FR3155576A1 - System for measuring axial and radial clearance at the tip of a turbomachine blade - Google Patents

Abstract

The present disclosure relates to a rotor blade (31) of a turbomachine component, an axial direction being defined by an axis of rotation of the rotor, a radial direction being defined as any direction perpendicular to the axial direction and passing through the axis of rotation of the rotor, a radially external surface (9) at the tip of the blade (31) having an axially upstream lip (5) and an axially downstream lip (6) in a gas flow direction in the axial direction in the turbomachine component when the turbomachine component is in operation, a plurality of targets (7) being arranged in relief on the radially external surface (9) of the blade between the axially upstream lip and the axially downstream lip of the blade, at least two of the targets (7) not being arranged in parallel directions. Figure for abstract: Fig. 3

Description

System for measuring axial and radial clearance at the tip of a turbomachine blade

The present disclosure relates to the measurement of blade displacements during the operation of a turbomachine. More particularly, it relates to a turbomachine component provided with a blade displacement measuring system, as well as a method for measuring such displacements.

STATE OF THE ART

A turbomachine has a main direction extending along a longitudinal axis, and typically comprises, from upstream to downstream in the direction of gas flow, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, and a low-pressure turbine.

By convention, in the present application, the terms "upstream" and "downstream" are defined in relation to the direction of air circulation in the turbine, i.e. from left to right on the FIG. 1 . Similarly, by convention in the present application, the terms "inner" and "outer", and "internal" and "external" are defined radially relative to the axis of the turbomachine. For a given turbomachine component, such as for example a compressor or a turbine, the component extends in a principal direction, also called an axial direction, defined along a longitudinal axis. A radial direction is defined as any direction perpendicular to the longitudinal axis and passing through it. A circumferential direction is defined as any direction perpendicular to the longitudinal axis and not passing through it.

Referring to the FIG. 1 attached, we can see an example of a turbine 1 for a turbomachine conforming to the state of the art.

This turbine comprises several successive stages, each comprising a downstream distributor 2 and an upstream bladed wheel 3.

Each distributor 2 comprises a radially internal annular platform 21 and a radially external annular platform 22 coaxial, between which extend radial or substantially radial blades 23, regularly spaced over the entire circumference of said platforms.

Each distributor 2 is attached radially outwards to an external casing 4 of the turbine.

The set of 2 distributors forms the fixed part of the engine called the "stator".

Each bladed wheel 3 comprises a disc 30 carrying at its external periphery radial or substantially radial blades 31, the discs 30 of the different wheels being connected coaxially to each other and to a drive shaft by appropriate means, so as to form the "rotor" of the turbine (see FIG. 1 ).

In order for the rotor blades 31 to be free to rotate around the axis of the rotor disk 30, a clearance is provided in the radial direction between the rotor blades 31 and a radially inner surface of the outer casing 4. The value of this radial clearance may vary during operation of the turbomachine, in particular when the blades 31 undergo a thermal expansion different from that of the outer casing 4. However, the value of this clearance must be within ranges of values which are defined during the design phase of the turbomachine. Thus, it is necessary to have both sufficient radial clearance to ensure that the blades 31 do not damage the inner surface of the casing 4, and low enough to avoid excessive aerodynamic losses. During the construction and maintenance of the turbomachine, the radial clearances between the rotor blades 31 and the external casing 4 can be compared with the ranges of values provided for in the design, in order to ensure the correct positioning of the blades relative to the casing.

Similarly, during operation of the turbomachine, the rotor blades 31 can move axially, and it is necessary to know the value of this axial displacement so as to ensure that it remains within a predetermined value range during the design of the turbomachine.

Several methods for measuring radial clearances and axial displacements of blades are commonly used in the state of the art.

To detect a variation in axial displacements, it is possible to use sensors located in front of the blades. These sensors detect an electrical capacitance that can be converted into a distance between the blade and the sensor. Due to the size of such sensors, it is difficult to integrate them into the external casing, so they are generally placed on a shaft of the turbomachine. The axial displacement detected by these sensors therefore does not correspond to the displacement at the blade tip, which we wish to measure, and it is necessary to extrapolate an axial displacement value at the blade tip from the displacement measured by the sensor, which is necessarily less precise than directly measuring the desired displacement.

