Gas turbine engine with a plurality of bleed valves
A health monitoring apparatus for a mechanical system includes: a microphone arranged to receive sound from the system; and a processor adapted to process the output of the microphone. The mechanical system may be a gas turbine engine. Further, the engine may have a plurality of bleed valves, each of the bleed valves being configured such that, when open, it produces a sound which is distinguishable from the sounds produced by the other bleed valves, and the microphone being arranged to detect the sound from the bleed valves.
1. A gas turbine engine comprising a plurality of bleed valves, each of said bleed valves being configured such that, when open, that bleed valve produces a sound which is distinguishable from the sounds produced by other bleed valves.
2. An engine according to claim 1 wherein each bleed value is configured such that the sound produced by each bleed valve is, for a given pressure differential across the valve, a tone of substantially uniform pitch.
3. An engine according to claim 1 further comprising a noise generator associated with each bleed valve and located in an air flow through or out of each bleed valve, which generates the sound.
4. An engine according to claim 1 further comprising a health monitoring apparatus for monitoring the health of the engine, the apparatus including:
a microphone arranged to receive sound from the bleed valves; and
a processor adapted to process an output of the microphone.
5. A method for monitoring the operation of one or more bleed valves in a gas turbine engine, wherein the engine has a plurality of bleed valves, each of said bleed valves being configured such that, when open, the bleed valve produces a sound which is distinguishable from the sounds produced by the other bleed valves, wherein the sound detected by a microphone includes the sound produced by said bleed valves, the method including the steps of:
monitoring an output of the microphone arranged to receive the sounds produced by said bleed valves; and
processing the output of the microphone.
6. A method according to claim 5 wherein the sound produced by each bleed valve is generated by a noise generator associated with each bleed valve and located in an air flow through or out of said bleed valve.
7. An engine according to claim 4 wherein the processor is adapted to filter random noise from the output of the microphone.
8. An engine according to claim 4 wherein the processor is adapted to analyze the output of the microphone.
9. An engine according to claim 4 wherein the processor is adapted to compare the output of the microphone with a model of a normal behavior of the engine.
10. An engine according to claim 9 wherein the processor is further adapted to produce an alarm or an alert if the output of the microphone deviates from the model by more than a pre-defined limit.
11. An engine according to claim 4 wherein the microphone is located in an under-cowl location.
12. A method according to claim 5 wherein said step of processing includes one or more of the following: removal of random noise, filtering, calculation of power spectra, zmod data, spectrum analysis, tracked order extraction, amplitude and phase extraction.
13. A method according to claim 5 including the further step of analyzing the output of the microphone.
14. A method according to claim 13 wherein the step of analyzing the output of the microphone includes the step of comparing the output with a model of a normal behavior of the system.
15. A method according to claim 14 including the further step of generating an alarm or an alert if the output deviates from the model by more than a pre-defined limit.
16. A method according to claim 5 further including the step of providing the microphone in an under-cowl location.
17. A method according to claim 5 wherein the bleed valves are configured such that the sound produced by each bleed valve is, for a given pressure differential across the valve, a tone of substantially uniform pitch.