Patent Description:
Turbine engines, such as turbofan engines, experience several different phases of operation including, but not limited to, startup to idle speed, warmup, acceleration to higher power and speed for takeoff, climb, cruise, steady-state, deceleration to lower speed and power for descent, landing and taxi, shutdown, and cool-down. Turbine engines may cycle through the different phases of operation several times a day depending on the use of the aircraft in which the turbine engines are attached. For example, a commercial passenger aircraft typically shuts down its engines in between flights as passengers disembark from the aircraft. As such, residual heat remains in the aircraft's engines, which can cause a phenomenon known as thermal rotor bow. Thermal rotor bow is generally defined by deformation in the rotating and stationary components of the turbine engine. Deformation in the components of the turbine engine can result in contact-related damage between the rotating and stationary components of the turbine engine during engine startup, thereby reducing the service life, performance, and operability of the turbine engine.

Thermal rotor bow is especially prominent at times after engine shutdown, and before the engine is allowed to fully cool. Moreover, many known turbine engines are unable to naturally mitigate thermal rotor bow during startup as the design of modern commercial turbofans shifts towards having higher bypass ratios and greater length-to-diameter ratios, as well as tighter clearances between rotors and stators of the engine.

<CIT> discloses methods and systems for mitigating distortion of a shaft of a gas turbine engine. <CIT> discloses means for cooling a bearing assembly. <CIT> discloses a method for cooling a gas turbine shaft. <CIT> discloses a method and system for operating a rotatable machine.

As used herein, the terms "axial" and "axially" refer to directions and orientations that extend substantially parallel to a centerline of the turbine engine. Moreover, the terms "radial" and "radially" refer to directions and orientations that extend substantially perpendicular to the centerline of the turbine engine. In addition, as used herein, the terms "circumferential" and "circumferentially" refer to directions and orientations that extend arcuately about the centerline of the turbine engine.

As used herein, the terms "processor" and "computer," and related terms, e.g., "processing device," "computing device," and "controller" are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a microcontroller, a microcomputer, a programmable logic controller (PLC), and application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. In the embodiments described herein, memory may include, but it not limited to, a computer-readable medium, such as a random access memory (RAM), a computer-readable non-volatile medium, such as a flash memory. Alternatively, a floppy disk, a compact disc - read only memory (CD-ROM), a magneto-optical disk (MOD), and/or a digital versatile disc (DVD) may also be used. Also, in the embodiments described herein, additional input channels may be, but are not limited to, computer peripherals associated with an operator interface such as a mouse and a keyboard. Alternatively, other computer peripherals may also be used that may include, for example, but not be limited to, a scanner. Furthermore, in the exemplary embodiment, additional output channels may include, but not be limited to, an operator interface monitor.

Further, as used herein, the terms "software" and "firmware" are interchangeable, and include any computer program storage in memory for execution by personal computers, workstations, clients, and servers.

As used herein, the term "non-transitory computer-readable media" is intended to be representative of any tangible computer-based device implemented in any method of technology for short-term and long-term storage of information, such as, computer-readable instructions, data structures, program modules and sub-modules, or other data in any device. Therefore, the methods described herein may be encoded as executable instructions embodied in a tangible, non-transitory, computer-readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. Moreover, as used herein, the term "non-transitory computer-readable media" includes all tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including without limitation, volatile and non-volatile media, and removable and non-removable media such as firmware, physical and virtual storage, CD-ROMS, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being transitory, propagating signal.

Embodiments of the present disclosure relate to systems and methods for use in mitigating the formation of thermal rotor bow in a turbine engine. More specifically, the systems and methods described herein exhaust residual heat from within the turbine engine after shutdown to reduce a thermal imbalance therein, thereby partially or fully inhibiting the formation of thermal rotor bow. The residual heat is exhausted from within the turbine engine by selectively operating a starter motor of the turbine engine after shutdown. The starter motor rotates the rotor assembly of the turbofan engine without the aid of combustion such that the turbine engine is allowed to cool in a faster and more efficient manner. As such, the systems and methods described herein provide an automatic post-flight mitigation procedure that reduces the occurrence of thermal rotor bow. Moreover, while described in the context of a turbofan engine, it should be understood that the systems and methods described herein are also applicable to turboprop engines, turboshaft engines, turbojet engines, and any other turbine engine where thermal rotor bow needs to be mitigated.