To overcome this problem, it is known to place, in addition to or instead of the axial clearance sensor, a wear indicator made of abradable material on the internal surface of the casing, the blades then eroding the wear indicator by mechanical friction during operation of the turbomachine. However, such a method has limited accuracy depending on the type of abradable material used. In addition, it is only possible to know the axial displacement after disassembly of the turbine to inspect the abradable use indicator, and the axial displacement of the blades remains unknown during the time interval between two disassemblies. It is therefore notably impossible to know the axial displacement corresponding to a given flight phase of the turbomachine.

To detect a variation in radial clearance, a known method consists of placing a distance sensor opposite a wiper of the turbine blade, on the turbine casing. The sensor then detects an electrical capacitance, which can be converted into a distance corresponding to a radial air gap between the wiper and the sensor. It is necessary to provide a projection or a recess on the wiper, so as to allow the sensor to detect the passage of the blade due to the variation in the air gap distance. The irregularity represented by this projection or this recess causes undesirable aerodynamic losses, and therefore a reduction in the performance of the turbomachine. In addition, if an axial displacement of the blades has occurred during operation of the turbine, the radial clearance sensor may no longer be located opposite the same part of the blades and the measurement made by the sensor is affected. When the axial displacement is significant, a licker located axially upstream or downstream of the licker for which the sensor measures the axial clearance – for example a licker belonging to a blade of a stage further upstream or further downstream of the turbomachine component – can also interfere with the measurement made by the sensor.

In addition, the integration of two separate sensors for measuring radial clearance and axial displacement of the blades uses a significant portion of the space available in the turbine.

An aim of the invention is to enable the measurement of both a radial clearance between rotor blades and an external casing of a turbomachine component, and an axial displacement of the blades.

Another aim of the invention is to enable more precise measurement of the axial displacement at the blade tip.

Another aim of the invention is to enable more precise measurement of the radial clearance despite axial displacement of the blades.

Another aim of the invention is to enable measurement of axial displacement of the blades without having to dismantle the turbomachine.

Another aim of the invention is to reduce the integration space required for measuring the movements of the blades in the turbomachine.

In order to achieve the above-mentioned objectives, there is provided, according to a first aspect of the present disclosure, a rotor blade of a turbomachine component, an axial direction being defined by an axis of rotation of the rotor, a radial direction being defined as any direction perpendicular to the axial direction and passing through the axis of rotation of the rotor, a radially external surface at the tip of the blade having an axially upstream lip and an axially downstream lip in a gas flow direction in the axial direction in the turbomachine component when the turbomachine component is in operation, a plurality of targets being arranged in relief on the radially external surface of the blade between the axially upstream lip and the axially downstream lip of the blade, at least two of the targets not being arranged in parallel directions.

This means that both the radial clearance between the blades and the internal surface of the casing and the axial displacement of the blades can be measured precisely and in real time using the same sensor, with limited integration space in the turbomachine.

According to one embodiment, a projection of the targets onto the radially outer surface extends substantially straight.

According to one embodiment, the targets are parts projecting from the radially outer surface towards the radially inner surface of the outer stator casing.

According to one embodiment, at least one of the targets extends substantially in the axial direction.

According to one embodiment, a maximum thickness of the targets in the radial direction is at least 2.5 millimeters.

According to one embodiment, at least one of the targets has a first surface in direct contact with the radially external surface of the blade, the first surface extending substantially in the radial direction.

• un carter externe de stator, et
• un rotor muni d’une aube telle que décrite précédemment, le rotor étant mobile par rapport au stator,

Another aspect of the present disclosure relates to a turbomachine component comprising:

• an external stator casing, and
• a rotor provided with a blade as described above, the rotor being movable relative to the stator,

the turbomachine component further comprising a capacitive sensor arranged on a radially internal surface of the external casing, the capacitive sensor being arranged so as to allow the measurement of a distance between the capacitive sensor and each target at least during a passage of the target opposite the capacitive sensor in the radial direction.

