Abstract:
An air seal includes a sealing gland configured to retain a ferro-fluid and one or more seals. A portion of the one or more seals is configured to extend into the sealing gland. A gas turbine engine, includes the air seal. A method of sealing low pressure air from high pressure air, includes the steps of providing a sealing gland configured to retain a ferro-fluid, distributing the ferro-fluid into the sealing gland, providing one or more seals, wherein a portion of the one or more seals is configured to extend into the sealing gland, and removing the ferro-fluid from the sealing gland.

Description:
BACKGROUND 
       [0001]    This disclosure relates to a gas turbine engine component, such a low-leakage air seal. 
         [0002]    Gas turbine engines typically include a fan section, a compressor section, a combustor section and a turbine section. The fan section may be housed in a fan case. During operation, air is pressurized in the compressor section and is mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases are communicated through the turbine section, which extracts energy from the hot combustion gases to power the compressor section and other gas turbine engine loads. 
         [0003]    Gas turbine engines use various types of sealing concepts to control or prevent leakage of air from higher pressure areas to lower pressure areas. Locations can include secondary (internal) flow seals intended to isolate cooler, lower pressure air for thermal conditioning of components (disks, shafts, etc.) and for establishing appropriate thermal environments for oil filled bearing compartments and other thermally sensitive components. For example, the source of secondary/ internal air comes from the engine flow path. Removal of this air—often already partially compressed via the engine&#39;s compression system—represents a loss to engine efficiency. 
         [0004]    In another example, seals where radial clearances between rotating knife edges and static cases form gaps through which higher pressure flow can circulate to lower pressure regions. In this example, the undesired circulation of flow detracts from either compressor (where work is added to the fluid to increase pressure) or turbine (where work is removed from the fluid thereby reducing pressure) efficiency. This leakage also has an adverse and more pronounced impact on component and overall cycle efficiency. Current sealing concepts between rapidly rotating components and static structures often use a knife-edge rotating against an abradable surface (for example, honeycomb, porous metal, aluminum polyester or another material). During engine operation, a combination of axial and radial displacements create wear, which can degrade the effectiveness of the seal during subsequent operation. 
       SUMMARY 
       [0005]    In one exemplary embodiment, an air seal includes a sealing gland configured to retain a ferro-fluid and one or more seals. A portion of the one or more seals extends into the sealing gland. 
         [0006]    In a further embodiment of the above, the sealing gland is subject to a magnetic field. 
         [0007]    In a further embodiment of any of the above, at least one rotating seal is a knife-edge seal. 
         [0008]    In a further embodiment of any of the above, at least one rotating seal is an airfoil tip seal. 
         [0009]    In a further embodiment of any of the above, the sealing gland extends circumferentially around a rotor. The rotor including at least one rotating seal. 
         [0010]    In a further embodiment of any of the above, the air seal comprises a ferro-fluid collection drain and a ferro-fluid collection tank. 
         [0011]    In a further embodiment of any of the above, the air seal comprises a cooler configured to change the temperature of the ferro-fluid. 
         [0012]    In a further embodiment of any of the above, at least one rotating seal includes a magnetic field configured to repel the ferro-fluid. 
         [0013]    In a further embodiment of any of the above, at least one rotating seal is located on a seal arm that extends from a rotating component. The seal is arranged perpendicular to an axis of rotation of the rotating component. 
         [0014]    In another exemplary embodiment, a gas turbine engine includes a high pressure area and a low pressure area. A sealing gland is subject to a magnetic field and is configured to retain a ferro-fluid. A rotating component has at least one seal that is configured to seal the high pressure area from the low pressure area. At least a portion of the seal extends into the sealing gland. 
         [0015]    In a further embodiment of the above, at least one seal is a knife edge seal. 
         [0016]    In a further embodiment of any of the above, the rotating component is an airfoil blade. 
         [0017]    In a further embodiment of any of the above, at least one seal is located on a seal arm that extends from a rotating component. The seal is arranged perpendicular to an axis of rotation of the rotating component. 
         [0018]    In a further embodiment of any of the above, the gas turbine engine further comprises a cooler that is configured to change the temperature of the ferro-fluid. 
         [0019]    In a further embodiment of any of the above, the cooler is located in one of a bypass flowpath, a secondary internal engine flowpath, and a fuel/oil cooler. 
         [0020]    In another exemplary embodiment, a method of sealing low pressure air from high pressure air includes the steps of providing a sealing gland configured to retain a ferro-fluid, distributing the ferro-fluid into the sealing gland and providing at least one rotating seal. A portion of the rotating seal is configured to extend into the sealing gland and interact with the ferro-fluid and remove the ferro-fluid from the sealing gland. 
