Apparatus and method for measuring gas flow through a rotary seal

A method of measuring a flow rate of a first fluid through a rotary seal of a gas turbine engine comprising controlling a probe flow of a second fluid at an intra-seal cavity and measuring a pressure change in the first fluid caused by the probe flow.

This invention claims the benefit of UK Patent Application No. 1220268.5, filed on 12 Nov. 2012, which is hereby incorporated herein in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention relate to an apparatus and method for measuring fluid flow through a rotary seal. In particular, they relate to an apparatus and method for measuring fluid flow through a rotary seal in gas turbine engines.

BACKGROUND TO THE INVENTION

Rotary seals are placed between two parts, one or both of which may rotate. Rotary seals may be used to seal the air system of a gas turbine engine.

Measurement of seal leakage flow in rotary seals is particularly difficult due to the multitude of inlet and outlet flow paths on each side of the seal.

Measurement of mechanical clearance of seal parts may be used to obtain information relating to the seal leakage flow, however such measurements have the disadvantage of requiring bulky probes to be introduced into the gas turbine engine. The rotary seal parts are unsuitable for mounting such probes and so the probes need to be mounted on nearby components which support the seal, introducing uncertainty into the clearance measurement due to the mechanical behavior of the components.

BRIEF DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

According to a first aspect of the invention there is provided a method of measuring a flow rate of a first fluid flow, the first fluid flow flowing through a rotary seal of a gas turbine engine comprising: applying a probe flow of a second fluid to an intra-seal cavity; controlling the probe flow at the intra-seal cavity; and measuring a pressure change in the first fluid flow through the rotary seal caused by the probe flow of the second fluid.

This provides an advantage that a direct measurement of pressure change within a cavity can be made, which relates to the seal leakage flow.

According to a second aspect of the invention there is provided a gas turbine engine comprising: a first cavity and a second cavity, whereby during operation of the gas turbine engine the first cavity receives a flow of a first fluid at a first pressure and the second cavity receives the first fluid flow at a second pressure, the first pressure being higher than the second pressure; a rotary seal separating the first cavity from the second cavity, comprising a first member, a second member radially proximal to the first member, that rotates relative to the first member during operation of the gas turbine engine and at least one intra-seal cavity formed between the first member and the second member; a probe flow control system configured to control a probe flow of a second fluid at the at least one intra-seal cavity; and a sensor configured to measure a pressure change in the first fluid flow as it flows through the rotary seal caused by the probe flow of the second fluid.

According to a third aspect of the invention there is provided a first member of a rotary seal for a gas turbine engine comprising: a sealing surface configured to form a seal with a second member of the rotary seal that rotates relative to the first member during operation of the gas turbine engine, the second member being radially proximal to the first member, wherein the seal comprises at least one intra-seal cavity formed between the sealing surface and the second member; and multiple apertures in the sealing surface configured to provide a probe flow of a second fluid and to measure a pressure change in a flow of a first fluid as it flows through the rotary seal at the at least one intra-seal cavity caused by the probe flow of the second fluid.

The figures illustrate a method of measuring a flow rate of a first fluid through a rotary seal20of a gas turbine engine110comprising, controlling a probe flow of a second fluid34at an intra-seal cavity22, and measuring a pressure change in the first fluid caused by the probe flow of the second fluid34.

Referring toFIG. 1, a gas turbine engine is generally indicated at110and comprises, in axial flow series, an air intake111, a propulsive fan112, an intermediate pressure compressor113, a high pressure compressor114, a combustor115, a turbine arrangement comprising a high pressure turbine116, an intermediate pressure turbine117and a low pressure turbine118, and an exhaust nozzle119.

The gas turbine engine110operates in a conventional manner so that air entering the intake111is accelerated by the fan112which produces two air flows: a first air flow into the intermediate pressure compressor113and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor114where further compression takes place.

The compressed air exhausted from the high pressure compressor114is directed into the combustor115where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines116,117and118before being exhausted through the nozzle119to provide additional propulsive thrust. The high, intermediate and low pressure turbines116,117and118respectively drive the high and intermediate pressure compressors114and113and the fan112by suitable interconnecting shafts126,128,130.

Rotary seals20may be used to separate one section of the gas turbine engine110from another section.

FIG. 2illustrates a rotary seal20and a system30for measuring fluid leakage flow at the rotary seal20, according to a first embodiment of the invention. The system30comprises a first cavity10and a second cavity12. During operation of the gas turbine engine, the first cavity10receives a first fluid at a first pressure and the second cavity receives the first fluid at a second pressure, the first pressure being higher than the second pressure. A rotary seal20separates the first cavity10from the second cavity12.

