Negative thermal expansion compressor case for improved tip clearance

A compressor with negative coefficient of thermal expansion case material comprising a rotor having blades with tips, the case including an inner case comprising a negative coefficient of thermal expansion material, and a tip clearance located between the tips and the inner case; wherein the tip clearance is maintained responsive to a flow of air over the negative coefficient of thermal expansion material.

BACKGROUND

The present disclosure is directed to a negative thermal expansion compressor case configured for improved tip clearance.

Gas turbine engines provide power by compressing air using a compressor, adding fuel to this compressed air, combusting this mixture such that it expands through the blades of a turbine and exhausting the produced gases. The turbine consists of a disc, rotating about the central shaft of the engine, and a plurality of blades extending radially out of the disc towards the engine casing of the engine. Expansion of the combustion gases through the turbine causes its blades to rotate at high speed and the turbine, in turn, drives the compressor.

The distance between the tips of the blades and the inner surface of the compressor casing is known as the tip clearance. It is desirable for the tips of the blades to rotate as close to the casing without rubbing as possible because as the tip clearance increases, a portion of the compressed gas flow will pass through the tip clearance decreasing the efficiency of the compressor. This is known as over-tip leakage. The efficiency of the compressor, which partially depends upon tip clearance, directly affects the specific fuel consumption (SFC) of the engine. Accordingly, as tip clearance increases, SFC also rises.

As the disc and the blades rotate, centrifugal and thermal loads cause the disc and blades to extend in the radial direction. The casing also expands as it is heated but there is typically a mismatch in radial expansion between the disc/blades and the casing. Specifically, the blades will normally expand radially more quickly than the housing, reducing the tip clearance and potentially leading to “rubbing” as the tips of blade come into contact with the interior of the casing. Over time in use, the casing heats up and expands away from the blade tip, increasing the tip clearance. This may result in a tip clearance at stabilized cruise conditions that is larger than desired resulting in poor efficiency.

Conventionally, tip clearances are set when the engine is cold to allow for radial extension of the disc and blades due to centrifugal and thermal loads, to prevent rubbing. This means that there is initially a large tip clearance, such that the engine is relatively inefficient. When the engine is running, the blades will eventually extend radially to close this clearance, making the engine run more efficiently. Over a longer period of time, however, the temperature of the casing will rise and the casing will expand radially, which will again increase the tip clearance.

The running tip clearance of the high-pressure compressor (HPC) of an aircraft engine has a significant bearing on the efficiency of the HPC module. This, in turn, impacts other module attributes such as turbine durability as well as the engine fuel burn metric. Consequently much effort has been expended in ensuring that the running tip clearance is at the smallest mechanically feasible value.

SUMMARY

In accordance with the present disclosure, there is provided a compressor with negative coefficient of thermal expansion case material comprising a rotor having blades with tips, the case including an inner case comprising a negative coefficient of thermal expansion material, and a tip clearance located between the tips and the inner case; wherein the tip clearance is maintained responsive to a flow of air over the negative coefficient of thermal expansion material.

In another and alternative embodiment, the air is configured to warm the inner case comprising the negative coefficient of thermal expansion and cause a contraction of the inner case and reduce the tip clearance.

In another and alternative embodiment, the compressor with negative coefficient of thermal expansion case material further comprises a collection manifold fluidly coupled to a distribution manifold fluidly coupled to the inner case comprising the negative coefficient of thermal expansion.

In another and alternative embodiment, the compressor with negative coefficient of thermal expansion case material further comprises a valve fluidly coupled between the collection manifold and the distribution manifold, the valve configured to control the flow of air over the negative coefficient of thermal expansion material.

In another and alternative embodiment, the compressor with negative coefficient of thermal expansion case material further comprises a controller coupled to the valve, the controller configured to actuate the valve to control the air flow rate to change the tip clearance by changing the temperature of the negative coefficient of thermal expansion case material.