According to one embodiment, the turbomachine component is chosen from a compressor stage or a turbine stage.

According to one embodiment, the capacitive sensor comprises a cylindrical electrode.

Another aspect of the present disclosure relates to a turbomachine comprising a blade as described above or a turbomachine component as described above.

Another aspect of the present disclosure relates to an aircraft comprising a turbomachine as described above.

DESCRIPTION OF FIGURES

Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and not limiting, and which must be read in conjunction with the attached drawings in which:

There FIG. 1 schematically illustrates a turbomachine component according to the state of the art;

There FIG. 2 schematically illustrates a view along a circumferential direction of a blade tip of a turbomachine component according to one aspect of the present disclosure;

There FIG. 3 schematically illustrates a view in a radial direction, and from a radially external position, of a blade tip of a turbomachine component according to an aspect of the present disclosure;

There FIG. 4 is a graph representing a time evolution of the distance between a capacitive sensor and a blade tip during rotation of the blade for two distinct axial positions of the blade relative to the capacitive sensor;

There FIG. 4 is a graph representing a time evolution of the distance between a capacitive sensor and a blade tip during blade rotation for two distinct values of a radial clearance between the capacitive sensor and the blade tip;

There FIG. 5 schematically represents an aircraft equipped with a turbomachine component according to one aspect of the present disclosure.

Throughout the figures, similar elements have identical references.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

According to a first aspect, a turbomachine comprises a plurality of components, including in particular one or more compressors and one or more turbines. FIG. 1 represents such a turbomachine component, namely a turbine. However, a turbomachine component as defined herein may include any part of a turbomachine comprising a static part and a rotating part relative to the static part, and for which it may be necessary to measure a variation in axial displacements and radial clearances of the rotating part relative to the static part. The rotating part may also, without limitation, be a fan stage, a shaft, a disc, a movable ring or a shroud.

Figures 2 and 3 show a radially external surface 9 at the top of a blade 31 of a bladed wheel 3 of a turbine or a turbomachine compressor. The radially external surface comprises a wiper 5 arranged axially upstream and a wiper 6 arranged axially downstream – hereinafter “upstream wiper” and “downstream wiper” respectively, the two wipers 5, 6 extending towards an internal surface of an external casing 4 of the turbomachine component.

A capacitive sensor 8 is arranged fixed relative to the internal surface of the external casing 4. The capacitive sensor 8 comprises at least one electrode, and is connected to information processing means. The capacitive sensor can detect a passage time of a target as well as a distance between the target and its electrode. The radially external surface 9 of the blade 31 comprises at least two targets 7, extending in relief in the space between the upstream 5 and downstream 6 wipers, these two targets not being parallel. At least a part of each target 7 has a radial distance with the capacitive sensor 8, when this part of the target 7 is opposite the capacitive sensor 8, different from a radial distance between the radially external surface 9 of the blade and the capacitive sensor 8. Thus, during a rotation of the rotating part of the turbomachine component, the capacitive sensor 8 detects a variation in radial distance when a target 7 passes opposite the capacitive sensor 8.

According to a first embodiment, shown in Figures 2 and 3, the raised targets 7 are parts projecting from the radially external surface 9, that is to say that at least a part of each target 7 has a radial distance with the capacitive sensor 8, when this part of the target 7 is located opposite the capacitive sensor 8, less than the radial distance between the radially external surface 9 of the blade and the capacitive sensor 8. This embodiment does not require making a recess in the radially external surface 9, and therefore makes it possible to minimize aerodynamic leaks between the external casing 4 and the blade 31. Thus, the impact of the presence of the targets 7 on the aerodynamic performance of the turbomachine component is minimized. For this embodiment, the passage of a target 7 in front of the capacitive sensor 8 is identified by means of a temporary reduction in the radial distance between the tip of the blade and the sensor when the target 7 passes in front of the sensor 8.

