Patent Publication Number: US-2023136475-A1

Title: Electric heating for turbomachinery clearance control powered by hybrid energy storage system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of, and claims priority to, and the benefit of U.S. patent application Ser. No. 16/938,579, filed on Jul. 24, 2020, and entitled “ELECTRIC HEATING FOR TURBOMACHINERY CLEARANCE CONTROL POWERED BY HYBRID ENERGY STORAGE SYSTEM.” The &#39;579 application is a divisional of, claims priority to and the benefit of, U.S. patent application Ser. No. 15/979,112, filed on May 14, 2018, and entitled “ELECTRIC HEATING FOR TURBOMACHINERY CLEARANCE CONTROL POWERED BY HYBRID ENERGY STORAGE SYSTEM,” (aka U.S. Pat. No. 10,760,444 issued Aug. 12, 2020). Both of which are incorporated by reference herein in their entirety for all purposes. 
    
    
     FIELD 
     The present disclosure relates to gas turbine engines, and more specifically, to the management of turbomachinery clearances. 
     BACKGROUND 
     Gas turbine engines typically include a fan delivering air into a compressor. The air is compressed in the compressor and delivered into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine blades, driving them to rotate. Turbine rotors, in turn, drive the compressor and fan rotors. The efficiency of the engine is impacted by ensuring that the products of combustion pass in as high a percentage as possible across the turbine blades. Leakage around the blades reduces efficiency. Thus, a blade outer air seal (BOAS) is provided radially outward of the blades to prevent leakage. 
     The BOAS is spaced from a radially outer part of the blade by a tip clearance. The BOAS is traditionally associated with a carrier element that is mounted to an engine case. Since the blades, the BOAS, and the structure that support the BOAS are different sizes and/or are formed of different materials, they respond to temperature changes in different manners. As these structures expand at different rates in response to temperature changes, the tip clearance may be reduced and the blade may rub on the BOAS, or the tip clearance may increase reducing efficiency, both of which are undesirable. 
     Clearance control systems are used to control the tip clearance under different operational conditions. Traditional clearance control systems utilize valves and manifolds to direct fan air to specific engine case locations. The cooling air thermally shrinks the engine case at these locations to improve tip clearance and thus fuel burn. However, these manifolds and valves are large, heavy, and expensive. These systems can also be slow to respond and provide limited clearance improvement. By further reducing tip clearances increasing engine efficiency demands can be met. 
     SUMMARY 
     A clearance control system for a gas turbine engine is disclosed, comprising a rotor blade, an outer structure disposed radially outward from the rotor blade, a heating element configured to cause the outer structure to be heated in response to electric current being supplied to the heating element, wherein a gap between the rotor blade and the outer structure is at least one of increased, decreased, and maintained in response to the outer structure being heated, a hybrid electric power source configured to supply the electric current to the heating element, and a controller configured to regulate the electric current being supplied to the heating element. 
     In various embodiments, the hybrid electric power source comprises at least one of a battery, a supercapacitor, and an ultracapacitor. 
     In various embodiments, the clearance control system further comprises a first converter in electronic communication with the battery and the capacitor. 
     In various embodiments, the clearance control system further comprises a second converter configured to receive DC power from the first converter and supply the heater element with electrical power. 
     In various embodiments, the second converter comprises a DC-AC inverter and the heating element is configured to cause the outer structure to be heated via induction heating. 
     In various embodiments, the clearance control system further comprises a valve assembly configured to meter a cooling air flow to the outer structure. 
     In various embodiments, the controller is configured to at least one of decrease, maintain, or increase the gap by coordinating the cooling air flow and the electric current being supplied to the heating element. 
     In various embodiments, the controller coordinates the cooling air flow via valve position control of the valve assembly. 
     In various embodiments, the controller is configured to send a first control signal to a power electronics for varying the electric current supplied to a heating element to cause the outer structure to move in a first radial direction, and send a second control signal to the valve assembly for varying a cooling air flow supplied to the outer structure to cause the outer structure to move in a second radial direction, wherein the first radial direction is opposite the second radial direction 
     A hybrid energy storage and control system for a clearance control system for a gas turbine engine is disclosed, comprising a hybrid electric power source, a first converter, a second converter configured to receive electric power from the hybrid electric power source via the first converter and configured to send the electric power to a heating element for controlling a blade tip clearance between a rotor blade and an outer structure of the gas turbine engine, and a controller in electronic communication with the second converter. 
     In various embodiments, the hybrid electric power source comprises at least one of a battery, a supercapacitor, and an ultracapacitor. 
     In various embodiments, the controller is configured to regulate the electric power supplied to the heating element via the second converter. 
     In various embodiments, the first converter is configured to regulate power between at least one of the battery, the supercapacitor, and the ultracapacitor. 
     In various embodiments, the second converter comprises a DC-DC converter, the heating element configured to heat up the outer structure by resistive heating. 
     In various embodiments, the second converter comprises a DC-AC inverter, the heating element configured to heat up the outer structure by induction heating. 
     In various embodiments, the second converter comprises a AC-AC converter, the heating element configured to heat up the outer structure by induction heating. 
     In various embodiments, at least one of the battery, the supercapacitor, and the ultracapacitor is configured to receive electric power from a generator in response to the at least one of the battery, the supercapacitor, and the ultracapacitor being depleted of electric power by the heating element. 
     A method for active bi-directional control of an outer structure of a gas turbine engine is disclosed, comprising sending, by a controller, a first control signal to a power electronics for varying an electric current supplied to a heating element to cause the outer structure to move in a first radial direction, and sending, by the controller, a second control signal to a valve assembly for varying a cooling air flow supplied to the outer structure to cause the outer structure to move in a second radial direction, wherein the first radial direction is opposite the second radial direction. 
     In various embodiments, the method further comprises varying a blade tip clearance in response to the outer structure moving. 