In another and alternative embodiment, the negative coefficient of thermal expansion case material is configured as a ring configured to produce a symmetric response to the case.

In another and alternative embodiment, the air is selected from the group consisting of compressor cooling air, combustor air and turbine air.

In accordance with the present disclosure, there is provided a gas turbine engine compressor having a tip clearance responsive to a negative coefficient of thermal expansion material comprising an inner case having a negative coefficient of thermal expansion material; at least one blade having a blade tip; the tip clearance located between the inner case and the blade tip; and a collection manifold fluidly coupled to a distribution manifold fluidly coupled to the inner case comprising the negative coefficient of thermal expansion material, wherein the collection manifold and the distribution manifold are configured to direct air to the negative coefficient of thermal expansion material and change the tip clearance.

In another and alternative embodiment, the gas turbine engine compressor further comprises a valve fluidly coupled between the collection manifold and the distribution manifold, the valve configured to control a flow of air over the negative coefficient of thermal expansion material.

In another and alternative embodiment, the gas turbine engine compressor further comprises a controller coupled to the valve, the controller configured to actuate the valve to control the air flow rate to change the tip clearance by changing the temperature of the negative coefficient of thermal expansion material.

In another and alternative embodiment, the gas turbine engine compressor further comprises instrumentation and controls coupled to the controller the instrumentation and controls configured to activate the controller responsive to gas turbine engine information.

In another and alternative embodiment, the negative coefficient of thermal expansion material comprises a case support ring.

In another and alternative embodiment, the air is selected from the group consisting of compressor cooling air, combustor air and turbine air.

In accordance with the present disclosure, there is provided a process for maintaining a tip clearance of a compressor by use of a negative coefficient of thermal expansion material comprises configuring at least a portion of an inner case of the compressor with the negative coefficient of thermal expansion material; at least one compressor blade having a blade tip; the tip clearance located between the inner case and the blade tip; fluidly coupling a collection manifold to a distribution manifold within the compressor; fluidly coupling the distribution manifold to the inner case comprising the negative coefficient of thermal expansion material; directing air from the collection manifold to the distribution manifold to the negative coefficient of thermal expansion material; and changing the tip clearance responsive to heat transfer between the negative coefficient of thermal expansion material and the air.

In another and alternative embodiment, the air heats the negative coefficient of thermal expansion material.

In another and alternative embodiment, the process further comprises fluidly coupling a valve between the collection manifold and the distribution manifold, and controlling the valve to control the air directed to the negative coefficient of thermal expansion material.

In another and alternative embodiment, the process further comprises coupling a controller to the valve, configuring the controller to actuate the valve to control the air flow rate to change the tip clearance by changing the temperature of the negative coefficient of thermal expansion material.

In another and alternative embodiment, the process further comprises coupling instrumentation and controls to the controller; configuring the instrumentation and controls to activate the controller responsive to gas turbine engine information.

In another and alternative embodiment, the air is selected from the group consisting of compressor cooling air, combustor air and turbine air.

The negative thermal expansion compressor disclosed can achieve a technical effect through a thermal contraction of the HPC case through the use of hot air in conjunction with a case architecture featuring negative thermal expansion.

Other details of the negative thermal expansion compressor are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.

DETAILED DESCRIPTION

FIG. 1is a simplified cross-sectional view of a gas turbine engine10in accordance with embodiments of the present disclosure. Turbine engine10includes fan12positioned in bypass duct14. Turbine engine10also includes compressor section16, combustor (or combustors)18, and turbine section20arranged in a flow series with upstream inlet22and downstream exhaust24. During the operation of turbine engine10, incoming airflow F1enters inlet22and divides into core flow Fcand bypass flow FB, downstream of fan12. Core flow Fccontinues along the core flowpath through compressor section16, combustor18, and turbine section20, and bypass flow FBproceeds along the bypass flowpath through bypass duct14.

