WO2005073667A1

WO2005073667A1 - Inductive apparatus and method for measuring compressor blade tip clearance in a gas turbine engine

Info

Publication number: WO2005073667A1
Application number: PCT/US2005/003036
Authority: WO
Inventors: Yakup Genc; Xiang Zhang
Original assignee: Siemens Corporate Research, Inc.
Priority date: 2004-01-27
Filing date: 2005-01-27
Publication date: 2005-08-11

Abstract

An apparatus and a method for measuring the clearance between the blade tips of the compressor blades of a rotatable compressor assembly and the housing in which the compressor assembly is mounted in a gas turbine engine are disclosed. The apparatus includes an inductive proximity sensor disposed in the housing and positioned in close proximity to but not touching the blade tips of the compressor blades of the compressor assembly. The inductive proximity sensor is adapted to generate a magnetic field and to sense changes in the magnetic field as the compressor assembly is rotated and the blade tips are sequentially brought into close proximity to the inductive proximity sensor. The inductive proximity sensor is mounted in one or more alignment ports defined in the housing of the gas turbine engine. A device displays the clearance between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly.

Description

INDUCTIVE APPARATUS AND METHOD FOR MEASURING COMPRESOR BLADE TIP CLEARANCE IN A GAS TURBINE ENGINE

This non-provisional application claims the benefit of Provisional Appl. Serial. No. 60/540,103, entitled "A Laser-Based Measurement System for the Compressor Blade Tip Clearance Measurement Procedure for Gas Turbines," filed on January 27, 2004.

BACKGROUND OF THE INVENTION [0001] The present invention relates generally to gas turbine engines, and more specifically, to an apparatus for, and method of using, a proximity sensor to measure the clearances between the tips of each blade of a compressor assembly and engine housing during the blade ring alignment process. [0002] Gas turbine engines typically include a core engine with a compressor for compressing air entering the core engine, a combustor where fuel is mixed with the compressed air and then burned to create a high energy gas stream, and a turbine which extracts energy from the gas stream to drive the compressor. In aircraft turbofan engines a second turbine or low pressure turbine located downstream from the core engine extracts more energy from the gas stream for driving a fan. The fan provides the main propulsive thrust generated by the engine. [0003] The rotating engine components of the turbine and compressor include a number of blades attached to a disc which are surrounded by a stationary shroud. In order to achieve high engine efficiency in a gas turbine, it is desirable to keep the space or gap between the tips of the blades and the shroud to a minimum. Tight running clearances must be maintained in order to minimize intrastage leakage. Compressor blade tip clearance measurement is part of the blade ring alignment process that is common in the maintenance of gas turbine engines. A well-known procedure for measuring this clearance employs the use of a mechanical tool. In this regard, the mechanical tool is used to measure the minimum clearance for each row or compressor stage by aligning the compressor blade rings to establish uniform clearances circumferentially. [0004] As depicted in FIG. 1, an illustrative tool 100 for ascertaining blade tip clearances generally comprises an elongated body 102, a probe tip 104 and a dial indicator 106. A calibration cap 108 is disposed over the probe tip 104 as shown. FIG. 2 depicts a gas turbine engine generally denoted by the reference numeral 212. The gas turbine engine 212 includes a housing 214 and a shroud 216 that surrounds a compressor assembly 218. A plurality of clearance measurement tools 200 are inserted through corresponding alignment ports 208a, 208b that are axially disposed in the housing 214 and shroud 216, respectively, of the gas turbine engine 212. In the example shown, the alignment ports 208a, 208b are located in axial positions corresponding to rows 7, 11, 13 and 15 of the compressor stages. For the purpose of description herein, each compressor stage of assembly 218 includes a plurality of compressor blades 220. Each blade 220 has an outer tip 222 that comes into contact with probe tip 204 of tool 200. The tool is calibrated so that when the probe tip 204 makes contact with the outer tip 222 of the blade 220, the clearance between the outer tip 222 and the engine shroud 216 can be read on the dial indicator 206. This current measurement process suffers from several inherent drawbacks: (1) the need to physically align all of the tools with the corresponding stages of the compressor can be rather tedious; and (2) slight errors in operating the tools can cause physical damage to the blade tips. [0005] Non-contact clearance measuring systems are also known in the art. For example, U.S. Patent No. 3,992,627 to Stewart discloses the use of x-rays to measure clearances in gas turbine engines. Similarly, a technical publication by Drinkuth et al, entitled "Laser Proximity Probes for the Measurement of Turbine Blade Tip Clearances," Instrumentation Society of America, 20^th Annual Instrumentation Symposium, May 21-23, 1974 ("Drinkuth"), discloses the use of a laser triangulation system to measure blade tip clearance in a gas turbine engine. In the Drinkuth system, a reflected laser beam is output onto a coherent fiber bundle which transmits the laser spot position to a vidicon. The televised spot is displayed on a television monitor and viewed directly by operating personnel. The spot images from all the blades are superimposed to provide an average spot position and therefore, an average clearance of the rotating blades. [0006] In view of the above, there exists a need for a new mechanically non-invasive method that eliminates the possibility of physical damage to the compressor blades during the clearance measuring process.

