Patent Publication Number: US-11655724-B1

Title: Clearance control of fan blades in a gas turbine engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent claims benefit to Indian Provisional Patent Application No. 2022/11024228, which was filed on Apr. 25, 2022, and which is hereby incorporated herein by reference in its entirety. Priority to Indian Provisional Patent Application No. 2022/11024228 filed with the Intellectual Property of India on Apr. 25, 2022, is hereby claimed. 
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to clearance control for fan blades in a gas turbine, and, more particularly, to clearance control of fan blades in a gas turbine engine. 
     BACKGROUND 
     A gas turbine engine generally includes, in serial flow order, an inlet section, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air enters the inlet section and flows to the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section, thereby creating combustion gases. The combustion gases flow from the combustion section through a hot gas path defined within the turbine section and then exit the turbine section via the exhaust section. 
     In particular configurations, the compressor section includes, in serial flow order, a high pressure (HP) compressor and a low pressure (LP) compressor. Similarly, the turbine section includes, in serial flow order, a high pressure (HP) turbine and a low pressure (LP) turbine. The HP compressor, LP compressor, HP turbine, and LP turbine include a one or more axially spaced apart rows of circumferentially spaced apart rotor blades. Each rotor blade includes a rotor blade tip. One or more shrouds may be positioned radially outward from and circumferentially enclose the rotor blades. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended Figures, in which: 
         FIG.  1    illustrates a cross-sectional view of a prior gas turbine engine. 
         FIG.  2    depicts a one-dimensional example of an electromagnetically-actuated clearance control system, implemented in accordance with the teachings of this disclosure. 
         FIG.  3    illustrates an example positioning of the electromagnetically-actuated clearance control system of  FIG.  2    within an example rotor. 
         FIG.  4    illustrates an example magnetic field generating system, including a cross-sectional view of the example electromagnetically-actuated clearance control system of  FIGS.  2  and/or  3   . 
         FIG.  5    illustrates an example coupling of the example ferromagnetic sheet to the example facesheet of  FIG.  2   . 
         FIG.  6 A  illustrates an example second electromagnetically-actuated clearance control system including an example kinetic plate and an example proximity sensor, the example kinetic plate depicted in a radially-inward position. 
         FIG.  6 B  illustrates the example second electromagnetically-actuated clearance control system of  FIG.  6 A  using the example kinetic plate and the example proximity sensors, the example kinetic plate depicted in a radially-outward position. 
         FIGS.  7 - 8    are flowcharts representing machine-readable instructions to execute the example electromagnetically-actuated clearance control system of  FIG.  2   . 
         FIG.  9    is a block diagram of an example processing platform including processor circuitry structured to execute the example machine readable instructions and/or the example operations of  FIGS.  7 - 8    to implement the example electromagnetically-actuated clearance control system of  FIG.  2   . 
     
    
    
     The figures are not to scale. Instead, the thickness of the layers or regions may be enlarged in the drawings. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, region, or plate) is in any way on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Connection references (e.g., attached, coupled, connected, joined, detached, decoupled, disconnected, separated, etc.) are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As used herein, the term “decouplable” refers to the capability of two parts to be attached, connected, and/or otherwise joined and then be detached, disconnected, and/or otherwise non-destructively separated from each other (e.g., by removing one or more fasteners, removing a connecting part, etc.). As such, connection/disconnection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. Stating that any part is in “contact” with another part means that there is no intermediate part between the two parts. 
     Descriptors “first,” “second,” “third,” etc., are used herein when identifying multiple elements or components which may be referred to separately. Unless otherwise specified or understood based on their context of use, such descriptors are not intended to impute any meaning of priority, physical order or arrangement in a list, or ordering in time but are merely used as labels for referring to multiple elements or components separately for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for ease of referencing multiple elements or components. 
     DETAILED DESCRIPTION 
     Known clearance control systems for fan blades within gas turbine engines include materials that provide a physical deflection response when a load is applied (e.g., when a blade comes into contact with a casing, shroud, etc.). Example clearance control systems disclosed herein utilize an electromagnetically-driven actuation mechanism wherein the clearance is actively monitored and adjusted through use of an electromagnetic field, in conjunction with a ferromagnetic sheet coupled to at least a facesheet and a set of springs. In some examples, the clearance control system is configured to widen a clearance (e.g., a clearance between the fan blade and fan casing) when aircraft cruise conditions cause the fan blade to expand towards the fan casing, preventing the blade from making significant contact. Additionally, example electromagnetically-actuated clearance control systems disclosed herein include a series of compression and/or leaf springs, which further assist the control mechanism in widening/narrowing the clearance in response to flight conditions. Examples disclosed herein may additionally include proximity sensors to actively monitor fan blade expansion and/or retraction to drive the electromagnetically-actuated clearance control system response. 
     Various terms are used herein to describe the orientation of features. As used herein, the orientation of features, forces and moments are described with reference to the yaw axis, pitch axis, and roll axis of the vehicle associated with the features, forces, and moments. In general, the attached figures are annotated with reference to the axial direction, radial direction, and circumferential direction of the gas turbine associated with the features, forces, and moments. In general, the attached figures are annotated with a set of axes including the roll axis R, the pitch axis P, and the yaw axis Y. As used herein, the terms “longitudinal,” and “axial” are used interchangeably to refer to directions parallel to the roll axis. As used herein, the term “lateral” is used to refer to directions parallel to the pitch axis. As used herein, the term “vertical” and “normal” are used interchangeably to refer to directions parallel to the yaw axis. 