Compressor16includes stages of compressor vanes26and blades28arranged in low pressure compressor (LPC) section30and high pressure compressor (HPC) section32. Turbine section20includes stages of turbine vanes34and turbine blades36arranged in high pressure turbine (HPT) section38and low pressure turbine (LPT) section40. HPT section38is coupled to HPC section32via HPT shaft42, forming the high pressure spool. LPT section40is coupled to LPC section30and fan12via LPT shaft44, forming the low pressure spool. HPT shaft42and LPT shaft44are typically coaxially mounted, with the high and low pressure spools independently rotating about turbine axis (centerline) CL.

Combustion gas exits combustor18and enters HPT section38of turbine20, encountering turbine vanes34and turbines blades36. Turbine vanes34turn and accelerate the flow of combustion gas, and turbine blades36generate lift for conversion to rotational energy via HPT shaft42, driving HPC section32of compressor16. Partially expanded combustion gas flows from HPT section38to LPT section40, driving LPC section30and fan12via LPT shaft44. Exhaust flow exits LPT section40and turbine engine10via exhaust nozzle24. In this manner, the thermodynamic efficiency of turbine engine10is tied to the overall pressure ratio (OPR), as defined between the delivery pressure at inlet22and the compressed air pressure entering combustor18from compressor section16. As discussed above, a higher OPR offers increased efficiency and improved performance. It will be appreciated that various other types of turbine engines can be used in accordance with the embodiments of the present disclosure.

Referring toFIG. 2, a lattice48of a material having a negative coefficient of thermal expansion50is illustrated according to various embodiments. A unit cell51may be formed from material that may comprise nickel, a nickel alloy, molysilicide nickel aluminide, zirconium tungstate, or any other suitable material. In other exemplary embodiments, materials that can have a negative coefficient of thermal expansion can include iron-nickel alloys, carbon fiber, graphite fiber, carbon nanotubes, aramid fiber, zeolite, and combinations thereof. In various embodiments, the material may be fabricated using additive manufacturing. The material may be fabricated using selective laser sintering or direct metal laser sintering, in which a laser fuses powdered metal into a solid part. The unit cell51shown is merely one example of a material having a negative coefficient of thermal expansion50, and those skilled in the art will appreciate that many different shapes may be used. In various embodiments, unit cell51may have a width W of less than 1 cm (0.4 inches), less than 1 mm (0.04 inches), or less than 100 microns (0.004 inches). However, in various embodiments, width W may be any suitable size A. The unit cell51may be formed in a repetitive pattern. The pattern may cause the lattice48to contract as a temperature of the material increases. As the temperature increases, a cross-sectional area of pores52between unit cells51may increase. Details of the exemplary lattice and unit cells51are described in greater detail in U.S. Pat. No. 9,845,731 incorporated by reference herein.

FIG. 3andFIG. 4illustrate exemplary structures of materials having a negative coefficient of thermal expansion50. Certain bi-material cellular structures can exhibit negative coefficient of thermal expansion behavior. The structure atFIG. 3includes a first portion54that has a high coefficient of thermal expansion. A second portion56includes a low coefficient of thermal expansion. In combination the two materials can exhibit an overall negative coefficient of thermal expansion. Similarly to the structures54,56inFIG. 3, the structure shown inFIG. 4includes a first element58with a low coefficient of thermal expansion and a second element60with a high coefficient of thermal expansion. The bi-material structure has a net negative coefficient of thermal expansion.