         [0021]    In a further embodiment of the above, the step of distributing the ferro-fluid into the sealing gland further comprises the steps of applying an alternating magnetic field to the sealing gland, allowing the ferro-fluid to form a uniform layer in the sealing gland and applying a static magnetic field to the sealing gland. 
         [0022]    In a further embodiment of any of the above, the method further comprises the step of adjusting the magnetic field to adjust the ferro-fluid to air surface. 
         [0023]    In a further embodiment of any of the above, the ferro-fluid is distributed into the sealing gland during an engine start-up sequence. 
         [0024]    In a further embodiment of any of the above, the ferro-fluid is removed from the sealing gland during engine shut-down. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0026]      FIG. 1  schematically illustrates an example gas turbine engine embodiment. 
           [0027]      FIG. 2   a  illustrates a schematic view of a low-leakage air seal. 
           [0028]      FIG. 2   b  illustrates a schematic view of the low-leakage air seal of  FIG. 2   a  in operation. 
           [0029]      FIG. 3  illustrates a low-leakage air seal system. 
           [0030]      FIG. 4   a  illustrates a schematic view of the low-leakage air seal with a magnetic field. 
           [0031]      FIG. 4   b  illustrates a schematic view of the low-leakage air seal of  FIG. 4   a  with an adjusted ferro-fluid-to-air surface profile. 
           [0032]      FIG. 5  illustrates a schematic view of the low-leakage air seal with the seal having a repelling magnetic field. 
           [0033]      FIG. 6  illustrates a schematic view of the low-leakage air seal during start-up. 
           [0034]      FIG. 7   a  illustrates a cross-sectional view of the low-leakage air seal of  FIG. 6  at a first time point during start up. 
           [0035]      FIG. 7   b  illustrates a cross-sectional view of the low-leakage air seal of  FIG. 6  at a second time point during start up. 
           [0036]      FIG. 7   c  illustrates a cross-sectional view of the low-leakage air seal of  FIG. 6  at a third time point during start up. 
           [0037]      FIG. 8   a  illustrates an airfoil having an air seal. 
           [0038]      FIG. 8   b  illustrates the airfoil of  FIG. 8   a  including the low-leakage air seal. 
           [0039]      FIG. 9  illustrates a low-leakage air seal mounted on a sealing arm. 
           [0040]      FIG. 10   a  illustrates a low leakage air seal with a cooler. 
           [0041]      FIG. 10   b  illustrates a portion of the schematic gas turbine engine with example cooler locations. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]      FIG. 1  schematically illustrates an example gas turbine engine  20  that includes a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . The fan section  22  is arranged in a fan case  23 . Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section  22  drives air along a bypass flow path B while the compressor section  24  draws air in along a core flow path C where air is compressed and communicated to a combustor section  26 . In the combustor section  26 , air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section  28  where energy is extracted and utilized to drive the fan section  22  and the compressor section  24 . 
         [0043]    Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines; for example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section. 
         [0044]    The example engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided. 
         [0045]    The low speed spool  30  generally includes an inner shaft  40  that connects a fan  42  and a low pressure (or first) compressor section  44  to a low pressure (or first) turbine section  46 . The fan  42  includes fan blades with tips  43 . The inner shaft  40  drives the fan  42  through a speed change device, such as a geared architecture  48 , to drive the fan  42  at a lower speed than the low pressure compressor  44  and low pressure turbine  46 . The high-speed spool  32  includes an outer shaft  50  that interconnects a high pressure (or second) compressor section  52  and a high pressure (or second) turbine section  54 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via the bearing systems  38  about the engine central longitudinal axis A. 
         [0046]    A combustor  56  is arranged between the high pressure compressor  52  and the high pressure turbine  54 . In one example, the high pressure turbine  54  includes at least two stages to provide a double stage high pressure turbine  54 . In another example, the high pressure turbine  54  includes only a single stage. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
         [0047]    The example low pressure turbine  46  has a pressure ratio that is greater than about five (5). The pressure ratio of the example low pressure turbine  46  is measured prior to an inlet of the low pressure turbine  46  as related to the pressure measured at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. 
         [0048]    A mid-turbine frame  57  of the engine static structure  36  is arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28  as well as setting airflow entering the low pressure turbine  46 . 