     In some examples used herein, the term “substantially” is used to describe a relationship between two parts that are within three degrees of the stated relationship (e.g., a substantially colinear relationship is within three degrees of being linear, a substantially perpendicular relationship is within three degrees of being perpendicular, a substantially parallel relationship is within three degrees of being parallel, etc.). As used herein, the term “linkage” refers to a connection between two parts that restrain the relative motion of the two parts (e.g., restrain at least one degree of freedom of the parts, etc.). “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc. may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, and (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” entity, as used herein, refers to one or more of that entity. The terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., a single unit or processor. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
     Many gas turbine engine architectures include fan casings circumferentially enclosing the rotor blades of the engine. The proximity of the rotor blades to the casing results in frequent physical contact between the blades and casing, particularly when flight conditions cause the fan blades to expand and come into contact with the casing, causing eventual blade tip loss. 
     Examples disclosed herein are intended to overcome the above-referenced deficiencies via use of electromagnets coupled to a sheet (e.g., facesheet, kinetic plate, etc.) to act as a clearance control system (referred to herein as an electromagnetically-actuated clearance control system). The electromagnetically-actuated clearance control system, in examples disclosed herein, allows for a narrowing and/or widening of the clearance between the blades and casing, in response to an expansion and/or reduction of the fan blades based on flight conditions (e.g., the expansion and/or reduction monitored by proximity sensors). The importance of this clearance control system is observed, for example, to prevent blade tip loss when a rotor blade rubs against the fan casing. The electromagnets, in conjunction with abradable materials, compression and/or leaf springs, and/or proximity sensors, allows for the dynamic mitigation of blade tip loss as flight conditions change, and acts an active clearance control system. 
     Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures,  FIG.  1    is a schematic cross-sectional view of a prior art turbofan-type gas turbine engine  100  (“turbofan  100 ”). As shown in  FIG.  1   , the turbofan  100  defines a longitudinal or axial centerline axis  102  extending therethrough for reference. In general, the turbofan  100  may include a core turbine  104  or gas turbine engine disposed downstream from a fan section  106 . 
     The core turbine  104  generally includes a substantially tubular outer casing  108  (“turbine casing  108 ”) that defines an annular inlet  110 . The outer casing  108  can be formed from a single casing or multiple casings. The outer casing  108  encloses, in serial flow relationship, a compressor section having a booster or low pressure compressor  112  (“LP compressor  112 ”) and a high pressure compressor  114  (“HP compressor  114 ”), a combustion section  116 , a turbine section having a high pressure turbine  118  (“HP turbine  118 ”) and a low pressure turbine  120  (“LP turbine  120 ”), and an exhaust section  122 . A high pressure shaft or spool  124  (“HP shaft  124 ”) drivingly couples the HP turbine  118  and the HP compressor  114 . A low pressure shaft or spool  126  (“LP shaft  126 ”) drivingly couples the LP turbine  120  and the LP compressor  112 . The LP shaft  126  may also couple to a fan spool or shaft  128  of the fan section  106  (“fan shaft  128 ”). In some examples, the LP shaft  126  may couple directly to the fan shaft  128  (i.e., a direct-drive configuration). In alternative configurations, the LP shaft  126  may couple to the fan shaft  128  via a reduction gearbox  130  (e.g., an indirect-drive or geared-drive configuration). 
     As shown in  FIG.  1   , the fan section  106  includes a plurality of fan blades  132  coupled to and extending radially outwardly from the fan shaft  128 . An annular fan casing or nacelle  134  circumferentially encloses the fan section  106  and/or at least a portion of the core turbine  104 . The nacelle  134  is supported relative to the core turbine  104  by a plurality of circumferentially-spaced apart outlet guide vanes  136 . Furthermore, a downstream section  138  of the nacelle  134  can enclose an outer portion of the core turbine  104  to define a bypass airflow passage  140  therebetween. Certain flight conditions (e.g., increase in engine temperature, decrease in engine temperature, etc.) may cause the plurality of fan blades  132  to expand radially-outward from the fan shaft  128  towards the nacelle  134  or may cause the plurality of fan blades  132  to retract radially-inward towards the fan shaft  128  and away from the nacelle  134 . The expansion and/or retraction of the plurality of fan blades  132  in response to changing flight conditions can result in tip loss of the plurality of fan blades  132 , and/or other unwanted damage to the component, if a dynamic clearance (e.g., gap) is not maintained between the plurality of fan blades  132  and the nacelle  134 . 
     As illustrated in  FIG.  1   , air  142  enters an inlet portion  144  of the turbofan  100  during operation thereof. A first portion  146  of the air  142  flows into the bypass airflow passage  140 , while a second portion  148  of the air  142  flows into the inlet  110  of the LP compressor  112 . One or more sequential stages of LP compressor stator vanes  150  and LP compressor rotor blades  152  coupled to the LP shaft  126  progressively compress the second portion  148  of the air  142  flowing through the LP compressor  112  en route to the HP compressor  114 . Next, one or more sequential stages of HP compressor stator vanes  154  and HP compressor rotor blades  156  coupled to the HP shaft  124  further compress the second portion  148  of the air  142  flowing through the HP compressor  114 . This provides compressed air  158  to the combustion section  116  where it mixes with fuel and burns to provide combustion gases  160 . 