     In various embodiments, the method further comprises receiving, by the controller, an electrical current value currently being supplied to the heating element, receiving, by the controller, a current valve position, determining, by the controller, a current blade tip clearance value based upon the electrical current value and the current valve position, and receiving, by the controller, a target blade tip clearance value, wherein the first control signal and the second control signal are based upon the current blade tip clearance value and the target clearance value. 
     The forgoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated herein otherwise. These features and elements as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the following illustrative figures. In the following figures, like reference numbers refer to similar elements and steps throughout the figures. 
         FIG.  1    illustrates a schematic representation of one example of a gas turbine engine, in accordance with various embodiments; 
         FIG.  2 A  illustrates a heating element coupled to an outer surface of an outer structure disposed radially outward from a blade for maintaining a blade tip clearance gap, in accordance with various embodiments; 
         FIG.  2 B  illustrates a heating element embedded in an outer structure disposed radially outward from a blade for maintaining a blade tip clearance gap, in accordance with various embodiments; 
         FIG.  2 C  illustrates a cross-section view of a heating element spaced apart from an outer surface of an outer structure disposed radially outward from a blade for maintaining a blade tip clearance gap, in accordance with various embodiments; 
         FIG.  2 D  illustrates a cross section axial view of a heating element embedded in an outer structure disposed radially outward from a blade for maintaining a blade tip clearance gap, in accordance with various embodiments; 
         FIG.  3 A  illustrates a schematic view of a hybrid electric power and control system for a clearance control system for a gas turbine engine, in accordance with various embodiments; 
         FIG.  3 B  illustrates a schematic view of a hybrid electric power and control system for a clearance control system for a gas turbine engine, in accordance with various embodiments; 
         FIG.  3 C  illustrates a schematic view of an active clearance control logic comprising a clearance estimator and a control algorithm, in accordance with various embodiments; 
         FIG.  4 A  and  FIG.  4 B  illustrate a section view of a full hoop clearance control ring and a BOAS assembly positioned between a blade and an engine case and an active clearance control system for controlling a position of the BOAS via the clearance control ring, in accordance with various embodiments; 
         FIG.  5 A  and  FIG.  5 B  illustrate a section view of a BOAS assembly positioned between a blade and an engine case and an active clearance control system for controlling a position of the BOAS via the engine case, in accordance with various embodiments; 
         FIG.  6    shows an annular component (e.g., a clearance control ring or an engine case) at room temperature (middle), a decreased temperature (left), and an elevated temperature (right), in accordance with various embodiments; 
         FIG.  7    shows a flow chart illustrating a method for active bi-directional control of an outer structure, in accordance with various embodiments; and 
         FIG.  8    shows a flow chart illustrating a method for active bi-directional control of an outer structure, in accordance with various embodiments. 
     
    
    
     Elements and steps in the figures are illustrated for simplicity and clarity and have not necessarily been rendered according to any particular sequence. For example, steps that may be performed concurrently or in different order are illustrated in the figures to help to improve understanding of embodiments of the present disclosure. 
     DETAILED DESCRIPTION 
     The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosures, it should be understood that other embodiments may be realized and that logical changes and adaptations in design and construction may be made in accordance with this disclosure and the teachings herein. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. 
     The scope of the disclosure is defined by the appended claims and their legal equivalents rather than by merely the examples described. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, coupled, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. Surface shading lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     As used herein, “distal” refers to the direction radially outward, or generally, away from the axis of rotation of a turbine engine. As used herein, “proximal” refers to a direction radially inward, or generally, towards the axis of rotation of a turbine engine. As used herein, “aft” refers to the direction associated with a tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of a gas turbine engine. As used herein, “forward” refers to the direction associated with a nose (e.g., the front end) of the aircraft, or generally, to the direction of flight or motion. 
     A clearance control system, as provided herein, may be useful gas turbine engines, including for use in the turbine section and/or in the compressor section of the gas turbine engine, and may be useful for any other suitable turbomachinery where rotor blade tip clearance control is desirable. 
     A clearance control system, as provided herein, may include a heating element for transferring thermal energy to an outer structure to cause the outer structure to thermally grow (e.g., to move in a first radial direction) and a valve assembly for regulating a cooling air flow directed to the outer structure to cause the outer structure to thermally shrink (e.g., to move in a second radial direction). Active bi-directional control of the outer structure in both radial directions may allow for decreased response time (i.e., decrease time for thermal expansion and/or contraction of the outer structure) and faster changes in blade tip clearance. A clearance control system, as provided herein, may allow for tighter tolerances manufactured into the system&#39;s components due to increased response time of blade tip clearance control. 
     In various embodiments, and with reference to  FIG.  1   , a gas turbine engine  120  is disclosed. Gas turbine engine  120  may comprise a two-spool turbofan that generally incorporates a fan section  122 , a compressor section  124 , a combustor section  126 , and a turbine section  128 . Gas turbine engine  120  may also comprise, for example, an augmenter section, and/or any other suitable system, section, or feature. In operation, fan section  122  may drive air along a bypass flow-path B, while compressor section  124  may further drive air along a core flow-path C for compression and communication into combustor section  126 , before expansion through turbine section  128 .  FIG.  1    provides a general understanding of the sections in a gas turbine engine, and is not intended to limit the disclosure. The present disclosure may extend to all types of applications and to all types of turbine engines, including, for example, turbojets, turboshafts, and three spool (plus fan) turbofans wherein an intermediate spool includes an intermediate pressure compressor (“IPC”) between a low pressure compressor (“LPC”) and a high pressure compressor (“HPC”), and an intermediate pressure turbine (“IPT”) between the high pressure turbine (“HPT”) and the low pressure turbine (“LPT”). 