In operation, the first fluid in the first cavity10will tend to flow towards the second cavity12. A fluid leakage flow14traverses through the rotary seal20from the higher pressure first cavity10to the lower pressure second cavity12during operation of the gas turbine engine110.

The rotary seal20comprises a radially outer, first member24, a radially inner, second member26that rotates relative to the first member24during operation of the gas turbine engine110and a series of intra-seal cavities22formed between a sealing surface25of the first member24and protrusions28, or fins, in the second member26. The protrusions28inFIG. 2are shown with a truncated triangular cross-section. However, protrusions28with other cross-sectional geometries may be used, such as those with square, rectangular or triangular cross-sections. Protrusions28with complex cross-sectional shapes could be used.

The rotary seal20may form a labyrinth seal where the fluid leakage flow14between the higher pressure, first cavity10and the lower pressure, second cavity12is forced to traverse through a series of clearance gaps29formed between the series of protrusions28or fins and the closely located sealing surface25. Each protrusion28may form a knife-edge seal with the sealing surface25. As the fluid leakage flow14expands as it passes through each clearance gap29, between each protrusion28and the sealing surface25, the flow is disturbed causing a reduction in fluid leakage flow14.

AlthoughFIG. 2illustrates a rotary seal20with two intra-seal cavities22, formed by three protrusions28on the inner, second member26, it will be appreciated that the rotary seal20may comprise any number of intra-seal cavities22formed between one or more sealing surfaces25of the outer, first member24and a plurality of protrusions28on the inner, second member26.

In the example ofFIG. 2, the outer, first member24of the rotary seal20is stationary and the inner, second member26of the rotary seal20is rotatable about an axis. The protrusions28on the inner, second member26extend from the body of the inner, second member26in a radial direction, such that the sealing surface25of the outer, first member24and the protrusions28of the inner, second member26are separated by a clearance gap29. The clearance gap29between the tip of a protrusion28and the corresponding sealing surface25of the outer, first member24may be in the order of 0.5 mm. Alternatively the clearance gap29between the tip of a protrusion28and the corresponding sealing surface25of the outer, first member24may be smaller or larger than a 0.5 mm separation. Each of the protrusions28may be positioned at a different location along the length of the axis. Each protrusion28extends circumferentially, forming a ring, separated from the sealing surface25of the outer, first member24by a clearance gap29. The clearance gap29between the tip of each protrusion28and a corresponding sealing surface25of the outer, first member24may be different or may be the same as the clearance gap29for one or more of the other protrusions28. The separation between adjacent protrusions28along the axis defines an annular intra-seal cavity22.

The system30further comprises a probe flow control system32. In the example ofFIG. 2the probe flow control system32is configured to control a probe flow of a second fluid34at each of the intra-seal cavities22.

In various example embodiments, the probe flow control system32may be configured to control a probe flow of the second fluid34at one or more intra-seal cavities22and at one or more locations within an intra-seal cavity22.

The probe flow34is a flow of the second fluid at the intra seal cavity22additional to the normal fluid leakage flow14traversing through the rotary seal20from the higher pressure, first cavity10to the lower pressure, second cavity12during operation of the gas turbine engine110.

The probe flow of the second fluid34may be a flow into or away from the intra-seal cavity22. In the embodiment illustrated inFIG. 2, the probe flow of gas34is a flow into the intra-seal cavity22.

The probe flow control system32is configured to control a probe flow of the second fluid34at any one of a plurality of intra-seal cavities22at a time.

The probe flow control system32may comprise a valve, which may be a remotely controllable valve such as an electric solenoid valve, and a flow measurement device, such as a differential pressure measurement device, an example of which is an orifice plate, in order to control and measure the probe flow of the second fluid34.

The system30further comprises a measurement system40. In the example ofFIG. 2the measurement system40is configured to measure fluid pressure at each of the intra-seal cavities22.

In various embodiments the measurement system40may be configured to measure fluid pressure at the one or more intra-seal cavities22and at one or more locations within an intra-seal cavity22.

The measurement system40uses pressure sensors42configured to measure a fluid pressure change in the first fluid caused by the probe flow of the second fluid34. In the example ofFIG. 2, one pressure sensor42is used in each intra-seal cavity22to measure pressure within that intra-seal cavity22. The pressure sensor42may be located in, or remote from (but interconnected to), the intra-seal cavity22.

Additionally, a temperature sensor44may be present and configured to measure a temperature change within the intra-seal cavity22. The temperature change may be responsive to the probe flow of the second fluid34.

In order to facilitate the transfer of a probe flow of gas34at the intra-seal cavity22, the intra-seal cavity22communicates with a pressure source50, which may be a source of atmospheric pressure, high pressure or negative pressure.