     The combustion gases  160  flow through the HP turbine  118  in which one or more sequential stages of HP turbine stator vanes  162  and HP turbine rotor blades  164  coupled to the HP shaft  124  extract a first portion of kinetic and/or thermal energy from the combustion gases  160 . This energy extraction supports operation of the HP compressor  114 . The combustion gases  160  then flow through the LP turbine  120  where one or more sequential stages of LP turbine stator vanes  166  and LP turbine rotor blades  168  coupled to the LP shaft  126  extract a second portion of thermal and/or kinetic energy therefrom. This energy extraction causes the LP shaft  126  to rotate, thereby supporting operation of the LP compressor  112  and/or rotation of the fan shaft  128 . The combustion gases  160  then exit the core turbine  104  through the exhaust section  122  thereof. 
     Along with the turbofan  100 , the core turbine  104  serves a similar purpose and sees a similar environment in land-based gas turbines, turbojet engines in which the ratio of the first portion  146  of the air  142  to the second portion  148  of the air  142  is less than that of a turbofan, and unducted fan engines in which the fan section  106  is devoid of the nacelle  134 . In each of the turbofan, turbojet, and unducted engines, a speed reduction device (e.g., the reduction gearbox  130 ) may be included between any shafts and spools. For example, the reduction gearbox  130  may be disposed between the LP shaft  126  and the fan shaft  128  of the fan section  106 .  FIG.  1    further includes a cowling  170  and offset-arch gimbals  172 - 176 . The cowling  170  is a covering which may reduce drag and cool the engine. The offset-arch gimbals  172 - 176  may, for example, include infrared cameras to detect a thermal anomaly in the under-cowl area of the engine  100 . 
       FIG.  2    depicts a one-dimensional example of an electromagnetically-actuated clearance control system  200 , implemented in accordance with the teachings of this disclosure. The example electromagnetically-actuated clearance control system  200  includes an example fan casing/nacelle  202 , an example fan blade  204 , an example facesheet  206 , an example honeycomb structure  208 , an example abradable material  210 , an example first spring  212 A, an example second spring  212 B, an example electromagnetic system  214 , an example clearance  216 , and an example ferromagnetic sheet  218 . 
     The example facesheet  206  is coupled to the fan casing  202  to provide a structure upon which the electromagnetic system  214  is coupled. Additionally, the example facesheet  206  may also be used as a structure to absorb impact from a blade (e.g., ice impact, etc.) without damaging the blade and/or blade tip (e.g., through use of abradable material). In examples disclosed herein, the facesheet  206  encloses a honeycomb structure  208 , the honeycomb structure  208  provides a rigidity to the facesheet  206  that allows for the facesheet  206  to remain stable under changing flight conditions. In examples disclosed herein, the example honeycomb structure  208  is used to provide a sound dampening effect and/or a blade tip damage mitigating effect in a blade out event (e.g., when flight conditions cause a fan blade to break off within an engine) through its collapsible nature. The example ferromagnetic sheet  218  is coupled on either end to the first and second springs,  212 A and  212 B, respectively. The first and second springs,  212 A and  212 B, respectively, compress when the ferromagnetic sheet  218  is drawn inwards towards the electromagnetic system  214  to widen the clearance  216 , when the electromagnetic system  214  is activated in response to the fan blade  204  expanding under flight conditions. In some examples disclosed herein, the electromagnetic system  214  includes a set of proximity sensors (not shown in the example of  FIG.  2    but including, for example, proximity sensor  602  described further in conjunction with  FIGS.  6 A and/or  6 B ). The example abradable material  210  (e.g., foil, ring, etc.) is coupled to the ferromagnetic sheet  218  and positioned radially outward from the fan blade  204  to create the clearance  216  between the fan casing  202  and the fan blade  204 . In examples disclosed herein, the example electromagnetic system  214  is an electromagnetic coil configured to generate a magnetic field when a power supply is turned on, and the power supply is to be turned on in response to flight conditions wherein the fan blade  204  is expanding towards the fan casing  202 . Additionally, in examples disclosed herein, the ferromagnetic sheet  218  may utilize any materials that are able to respond to magnetization by the electromagnetic system  214  (e.g., iron, cobalt, nickel, etc.). In the example of  FIG.  2   , the clearance  216  is shown as distance “d,” which can be quantified as any distance between the abradable material  210  and the fan blade  204 . 
       FIG.  3    illustrates an example positioning of the electromagnetically-actuated clearance control system  200  of  FIG.  2    within an example rotor  300 , in accordance with the teachings of this disclosure. In examples disclosed herein, the example electromagnetically-actuated clearance control system  200 , including the example fan casing  202 , example facesheet  206 , example abradable material  210 , example electromagnetic system  214 , and example clearance  216  of  FIG.  2   , is positioned to circumferentially enclose the example fan blades  204 A,  204 B,  204 C,  204 D,  204 E,  204 F,  204 G, and  204 H approximately every 30 degrees of the rotor  300 . 
       FIG.  4    illustrates an example magnetic field generating system  400 , including a cross-sectional view of the example electromagnetically-actuated clearance control system  200  of  FIGS.  2  and/or  3   . The example magnetic field generating system  400  includes an example electromagnetic coil  402 , the electromagnetic coil  402  configured to generate a magnetic field when connected to a power supply (e.g., the Full Authority Digital Engine Control (FADEC)). In examples disclosed herein, the electromagnetic coil  402  is additionally configured to lie within the electromagnetic system  214  described in  FIG.  2   . Additionally, in operation, the example magnetic field generating system  400  is dependent on a current supplied by the power supply (e.g., FADEC), to generate a magnetic field in response to an indication of a widening and/or narrowing of the clearance  216  of  FIG.  2   . As described in  FIG.  2   , when the electromagnetic coil  402  is provided current for activation, the ferromagnetic sheet  218  of  FIG.  2    is drawn inwards towards the electromagnetic system  214  of  FIG.  2    to widen the clearance  216  of  FIG.  2   . 