     In various embodiments, gas turbine engine  120  may comprise a low speed spool  130  and a high speed spool  132  mounted for rotation about an engine central longitudinal axis A-A′ relative to an engine static structure  136  via one or more bearing systems  138  (shown as, for example, bearing system  138 - 1  and bearing system  138 - 2  in  FIG.  1   ). It should be understood that various bearing systems  138  at various locations may alternatively or additionally be provided, including, for example, bearing system  138 , bearing system  138 - 1 , and/or bearing system  138 - 2 . 
     In various embodiments, low speed spool  130  may comprise an inner shaft  140  that interconnects a fan  142 , a low pressure (or a first) compressor section  144 , and a low pressure (or a second) turbine section  146 . Inner shaft  140  may be connected to fan  142  through a geared architecture  148  that can drive fan  142  at a lower speed than low speed spool  130 . Geared architecture  148  may comprise a gear assembly  160  enclosed within a gear housing  162 . Gear assembly  160  may couple inner shaft  140  to a rotating fan structure. High speed spool  132  may comprise an outer shaft  150  that interconnects a high pressure compressor (“HPC”)  152  (e.g., a second compressor section) and high pressure (or a first) turbine section  154 . A combustor  156  may be located between HPC  152  and high pressure turbine  154 . A mid-turbine frame  157  of engine static structure  136  may be located generally between high pressure turbine  154  and low pressure turbine  146 . Mid-turbine frame  157  may support one or more bearing systems  138  in turbine section  128 . Inner shaft  140  and outer shaft  150  may be concentric and may rotate via bearing systems  138  about engine central longitudinal axis A-A′. As used herein, a “high pressure” compressor and/or turbine may experience a higher pressure than a corresponding “low pressure” compressor and/or turbine. 
     In various embodiments, the air along core airflow C may be compressed by low pressure compressor  144  and HPC  152 , mixed and burned with fuel in combustor  156 , and expanded over high pressure turbine  154  and low pressure turbine  146 . Mid-turbine frame  157  may comprise airfoils  159  located in core airflow path C. Low pressure turbine  146  and high pressure turbine  154  may rotationally drive low speed spool  130  and high speed spool  132 , respectively, in response to the expansion. 
     With combined reference to  FIG.  2 A ,  FIG.  2 B , and  FIG.  2 C , an outer structure  220  spaced by a clearance gap G from a radially outer tip of a rotor blade  262 , is illustrated, in accordance with various embodiments. Outer structure  220  may generally surround rotor blade  262  in a hoop structure or a segmented hoop structure, as described herein in further detail. In various embodiments, outer structure  220  may be similar to control ring  66  as described with respect to  FIG.  4 A . In various embodiments, outer structure  220  may be similar to engine case  570  as described with respect to  FIG.  5 A . In various embodiments, the rotor blade  262  is a component of the turbine section  128  as shown in  FIG.  1   . In various embodiments, the rotor blade  262  is a component of the compressor section  124  as shown in  FIG.  1   . 
     A heating element is generally shown at  210 . In various embodiments, the heating element  210  may be coupled to an outer surface  222  of outer structure  220  ( FIG.  2 A ). Coupling the heating element  210  to an outer surface  222  may allow for ease of installation of the heating element  210  onto outer structure  220  as well as accessibility to the heating element  210  when installed on the outer structure  220  (e.g., for inspection, repair, and/or replacement). 
     In various embodiments, the heating element  210  is embedded in the outer structure  220  ( FIG.  2 B ). Embedding the heating element  210  within the outer structure  220  may provide responsive, as well as evenly distributed, heating to the outer structure  220 . 
     In various embodiments, the heating element  210  is spaced apart from the outer structure  220  ( FIG.  2 C ). Spacing apart heating element  210  from the outer structure  220  may allow heating element  210  and outer structure  220  to move relative to each other without imparting mechanical stress therebetween (e.g., thermally induced stresses). Spacing apart heating element  210  from the outer structure  220  may be particularly useful for induction heating applications, as described herein. 
     The heating element  210  may be wired to an electric power source  205 , for instance by way of wires  202  (i.e., leads, lead wires) on opposite sides of the heating element  210 . Any appropriate type of arrangements may be used to allow a current supply through the heating element  210  from the electric power source  205 . Electric power source  205  may also comprise multiple circuits for instance in parallel to heat up the heating element  210  in segments. 
     A processor, such as controller  280  may regulate electric power sent to heating element  210 . Controller  280  may be implemented as a single controller or as multiple controllers. The controller  280  may be electrically coupled to at least one component of a gas turbine engine. The controller  280  may control the temperature of heating element  210  based upon an operating condition of the gas turbine engine to maintain blade tip clearance gap G. In various embodiments, controller  280  may control the temperature of heating element  210  based upon various operating conditions or states, including altitude, throttle position, rotor speed, and bleed pressure, among others. 
     In various embodiments, heating element  210  may cause outer structure  220  to increase in temperature via resistive heating using thermal conduction (interface heat transfer). Thus, heating element  210  may increase in temperature in response to an electrical current being passed there through, for instance a resistive heating element (e.g., Joule heating). In this regard, electric power source  205  may provide electric power to heating element  210 , wherein in response to the electric power, heating element  210  increases in temperature and conductively transfers thermal energy to outer structure  220 . 
     In various embodiments, with particular focus on  FIG.  2 C , heating element  210  may cause outer structure  220  to heat up via induction heating. Electric power source  205  may be configured to send alternating current (AC) to heating element  210 , wherein in response to receiving the alternating current there through, an electric field, illustrated by lines at  204 , is generated by heating element  210 . The electric field  204  may penetrate outer structure  220 , generating electric currents inside outer structure  220 , referred to as eddy currents. The eddy currents, illustrated by lines at  206 , flowing through outer structure  220  cause outer structure  220  to heat by Joule heating. Although, heat may also be generated by magnetic hysteresis losses. In this regard, heating element  210  may comprise an electromagnet. Heating element  210  may be made from an electrically conducting material, such as copper for example. Outer structure  220  may be made from an electrically conducting material, including metals such as iron, or an iron alloy, among others. Outer structure  220  may be made from a ferromagnetic material, such as iron for example. 
