GB2358059A

GB2358059A - Pyrometric determination of radiance and/ or temperature

Info

Publication number: GB2358059A
Application number: GB0000122A
Authority: GB
Inventors: Joseph Douglas
Original assignee: ROTADATA Ltd
Current assignee: ROTADATA Ltd
Priority date: 2000-01-07
Filing date: 2000-01-07
Publication date: 2001-07-11
Also published as: GB0000122D0

Abstract

A method for determining the radiance and/ or temperature of a rotating object such as a turbine blade B comprises determining the reflectivity of the object B under low-temperature conditions where the object is non-emissive, the radiance of the blade under high temperature conditions and measuring the intensity of incident radiation from external sources such as a combustor C. The radiance measurement may be corrected for reflected radiation by a factor depending on the reflectivity and the incident radiation intensity. A minimum-picking process may be used on the resulting data to reduce the effects of flare. The apparatus may comprise a retractable probe P which rotates about an axis A1. The incident radiation and the radiance of the object may be monitored by two separate detectors D2, D1, or alternatively, by a common pyrometer system (figure 2).

Description

2358059 PYROMETER APPARATUS AND METHOD The present invention relates to a

pyrometer apparatus and method for determining the radiance or a related parameter (particularly temperature) of a rotary component (particularly a turbine blade) of a gas turbine.

The most significant problem affecting the accuracy of pyrometer turbine blade temperature measurements is the significant, and variable effect of the combustor radiation reflected from the blades, which results in a corresponding offset in the apparent blade temperature.

Most research has been directed towards trying to recognising and quantifying the reflected component of the pyrometer output by the way it distorts the spectral content of the received radiation. Two, three and more spectral bands have been used with varying success to make corrections but they all rely on maldng assumptions about the nature of the radiation.

Blade surface thermocouples provide a single point reference which, if the thermocouple were ideal and formed an integral part of the surface, would provide an exact measurement of the reflected radiation component at that unique point. The application of the resulting correction to other blades/blade areas requires further assumptions about surface properties, blade geometries and inter-blade heat transfer. Although the accuracy of the results can be improved by using thermocouple data, considerable uncertainties still exist.

2 Temperature-sensitive paint and thermal paints, which have been the mainstay of blade cooling development for many years, can also provide some reference data but the reliability of the data is subject to the well known uncertainties of thermal paint which include thermal conductivity, temperature gradients and surface properties.

An object of the present invention is to overcome or alleviate at least some of the above problems.

In one aspect the present invention provides a method of determining the radiance or a related parameter of a rotary component of a gas turbine, the method comprising the steps of.

a) pyrometrically determining the reflectivity of the rotary component in a first condition in which it is substantially non-emissive in the measurement waveband; b) pyrometrically determining radiance of the rotary component in a second condition in which the rotary component is emissive in the measurement waveband, and c) correcting the radiance determined in step b) by subtracting a correction parameter derived from the product of incident radiation intensity in said second condition and said reflectivity.

3 Preferably the incident radiation intensity and radiance of step b) are determined pyrometrically.

In another aspect the invention provides apparatus for determining the radiance or a related parameter of a rotary component of a gas turbine, the apparatus comprising:

pyrometer means arranged to determine: a) the reflectivity of the rotary component in a first condition in which the rotary component is substantially non-emissive in the measurement waveband, b) the radiance of the rotary component in a second condition in which the rotary component is emissive in the measurement waveband and c) the incident radiation intensity in said second condition, and ii) processing means arranged to derive a correction parameter from the product of said incident radiation intensity and said reflectivity, and to correct the radiance as determined by the pyrometer means by subtracting the correction parameter from said radiance.

Preferably said pyrometer means comprises a single pyrometer assembly arranged to measure both the radiance or reflectivity of the rotary component and said incident radiation intensity.

Further preferred features are defined in the dependent claims.

Preferred embodiments of the invention are described below by way of example only with reference to Figures 1 and 2 of the accompanying drawings, wherein:

4 Figure 1 is a diagrammatic axial cross-section of a gas turbine provided with a pyrometer apparatus in accordance with the invention, and Figure 2 is a diagrammatic axial cross-section of a gas turbine showing a variant of the arrangement of Figure 1.

Referring to Figure 1, the gas turbine T comprises a combustor C having an array of nozzle guide vanes 5 aligned with blades B of the rotor assembly (not shown) which is mounted for rotation about longitudinal axis A2.

A sighting tube 8 provided with a source 2 of high pressure air for cooling and purging extends radially through the turbine casing in the vicinity of the nozzle guide vanes 5 and has its inner end and thus its field of view V2 directed towards combustor C. Radiation from combustor C is collected and conveyed by the reflective inner wall of sighting tube 8 to a photodetector D2 whose output is digitised by an analogue - to digital converter 3 and fed to a personal computer 4. In this manner a measurement of the intensity of radiation incident on blade B can be obtained.