       FIG.  5    illustrates an example wedge-shaped coupling  500  of the example ferromagnetic sheet  218  to the example facesheet  206  of  FIG.  2   . The wedge-shape coupling  500  locks the facesheet  206  to the ferromagnetic sheet  218  in a given radial position along the fan casing  202  of  FIG.  2   . In examples disclosed herein, the radial position is held in place by the wedge-shape coupling  500  to minimize use of power provided via the example FADEC system in maintaining a fixed position of the facesheet  206 , relative to the fan casing  202 . 
       FIG.  6 A  illustrates an example second electromagnetically-actuated clearance control system  600 . The example second electromagnetically-actuated clearance control system  600  includes the example fan casing  202 , the example fan blade  204 , the example first spring  212 A, the example second spring  212 B, and the example clearance  216  of  FIG.  2   . In examples disclosed herein, the example second electromagnetically-actuated clearance control system  600  additionally includes an example proximity sensor  602 , an example kinetic plate  604 , an example first electromagnet  606 A, an example second electromagnet  606 B, an example third electromagnet  606 C, and an example fourth electromagnet  606 D. In examples disclosed herein, the second electromagnetically-actuated clearance control system  600  is segmented along the circumference of the fan casing  202 , as depicted in  FIG.  3     
     In examples disclosed herein, the proximity sensor  602  is configured to rest along the kinetic plate  604  and the proximity sensor  602  is configured to measure the distance between the kinetic plate  604  and the fan blade  204  (e.g., measuring the width of the clearance  216 ). The first electromagnet  606 A and second electromagnet  606 B are positioned against the same pole (e.g., the north pole of the first electromagnet  606 A is configured to face the north pole of the second electromagnet  606 B), causing the first and second electromagnets,  606 A and  606 B, respectively to repel against each other. The repelling first and second electromagnets,  606 A and  606 B, respectively are held in place and/or compressed by the first spring  212 A, the first spring  212 A to compress and decompress in response to the measured clearance  216  by the proximity sensor  602 . Similarly, the third electromagnet  606 C and fourth electromagnet  606 D are positioned against the same pole (e.g., the north pole of the third electromagnet  606 C is configured to face the north pole of the fourth electromagnet  606 D), causing the third and fourth electromagnets,  606 C and  606 D, respectively to repel against each other. The repelling third and fourth electromagnets,  606 C and  606 D, respectively are held in place and/or compressed by the second spring  212 B, the second spring  212 B to compress and decompress in response to the measured clearance  216  by the proximity sensor  602 . 
     In examples disclosed herein, the second electromagnet  606 B and fourth electromagnet  606 D are coupled to the kinetic plate  604 , the first, second, third, and fourth electromagnets,  606 A,  606 B,  606 C, and  606 D, respectively configured to generate a magnetic field when connected to a power supply (e.g., FADEC). In response to a reading of the proximity sensor  602 , the first and second springs,  212 A and  212 B, respectively, compress and/or decompress against the first and third electromagnets,  606 A and  606 C, respectively, to repel against the second and fourth electromagnets,  606 B and  606 D, respectively, to move the kinetic plate  604 . Additionally, in examples disclosed herein, the kinetic plate  604  is housed within the fan casing  202 , to widen and/or narrow the clearance  216  to mitigate tip loss of the example fan blade  204 . 
     The kinetic plate  604 , as depicted in  FIG.  6 A , is shown in a radially-inward position, thus widening the clearance  216 . As shown in the example of  FIG.  6 A , the kinetic plate  604  moves radially-inward in response to a reading from the proximity sensor  602  that indicates that the example fan blade  204  is expanding towards the fan casing  202 . The radially-inward movement of the kinetic plate  604  is facilitated by the compression of the first and second spring,  212 A and  212 B, respectively. The first spring  212 A is coupled to the first electromagnet  606 A to repel the second electromagnet  606 B. The second electromagnet  606 B is coupled to a first end of the kinetic plate  604 . The second spring  212 B is coupled to the third electromagnet  606 C to repel the fourth electromagnet  606 D. The fourth electromagnet is coupled to a second end of the kinetic plate  604 , which causes the kinetic plate  604  to shift radially-inwards towards the fan casing  202  (e.g., widening the clearance  216 ). 
     Additionally, in examples disclosed herein, variable clearance is maintained along the length of the example fan blade (e.g., fan blade  204  of  FIG.  2   ). The first and second electromagnets,  606 A and  606 B, respectively, may be configured to move with a different displacement than the third and fourth electromagnets,  606 C and  606 D, respectively, the difference in displacement tilting the kinetic plate  604  such that any variable clearance along the blade length is maintained. 
       FIG.  6 B  illustrates a second configuration of the example second electromagnetically-actuated clearance control system  600  of  FIG.  6 B . The kinetic plate  604 , as depicted in  FIG.  6 B , is shown in a radially-outward position, thus narrowing the clearance  216  in response to a reading from the proximity sensor  602  that indicates that the example fan blade  204  is retracting away from the fan casing  202 . The radially-outward movement of the kinetic plate  604  is facilitated by the decompression of the first and second springs,  212 A and  212 B, respectively. The first spring  212 A is coupled to the first electromagnet  606 A to repel 
     the second electromagnet  606 B. The second electromagnet is coupled to a first end of the kinetic plate  604 . The second spring  212 B is coupled to the third electromagnet  606 C to repel the fourth electromagnet  606 D. The fourth electromagnet is coupled to a second end of the kinetic plate  604  to cause the kinetic plate  604  to shift radially-outwards away from the fan casing  202  (e.g., narrowing the clearance  216 ). 