SUMMARY OF INVENTION [0007] In accordance with an aspect of the present invention, an apparatus is provided for measuring the clearance between the blade tips of the compressor blades of a rotatable compressor assembly and the housing in which the compressor assembly is mounted in a gas turbine engine. The apparatus comprises: an inductive proximity sensor disposed in the housing and positioned in close proximity to but not touching the blade tips of the compressor blades of the compressor assembly, the inductive proximity sensor being adapted to generate a magnetic field and to sense changes in the magnetic field as the compressor assembly is rotated and the blade tips are sequentially brought into close proximity to the inductive proximity sensor; the inductive proximity sensor being mounted in one or more alignment ports defined in the housing of the gas turbine engine, the alignment ports being disposed axially and corresponding to different stages of the compressor assembly; and a device for displaying the clearance between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly, which displays the electrical analog voltage corresponding to the separation between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly as a function of the changes in the magnetic field. [0008] In accordance with another aspect of the invention, a method is provided for measuring the clearance between the blade tips of the compressor blades of a rotatable compressor assembly and the housing in which the compressor assembly is mounted in a gas turbine engine. The method generally comprises the steps of: positioning an inductive proximity sensor in close proximity to but not touching the blade tips of the compressor blades of the compressor assembly; generating a magnetic field with the inductive proximity sensor in close proximity to the blade tips of compressor assembly; rotating the compressor assembly; sensing changes in the magnetic field as the compressor assembly is rotated and the blade tips are sequentially brought into close proximity to the inductive proximity sensor; and displaying the clearance between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly. In one expedient, the displaying step comprises displaying the electrical analog voltage corresponding to the separation between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly as a function of the changes in the magnetic field. A plurality of inductive proximity sensors may be disposed in a corresponding plurality of axially located alignment ports to facilitate aligning the axis of the rotating compressor assembly relative to the engine housing. The inductive proximity sensor may be calibrated by: using a mechanical tool to measure the smallest clearance between the blade tips and the housing; setting the clearance between the inductive proximity sensor and the blade tip to a plurality of different values; recording the output voltages for each set clearance; and utilizing these recorded output voltage values to fit an inductive sensor output voltage curve. [0009] These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is a schematic diagram of a prior art mechanical tool used to measure blade tip clearances; [0011] FIG. 2 is a schematic depicting several compressor stages in a gas turbine engine and the mechanical tool shown in FIG. 1 mounted in a plurality of alignment ports to measure the compressor blade tip clearances at several axial locations; [0012] FIG. 3 is a schematic depicting several compressor stages in a gas turbine engine and inductive proximity sensors in accordance with the present invention disposed in a plurality of axial locations; [0013] FIG. 4 is an enlarged detail view of an inductive proximity sensor mounted in the gas turbine engine of FIG. 3; [0014] FIG. 5. is a graph showing how analog output voltage of a sample inductive proximity sensor varies as a function of measuring distance for a plurality of different metals; [0015] FIG. 6. is a graph showing how the analog output voltage from the sensor can be used to depict blade tip clearances for individual compressor blades as the compressor assembly is rotated; and [0016] FIG. 7 is a detail view of an alternative embodiment in accordance with the invention utilizing a laser sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0017] Referring to FIG. 3, there is depicted a first embodiment of the present invention that utilizes inductive proximity sensors for measuring the blade tip clearance in a gas turbine engine. In an illustrative application, a gas turbine engine 312 includes a housing 314 and a shroud 316 that surrounds a