     Heating element  210  may cause outer structure  220  to heat up via induction heating when heating element  210  is in contact with outer structure  220  (see  FIG.  2 A  and  FIG.  2 B ) or when heating element  210  is spaced apart from outer structure  220  (see  FIG.  2 C ). 
     In various embodiments, heating element  210  may comprise a wire, a coil, a hollow tube, a plate, or any other suitable heating element for Joule heating and/or induction heating. 
     In various embodiments, heating element  210  may be powered after engine shutdown in order to prevent adverse effects caused by rotor bow in compressor section  124 . Stated differently, heating element  210  may be powered after engine shutdown in order to prevent gap G from closing. Rotor bow, or thermal bowing, is typically due to asymmetrical cooling after shut-down on a previous flight. Differences in temperature across a shaft section, e.g., low speed spool  130  and/or high speed spool  132  the gas turbine engine supporting the rotor may lead to different thermal deformation of the shaft material, causing the rotor axis to bend. This results in an offset between the center of gravity of the bowed rotor and the bearing axis, causing a slight imbalance and potentially reducing the tight clearance between the rotor blade tips and the compressor wall, which can adversely affect engine performance. 
     In this regard, a method for controlling a heating element  210  for a gas turbine engine may include detecting, by controller  280 , a shutdown of gas turbine engine  120 , sending, by controller  280 , electrical current to a heating element  210 , and heating outer structure  220 , via heating element  210 , to maintain blade tip clearance gap G. 
     In accordance with various embodiments, in an active clearance control (ACC) system, air impinges on the turbine case when activated to cool and shrink the case diameter. This in turn reduces the diameter of the segmented blade outer air seal assembly. The seal body in this application is in segments to prevent thermal fighting between the seal and the turbine case to which the seal ultimately mounts to and which is a full hoop. The turbine case that comprises the full hoop structure is what controls the position of the blade outer air seal. Due to the mass of the turbine case and the thermal environment within which the turbine case operates, the turbine case is slow to respond thermally as the engine power level is increased. The turbine rotor diameter, however, will increase rapidly as the rotational speed and temperature of the engine increases. For this reason, extra clearance may be added between the tip of the blade and the blade outer air seal assembly to prevent rubbing contact between these two structures. However, this extra clearance can adversely affect engine performance. 
     In various embodiments, the present disclosure provides a system and method for mitigating the desire for an ACC system to reduce clearance gap G. Outer structure  220  and rotor blade  262  may be configured such that under “cold” temperatures, e.g., during cruise, clearance gap G is minimal or at a desired dimension without the use of cooling air from an ACC system. In this regard, extra clearance is not added during manufacturing between the tip of the rotor blade  262  and outer structure  220 . Rather, blade tip clearance G is configured to be optimal at cruise conditions (“default closed”) and heating element  210  is used to maintain clearance gap G in response to events that would otherwise cause blade tip strike, e.g., in response to a throttle acceleration. 
     In this regard, a method for controlling a heating element  210  for a gas turbine engine may include detecting, by controller  280 , an increase in engine throttle of gas turbine engine  120 , sending, by controller  280 , electrical current to a heating element  210 , and heating outer structure  220 , via heating element  210 , to maintain blade tip clearance gap G. 
     With respect to  FIG.  2 D , elements with like element numbering, as depicted in  FIG.  2 B , are intended to be the same and will not necessarily be repeated for the sake of clarity. 
     With reference to  FIG.  2 D , a cross section axial view of clearance control system  200 B is illustrated in accordance with various embodiments. In various embodiments, heating element  210  may be embedded in outer structure  220 , similar to  FIG.  2 B , and in various embodiments, heating element  210  may be coupled to the outer surface of outer structure, similar to  FIG.  2 A , and in various embodiments, heating element  210  may be spaced apart from outer structure  220 , similar to  FIG.  2 C . Outer structure  220  may define an engine centerline axis  290 . Outer structure  220  may surround a plurality of rotor blades  262 . Rotor blades  262  may rotate about engine centerline axis  290  with respect to outer structure  220 . 
     With reference to  FIG.  3 A , clearance control system  300  may be located aboard an aircraft. Weight and packaging are factors when considering design of a clearance control system for an aircraft. Furthermore, clearance control system  300  may require a substantial amount of power in order to heat an outer structure, such as an engine case for example, to provide the thermal expansion desirable to maintain a blade tip clearance gap G. In this regard, a hybrid electric power source  305  is provided for providing suitable power to clearance control system  300 , in accordance with various embodiments. Hybrid electric power source  305  may be capable of providing electric power on the order of kilowatts and/or megawatts of power to clearance control system  300  without depriving the aircraft of electrical power required to operate all other electrical components aboard the aircraft or burdening the engine with additional power offtake at moments when high engine thrust is required. 
     In various embodiments, hybrid electric power source  305  may comprise one or more batteries, one or more supercapacitors, one or more ultracapacitors, and/or one or more generators, or any other suitable power source, such as a fuel cell for example. 
     Clearance control system  300  may include power electronic  358 . Power electronics  358  may include any suitable power electronics for the control and conditioning of electric power received from hybrid electric power source  305  to heating element  310  and/or valve assembly  372 . For example, power electronics  358  may include a bi-directional DC-DC converter for energy storage charging and discharging, an AC-DC rectifier, e.g., a full bridge or a diode, a DC-AC inverter, a silicone control rectifier (SCR), a pulse width modulated (PWM) controlled inverter, a pressure sensor, a temperature sensor, etc. Power electronics  358  may be in electronic communication with hybrid electric power source  305  and an ACC control logic  370 . 