     A flowchart representative of example hardware logic circuitry, machine readable instructions, hardware implemented state machines, and/or any combination thereof for implementing the example second electromagnetically-actuated clearance control system  600  of  FIGS.  6 A-B  is shown in  FIG.  7   . The machine readable instructions may be one or more executable programs or portion(s) of an executable program for execution by processor circuitry, such as the processor circuitry  912  shown in the example processor platform  900  discussed below in connection with  FIG.  9   . The program may be embodied in software stored on one or more non-transitory computer readable storage media such as a compact disk (CD), a floppy disk, a hard disk drive (HDD), a solid-state drive (SSD), a digital versatile disk (DVD), a Blu-ray disk, a volatile memory (e.g., Random Access Memory (RAM) of any type, etc.), or a non-volatile memory (e.g., electrically erasable programmable read-only memory (EEPROM), FLASH memory, an HDD, an SSD, etc.) associated with processor circuitry located in one or more hardware devices, but the entire program and/or parts thereof could alternatively be executed by one or more hardware devices other than the processor circuitry and/or embodied in firmware or dedicated hardware. The machine readable instructions may be distributed across multiple hardware devices and/or executed by two or more hardware devices (e.g., a server and a client hardware device). For example, the client hardware device may be implemented by an endpoint client hardware device (e.g., a hardware device associated with a user) or an intermediate client hardware device (e.g., a radio access network (RAN)) gateway that may facilitate communication between a server and an endpoint client hardware device). Similarly, the non-transitory computer readable storage media may include one or more mediums located in one or more hardware devices. Further, although the example program is described with reference to the flowchart illustrated in  FIG.  7   , many other methods of implementing the example second electromagnetically-actuated clearance control system  600  may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined. Additionally or alternatively, any or all of the blocks may be implemented by one or more hardware circuits (e.g., processor circuitry, discrete and/or integrated analog and/or digital circuitry, an FPGA, an ASIC, a comparator, an operational-amplifier (op-amp), a logic circuit, etc.) structured to perform the corresponding operation without executing software or firmware. The processor circuitry may be distributed in different network locations and/or local to one or more hardware devices (e.g., a single-core processor (e.g., a single core central processor unit (CPU)), a multi-core processor (e.g., a multi-core CPU), etc.) in a single machine, multiple processors distributed across multiple servers of a server rack, multiple processors distributed across one or more server racks, a CPU and/or a FPGA located in the same package (e.g., the same integrated circuit (IC) package or in two or more separate housings, etc.). 
     The machine readable instructions described herein may be stored in one or more of a compressed format, an encrypted format, a fragmented format, a compiled format, an executable format, a packaged format, etc. Machine readable instructions as described herein may be stored as data or a data structure (e.g., as portions of instructions, code, representations of code, etc.) that may be utilized to create, manufacture, and/or produce machine executable instructions. For example, the machine readable instructions may be fragmented and stored on one or more storage devices and/or computing devices (e.g., servers) located at the same or different locations of a network or collection of networks (e.g., in the cloud, in edge devices, etc.). The machine readable instructions may require one or more of installation, modification, adaptation, updating, combining, supplementing, configuring, decryption, decompression, unpacking, distribution, reassignment, compilation, etc., in order to make them directly readable, interpretable, and/or executable by a computing device and/or other machine. For example, the machine readable instructions may be stored in multiple parts, which are individually compressed, encrypted, and/or stored on separate computing devices, wherein the parts when decrypted, decompressed, and/or combined form a set of machine executable instructions that implement one or more operations that may together form a program such as that described herein. 
     In another example, the machine readable instructions may be stored in a state in which they may be read by processor circuitry, but require addition of a library (e.g., a dynamic link library (DLL)), a software development kit (SDK), an application programming interface (API), etc., in order to execute the machine readable instructions on a particular computing device or other device. In another example, the machine readable instructions may need to be configured (e.g., settings stored, data input, network addresses recorded, etc.) before the machine readable instructions and/or the corresponding program(s) can be executed in whole or in part. Thus, machine readable media, as used herein, may include machine readable instructions and/or program(s) regardless of the particular format or state of the machine readable instructions and/or program(s) when stored or otherwise at rest or in transit. 
     The machine readable instructions described herein can be represented by any past, present, or future instruction language, scripting language, programming language, etc. For example, the machine readable instructions may be represented using any of the following languages: C, C++, Java, C#, Perl, Python, JavaScript, HyperText Markup Language (HTML), Structured Query Language (SQL), Swift, etc. 
     As mentioned above, the example operations of  FIG.  7    may be implemented using executable instructions (e.g., computer and/or machine readable instructions) stored on one or more non-transitory computer and/or machine readable media such as optical storage devices, magnetic storage devices, an HDD, a flash memory, a read-only memory (ROM), a CD, a DVD, a cache, a RAM of any type, a register, and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the terms non-transitory computer readable medium and non-transitory computer readable storage medium are expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. 