compressor assembly 318. The compressor assembly is comprised of a plurality of axial flow stages attached to each other. These stages have slightly different outer diameters and are ground to these diameters in sequence. Each rotor assembly is comprised of a disk having a circumferential slot containing a multiplicity of titanium alloy compressor blades, such as, for example, Ti-6A1-4V, Ti-8Al-lV-lMo, Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-2Sn-4Zr-6Mo and the like. The gas turbine engine 312 is further provided with a plurality of alignment ports 308a, 308b that are axially disposed in the housing 314 and shroud 316, respectively, of the gas turbine engine 312. In the example shown, the alignment ports 308a, 308b are located in axial positions corresponding to rows 7, 11, 13 and 15 of the compressor stages, but these ports could be disposed at other locations as well. For the purpose of description herein, each compressor stage of assembly 318 includes a plurality of compressor blades 320. Each blade 320 has an outer tip 322 that is to be radially positioned at a particular distance from the internal surface of the shroud 316. Nominal blade clearance is typically 2.3mm (0.09in) with a potential range of 0 - 4.6mm (0.18in). As shown in FIGS. 3 and 4, an inductive proximity sensor assembly 324 is disposed in each alignment port 308b located at rows 7, 11, 13 and 15 of the compressor assembly of the gas turbine engine. The inductive proximity sensor assembly 324 communicates with a device 326 for displaying distance as a function of analog output voltage. The distance may be read from a display 328 associated with device 326. When calibrated with the size and metallic properties of the blade tips, the inductive proximity sensor assembly produces a different level of analog output voltage corresponding to the distance from the tip 322 of the blade 320. Such signals can be sampled and measured at a frequency from IK to 20kHz, thereby enabling a signal processing system to digitize and infer the minimum clearance between a reference point and the tip 322 of blade 320. It will be appreciated by those skilled in the art that by using a multiple number of inductive proximity sensor assemblies 324 in unison, the actual alignment of the axis 319 of the rotating compressor assembly 318 may be measured relative to the shroud 316 or engine casing. These measurements can be utilized by software to ascertain the geometry of the central rotating axis 319 for the compressor assembly 318. In turn, the necessary correction feedback can be provided to the user, i.e. how much the axis needs to be moved for an optimal alignment. With such a tool, realtime feedback can be given to the user. FIG. 4 depicts an enlarged detail view of an inductive proximity sensor assembly 424 corresponding to the proximity sensor assembly 324 depicted in FIG. 3. The inductive proximity sensor assembly generally comprises an inductive proximity sensor 428 and a mounting fitting 430 adapted to fit within the alignment port 308b. The fitting 430 is similar to the fitting associated with the prior art mechanical tip clearance measurement device. The inductive proximity sensor 428 produces electrical signals that are dependent on the distance to a nearby piece of metal. The proximity sensor 428, which is referred to as a high frequency oscillation type, generates a magnetic field ahead of the sensor head. The inductive proximity sensor 428 contains a tuned circuit with a capacitor and a sensing coil, whose impedance changes as a metallic target (e.g., the blade tip) is moved within a certain distance thereof. In the case of an inductive proximity sensor, the inductance of the tuned circuit sensing coil is influenced by the initiator. As a result of the change in the impedance of the tuned circuit, an amplitude of the tuned circuit signal changes. The signal is rectified and converted by a discriminator into an analog output voltage that can be correlated to the distance of the sensed blade tip from the sensor. The side face of the sensing coil is embedded in metal shielding to enable the sensor assembly 424 to be embedded in a metal base (i.e., shroud 416). [0018] FIG. 5 is a graph showing how analog output voltage varies as a function of measuring distance for a plurality of different metals, using a sample inductive sensor, such model no. EX-305 from Keyence Corporation of America. [0019] FIG. 6 is a graph showing how the analog output voltage from the sensor can be used to depict blade tip clearances for the individual compressor blades as the compressor assembly is rotated. The apex of the curve depicts