The targets 7 may comprise two first surfaces 13 in direct contact with the radially external surface 9 and a second surface 14 joining the two first surfaces 13. The second surface 14 may extend substantially parallel to the radially external surface 9.

According to another embodiment, the raised targets 7 are recesses made by removing material from the radially external surface 9, that is to say that at least a part of each target 7 has a radial distance with the capacitive sensor 8, when this part of the target 7 is located opposite the capacitive sensor 8, greater than the radial distance between the radially external surface 9 of the blade and the capacitive sensor 8. For this embodiment, the passage of a target 7 in front of the capacitive sensor 8 is identified by means of a temporary increase in the distance between the tip of the blade and the sensor when the target 7 passes in front of the sensor 8.

The capacitive sensor 8 is configured to measure a radial clearance 11 between its electrode and the targets 7. A variation in radial clearance 11 is therefore seen by the capacitive sensor 8 as being a variation in the distance between a target 7 and the electrode of the capacitive sensor 8. Whatever the nature of the raised targets 7 – that is to say whether they are parts projecting from the radially external surface 9 or recesses made in the radially external surface 9, as described previously – a reduction (respectively increase) in the radial clearance 11 is identified by the capacitive sensor 8, because the distance between a target 7 and the capacitive sensor 8 when the target 7 passes in front of the sensor 8 decreases (respectively increases).

There FIG. 4 also illustrates this phenomenon. Curves I and II represent the variation in radial distance between the capacitive sensor 8 and the tip of the blade 31 when the blade is in motion. Curve I corresponds to the case where the radial clearance 11 between the tip of the blade 31 and the capacitive sensor 8 takes a first value, while curve II corresponds to the case where the radial clearance 11 between the tip of the blade 31 and the capacitive sensor 8 takes a second value, lower than the first value – the blade 31 having moved closer to the external casing 4.

Furthermore, an axial displacement 10 of the blade 31 has the consequence that the capacitive sensor 8 is not located opposite the same part of the targets 7. Indeed, the electrode of the sensor has an axial position relative to the targets which can vary between the upstream lip 5 and the downstream lip 6. When this relative axial position varies, due to the fact that the targets 7 do not extend parallel to each other, the circumferential distance 12 between the two targets 7 seen by the capacitive sensor 8 necessarily changes. More specifically, it is possible to establish a direct correlation between this circumferential distance 12 and the axial position of the targets 7, so that an axial displacement 10 of the blades can be precisely measured, both upstream and downstream.

For example, in reference to the FIG. 3 , two targets 7 extend on the radially external surface 9 with a circumferential distance 12 increasing between them from upstream to downstream. If the capacitive sensor 8 is located opposite a first axial position P _a1 of the radially external surface 9, the circumferential distance 12 has a value 12.1. If, during operation of the turbomachine component, the relative axial position of the capacitive sensor 8 with respect to the radially external surface 9 changes so that the capacitive sensor 8 comes to be located opposite a second axial position P _a2 of the radially external surface 9, the circumferential distance 12 between the two targets 7 then has a value 12.2, greater than the value 12.1. The duration between the successive passage of the two targets 7 in front of the electrode is therefore longer at the second axial position P _a2 than at the first axial position P _a1 , the variation of this duration making it possible to deduce the relative axial displacement of the blade 31 with respect to the capacitive sensor 8.

There FIG. 4 also illustrates this phenomenon. Curves I and II represent the variation in radial distance between the capacitive sensor 8 and the tip of the blade 31 when the blade is in motion. Curve I corresponds to the case where the capacitive sensor 8 is at the first axial position P _a1 , while curve II corresponds to the case where the capacitive sensor 8 is at the second axial position P _a2 . It can be seen that, for the second axial position P _a2 , the passage time between the two targets 7 is longer than for the first axial position P _a1 .

Thus, the assembly formed by the capacitive sensor 8 and the targets 7 makes it possible to know both the axial displacement 10 of the blades 31 relative to the external casing 4, and the radial clearance 11 between the sensor 8 and the tip of the blades 31. This assembly occupies a reduced space in the turbomachine component, compared with systems comprising separate components for measuring the radial clearance 11 and the axial displacement 10. No abradable material is necessary to know the variation of the radial clearance 11. In addition, the capacitive sensor 8 can be chosen with a predetermined frequency so as to obtain measurements of the axial displacement 10 and the radial clearance 11.