     “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc., may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, or (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” object, as used herein, refers to one or more of that object. The terms “a” (or “an”), “one or more”, and “at least one” are used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., the same entity or object. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
       FIG.  7    is a flowchart representative of example machine readable instructions and/or example operations  700  that may be executed and/or instantiated by processor circuitry to actively monitor widening and/or narrowing of the clearance  216  and provide a response to mitigate blade tip loss. The machine readable instructions and/or the operations  700  of  FIG.  7    begin at block  702 , at which the processor circuitry  912  shown in the example processor platform  900  discussed below in connection with  FIG.  9    causes the proximity sensors to detect the width of the clearance  216 . 
     At block  704 , as shown in  FIG.  7   , the processor circuitry  912  determines whether the width of the clearance  216 , as measured in block  702 , is greater than a first threshold (e.g., 0.010 inches, 0.020 inches, 0.030 inches, 0.050 inches, etc.) (e.g., indicating that the clearance  216  has widened beyond the first threshold value, such as a maximum threshold value). In examples disclosed herein, the width of clearance  216  may be measured in inches, centimeters, and/or any other unit of measurement. When the clearance  216  is determined to not be greater than the first threshold, the process moves forward to block  706 . However, when the clearance  216  is determined to be greater than the first threshold, the process moves to block  708 . 
     At block  708 , the processor circuitry  912  establishes whether the width of the clearance  216 , as measured in block  702 , is less than a second threshold value (e.g., 0.005 inches, 0.006 inches, 0.007 inches, 0.008 inches, etc.) (e.g., indicating that the clearance has narrowed beyond the second threshold value, such as a minimum threshold value). In examples disclosed herein, the width of clearance  216  may be measured in inches, centimeters, and/or any other unit of measurement When the clearance  216  is determined to not be less than the second threshold, the process moves forward to block  710 . However, when the clearance  216  is determined to be less than the second threshold, the process moves to block  716 . 
     At block  708 , in response to having determined at block  704  that the width of the clearance  216  is greater than the first threshold, the processor circuitry  912  causes the magnetic field of the example first, second, third, and/or fourth electromagnets,  606 A,  606 B,  606 C, and  606 D, respectively, to be activated. In examples disclosed herein, the magnetic field is activated by connecting the first, second, third, and fourth electromagnets,  606 A,  606 B,  606 C, and  606 D, respectively, to a power supply (e.g., FADEC). 
     At block  710 , in response to having determined at block  706  that the width of the clearance  216  is less than the second threshold, the processor circuitry  912  causes the magnetic field of the example first, second, third, and/or fourth electromagnets,  606 A,  606 B,  606 C, and  606 D, respectively, to be reduced. In some examples, the magnetic field may be deactivated by the processor circuitry  912  by disconnecting the first, second, third, and fourth electromagnets,  606 A,  606 B,  606 C, and  606 D, respectively from the power supply. 
     At block  712 , in response to the magnetic field having been reduced in intensity by the processor circuitry  912  at block  710 , the kinetic plate  604  moves radially-inward, as described further in conjunction with  FIG.  6 A , to narrow the width of the clearance  216 , as illustrated in  FIG.  2   . 
     At block  714 , in response to the magnetic field having been activated by the processor circuitry  912  (at block  708 ), the kinetic plate  604  moves radially-outward, as described further in conjunction with  FIG.  6 A , to widen the width of the clearance  216 , as illustrated in  FIG.  2   . 
     At block  716 , in response to the processor circuitry  912  having determined that the measured width of the clearance  216  falls within the range of a minimum threshold and maximum threshold (e.g., the first and second thresholds), the kinetic plate  604  is locked in place to neither narrow nor widen the clearance  216 . 
       FIG.  8    is a flowchart representative of example machine readable instructions and/or example operations  800  that may be executed and/or instantiated by processor circuitry to provide a response to mitigate blade tip loss, based on a determined current flight condition (e.g., stage of flight), as performed by the examples of  FIGS.  6 A and/or  6 B . The machine readable instructions and/or the operations  800  of  FIG.  8    begin at block  802 , at which the processor circuitry  912  shown in the example processor platform  900  discussed below in connection with  FIG.  9    causes the proximity sensors to detect the width of the clearance  216  of  FIG.  2   . 
     As illustrated in  FIG.  8   , at block  802 , the processor circuitry  912  determines the current stage of flight. In examples disclosed herein, the stages of flight may include an aircraft stationed at ground level, an aircraft in takeoff/transient aircraft, cruise, thrust reversal, and/or shutdown. 
     At block  804 A, the processor circuitry  912  checks whether the aircraft is at ground level (e.g., ground level stage of flight). When the processor circuitry  912  determines that the aircraft is indeed at ground level, the process moves to block  806 . However, when the processor circuitry  912  determines that the aircraft is not at ground level, the process may move to any one of blocks  804 B,  804 C,  804 D, and/or  804 E. 
     At block  804 B, the processor circuitry  912  checks whether the aircraft is in takeoff or is transient (e.g., takeoff/transient stage of flight). When the processor circuitry  912  determines that the aircraft is in takeoff or is transient, the process moves to block  808 . However, when the processor circuitry  912  determines that the aircraft is not in takeoff and is not transient, the process may move to any one of blocks  804 A,  804 C,  804 D, and/or  804 E. 
     At block  804 C, the processor circuitry  912  checks whether the aircraft is in cruise (e.g., cruise stage of flight). When the processor circuitry  912  determines that the aircraft is in cruise, the process moves forward to block  808 . However, when the processor circuitry  912  determines that the aircraft is not in cruise, the process may move to any one of blocks  804 A,  804 B,  804 D, and/or  804 E. 