the region of minimum clearance between the compressor blade tips and the shroud. This can be depicted on the display 328 of device 326 illustrated in FIG. 3. It will be appreciated by those skilled in the art that the device 326 can be any apparatus constructed and arranged to display a waveform. The minimum blade clearance can be ascertained after one revolution of the compressor rotor hub. [0020] The analog output voltage from an inductive proximity sensor varies with many different working environmental parameters, such as, for example, temperature. The inductive measurement system, therefore, has to be calibrated offline for each operative environment. Accordingly, it will be appreciated by those skilled in the art that an electronic calibration system can be used to estimate the curve of the output voltage of the sensor relative to the distance between the sensor and blade tip. For the proposed semi-automatic measurement, this calibration can be used together with the existing mechanical tip clearance measurement apparatus depicted in FIG. 1. In this connection, the mechanical device 100 is used to measure the closest blade tip clearance for any measurement spot. Then, the mechanical device 100 is replaced with the inductive sensor depicted in FIGS. 3 and 4. The clearance between the tip of the inductive sensor and the blade tip is then set to different values, e.g., 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, etc, and the output voltage for each clearance value is recorded. Then, these recorded values are utilized to fit the inductive sensor output voltage curve. This procedure can be implemented with software. In carrying out the foregoing calibration, the user only needs to do the current measurement once and the rest can be handled by a computer semi-automatically. [0021] Referring now to FIG. 7, there is depicted an alternative embodiment that utilizes a laser sensor assembly 724 to measure the blade tip clearance between the blade tip 722 of blade 720 and shroud 716. The laser sensor assembly 724 comprises a laser sensor 728 and fitting 730. An exemplary laser based distance measurement device is model number LC-2430, available from Keyence Corporation of America. The laser sensor 728 communicates with a controller generally denoted by the reference numeral 732 via a cable 734. The laser device is capable of providing measurements from a 30mm range with 0.08 micrometers resolution at a 50kHz sampling rate. The operation of the laser proximity probe is based on a triangulation system where light from a point source is focused from a first small diameter long focal lens on surface 736 as a narrow beam that intersects the blade tip at a given angle, forming a bright spot. The light reflected from this bright spot is imaged through the output lens in the direction of a second angle onto a second lens along surface 738 of the laser sensor 728. The distance from the laser sensor 728 to the blade tips can be displayed on the controller 732. As with the first embodiment, the position of the laser sensor assembly 724 needs to be calibrated relative to the shroud 716 in order to facilitate proper measurement. Once the relationship between laser spot position received by the laser sensor 728 and blade position is established, no further calibration is required. The output spot position is linearly related to blade clearance so that the absolute accuracy of measured blade position is constant over the complete measurable range. As the compressor assembly is rotated, the distances between the laser sensor 728 and the tips 722 of the respective compressor blades 720 can be graphed as shown in FIG. 6 based on the output voltages corresponding to the measured distances. When one or more rotations of the compressor assembly are completed, the distances integrated over time will provide the desired clearances. [0022] The present invention has been shown and described in what are considered to be the most practical and preferred embodiments. It is anticipated, however, that departures may be made therefrom and that obvious modifications will be implemented by those skilled in the art. It is further anticipated that the apparatus and method described herein may be used to ascertain the tip clearance between any rotating member and housing structure, including turbine blade tip clearances or other rotating machinery. It will be appreciated that those skilled in the art will be able to devise numerous arrangements and variations which, although not explicitly shown or described herein, embody the principles of the invention and are within their spirit and scope.