In the example ofFIG. 2, a conduit such as a pipe33is located through the outer, first member24defining, at one end, an aperture35in a sealing surface25of the outer, first member24and defining, at the other end, an interface37for transfer of the probe flow of the second fluid34from a regulated store of compressed gas50via the probe flow control system32and a meter36configured to measure the flow rate of the probe flow34. Typically the internal diameter of pipe33will be in the region of 5 mm or less in order to apply a sufficient flow rate of the second fluid34to compete with the gas leakage flow14and therefore influence the pressure in the intra-seal cavity22sufficiently to be measured by a pressure sensor42. However different internal pipe33diameters may be used depending on the magnitude of the gas leakage flow14. A smaller fluid leakage flow14may allow a smaller internal diameter pipe33to be used and a larger fluid leakage flow14may require a larger internal diameter pipe33.

FIG. 3shows a rotary seal20according to a second embodiment of the invention. The rotary seal20ofFIG. 3comprises an outer, first member24, an inner, second member26that rotates relative to the outer, first member24during operation of the gas turbine engine110and a series of intra-seal cavities22formed between a stepped sealing surface25of the outer, first member24and a stepped arrangement of protrusions28on the inner, second member26. The stepped sealing surface25of the outer, first member24and a stepped arrangement of protrusions28on the inner, second member26forms a stepped seal arrangement. In contrast, the arrangement of the sealing surface25of the outer, first member24and the arrangement of protrusions28on the inner, second member26shown inFIG. 2illustrates a linear seal arrangement.

The embodiment ofFIG. 3illustrates two intra-seal cavities22, formed by three protrusions28from the inner, second member26. It will be appreciated that the rotary seal20may comprise any number of intra-seal cavities22formed between a sealing surface25of the outer, first member24and a plurality of protrusions28in the inner, second member26.

The stepped arrangement of the sealing surfaces25, the protrusions28and the intra-seal cavities22, provides a more tortuous path for the fluid leakage flow14, which may reduce overall fluid leakage in the system30, by introducing additional vortices into the fluid leakage flow14.

The flow chart ofFIG. 4illustrates a method for measuring fluid flow through a rotary seal20, according to the invention, and in particular a method for measuring fluid flow through a rotary seal20of a gas turbine engine110, according to the invention.

The method of measuring fluid flow through a rotary seal20of a gas turbine engine110comprises, in block200, the step of controlling a probe flow of the second fluid34at an intra-seal cavity22and, in block210, the step of measuring a pressure change in the first fluid caused by the probe flow of the second fluid34.

For a given amount of the second fluid introduced into or extracted from an intra-seal cavity22, the change in fluid pressure measured will depend on the fluid leakage flow14at the intra-seal cavity22. The variation of intra-seal cavity22pressure change with a known applied probe flow of the second fluid34may be calibrated using computational fluid dynamics, through experimental simulation or by another calibration method. Alternatively the system30could be configured to perform measurements over a period of time, with an initial measurement or series of measurements providing a baseline value of the fluid pressure change responsive to the probe flow of the second fluid34to which subsequent measurements are compared. Such a system would not necessarily require calibration. The deviation in the measurement from the baseline could be used to flag up a requirement for maintenance or an emergency shutdown for example.

The probe flow of the second fluid34may be measured using a meter36, such that a known flow rate of the second fluid34may be applied at the intra-seal cavity22. The flow rate of the second fluid34may be controlled in part by a valve, which may be a remotely controlled valve such as an electric solenoid valve, and the flow rate of the second fluid34may be measured using a flow measurement device such as an orifice plate.

A probe flow of the second fluid34may be controlled at any one of a plurality of intra-seal cavities22.

The probe flow of the second fluid34may be modulated in time such that it is alternately turned on or off, for example by applying a high pressure probe flow of the second fluid34followed by cessation of the application of the probe flow34. Alternatively, the probe flow of gas34may be modulated in time by applying a negative pressure probe flow34followed by cessation of the application of the probe flow34. Alternatively, the probe flow of the second fluid34may be modulated in time by applying a probe flow34at atmospheric pressure followed by cessation of the application of the probe flow34.

Alternatively the probe flow of the second fluid34may be modulated between two or more different pressure levels of an applied probe flow34. These pressures could be different high pressures or different negative pressures, or a combination of high, negative and atmospheric pressures.

The probe flow of the second fluid34may be additionally or alternatively modulated in space. Different probe flows of the second fluid34may be applied to different circumferential points around the rotary seal20. In one example embodiment the probe flow of the second fluid34may be modulated such that different probe flows34may be applied to different circumferential points around an intra-seal cavity22of the rotary seal20at different times. The different probe flows34may comprise the same pressures applied at the different locations around the rotary seal20in order to obtain spatial information relating to the operation of the rotary seal20.