         [0049]    The core airflow C is compressed by the low pressure compressor  44  then by the high pressure compressor  52  mixed with fuel and ignited in the combustor  56  to produce high speed exhaust gases that are then expanded through the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes vanes  59 , which are in the core airflow path and function as an inlet guide vane for the low pressure turbine  46 . Utilizing the vane  59  of the mid-turbine frame  57  as the inlet guide vane for low pressure turbine  46  decreases the length of the low pressure turbine  46  without increasing the axial length of the mid-turbine frame  57 . Reducing or eliminating the number of vanes in the low pressure turbine  46  shortens the axial length of the turbine section  28 . Thus, the compactness of the gas turbine engine  20  is increased and a higher power density may be achieved. 
         [0050]    The disclosed gas turbine engine  20  in one example is a high-bypass geared aircraft engine. In a further example, the gas turbine engine  20  includes a bypass ratio greater than about six (6), with an example embodiment being greater than about ten (10). The example geared architecture  48  is an epicyclical gear train, such as a planetary gear system, star gear system or other known gear system, with a gear reduction ratio of greater than about 2.3. 
         [0051]    In one disclosed embodiment, the gas turbine engine  20  includes a bypass ratio greater than about ten (10:1) and the fan diameter is significantly larger than an outer diameter of the low pressure compressor  44 . It should be understood, however, that the above parameters are only exemplary of one embodiment of a gas turbine engine including a geared architecture and that the present disclosure is applicable to other gas turbine engines. 
         [0052]    A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 m). The flight condition of 0.8 Mach and 35,000 ft (10,668 m)., with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFC’)”—is the industry standard parameter of pound-mass (lbm) of fuel per hour being burned divided by pound-force (lbf) of thrust the engine produces at that minimum point. 
         [0053]    “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.50. In another non-limiting embodiment the low fan pressure ratio is less than about 1.45. 
         [0054]    “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R)/(518.7 °R)]0.5. The “Low corrected fan tip speed”, as disclosed herein according to one non-limiting embodiment, is less than about 1150 ft/second (350 m/second). 
         [0055]    As is shown schematically in  FIGS. 2   a - 2   b,  a ferro-fluid  100  (or other magnetically controlled or magnetorheological fluid) is suspended by a controlled magnetic field in a static seal gland  102  and provides a surface for a rotating seal  104  to interact with. The seal  104  extends into the seal gland  102  and interacts with the ferro-fluid  100 . In this example, the seal  104  is a knife edge seal. In another example, it may be another kind of seal. Seal  104  rotates about the axis A. Referring to  FIG. 2   b , the seal  104  may shift during operation. The interaction between the seal  104  and the ferro-fluid  100  and the associated sealing characteristic is maintained over a range of axial and radial relative motion of the seal  104 . For example, if the seal  104  shifts to the position of seal  204 , the sealing characteristic is maintained by the ferro-fluid  100 . That is, the seal  104  still interacts with the ferro-fluid  100  in the example shifted position  204 . 
         [0056]      FIG. 3  depicts a general schematic of a ferro-fluid sealing system  106  allowing for collection of the ferro-fluid  100 , for example, during engine shut down, lack of engine operation, or other instances where the magnetic field may be removed. The system  106  may also distribute the ferro-fluid  100  during the engine starting sequence. The system  106  includes a circumferential magnetic field generator  108 , for example, an electromagnet or another device, which provides a magnetic field to the static seal gland  102 . A ferro-fluid collection drain  110  allows the ferro fluid  100  to drain into a collection tank  112 . A valve  114  may control the flow of ferro-fluid  100  through the collection drain  110  and into the collection tank  112 . The collection drain  110  may hold excess ferro-fluid  100  when the magnetic field is reduced, and the collection tank  112  may hold ferro-fluid  100  during engine shut-down. A pump  116  may move the ferro-fluid  100  through the system  106 . During engine startup, ferro-fluid  100  may be drawn from the collection tank  112  via a ferro-fluid collection supply  118  and delivered to the seal gland  102 . 
         [0057]      FIGS. 4   a - 4   b  depict the magnetic interaction of the ferro-fluid  100  and the static sealing gland  102 . The magnetic field  101  generated by the magnetic field generator  108  causes the negatively-charged ferro-fluid  100  to be pulled into the sealing gland  102 . The air-to-ferro-fluid surface  120  may be tailored under both steady-state and transient operating conditions. The surface  120  may be altered for various operating conditions, such as engine start, acceleration, or deceleration, engine surge or variation or reversal of high pressure/load conditions, or engine shut down or re-light, depending on the desired sealing characteristics. Referring to  FIG. 4   b , the air-to-ferro fluid surface  120  may be adjusted by preferentially controlling the magnetic field  101  to enable or disable ferro-fluid  100  distribution within the seal gland  102 . For example, the surface  120  may take on a profile  220 . 