     An injection source  373  may supply a cooling air flow  375  to outer structure  320 . The cooling air flow may be supplied from compressor section  124 , with momentary reference to  FIG.  1   . A conduit  374  may route the cooling air flow  375  towards the outer surface  322  of outer structure  320 . A valve assembly  372  may be provided for metering the cooling air flow  375 . 
     An ACC control logic  370  may coordinate the operation of the two subsystems (i.e., heating element  310  and cooling air flow  375 ). Control logic  370  may be implemented on a single processor or on separate processors. The cooling air flow contributes to shrinking the outer structure  320  and therefore reduces blade tip clearance gap G. Because the heat transfer has a long time constant it may be desirable to use the cooling air flow  375  subsystem in near steady-state operation conditions. In transient conditions it may be desirable to conservatively control the cooling air flow  375  to ensure that blade tip clearance gap G is maintained and that rotor blades  363  do not contact outer structure  320 . As described, the electrical heating subsystem (i.e., heating element  310 ) has the opposite effect and leads to a more quick expansion of the outer structure  320 . This effect may be desirable when there is potential for the turbomachinery clearances (blade tip clearance gap G) to decrease in a short duration of time, such as for example, when the speed of rotor blades  362  increases abruptly, e.g., increased throttle, and the mechanical growth of rotor blades  362  exceeds the thermal growth of outer structure  320 . 
     With respect to  FIG.  3 B , elements with like element numbering, as depicted in  FIG.  3 A , are intended to be the same and will not necessarily be repeated for the sake of clarity. 
     With reference to  FIG.  3 B , a clearance control system  301  is illustrated, in accordance with various embodiments. In various embodiments, hybrid electric power source  305  may comprise one or more batteries  306 , one or more capacitors  307 , and/or one or more generators  308 . In various embodiments, battery  306  may comprise any suitable battery, such as a lithium-ion battery for example. Capacitor  307  may comprise a supercapacitor or an ultracapacitor. In various embodiments, generator  308  may be an auxiliary generator driven by low speed spool  130  or high speed spool  132 , with momentary reference to  FIG.  1   . Any number of batteries  306 , capacitors  307  and/or generators  308  may be provided in any suitable arrangement (parallel, series) to provide the electric power suitable for powering clearance control system  300 . 
     In various embodiments, power electronics  358  may include a converter  360 . In various embodiments, converter  360  is a bidirectional converter for energy storage charging and discharging. For example, generator  308  may charge battery  306  and/or capacitor  307  via converter  360  in response to battery  306  and/or capacitor  307  being depleted of electrical energy. Furthermore, battery  306  may charge capacitor  307  via converter  360 . In various embodiments, converter  360  is a DC/DC converter for supplying DC power to heating element  310 . Converter  360  may supply power to heating element  310  via a DC bus  366 . Converter  360  may be in electronic communication with ACC control logic  370 . Converter  360  may direct energy to and/or from hybrid electric power source  305  in response to commands received from ACC control logic  370 . 
     In various embodiments, power electronics  358  may include a second converter  361 . In various embodiments, second converter  361  may be provided to control the electrical power provided to heating element  310 . In various embodiments, second converter  361  is a DC/DC converter for converting DC power supplied from DC bus  366  to DC power for heating element  310  (e.g., for resistive heating). In various embodiments, second converter  361  is a DC/AC inverter for converting DC power supplied from DC bus  366  to AC power for heating element  310  (e.g., for induction heating). In various embodiments, second converter  361  is an AC/AC converter and/or a transformer for converting AC power supplied from generator  308  to AC power for heating element  310  (e.g., for induction heating). Second converter  361  may step up, or step down, the voltage and/or current of the AC power, as well as vary the signal frequency, based upon the desired AC power for heating element  310 . 
     With reference to  FIG.  3 C , ACC control logic  370  logic may receive inputs including source pressure P 1  (i.e., pressure of cooling air flow  375  upstream of valve assembly  372 ), sink pressure P 2  (i.e., pressure of cooling air flow  375  downstream of valve assembly  372 ), outer structure temperature T (i.e., temperature of outer structure  320 ), a target blade tip clearance value (e.g., a desired blade tip clearance gap G), etc. One or more sensors may be used to measure the pressures of the cooling air flow, as well as any other inputs to ACC control logic  370 . One or more sensors may be used to measure the temperature of the outer structure. ACC control logic  370  may utilized a constrained model-based control algorithm based upon known and/or measured parameters of the gas turbine engine to estimate the blade tip clearance gap G for supplying control signals to second converter  361  and valve assembly  372 . 
       FIG.  4 A  illustrates an outer air seal assembly  60  spaced by a clearance gap G from a radially outer tip of a rotating blade  62 . In various embodiments, the blade  62  is a component of the turbine section  128  as shown in  FIG.  1   . However, the outer air seal assembly  60  may be used in other engine configurations and/or locations, for example in the compressor sections. The outer air seal assembly  60  includes an outer air seal body  64  that is mounted to a clearance control ring  66 . An internal cavity  68  is formed between an engine case  70  and the outer air seal assembly  60 . A support structure  72  is associated with the engine case  70  to provide support for the outer air seal assembly  60 . 
     The subject disclosure provides a configuration where the clearance control ring  66  is positioned adjacent the support structure  72  but is not directly tied to the engine case  70  or support structure  72 . In various embodiments, clearance control ring  66  may be formed as an annular ring. In one example configuration, the clearance control ring  66  includes a first mount feature  74  and the seal body  64  includes a second mount feature  76  that cooperates with the first mount feature  74  such that the clearance control ring  66  can move within the internal cavity  68  independently of the support structure  72  and engine case  70  in response to changes in temperature. In various embodiments, the clearance control ring  66  is a full hoop ring (i.e., annular) made from a material with a high thermal expansion coefficient, for example. For example, clearance control ring  66  may comprise a thermal expansion coefficient that is greater than that of engine case  70 . For example, with momentary reference to  FIG.  6   , in accordance with various embodiments, clearance control ring  66  may grow (i.e., increase in diameter) in response to an increase in temperature and, in accordance with various embodiments, clearance control ring  66  may shrink (i.e., decrease in diameter) in response to a decrease in temperature. 