<FIG> is a schematic illustration of an exemplary turbine engine <NUM>, such as a turbofan engine. Turbine engine <NUM> includes a fan assembly <NUM>, a low pressure or booster compressor assembly <NUM>, a high-pressure compressor assembly <NUM>, and a combustor assembly <NUM>. Fan assembly <NUM>, booster compressor assembly <NUM>, high-pressure compressor assembly <NUM>, and combustor assembly <NUM> are coupled in flow communication. Turbine engine <NUM> also includes a high-pressure turbine <NUM> coupled in flow communication with combustor assembly <NUM> and a low-pressure turbine <NUM>. Fan assembly <NUM> includes an array of fan blades <NUM> extending radially outward from a rotor disk <NUM>. Low-pressure turbine <NUM> is coupled to fan assembly <NUM> and booster compressor assembly <NUM> through a first drive shaft <NUM>, and high-pressure turbine <NUM> is coupled to high-pressure compressor assembly <NUM> through a second drive shaft <NUM>. Turbine engine <NUM> has an intake <NUM> and an exhaust <NUM>. Turbine engine <NUM> further includes a centerline <NUM> about which fan assembly <NUM>, booster compressor assembly <NUM>, high-pressure compressor assembly <NUM>, and turbines <NUM> and <NUM> rotate.

In operation, air entering turbine engine <NUM> through intake <NUM> is channeled through fan assembly <NUM> towards booster compressor assembly <NUM>. Compressed air is discharged from booster compressor assembly <NUM> towards high-pressure compressor assembly <NUM>. Highly compressed air is channeled from high-pressure compressor assembly <NUM> towards combustor assembly <NUM>, mixed with fuel, and the mixture is combusted within combustor assembly <NUM>. High temperature combustion gas generated by combustor assembly <NUM> is channeled towards turbines <NUM> and <NUM>. Combustion gas is subsequently discharged from turbine engine <NUM> via exhaust <NUM>.

Turbine engine <NUM> also includes a starter motor <NUM> and a starter shaft <NUM> coupled to the rotor assembly of turbine engine <NUM>. More specifically, in one embodiment, starter shaft <NUM> is coupled to second drive shaft <NUM>, and starter motor <NUM> provides motoring power to turbine engine <NUM> during startup thereof via starter shaft <NUM>. As shown in <FIG>, an auxiliary power unit (APU) <NUM> is coupled in flow communication with starter motor <NUM> via a pneumatic line <NUM>. APU <NUM> selectively channels a flow of air towards starter motor <NUM> to facilitate actuating starter motor <NUM>. Moreover, a starter valve <NUM> coupled along pneumatic line <NUM> is selectively operable to control the flow of air channeled towards starter motor <NUM>. In an alternative embodiment, starter motor <NUM> receives airflow from a pneumatic power source other than APU <NUM> such as, but not limited to, an already-started turbine engine or a static pressure tank located onboard a ground cart, for example. In addition, starter motor <NUM> may be actuated by a power source other than pneumatic airflow, such as electricity.

In the exemplary embodiment, turbine engine <NUM> further includes an onboard computing device, such as a full authority digital engine control (FADEC) system <NUM>. As will be explained in more detail below, FADEC system <NUM> is coupled, either wired or wirelessly, in communication with one or more subsystems or components of turbine engine <NUM> to control the operation thereof. In one embodiment, FADEC system <NUM> is also coupled in communication with starter valve <NUM>. In an alternative embodiment, the subsystems or components of turbine engine <NUM> are controlled by a computing device onboard an aircraft (not shown) in which turbine engine <NUM> is attached.