         [0058]    While the ferro-fluid  100  under the influence of the magnetic field  101  does not act as a solid, it is recognized that interaction between the rotating knife-edge seal  104  and the ferro-fluid  100  will have frictional characteristic that can contribute to a loss in system efficiency (for example, by inducing rotor drag, fluid heat-up, etc.). In one example shown schematically in  FIG. 5 , a repelling magnetic field  122  in the rotating knife-edge seal  104  is used at the micro-level to repel the ferro-fluid  100  to reduce friction. It is recognized that this reduction in friction may be accompanied by a minor increases in leakage around the seal  104 . 
         [0059]    As is shown schematically in  FIG. 6 , the seal  104  may have multiple teeth  125 . While the magnetic field  101  (not shown) is being generated, for example, during initial engine motoring pre-start sequence, ferro-fluid  100  is distributed to the sealing gland  102  from the ferro-fluid collection supply  118 . Initially, ferro-fluid  100  may collect between teeth  125 . 
         [0060]      FIGS. 7   a - 7   c  show a cross sectional view of the system  106  of  FIG. 6  at three different time points during start-up and ferro-fluid  100  distribution. A rotor  124  includes the seal  104  ( FIG. 6 ). The rotor  124  inertia and the magnetic field  101  (not shown) form a uniform distribution of fluid that is sustained by the magnetic field  101  in response to gravitational and other forces. Referring to  FIG. 7   a , the ferro-fluid  100  is introduced into the sealing gland  102  when the rotor starts up and is rotating slowly. The static magnetic field  101  is turned off. The dominant fluid distribution force is gravity. Referring to  FIG. 7   b  depicting a second time point in the ferro-fluid  100  distribution, the ferro-fluid  100  moves radially outward in the sealing gland  102  as the magnetic field  101  (not shown) is applied in an alternating manner. This allows ferro-fluid friction/inertia forces to distribute the ferro-fluid  100 . In this stage, inertia and magnetism are the dominant ferro-fluid distribution forces. 
         [0061]    Referring to  FIG. 7   c  depicting a third time point in the ferro-fluid  100  distribution process, the ferro-fluid  100  has formed a uniform layer and the magnetic field  101  is static, allowing the ferro-fluid  100  to overcome rotor  124  friction. Inertia interaction may be influenced by a repelling magnetic field  122  surrounding rotating seal  104  ( FIG. 5 ). The dominant ferro-fluid  100  distribution force in this stage is magnetism. 
         [0062]    In one example, the low-leakage air seal can be used for an airfoil tip seal. Referring to  FIGS. 8   a  and  8   b , an airfoil  126  may include tip seals  128  on a full-hoop outer shroud  130 . The tip seals  128  interact with the ferro-fluid  100 . 
         [0063]    In another example, the low-leakage air seal can be used for an axial seal mounted on a rotating component. Referring to  FIG. 9 , the seal  104  extends from a rotating component  132  by an integrally or mechanically attached extending seal arm  134 . The component  132  rotates about the axis A and the seal  104  interacts with the ferro-fluid  100 . 
         [0064]    In a further example, the ferro-fluid sealing system  106  includes a cooler  136  utilizing the known effect of temperature on ferro-fluid  100  magnetic properties. Ferro-fluid  100  transport can thus be influenced. For example, cooler ferro-fluid  100  is more magnetic and displaces the warmer ferro-fluid  100  as it is pulled toward a magnetic field with more force. A heat load Q may be applied to the ferro-fluid  100  in a localized environment of the air seal to provide controlled convection of ferro-fluid  100  to or from the seal gland  104  by changing the local magnetic properties of the ferro-fluid  100 . For instance, heating the ferro-fluid  100  in a first area may cause it to be pulled towards the magnetic field  101  (not shown) and thus cooler ferro-fluid  100  may flow into the first area from a second area. The heat load Q may be electromagnetically induced, may be created by rotor interactions, or may be derived from another source. 
         [0065]      FIG. 10   b  schematically shows a portion of the gas turbine engine  20 . The cooler  136  may be located, for example, at location  138  in the bypass flow B flow stream, location  140  in a secondary internal engine flowpath provided by a mid-stage bleed  141  from the core flowpath C, or location  142  in a fuel and/or air cooler  144 . 
         [0066]    Although example embodiments have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that and other reasons, the following claims should be studied to determine their true scope and content.