Referring now toFIG. 5an exemplary portion of a gas turbine compressor30,32section is shown. The negative thermal expansion compressor61disclosed can achieve a technical effect through a thermal contraction of the case62through the use of hot air in conjunction with a case architecture featuring negative thermal expansion material50. In the exemplary embodiment, the inner case62proximate the compressor61can comprise a negative coefficient of thermal expansion material50. Various portions of the inner case62architecture can be employed for the use of the negative coefficient of thermal expansion material50. In an exemplary embodiment, portions nearest the rotating blades can be utilized. The portions of the inner case62that are configured to maintain the tip clearance74can be configured with the negative coefficient of thermal expansion material50. Either axial portions and/or radial portions of the inner case62can be employed as well. In another exemplary embodiment, the negative coefficient of thermal expansion material50can be formed as a ring64that produces a symmetric response to the case62. The negative coefficient of thermal expansion material50can be formed as a connector case90that produces a symmetric response to the case62. In an exemplary embodiment the inner case62can be configured to experience the negative coefficient of thermal expansion to produce a predetermined blade tip to case clearance change for from about 5 mils to about 10 mils.

The compressor61includes passageways68that are used to direct air70into the location of the inner case62that includes the negative coefficient of thermal expansion material50. Compressor61exit air72(e.g., station3air) high pressure turbine air can be utilized to change the temperature of the negative coefficient of thermal expansion material50to adjust the case62dimensions in order to reduce the tip clearance74between the case62and blade tip76. In an exemplary embodiment, a collection manifold78can be fluidly coupled to the air70to collect the air70and direct the air70to a distribution manifold80. The distribution manifold80can be configured to fluidly couple the air70with the portion of the case62that includes the negative coefficient of thermal expansion material50. The air70can flow over the negative coefficient of thermal expansion material50and exchange thermal energy to heat the material50. Radial or axial portions of the inner case62that are required to control the tip clearance can receive the air70. A valve82can be fluidly coupled between the collection manifold78and the distribution manifold80. The valve82can be positioned to control the flow of air70. The valve82can be adjusted to direct the air70toward the distribution manifold80or to a bypass manifold88. The valve82can be used to control the temperature of the negative coefficient of thermal expansion material50and control the tip clearance74dimensions between the blade tip76and case62responsive to the temperature of the material50. In an exemplary embodiment, the temperature differential employed to change the negative coefficient of thermal expansion material50can be from about 50 degrees Fahrenheit to about 100 degrees Fahrenheit. In an exemplary embodiment, a controller84can be coupled with the valve82and configured to control the valve position. The valve82can be controlled to maintain/reduce the allocation of the air70to the distribution manifold80and/or the bypass manifold88, since the total flow rate of bleed air70remains fixed and the valve position determines whether or not it is utilized to effect the thermal contraction of the case62. The valve82is not intended to control the mass flow rate of bleed air70. That mass flow rate is fixed by the requirement of turbine cooling, which is the intended final destination of bleed air70.

In an exemplary embodiment, the controller84can be utilized to control the air70flow direction to change the tip clearance by changing the temperature of the material50. The controller84can operate based on a predetermined schedule derived from engine operational data. For example, flight profile, predetermined schedules, and engine conditions can be utilized to modify the air70temperature and activate the negative coefficient thermal expansion material50to change dimension. In another embodiment, the controller84can be operated based on instrumentation and controls86coupled to the controller84and based on real time information (temperature, dimensions, operational mode) from the gas turbine engine10. The instrumentation and controls86include sensors (temperature, pressure, flow rate, altitude), programs, signals, communications links, engine operational data and the like. In an exemplary embodiment, the material50can be activated during engine cruise conditions and deactivated during engine transient conditions.

A technical advantage of the negative coefficient of thermal expansion material incorporated with the case is for better control the tip clearance between the case and the blade tips of the high pressure compressor.

A technical advantage of the negative coefficient of thermal expansion material incorporated with the case includes improving engine cycle performance and maintaining the bleed flow rate, thereby enhancing high pressure compressor life.

Another technical advantage of the negative coefficient of thermal expansion material incorporated with the case includes the capacity to control the flow of air supplied to the case and actively control the tip clearance responsive to gas turbine engine conditions.

There has been provided a negative thermal expansion compressor. While the negative thermal expansion compressor has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations which fall within the broad scope of the appended claims.