<FIG> is a logic diagram illustrating an exemplary method of cooling turbine engine <NUM> (shown in <FIG>). More specifically, FADEC system <NUM> (shown in <FIG>) operates turbine engine <NUM> in accordance with at least the logic shown in <FIG> to determine whether to implement post-shutdown mitigation of thermal rotor bow. As described above, the formation of thermal rotor bow in first drive shaft <NUM> and second drive shaft <NUM> (each shown in <FIG>), for example, can occur after shutdown of turbine engine <NUM> and before turbine engine <NUM> has fully cooled. The determination of the existence of thermal rotor bow, and of whether a post-shutdown mitigation procedure is to be executed after engine shutdown is based on a variety of factors, as will be explained in more detail below.

For example, during a typical shutdown procedure, FADEC system <NUM> shuts down turbine engine <NUM>. In one embodiment, FADEC system <NUM> shuts off a flow of fuel to combustor assembly <NUM> (shown in <FIG>) after receiving a full stop command such that the rotational speed of turbine engine <NUM> decreases. FADEC system <NUM> then determines whether to actuate starter motor <NUM> such that residual heat is exhausted from turbine engine <NUM> based on any suitable feedback that enables the systems and methods to function as described herein. For example, FADEC system <NUM> determines whether to actuate starter motor <NUM> based on a running time of turbine engine <NUM> and/or a temperature within turbine engine <NUM>. Moreover, in one embodiment, vibratory feedback of turbine engine <NUM> is used to determine how long to motor turbine engine <NUM> after engine shutdown.

Starter motor <NUM> is actuated at any time between engine shutdown and restart, and does not need to be actuated immediately after engine shutdown. In one embodiment, starter motor <NUM> is actuated as the rotational speed of turbine engine <NUM> decreases and/or at a preset time after turbine engine <NUM> receives a full stop command. The preset time is selected to ensure thermal rotor bow has not fully formed before actuating starter motor <NUM>. For example, starter motor <NUM> can be actuated immediately after turbine engine <NUM> receives the full stop command (i.e., the preset time equals <NUM> seconds), or can be actuated after the preset time has passed between engine shutdown and motoring (i.e., the preset time is greater than <NUM> seconds). When turbine engine <NUM> receives the full stop command and time has passed between engine shutdown and a potential motoring time, starter motor <NUM> operates such that the rotor speed is less than a resonant rotational speed. As used herein, "resonant rotational speed" refers to a single rotational speed or a range of rotational speeds of the turbine engine that causes high dynamic vibration or displacement in the presence of a rotor imbalance such as thermal rotor bow. Moreover, starter motor <NUM> is actuatable for one or more motoring cycles between engine shutdown and restart to reduce unnecessary wear on starter motor <NUM>. In addition, the rotors can be positioned in different resting orientations after each motoring cycle to reduce rotor bow formation in a single orientation.

As described above, FADEC system <NUM> receives feedback on a running time of turbine engine <NUM>, and actuates starter motor <NUM> if the running time of turbine engine <NUM> is greater than a predetermined threshold. The longer the running time of turbine engine <NUM>, the greater the likelihood that turbine engine <NUM> had reached steady state operating speeds and temperatures that will result in formation of thermal rotor bow upon engine shutdown. Moreover, additionally , FADEC system <NUM> receives feedback on a temperature within turbine engine <NUM> post-shutdown, and actuates starter motor <NUM> if the temperature is greater than a predetermined threshold. The greater the temperature within turbine engine <NUM>, the greater the likelihood that a thermal gradient capable of forming thermal rotor bow will form in turbine engine <NUM>. If both the running time of turbine engine <NUM> is less than the predetermined threshold and the temperature within turbine engine <NUM> is less than the predetermined threshold, the post-shutdown mitigation procedure is not implemented and the logic ends. Alternatively, starter motor <NUM> motors turbine engine <NUM> every time turbine engine <NUM> is shutdown on the ground. In an alternative embodiment, FADEC system <NUM> also receives vibratory response feedback and starter motor <NUM> motors turbine engine <NUM> at a speed such that the vibratory response is less than a predetermined threshold.