     At block  804 D, the processor circuitry  912  checks whether the aircraft is in thrust reversal (e.g., thrust reversal stage of flight). When the processor circuitry  912  determines that the aircraft is in thrust reversal, the process moves forward to block  808 . However, when the processor circuitry  912  determines that the aircraft is not in thrust reversal, the process may move to any one of blocks  804 A,  804 B,  804 C, and/or  804 E. 
     At block  804 E, the processor circuitry  912  checks whether the aircraft is in shutdown (e.g., shutdown stage of flight). When the processor circuitry  912  determines that the aircraft is in shutdown, the process moves forward to block  818 . However, when the processor circuitry  912  determines that the aircraft is not in shutdown, the process may move to any one of block  804 A,  804 B,  804 C, and/or  804 D. 
     At block  806 , upon determination by the processor circuitry  912  at block  804 A that the current stage of flight is ground level, cold clearance is maintained. In examples disclosed herein, cold clearance refers to a state in which the magnetic field is not in activation, but rather, the springs (e.g., first spring  212 A and/or second spring  212 B of  FIG.  2   ) are used to mechanically-maintain clearance width (e.g., using the wedge-shaped coupling  500  of  FIG.  5   ). 
     At block  808 , upon determination by the processor circuitry  912  at block  804 B that the current stage of flight is takeoff/transient, the processor circuitry  912  obtains a reading from the example proximity sensor  602  of  FIGS.  6 A and/or  6 B . In examples disclosed herein, this proximity sensor reading may indicate a width of the example clearance  216  of  FIG.  2    (e.g., 0.010 inches, 0.005 centimeters, etc.). 
     At block  810 , the processor circuitry  912  determines whether the sensor reading obtained in block  808  falls within an acceptable range. In examples disclosed herein, the acceptable range may be marked by an example minimum threshold (e.g., 0.005 inches, 0.006 inches, 0.007 centimeters, 0.008 centimeters) and an example maximum threshold (e.g., 0.010 inches, 0.011 inches, 0.012 centimeters, 0.013 centimeters), indicating an example minimum and/or maximum width of the clearance  216  that is acceptable to mitigate blade tip loss. In examples disclosed herein, a controller may be used to drive proximity sensor readings and/or the resulting transmission of signal for activation and/or deactivation of the magnetic field. 
     At block  812 , a signal is sent by the processor circuitry  912  to activate the magnetic field. In examples disclosed herein, the signal is sent to the Full Authority Digital Engine Control (FADEC) of the aircraft, which controls a power supply from which current can be sent to activate the magnetic field. 
     At block  814 , the processor circuitry  912 , calculates the amount of power (e.g., current) required by the example magnetic field generating system  400  of  FIG.  4   , to generate the magnetic field for clearance control. 
     At block  816 , current is supplied by FADEC to the example magnetic field generating system  400  of  FIG.  4   , and clearance is maintained (e.g., the clearance is actively adjusted in response to proximity sensor readings) 
     At block  818 , upon determination by the processor circuitry  912  that the current stage of flight is shutdown, the processor circuitry  912  establishes that no clearance adjustment is necessary. 
       FIG.  9    is a block diagram of an example processor platform  900  structured to execute and/or instantiate the machine readable instructions and/or the operations of  FIGS.  7 - 8    to implement the example second electromagnetically-actuated clearance control system  600  of  FIGS.  6 A and/or  6 B . The processor platform  900  can be, for example, a server, a personal computer, a workstation, a self-learning machine (e.g., a neural network), a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance, a DVD player, a CD player, a digital video recorder, a Blu-ray player, a gaming console, a personal video recorder, a set top box, a headset (e.g., an augmented reality (AR) headset, a virtual reality (VR) headset, etc.) or other wearable device, or any other type of computing device. 
     The processor platform  900  of the illustrated example includes processor circuitry  912 . The processor circuitry  912  of the illustrated example is hardware. For example, the processor circuitry  912  can be implemented by one or more integrated circuits, logic circuits, FPGAs, microprocessors, CPUs, GPUs, DSPs, and/or microcontrollers from any desired family or manufacturer. The processor circuitry  912  may be implemented by one or more semiconductor based (e.g., silicon based) devices. 
     The processor circuitry  912  of the illustrated example includes a local memory  913  (e.g., a cache, registers, etc.). The processor circuitry  912  of the illustrated example is in communication with a main memory including a volatile memory  914  and a non-volatile memory  916  by a bus  918 . The volatile memory  914  may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAMBUS® Dynamic Random Access Memory (RDRAM®), and/or any other type of RAM device. The non-volatile memory  916  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  914 ,  916  of the illustrated example is controlled by a memory controller  917 . 
     The processor platform  900  of the illustrated example also includes interface circuitry  920 . The interface circuitry  920  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a universal serial bus (USB) interface, a Bluetooth® interface, a near field communication (NFC) interface, a Peripheral Component Interconnect (PCI) interface, and/or a Peripheral Component Interconnect Express (PCIe) interface. 
     In the illustrated example, one or more input devices  922  are connected to the interface circuitry  920 . The input device(s)  922  permit(s) a user to enter data and/or commands into the processor circuitry  912 . 
     One or more output devices  924  are also connected to the interface circuitry  920  of the illustrated example. The interface circuitry  920  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip, and/or graphics processor circuitry such as a GPU. 