In order to measure the corresponding reflected intensity from blade B (under lowtemperature conditions in which the blades B are not emissive in the measurement waveband) and also the radiance of blade B under hightemperature conditions, a pyrometer probe P is provided which can be advanced and retracted along radial axis A1 (as indicated by arrow 6) and swivelled about this axis (as indicated by arrow 7). Radiation within its field of view V1 is collected and reflected by a mirror M and focussed by a lens arrangement L onto a detector D 1, whose output is digitised by analogue - to - digital converter 1 and fed to computer 4.

In use, the pyrometer probe P is rapidly advanced along axis A1 whilst rotating as indicated by arrow 7. The output of detector D 1 is sampled at a rate of one million measurements/ second and the resulting helical scan is synchronised with the output (REV TIMER) of a tachogenerator coupled to the turbine rotor whereby individual helical scans for each turbine blade B are obtained.

Each of these individual scans is in the form of a thermal image of the blade and is heavily overscanned, especially in the radial direction, since the pyrometer field of view V 1, typically 2 nim in diameter, is much less than the distance moved by the traverse in one revolution. In the chordwise direction the degree of overscanning will be approximately 2/0.5 = 4, since at maximum speed the blade surface speed is approximately 0.5 mm/microsecond.

The output of detector D2 is sampled in synchronism with that of detector D 1 and accordingly a series of measurements of combustor radiation intensity (i.e. incident radiation intensity on blade B1) is associated with the series of measurements of blade radiation intensity.

As noted above, two series of measurements are taken:

A) under low-temperature conditions (negligible emissivity of blade) giving typical sets of data as follows:

6 TABLE 1

PIXEL LOW TEMP LOW TEMP REFLECTANCE BLADE DATA COMBUSTOR VALUE Ri R16 B1 B16 DATA Cl - C16 1 193 399 Ri 2 196 400 R2 3 208 595 R3 4 371 666 6661191 = R4 310 560 560/191 = R5 6 308 622 6221191 = R6 7 191 639 639/191 = R7 8 248 497 497/191 = & 9 324 611 611/141 = R9 1-3 PIXELS 243 601 601/141 = Rio 11 315 561 561/141 = Rli 12 141 486 486/141 =3.447 13 249 390 390/141 = R13 14 281 586 586/141 = R14 339 581 ----t 581/141 = Ris j+3 PIXELS 16 275 620 R16 The BLADE DATA are as output by A/D converter 3 and the COMBUSTOR DATA are as output by A/D connector 1. Each datum relates to a pixel in series in a helical scan (only 16 pixels being shown for the sake of simplicity in Table 1).

The reflectance value in respect of each pixel is obtained by the following method:

i) the BLADE DATA valves B, to B 16 are processed to find the minimum value (assumed to be unaffected by flare in the optical path between the blade surface and the window of probe P) - in this case the minimum B min is 141 (in respect of B12); ii) the reflectance value R,2 for this pixel is obtained by dividing the corresponding combustor datum C12 (486 in this case) by the minimum -in this case giving a result for R12 for 3.447; 7 the minimum BLADE DATA value B min (which is assumed to be applicable to the entire field of view of the pyrometer within 3 pixels as shown in Table 1, i.e. to the group of four pixels up to and including pixel 12 and to the group of four pixels beginning with and following pixel 12) is divided into the corresponding COMBUSTOR DATA value of pixels P9 to P15; iv) the four adjacent values B5 to B8 are then checked and the minimum BLADE DATA selected (in this case B7, having a value of 19 1); v) this BLADE DATA value is then utilised to calculate the reflectance values of all pixels (other than those for which reflectance values have already been calculated) within three pixels of the above minimum B7 - i. e. reflectance values R4 to IZs in this case; vi) a procedure analogous steps iv) and v) is repeated for successive adjacent groups of pixels until reflectance values R, to R16 has been calculated in respect of each pixel.