In one embodiment, additional logic is included in FADEC system <NUM> to determine when to implement the post-shutdown mitigation procedure even if either the running time or the temperature is greater than the respective predetermined thresholds. More specifically, FADEC system <NUM> determines a flight status of an aircraft to which turbine engine <NUM> is attached, and actuates starter motor <NUM> only if the aircraft is not in flight. The additional logic is included to ensure starter motor <NUM> is not erroneously actuated if a malfunction occurs while the aircraft is in flight. If in flight, the residual heat within turbine engine <NUM> would be exhausted naturally and the post-shutdown mitigation procedure is not implemented. As such, FADEC system <NUM> actuates starter motor <NUM> if the aircraft is not in flight, and the logic ends if the aircraft is in flight.

In the exemplary embodiment, FADEC system <NUM> controls the operation of turbine engine <NUM> and associated starter components (i.e., starter motor <NUM>, APU <NUM>, and starter valve <NUM>) if a determination is made to implement post-shutdown mitigation of thermal rotor bow. For example, APU <NUM> channels a flow of air through starter valve <NUM> for providing pneumatic power to starter motor <NUM>, and FADEC system <NUM> selectively adjusts a position of starter valve <NUM> to control the flow of air channeled towards starter motor <NUM>. Alternatively, starter motor <NUM> receives airflow from a pneumatic power source other than APU <NUM> such as, but not limited to, an already-started turbine engine or a static pressure tank located onboard a ground cart, for example. In addition, starter motor <NUM> may be actuated by a power source other than pneumatic airflow, such as electricity.

FADEC system <NUM> also determines how long starter motor <NUM> is to be operated once actuated to ensure the residual heat within turbine engine <NUM> is exhausted therefrom. In one embodiment, FADEC system <NUM> operates starter motor <NUM> for at least a preset motoring time, where the preset motoring time is selected to provide a sufficient amount of residual heat exhaustion from turbine engine <NUM>. In addition, FADEC system <NUM> shuts down starter motor <NUM> such that starter motor <NUM> operates for an amount of time equal to or less than a predetermined duration. The predetermined duration is selected to reduce unnecessary wear to starter motor <NUM>.

In accordance with the invention, FADEC system <NUM> receives feedback on the running time of turbine engine <NUM>, and determines an amount of time for operating starter motor <NUM> based on the running time of turbine engine <NUM>. For example, the longer the running time of turbine engine <NUM>, the longer starter motor <NUM> is operated to provide sufficient residual heat exhaustion from turbine engine <NUM>. Moreover, in one embodiment, FADEC system <NUM> receives feedback on the temperature within turbine engine <NUM>, and operates starter motor <NUM> until the temperature is reduced to below a second predetermined threshold.

An exemplary technical effect of the system and methods described herein includes at least one of: (a) exhausting residual heat from a turbine engine to reduce the likelihood of formation of thermal rotor bow; (b) reducing contact-related wear between rotating and stationary components of the turbine engine caused as a result of thermal rotor bow; and (c) reducing startup time for the turbine engine.

Exemplary embodiments of a turbine engine and related components are described above in detail. The system is not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the configuration of components described herein may also be used in combination with other processes, and is not limited to practice with only turbine engines and related methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many applications where improving turbine engine performance is desired.

Although specific features of various embodiments of the present disclosure may be shown in some drawings and not in others, this is for convenience only.

Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor or controller, such as a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), and/or any other circuit or processor capable of executing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. The above examples are exemplary only, and thus are not intended to limit any way the definition and/or meaning of the term processor.

Claim 1:
A method of mitigating thermal rotor bow in a rotor assembly of a turbine engine (<NUM>), the method comprising:
receiving feedback on a running time of the turbine engine;
performing a plurality of motoring cycles between engine shutdown and restart, each of the plurality of motoring cycles comprising:
receiving feedback on a temperature within a turbine engine in a post-shutdown state;
actuating a starter motor (<NUM>) when the temperature is greater than a predetermined temperature threshold and when the running time of the turbine engine is greater than a predetermined running time-threshold;
operating the starter motor (<NUM>) for at least a preset motoring time to exhaust residual heat from the turbine engine; and
shutting down the starter motor after the preset motoring time.