Alternatively, or in addition to the circumferential spatial modulation, different probe flows of the second fluid34may be applied to different axial locations along the rotary seal20. In one example embodiment the probe flow of the second fluid34may be modulated such that different probe flows34may be applied to different intra-seal cavities22of the rotary seal20at different times. The different probe flows34may comprise the same pressures applied at the different locations along the rotary seal20in order to obtain spatial information relating to the operation of the rotary seal20.

The probe flow of the second fluid34may be intermittently provided such that measurements can be taken during the application of the probe flow34and after applying the probe flow34. A comparison of the pressure measurement at the intra-seal cavity22with and without the influence of the probe flow34can then be used to determine seal efficiency.

Alternatively measurements can be taken during pressurization and/or depressurization of the intra-seal cavity22by observing the rate of change of pressure during application of or following cessation of the application of a probe flow of the second fluid34. The rate of change of pressure may be calibrated with seal clearance using computational fluid dynamics, experimental simulation or by another calibration method. Alternatively the system30could be configured to perform measurements over a period of time, with an initial measurement or series of measurements providing a baseline value of the gas pressure change responsive to the probe flow34to which subsequent measurements are compared. Such a system30would not necessarily require calibration. The deviation in the measurement from the baseline could be used to flag up a requirement for maintenance or an emergency shutdown for example.

The probe flow of the second fluid34may be provided at a controllable flow rate dictated by the operation of the probe flow control system32. A meter36may be used to measure the flow rate of the probe flow34applied at the intra-seal cavity22.

The gas pressure change responsive to the probe flow of the second fluid34may be measured at one or at multiple locations within the rotary seal20. InFIG. 2measurement of the gas pressure change responsive to the probe flow34is measured in each intra-seal cavity22, by a separate pressure sensor42.

The gas pressure change responsive to the probe flow of the second fluid34may be measured at one or at multiple locations within the intra-seal cavity22. InFIG. 2only one measurement location is shown in each intra-seal cavity22, however it is to be understood that multiple measurement locations may be provided around the circumference of one or more intra-seal cavity22.

Alternatively, or in addition, a gas pressure change responsive to the probe flow of the second fluid34may be measured at one or more locations in a further intra-seal cavity22different to the intra-seal cavity22that the probe flow34is applied to. For example, the measurement may be made in an adjacent intra-seal cavity22, or may be made in any of the intra seal cavities22of the rotary seal20.

Alternatively, or in addition, a temperature change responsive to the probe flow of the second fluid34may be measured. Such a temperature change may be due to thermodynamic effects of increasing or decreasing pressure in the intra-seal cavity22and/or may be due to the temperature of the probe flow34being at a different value to the fluid of the fluid leakage flow14.

A controller may be provided to control the operation of the system30. The controller may comprise a program which is executed on a processor. The program may be stored in a memory. Such a controller may be comprised in a computer.

The controller may control the flow rate of the probe flow of the second fluid34together with the operation of the probe flow control system32. The controller may additionally or alternatively control the operation of the measurement system40. The controller may receive measurement values from one or more pressure sensors42and/or one or more temperature sensors44. The controller may perform analysis on the measurement values. The analysis of the measurement values may provide information relating to the seal leakage flow14, and therefore provide information relating to the efficiency of the rotary seal20.

The method provided inFIG. 4may be carried out during testing of a gas turbine engine110. Alternatively or in addition it may be carried out during in-service operation of the gas turbine engine110.

FIG. 5shows an outer, first member24of a rotary seal20of a gas turbine engine110according to a third embodiment of the invention.

In the embodiment shown inFIG. 5, the outer, first member24of the rotary seal20of a gas turbine engine110comprises a sealing surface25configured to form a seal with an inner, second member26of the rotary seal20, and in particular form a seal with protrusions28on the inner, second member26of the rotary seal20, that rotates relative to the outer, first member24during operation of the gas turbine engine110. The rotary seal20comprises at least one intra-seal cavity22formed between the sealing surface25and the inner, second member26, and in particular formed between the sealing surface25and the protrusions28on the inner, second member26, of the rotary seal20. The outer, first member24of the rotary seal20comprises multiple apertures35,47in the sealing surface25configured to provide a probe flow of the second fluid34and to measure fluid pressure at an intra-seal cavity22.