     The interface circuitry  920  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem, a residential gateway, a wireless access point, and/or a network interface to facilitate exchange of data with external machines (e.g., computing devices of any kind) by a network  926 . The communication can be by, for example, an Ethernet connection, a digital subscriber line (DSL) connection, a telephone line connection, a coaxial cable system, a satellite system, a line-of-site wireless system, a cellular telephone system, an optical connection, etc. 
     The processor platform  900  of the illustrated example also includes one or more mass storage devices  928  to store software and/or data. Examples of such mass storage devices  928  include magnetic storage devices, optical storage devices, floppy disk drives, HDDs, CDs, Blu-ray disk drives, redundant array of independent disks (RAID) systems, solid state storage devices such as flash memory devices and/or SSDs, and DVD drives. 
     The machine executable instructions  932 , which may be implemented by the machine readable instructions of  FIGS.  7 - 8   , may be stored in the mass storage device  928 , in the volatile memory  914 , in the non-volatile memory  916 , and/or on a removable non-transitory computer readable storage medium such as a CD or DVD. 
     Examples disclosed herein include electromagnetically-actuated clearance control systems. The examples disclosed herein mitigate the rotor blade tip loss by employing a dynamic clearance widening and/or narrowing response to blade tip expansion and/or retraction during changing flight conditions. Examples disclosed can reduce the cost of continual replacement of rotor blades of gas turbine engines by reducing significant contact between the rotor blades and fan casing. Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 
     Further aspects of the present disclosure are provided by the subject matter of the following clauses: 
     Example 1 includes an electromagnetically-actuated clearance control system for a gas turbine engine comprising an electromagnetic coil coupled to a first end of a facesheet, the electromagnetic coil to generate a magnetic field in response to a connection of a power supply, and a ferromagnetic sheet coupled to a second end of the facesheet, the ferromagnetic sheet drawn radially-inward toward the electromagnetic coil when the magnetic field is generated, a first end of the ferromagnetic sheet coupled to a first compression spring and a second end of the ferromagnetic sheet coupled to a second compression spring, the first and second compression springs to compress in response to the ferromagnetic sheet being drawn radially-inward. 
     Example 2 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the electromagnetic coil is a plurality of electromagnets, a first and second electromagnet of the plurality of electromagnets configured to repel against each other when connected to the power supply. 
     Example 3 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the first electromagnet is coupled to the first compression spring and the second electromagnet is coupled to a kinetic plate. 
     Example 4 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the kinetic plate is further to move radially-inward in response to a measured clearance satisfying a maximum threshold, and move radially-outward in response to the measured clearance satisfying a minimum threshold. 
     Example 5 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the clearance is measured using a proximity sensor. 
     Example 6 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the first and second compression springs decompress to move the ferromagnetic sheet radially-outward, in response to deactivation of the magnetic field. 
     Example 7 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the magnetic field is deactivated in response to a reading of the proximity sensor. 
     Example 8 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the facesheet contains a honeycomb structure to provide sound dampening. 
     Example 9 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the first and second electromagnets of the plurality of electromagnets are configured to move with a different displacement than a third and fourth electromagnet of the plurality of electromagnets. 
     Example 10 includes the electromagnetically-actuated clearance control system of any preceding clause, wherein the difference in displacement causes the kinetic plate to tilt. 
     Example 11 includes a gas turbine comprising a compressor including a compressor casing and a plurality of compressor blades, the compressor casing defining first and second compressor casing slots, a turbine, comprising a turbine casing and a plurality of turbine blades, a shaft rotatably coupling the compressor and the turbine, and a shroud for at least one of the compressor or the turbine, the shroud comprising an electromagnetic coil coupled to a first end of a facesheet, the electromagnetic coil to generate a magnetic field in response to a connection of a power supply, and a ferromagnetic sheet coupled to a second end of the facesheet, the ferromagnetic sheet drawn radially-inward toward the electromagnetic coil when the magnetic field is generated, a first end of the ferromagnetic sheet coupled to a first compression spring and a second end of the ferromagnetic sheet coupled to a second compression spring, the first and second compression springs to compress in response to the ferromagnetic sheet being drawn radially-inward. 
     Example 12 includes the apparatus of any preceding clause, wherein the electromagnetic coil is a plurality of electromagnets, a first and second electromagnet of the plurality of electromagnets configured to repel against each other connected to the power supply. 
     Example 13 includes the apparatus of any preceding clause, wherein the first electromagnet is coupled to the first compression spring and the second electromagnet is coupled to a kinetic plate. 
     Example 14 includes the apparatus of any preceding clause, wherein the kinetic plate is further to move radially inward in response to a measured clearance satisfying a maximum threshold, and move radially-outward in response to the measured clearance satisfying a minimum threshold. 
     Example 15 includes the apparatus of any preceding clause, wherein the clearance is measured using a proximity sensor. 
     Example 16 includes the apparatus of any preceding clause, wherein the first and second compression springs decompress to move the ferromagnetic sheet radially-outward, in response to deactivation of the magnetic field. 
     Example 17 includes the apparatus of any preceding clause, wherein the magnetic field is deactivated in response to a reading of the proximity sensor. 
     Example 18 includes the apparatus of any preceding clause, wherein the facesheet contains a honeycomb structure to provide sound dampening. 
     Example 19 includes the apparatus of any preceding clause, wherein the first and second electromagnets of the plurality of electromagnets are configured to move with a different displacement than a third and fourth electromagnet of the plurality of electromagnets. 
     Example 20 includes the apparatus of any preceding clause, wherein the difference in displacement causes the kinetic plate to tilt. 
     The following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.