     With continued reference to  FIG.  4 A , in various embodiments, the seal body  64  may include a ring mount portion  92 . The clearance control ring  66  is radially moveable relative to the first  84  and second  86  radial wall portions in response to temperature changes via the connection interface to the ring mount portion  92 . A main seal portion  94  extends from the ring mount portion  92  to face the blade  62 . 
     In various embodiments, clearance control ring  66  may define a slot  98  to receive ring mount portion  92 . In the example shown, the clearance control ring  66  includes the slot  98  and the seal body  64  includes the ring mount portion  92 ; however, the reverse configuration could also be used. In various embodiments, the slot  98  and the ring mount portion  92  comprise a key-shape, with each of the slot  98  and ring mount portion  92  having a first portion extending in a radial direction and a second portion extending in an axial direction. This type of configuration provides a floating connection interface that fully supports and properly locates the seal  64  while still controlling the seal  64  to move radially inwardly and outwardly as needed. 
     With continued reference to  FIG.  4 A , clearance control ring  66  may be similar to outer structure  220  of  FIG.  2 A ,  FIG.  2 B , and/or  FIG.  2 C , in accordance with various embodiments. A heating element  310  may be configured to cause clearance control ring  66  to vary in temperature to cause clearance control ring  66  to move radially (Y-direction) within internal cavity  68  to maintain or vary clearance gap G. Heating element  310  may be similar to heating element  210  of  FIG.  1 A ,  FIG.  1 B , and/or  FIG.  1 C , in accordance with various embodiments. In the illustrated embodiment, heating element  310  is embedded in clearance control ring  66 ; however, in various embodiments, heating element  310  may be coupled to an outer surface of clearance control ring  66 , for instance similar to the illustrated embodiment of  FIG.  2 C , or may be spaced apart from clearance control ring  66 , for instance similar to the illustrated embodiment of  FIG.  2 C . Control  80  may control the supply of electrical current from one or more power supplies  405  to heating element  310 . 
     The illustrated configuration with the clearance control ring  66  may react faster than prior active control systems due to the reduced thermal mass and due to being exposed to air from the engine gaspath in contrast to prior systems where the heavy turbine case was exposed to the engine core compartment temperatures. 
     With reference to  FIG.  4 B , an injection source  78  may inject or deliver cooling fluid flow, for example, air flow, into the internal cavity  68  to control a temperature of the clearance control ring  66  to allow the outer air seal body  64  to move in a desired direction to maintain a desired clearance between the outer air seal body  64  and a tip of the blade  62 , i.e., to control the size of the clearance gap G. In one example, the injection source  78  comprises a tube or conduit  78   a  that receives air flow from the compressor section  124  ( FIG.  1   ) of the gas turbine engine. As shown in  FIG.  4 B , a control  80  is configured to deliver the compressor air at a first temperature T 1  into the internal cavity  68  and against the clearance control ring  66  to allow the outer air seal body  64  to move in a first direction to maintain a desired clearance during a first operating condition, and is configured to deliver compressor air at a second temperature T 2  into the internal cavity  68  and against the outer air seal body  64  to allow the outer air seal body  64  to move in a second direction to maintain a desired clearance during a second operating condition. In one example, the first operating condition comprises a takeoff or high load event, and the second operating condition comprises a descending event. In various embodiments, the first operating condition comprises a first throttle setting, and the second operating condition comprises a second throttle setting, the first throttle setting being greater than the second throttle setting. 
     In these example operating conditions, the second temperature T 2  is less than the first temperature T 1 . In this example, the compressor air at the second temperature T 2  can comprise cooled cooling air from the compressor exit while the air at the first temperature can comprise uncooled compressor exit air. The control  80  comprises a microprocessor and/or control unit that is programmed to deliver air flow at the first T 1  or second T 2  temperature as needed dependent upon the engine operating condition. The control  80  may further include valves V, flow conduits, and/or heat exchangers as needed to deliver the compressor air at the desired temperature. The control  80  delivers higher temperature air T 1  into the cavity  68  when the clearance control ring  66  is to increase in diameter and delivers lower temperature air T 2  into the cavity  68  when the clearance control ring  66  is to decrease in diameter. It should be understood that while two different temperatures are discussed as examples, the system is variable and the system can deliver fluid at any desired temperature. 
     The engine case  70  may include an opening  82  to receive the conduit  78   a  which directs compressor air into the cavity  68 . The support structure  72  includes a first radial wall portion  84  extending radially inward from the engine case  70  and a second radial wall portion  86  axially spaced from the first radial portion  84  to define the internal cavity  68 . The opening  82  may be positioned axially between the first  84  and second  86  radial portions. The engine case  70  includes trenches or grooves  88  adjacent to each of the first  84  and second  86  radial wall portions. 
     In various embodiments, heating element  310  may work in concert with injection source  78  to maintain clearance gap G, enabling two-directional clearance control and tighter running clearances as a result of smaller margins for maneuvers where outer seal assembly  60  would otherwise be too slow to expand. Heat caused by heating element  310  may cause outer seal body  64  to move in the radially outward direction (positive Y-direction, also referred to herein as a first direction). The cooling air flow supplied by injection source  78  may cause outer seal body  64  to move in the radially inward direction (negative Y-direction, also referred to herein as a second direction). 
     With respect to  FIG.  5 A  and  FIG.  5 B , elements with like element numbering, as depicted in  FIG.  4 A  and  FIG.  4 B , are intended to be the same and will not necessarily be repeated for the sake of clarity. 