Hence a complete set of reflectance values is obtained.

under high temverature conditions (significant emissivity of blade) A set of combustor data and blade data are obtained under high temperature conditions:

8 TABLE 2

PIXEL 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 HIGH TEMP HIGH TEMP REFLECTANCE CORRECTION FLARE CORRECTED BLADE DATA COMBUSTOR VALUE Ri-RI6 PARAMETER CORRECTED RADIANCE DATA Cl'- Ci6' (FROM Cn R. HIGH TEMP W- C Rn TABLE 1) BLADE DATA Bl'- Bi6' 2027 cl Ri pi 2027 2027 - pi 2541 C2' R2 P2 2027 2027 - P2 2608 C3 ' R3 P3 2027 2027 - P3 2700 C4' R4 P4 2027 2027 P4 2504 C5 R5 PS 2219 2219 - Ps 2300 C6 R6 P6 2219 2219 - P6 2219 C7' R7 P7 2,2 A 9 2219 - P7 2808 C8 R8 P8 2219 2219 - P8 2900 C9 R9 P9 2219 2219 - P9 3076 clo, Rio Plo 2219 2219 - Plo 3189 cil, Ril pil Wii B11 - Pn 2432 C12' R12 P12 W12 W12 - P12 R12 2131 C13' R13 P13 W13 W13 - P13 R13 2540 C14' R14 P14 W14 W14 - P14 R14 2030 cls, Ris Pis Wis Wis - P15 R15 2150 C16, R16 P16 Wi6 W16 - P16 Ri 9 The corrected radiance in respect of each pixel is then obtained by the following method:

i) the HIGH TEMP BLADE DATA values are processed to find the minimum value (assumed to be unaffected by flare in the optical path between the blade surface and the window of probe P) - in this case the minimum is 2027 (pixel 1); ii) this value is substituted for the pixels within each adjacent group of four pixels (of step iii) above - giving corrected values of (in this case) 2027 in respect of pixels 1 to 4 (see column six of Table 2); iii) the pixels within four pixels of pixel 4 are examined to find the minimum HIGH TEMP BLADE DATA value (in this case 2219 for pixel 7); iv) this minimum is substituted in column six of Table 2 in respect of all unallocated pixels within 3 pixels of pixel 7; v) a process analogous to steps iii) and iv) is applied to successive adjacent groups of pixels to complete column six of Table 2; vi) a correction parameter Pi - P16 representing the intensity due to reflection, is calculated in respect of each pixel by multiplying the appropriate reflectance value Rn (n = 1 to 16) from Table 1 by the corresponding high temperature combustor data Cn'(n'= 1 to 16) - see column five of Table 2; vii) this correction parameter is subtracted from the FLARE-CORRECTED HIGH TEMP BLADE DATA (of column six of Table 2) to give corrected radiance data in respect of each pixel (column seven of Table 2).

The data of colun-in seven can be processed to determine the blade temperature distribution by applying a known formula.

Claims

1. A method of determining the radiance or a related parameter of a rotary component of a gas turbine, the method comprising the steps of.

2. A method as claimed in Claim 1, wherein the incident radiation intensity and radiance of step b) are determined by a common pyrometer assembly.

3. A method as claimed in Claim 1, wherein the incident radiation intensity and radiance of step b) are determined by respective sensors located in the turbine combustor and adjacent the rotary component respectively.

12 4. A method as claimed in any preceding claim, wherein the detected radiation intensity values are processed to eliminate or reduce spurious radiation intensity data caused by combustion products in the turbine gas stream.

5. A method as claimed in any preceding claim, wherein the temperature of the rotary component is determined from the corrected radiance.

6. A method according to any preceding claim wherein the rotary component is a turbine blade.

7. Apparatus for determining the radiance or a related parameter of a rotary component of a gas turbine, the apparatus comprising:

i) pyrometer means arranged to determine: a) the reflectivity of the rotary component in a first condition in which the rotary component is substantially non-emissive in the measurement waveband, b) the radiance of the rotary component in a second condition in which the rotary component is emissive in the measurement waveband and c) the incident radiation intensity in said second condition.

ii) processing means arranged to derive on correction parameter from the product of said incident radiation intensity and said reflectivity, and to correct the radiance as determined by the pyrometer means by subtracting the correction parameter from said radiance.

13 8. Apparatus as claimed in Claim 7, wherein said pyrometer means comprises a single pyrometer assembly arranged to measure both the radiance or reflectivity of the rotary component and said incident radiation intensity.

9. Apparatus as claimed in Claim 8, wherein the pyrometer extends into the gas turbine along a first aids which is transverse to the longitudinal axis of the gas turbine and is rotated about said first axis during data acquisition.

10. Apparatus as claimed in Claim 8 or Claim 9, wherein said pyrometer is advanced and/or retracted along said first axis during data acquisition.

11. Apparatus as claimed in any of Claims 7 to 10, further comprising processing means arranged to process detected radiation intensity data to eliminate or reduce spurious data caused by combustion products in the turbine gas stream.

12. Apparatus for determining the radiance or a related parameter of a rotary component of a gas turbine, substantially as described hereinabove with rdlerence to Figures 1 and 2 of the accompanying drawings.

13. A method of determining the radiance or a related parameter of a rotary component of a gas turbine, substantially as described hereinabove with reference to Figures 1 and 2 of the accompanying drawings.