308. Thus, at relatively low speeds the vibration isolator 150 behaves as a simple, optimal, linear spring. However, as speed increases, the load needed to force the hydraulic fluid 418 through the orifice 406 increases, which causes fluid pressure to begin to deflect the second flexural member 404. This effectively begins to reintroduce the second linear spring element 308, and also provides damping so long as fluid motion through the orifice 406 continues. As speed continues to increase, the force needed to rapidly force fluid through the orifice 406 increases to such a level that the hydraulic fluid 418 effectively acts as a solid. This causes the second linear spring element 308 (e.g., the volumetric stiffness of the fluid cavity 414 and the hydraulic fluid 418) to deflect exactly as the first linear spring element 306, effectively transitioning the vibration isolator 150 into a system with the first and second linear spring elements 306, 308 in parallel, without any damping.
The gas turbine engine 100 and vibration isolators 150 depicted in
Various exemplary embodiments of active gas turbine engine rotor tip clearance and shaft dynamics systems are depicted in
Turning first to
The control 504 is coupled to receive sensor signals from the sensor(s) 506 and is configured, in response to the sensor signals, to supply the actuation control signals to the actuator 502. Although the type, configuration, and placement of the sensor(s) 506 may vary, in the depicted embodiment the sensor(s) 506 is (are) implemented using one or more strain gauges, which are coupled to the strut 208 that couples the associated vibration isolator 150 to the rotor bearing assemblies 202, 204. With this configuration, during engine lateral acceleration, the one or more sensors 506 on the strut 208 on one side of the engine 100 will sense a load shift toward tension, while the one or more sensors 506 on the strut 208 on the other side of the engine 100 will sense a load shift toward compression. The sensor signals would result in the control 504 supplying actuator commands to the appropriate actuators 502 to move in opposite directions, and thereby center the rotors 134, 136.
In another embodiment, which is depicted in
With the system 600 depicted in
Another active gas turbine engine rotor tip clearance and shaft dynamics system 700 is depicted in
The adjustable fulcrum 704 is disposed in the vibration isolator housing assembly 408, and engages the housing assembly 408 and one of the flexural members 402 or 404. In the depicted embodiment, however, the adjustable fulcrum 704 engages the first flexural member 402. The adjustable fulcrum 704 is movable, in response to the actuator 702, relative to the housing assembly 408 and the first flexural member 402. As may be appreciated, controlling the position of the adjustable fulcrum 704 on the first flexural member 402 will concomitantly control the stiffness of the first flexural member 402.
It is noted that the one or more sensors 506 in this system 700 preferably include one or more vibration sensors and one or more speed sensors. Moreover, the control 504 preferably generates the actuator commands using control algorithms based in an awareness of sensed rotor speed and vibration levels. The control algorithms are implemented to optimally position the critical speed in an active way by continuously sensing the vibration and speed.
With the system 700 depicted in
In addition to passively or actively controlling engine rotor tip clearance and shaft dynamics, the configuration of the vibration isolators 150 enables the rotor centerline to be precisely located via adjustment devices 410. This may be accomplished by use of tooling or specific measurements during assembly. For example, after the precise location of the rotor is determined and achieved, the rotor may be locked in place via the adjustment devices 410. This effectively removes all the geometric tolerances otherwise impacting the position of the rotor within the engine casing 122. Improved engine efficiency, due to reduced operating clearances, and reduced manufacturing costs, due to the extremely close tolerances on multiple parts, are achieved along with optimal rotor dynamics.
The vibration isolators 150 depicted and described herein alleviate the need for traditional squeeze film dampers and simplifies the design in the vicinity of the bearings. The vibration isolators 150 have been proven to be extremely linear, and to precisely match an optimized design goal across relatively broad ranges of load, displacement, speed and temperature. The “roll-off,” which can be thought of here as the rate of decrease in displacement transmissibility as a function of speed above critical speed, approaches that of an un-damped system, allowing reduced vibration at rotor speeds above the critical speeds. However, at transient speeds near critical speeds, where damping is desired, the vibration isolator 150 provides relatively high levels of linear damping.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