       FIG.  5 A  illustrates an outer air seal assembly  560  spaced by a clearance gap G from a radially outer tip of a rotating blade  62 . In various embodiments, the blade  62  is a component of the turbine section  128  as shown in  FIG.  1   . However, the outer air seal assembly  560  may be used in other engine configurations and/or locations, for example in the compressor sections. The outer air seal assembly  560  includes an outer air seal body  564  that is mounted to a support structure  572 . The support structure  572  is associated with the engine case  570  to provide support for the outer air seal assembly  560 . The outer air seal body  564  may be mounted to engine case  570  via support structure  572  and may move with engine case  570  in response to changes in temperature. 
     Engine case  570  may be similar to outer structure  220  of  FIG.  2 A ,  FIG.  2 B , and/or  FIG.  2 C , in accordance with various embodiments. A heating element  510  may be configured to cause engine case  570  to vary in temperature to cause engine case  570  to move radially (Y-direction) to maintain or vary clearance gap G. Heating element  510  may be similar to heating element  210  of  FIG.  1 A ,  FIG.  1 B , and/or  FIG.  1 C , in accordance with various embodiments. In the illustrated embodiment, heating element  510  is coupled to a distal surface  574  of engine case  570 ; however, in various embodiments, heating element  510  may be coupled to the proximal surface  576  of engine case  570 , may be embedded in engine case  570 , for instance similar to the illustrated embodiment of  FIG.  2 B , or may be spaced apart from engine case  570 , for instance similar to the illustrated embodiment of  FIG.  2 C . Control  580  may control the supply of electrical current from one or more power supplies  505  to heating element  80 . 
     With reference to  FIG.  5 B , an injection source  578  may inject or deliver cooling fluid flow, for example, air flow, onto distal surface  574  of engine case  570  to cause the outer air seal body  564  to move in a desired direction to maintain a desired clearance between the outer air seal body  564  and a tip of the blade  62 , i.e. to control the size of the clearance gap G. Injection source  578  may operate similarly as described with respect to injection source  78  of  FIG.  3 B . Stated differently, injection source  578  may be similar to injection source  78  of  FIG.  3 B , except that injection source  578  directs cooling fluid flow to engine case  570 , instead of a clearance control ring. 
     In various embodiments, heating element  510  may work in concert with injection source  578  to maintain clearance gap G, enabling active bi-directional clearance control and tighter running clearances as a result of smaller margins for maneuvers where outer air seal assembly  560  would otherwise be too slow to expand. In this regard, with reference now to  FIG.  3 A , ACC control logic  370  may control both electrical current supplied to heating element  310  and the position of valve assembly  372  for controlling cooling air flow  375  for both expansion and contraction of outer structure  320 . In this regard, the term “bi-directional control” as used herein may refer to the control of the expansion and contraction of outer structure  320  (e.g., the engine case and/or the clearance control ring). 
     With reference to  FIG.  7   , a method  700  for active bi-directional control of an outer structure for blade tip clearance management is illustrated, in accordance with various embodiments. Method  700  includes sending a first control signal to power electronics for varying electrical current supplied to a heating element to cause an outer structure to move in a first radial direction (step  710 ). Method  700  includes sending a second control signal to a valve assembly for varying a cooling air flow supplied to the outer structure to cause the outer structure to move in a second radial direction (step  720 ). 
     With combined reference to  FIG.  3 B  and  FIG.  7   , step  710  may include sending, by ACC control logic  370 , the first control signal to second converter  361  to vary the blade tip clearance G. The first control signal may be any suitable control signal for controlling the power output of second converter  361  (e.g., a voltage signal and/or a current signal). 
     Step  720  may include sending, by ACC control logic  370 , a second control signal to valve assembly  372  to vary the blade tip clearance G. The second control signal may be any suitable control signal for controlling the position of valve assembly  372  (e.g., a voltage signal and/or a current signal) to vary the cooling air flow  375 . 
     With additional reference to  FIG.  8   , in various embodiments, step  710  and step  720  may include receiving, by ACC control logic  370 , an electrical current value currently being applied to heating element  310  (see step  802 ). Step  710  and step  720  may include receiving, by ACC control logic  370 , a valve position of valve assembly  372  (e.g., open, closed, etc.) (step  804 ). 
     Step  710  and step  720  may include receiving, by ACC control logic  370 , one or more state inputs (step  804 ). The state inputs may include various engine operating states or conditions. The state inputs may include a temperature value of outer structure  320 , at least one pressure value (e.g., pressure value P 1  and/or pressure value P 2 ), engine throttle position, rotor speed (e.g., rotational velocity of rotor blades  362  (see  FIG.  3 A )), and/or altitude, among others. In various embodiments, a temperature sensor  324  may be in thermal communication with heating element  310  and/or outer structure  320  whereby ACC control logic  370  may detect the temperature of outer structure  320 . In various embodiments, a first pressure sensor  378  may me located upstream from valve assembly  372  and a second pressure sensor  379  may be located downstream from valve assembly  372  whereby ACC control logic  370  may detect pressure P 1  and pressure P 2 , respectively. In various embodiments, the pressure values may be directly measured or may be synthesized. 
     Step  710  and step  720  may include measuring, by ACC control logic  370 , the actual blade tip clearance gap (e.g., blade tip clearance gap G) (step  810 ). blade tip clearance gap G may be measured using any suitable method. For example, blade tip clearance gap G may be measured using capacitive measurements between rotor blades  362  and outer structure  320  with momentary reference to  FIG.  3 A . In various embodiments, blade tip clearance gap G may be measured using X-ray techniques, among others. 
     Step  710  and step  720  may include estimating, by ACC control logic  370 , the actual blade tip clearance gap (e.g., blade tip clearance gap G) (step  810 ). The estimated blade tip clearance may be determined using any suitable method. For example, the estimated blade tip clearance may be determined based upon the electrical current currently being applied to heating element  310 , the valve position of valve assembly  372 , and the state inputs. 