In the embodiment ofFIG. 5, a conduit such as a pipe33is located through the outer, first member24defining, at one end, an aperture35in a sealing surface25of the outer, first member24and defining, at the other end, an interface37for transfer of the probe flow of the second fluid34from a source of atmospheric pressure, high pressure or negative pressure, such as a regulated store of compressed gas50, via a probe flow control system32and a meter36configured to measure the probe flow34.

A pressure sensor42may be configured to measure fluid pressure in the intra-seal cavity22. The pressure sensor42may be located within an aperture47in the body of the outer, first member24, as illustrated inFIG. 5, or may be located external to the outer, first member24. A pipe or conduit interconnects the intra-seal cavity22to the pressure sensor42via an aperture47. The internal diameter of the pipe or conduit interconnected with the pressure sensor42may be smaller than the internal diameter of the pipe33for the probe flow34. In one non-limiting example the internal diameter of the pipe or conduit interconnected with the pressure sensor42may be 1 mm, whilst the internal diameter of the pipe33providing the probe flow of the second fluid34is 5 mm. The internal diameter of the pipe or conduit interconnected with the pressure sensor42may be chosen such that the pneumatic speed of response is sufficient to allow the pressure at the pressure sensor42to stabilize and produce a steady measurement within each on-off cycle of the probe flow of the second fluid34. The speed of response may be determined by the length and internal diameter of the pipe or conduit interconnected with the pressure sensor42between the aperture47and the pressure sensor42.

The pressure sensor42may be located within a cavity or tapping in the body of the outer, first member24, or alternatively within the intra-seal cavity22. An electrical connection43may be used to transmit measurements from the pressure sensor42to control and measurement electronics, such as a controller as previously described.

A temperature sensor44may be configured to measure temperature in the intra-seal cavity22. The temperature sensor44may be located within the body of the outer, first member24, in a cavity or tapping, as illustrated inFIG. 5, or alternatively within the intra-seal cavity22. An electrical connection45may be used to transmit measurements from the temperature sensor44to control and measurement electronics, such as a controller as previously described.

The outer, first member24may comprise multiple apertures35in the sealing surface25, configured to provide multiple probe flows of the second fluid34at an intra-seal cavity22or at multiple intra-seal cavities22of the rotary seal20.

The outer, first member24may comprise multiple apertures47in the sealing surface25, through which pressure and/or temperature measurements can be made using pressure sensors42and/or temperature sensors44respectively.

In one example embodiment, multiple apertures35in the sealing surface25or the outer, first member24are provided, and are configured to provide multiple probe flows of the second fluid34at the intra-seal cavity22equidistantly spaced circumferentially around the intra-seal cavity22. Further multiple apertures47in the sealing surface25are provided, and are configured to allow pressure and/or temperature measurements to be made using pressure sensors42and/or temperature sensors44respectively. These further multiple apertures47may be disposed between the multiple apertures35for the multiple probe flows34. In one example embodiment the apertures47are equidistant from adjacent apertures35. In an alternative example embodiment the apertures47are in close proximity to an adjacent aperture35.

In an alternative example embodiment, the apertures35in the sealing surface25that are configured to provide multiple probe flows of the second fluid34may be the same apertures47which are configured to allow pressure and/or temperature measurements to be made. Such a configuration is possible when the rate of gas leakage flow14from an intra-seal cavity22is small compared to the volume of the intra-seal cavity22, such that the influence of the probe flow34lasts longer than the speed of response of the pipe or conduit interconnected with the pressure sensor42.

The sealing surface25of the outer, first member24may be formed of an abradable material which may be a soft abradable material. Alternatively a deformable material, such as a honeycomb structure, which may also be an abradable material, can be provided for the sealing surface25. The material of the sealing surface25allows for contact between the sealing surface25and the protrusions28, without causing significant damage to the protrusions28. The outer, first member24and/or the sealing surface25may be replaceable.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. For example although the leakage flow has been described in relation to a gas, the apparatus and method could equally be applied to leakage flow in relation to other fluids, such as a liquid.

Although the protrusion28on the inner, second member26has been described as extending from the body of the inner, second member26in a radial direction, it will be apparent that the protrusion may be canted from the radial axis such that the protrusion28is inclined into the fluid leakage flow14.

Although the rotary seal20and a system30for measuring fluid leakage flow at the rotary seal20have been described in relation to a gas turbine engine110, it will be apparent to the person skilled in the art that the rotary seal20and the system30for measuring fluid leakage flow at the rotary seal20may be applied to other power generation systems such as steam turbines and electrical generators or other systems comprising two parts between which there is relative rotation and for which sealing between the two parts is required. The method may also be applied to any other fluid flow measurements which involve intermediate cavities in the flow path, such as between the multiple sealing rings on a piston of a reciprocating engine.