Claims

CLAIMSWe claim:

1. An apparatus for measuring the clearance between the blade tips of the compressor blades of a rotatable compressor assembly and the housing in which the compressor assembly is mounted in a gas turbine engine, comprising: an inductive proximity sensor disposed in the housing and positioned in close proximity to but not touching the blade tips of the compressor blades of the compressor assembly, the inductive proximity sensor being adapted to generate a magnetic field and to sense changes in the magnetic field as the compressor assembly is rotated and the blade tips are sequentially brought into close proximity to the inductive proximity sensor; and means for displaying the clearance between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly.

2. The apparatus recited in claim 1, wherein the means for displaying the clearance displays the electrical analog voltage corresponding to the separation between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly as a function of the changes in the magnetic field.

3. The apparatus recited in claim 1, wherein a plurality of inductive proximity sensors are mounted in a plurality of alignment ports defined in the housing of the gas turbine engine, the alignment ports being disposed axially and corresponding to different stages of the compressor assembly, to enable alignment of a central axis of the compressor assembly relative to the housing.

4. The apparatus recited in claim 3, wherein each inductive proximity sensor is disposed within a fitting adapted to fit within the plurality of alignment ports.

5. The apparatus recited in claim 1, further comprising a mechanical calibration tool for defining a reference standard for the inductive proximity sensor.

6. An apparatus for measuring the clearance between the blade tips of the compressor blades of a rotatable compressor assembly and the housing in which the compressor assembly is mounted in a gas turbine engine, comprising: a plurality of inductive proximity sensors, each inductive proximity sensor disposed in the housing and positioned in close proximity to but not touching the blade tips of the compressor blades of the compressor assembly, the inductive proximity sensors being adapted to generate a magnetic field and to sense changes in the magnetic field as the compressor assembly is rotated and the blade tips are sequentially brought into close proximity to the inductive proximity sensors, the inductive proximity sensors being mounted in a plurality of alignment ports defined in the housing of the gas turbine engine, the alignment ports being disposed axially and corresponding to different stages of the compressor assembly; and means for displaying the clearance between the inductive proximity sensors and the blade tips of the compressor blades of the rotatable compressor assembly, wherein the means for displaying the clearance displays the electrical analog voltage corresponding to the separation between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly as a function of the changes in the magnetic field, the means for displaying enabling an axis of the compressor assembly to be aligned relative to the housing.

7. A method of measuring the clearance between the blade tips of the compressor blades of a rotatable compressor assembly and the housing in which the compressor assembly is mounted in a gas turbine engine, comprising the steps of: positioning an inductive proximity sensor in close proximity to but not touching the blade tips of the compressor blades of the compressor assembly; generating a magnetic field with the inductive proximity sensor in close proximity to the blade tips of compressor assembly; rotating the compressor assembly; sensing changes in the magnetic field as the compressor assembly is rotated and the blade tips are sequentially brought into close proximity to the inductive proximity sensor; and displaying the clearance between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly.

8. The method recited in claim 7, wherein the displaying step comprises displaying the electrical analog voltage corresponding to the separation between the inductive proximity sensor and the blade tips of the compressor blades of the rotatable compressor assembly as a function of the changes in the magnetic field.

9. The method recited in claim 7, further comprising the steps of mounting a plurality of inductive proximity sensor in a plurality of alignment ports defined in the housing of the gas turbine engine, the alignment ports being disposed axially and corresponding to different stages of the compressor assembly, to enable alignment of a central axis of the compressor assembly relative to the housing.

10. The method recited in claim 7, further comprising the steps of calibrating the inductive proximity sensor by: using a mechanical tool to measure the smallest clearance between the blade tips and the housing; setting the clearance between the inductive proximity sensor and the blade tip to a plurality of different values; recording the output voltages for each set clearance; and utilizing these recorded output voltage values to fit an inductive sensor output voltage curve.