     Step  710  and step  720  may include receiving, by ACC control logic  370 , a target blade tip clearance value (step  812 ). The target blade tip clearance value may be a predetermined blade tip clearance value. The target blade tip clearance value may be a desired blade tip clearance. In various embodiments, the first control signal is based upon the estimated blade tip clearance gap G. For example, the first control signal may be configured to adjust the power output of second converter  361  to cause outer structure  320  to increase in temperature or decrease in temperature based upon a difference between the estimated blade tip clearance gap and the target blade tip clearance gap. Stated differently, ACC control logic  370  may be configured to adjust the electrical current supplied to heating element  310  to minimize the difference between the estimated blade tip clearance gap and the target blade tip clearance gap. 
     In various embodiments, the first control signal is based upon the measured blade tip clearance gap G. For example, the first control signal may be configured to adjust the power output of second converter  361  to cause outer structure  320  to increase in temperature or decrease in temperature based upon a difference between the measured blade tip clearance gap and the target blade tip clearance gap. Stated differently, ACC control logic  370  may be configured to adjust the electrical current supplied to heating element  310  to minimize the difference between the measured blade tip clearance gap and the target blade tip clearance gap. 
     In various embodiments, the second control signal is based upon the estimated blade tip clearance gap. For example, the second control signal may be configured to adjust a position of valve assembly  372  (e.g., between an open position and a closed position) to cause outer structure  320  to increase in temperature or decrease in temperature based upon a difference between the estimated blade tip clearance gap and the target blade tip clearance gap. Stated differently, ACC control logic  370  may be configured to adjust the cooling air flow  375  supplied outer structure  320  to minimize the difference between the estimated blade tip clearance gap and the target blade tip clearance gap. 
     In various embodiments, the second control signal is based upon the measured blade tip clearance gap. For example, the second control signal may be configured to adjust a position of valve assembly  372  (e.g., between an open position and a closed position) to cause outer structure  320  to increase in temperature or decrease in temperature based upon a difference between the measured blade tip clearance gap and the target blade tip clearance gap. Stated differently, ACC control logic  370  may be configured to adjust the cooling air flow  375  supplied outer structure  320  to minimize the difference between the measured blade tip clearance gap and the target blade tip clearance gap. 
     In various embodiments, step  710  and/or step  720  may include computing the thermal power needed to be transferred to the outer structure, while taking into account the delays and constraints associated with heat transfer from both subsystems (i.e., heating element  310  and cooling air flow  375  (step  814 ). Computing the thermal power may be implemented using various control methods. For example, the thermal power may be computed using internal models of the turbomachinery clearance that represent the transient response of the clearance to both inputs (i.e., electrical current/voltage/PWM duty-cycle, and cold flow). The models may use both estimated and measured parameters. The two inputs may be coordinated in order to track as closely as possible the target clearance value (rapid expansion during rapid accelerations realized via heating element, and slower contraction control via the cooling air flow). Control methods may include single-input single-output (SISO) methods. Various rules may be combined with the SISO method(s). In various embodiments, a single proportional-integral-derivative control logic may use the error between the target clearance and the current clearance (estimated or measured) for generating the control signal communicated to the power electronics module (e.g., for case expansion) or to the cold flow control valve (e.g., for case contraction). In various embodiments, a rule combined with two SISO loops may be used—one for the power electronics module and one for the cold flow control. The rule may determine which loop is active, and the respective SISO logic determines the level of current/voltage/duty-cycle or the cold flow valve control signal. Control methods may include multi-input multi-output (MIMO) control methods. MIMO methods may use an integrated model for outer structure radial displacement (contraction/expansion) capturing the dynamics from valve position to outer structure contraction and power electronics signal to outer structure expansion into a single model. MIMO methods may include nonlinear control methods. For example, switching-based control logic that select the active subsystem and its corresponding control signal in the same design (with no additional rules). Constrained model-based control (e.g., currently implemented in the full authority digital engine control (FADEC) for controlling other effectors) that in addition to dynamical system model also include constraints associated with valve current, heating element current and/or voltage, rates of expansion/contraction, etc. MIMO methods may include predictive control that, at any time step, uses a prediction of the outer structure radial displacement levels over a few future time steps. These methods may improve the clearance control accuracy by compensating for the effects of the delays associated with the heat transfers. 
     In various embodiments, ACC control logic  370  may send a heating thermal power command to converter control  364  (step  816 ). Converter control  364  may compute and send the first control signal to converter  361  for varying the electrical current supplied to heating element  310  to vary the heating thermal power applied to outer structure  320  (step  818 ). In various embodiments, converter control  363  may be implemented in ACC control logic  370 ; for example, converter control  363  and ACC control logic  370  may be implemented in a single processor. In various embodiments, converter control  363  may be implemented separately from ACC control logic  370 ; for example, converter control  363  and ACC control logic  370  may be implemented in separate processors. 
     In various embodiments, ACC control logic  370  may send a cooling thermal power command to valve control  376  (step  820 ). Valve control  376  may compute and send the second control signal to valve assembly  372  (e.g., to a solenoid) for varying the cooling air flow  375  supplied to outer structure  320  to vary the cooling thermal power applied to outer structure  320  (step  822 ). In various embodiments, valve control  376  may be implemented in ACC control logic  370 ; for example, valve control  376  and ACC control logic  370  may be implemented in a single processor. In various embodiments, valve control  376  may be implemented separately from ACC control logic  370 ; for example, converter control  363  and ACC control logic  370  may be implemented in separate processors. 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosures. The scope of the disclosures is accordingly to be limited by nothing other than the appended claims and their legal equivalents, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “various embodiments”, “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element is intended to invoke 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.