A projection of the targets 7 onto the radially outer surface 9 may extend substantially straight, so that there is a linear variation of the circumferential distance 12 between two targets 7 along the axial direction. In this case, a main axis X7 of each target 7 defines with the axial direction an angle α, preferably between 0° and 80°, preferably 0° to 45°. It is necessary to avoid being close to 90° because we end up with a target 7 in the plane perpendicular to the motor axis and we can no longer measure the speed of the rotor, we only measure an axial position (which is either the axial position of the capacitive sensor 8, or a different position). The closer the angle α is to 90°, but different from 90°, the worse the measurement accuracy is because the dimension of the target 7 along the circumferential direction becomes very large compared to its effective width. But the targets are not necessarily placed symmetrically with respect to the axial direction, and there is no point in being symmetrical. Rather, we are trying to adapt to the space available at the blade tip, on the radially external surface 9 or on the rotor portion. It is possible to have a target 7 extending in the axial direction and a target having a non-zero angle α with the axial direction. It therefore seems interesting to us to discuss the angle between two targets 7. The angle between the two targets 7 must be greater than at least 10° to have an effective axial displacement measurement 10 (the targets 7 must move away in the axial direction in a clear manner to associate an axial displacement 10 with a difference between two targets). The space on a blade, on a radially external surface 9 or on a portion of the rotor may be limited, in which case going beyond an angle between two targets 7 greater than 160°, preferably 135°, does not seem relevant. An angle between 45 and 90° makes it easier to interpret the measurements so that the circumferential dimension of the targets remains acceptable.

A maximum thickness 16 of the targets 7 in the radial direction may be at least 2.5 millimeters. Thus, the variation of the radial clearance 11 between, on the one hand, the electrode 8 and the radially external surface 9 and, on the other hand, between the electrode 8 and the targets 7 is sufficiently large to ensure the detection of the passage of the targets 7 by the electrode 8.

A maximum dimension 15 of the targets 7 in the circumferential direction may furthermore be between 2 millimeters and 10 millimeters. The maximum dimension 15 is chosen in particular as a function of the frequency of the capacitive sensor 8 and the rotational speed of the blade 31, as well as the dimensions of the blade 31, of the radially external surface 9 and of the rotor comprising the blade 31.

In particular, it can be considered that a target detection is validly confirmed when at least 3, preferably at least 5 successive target detections are carried out by the capacitive sensor 8.

The use of a capacitive sensor 8 of sufficient frequency allows the measurement of the radial clearance 11 and the axial displacement 10 of the blades in real time. The frequency of the capacitive sensor 8 can in particular be between 10 Hz and 400 Hz. In particular, it is therefore possible to study the variations in these distances during operation of the turbomachine, depending on its speed. It is not necessary to dismantle the turbomachine component to know these variations.

According to one embodiment, the sensor 8 comprises a cylindrical electrode. In comparison with a non-circular electrode which has edges, for example a polygonal electrode, this avoids edge effects at the corners of the electrode, which could disturb the signal that it measures. Such edge effects are particularly problematic because both an axial displacement 10 and a radial clearance 11 are measured, these effects can therefore occur in several directions.

According to one embodiment, at least one of the targets 7 extends substantially in the axial direction, that is to say that the angle α between the axis X7 of said target and the axial direction is 0°. At least one other of the targets 7 then extends in a direction not parallel to the axial direction, with a non-zero angle α. When the circumferential distance between two successive blade tips is small, this makes it possible to reduce as much as possible the circumferential distance necessary for the integration of the targets 7.

It is also possible to provide that the first surface 13 of the targets 7 extends substantially in the radial direction. This also facilitates the detection of the targets 7 by the electrode 8, by ensuring an abrupt variation of the radial clearance 11 seen by the electrode 8.

According to one embodiment, and as shown in the FIG. 3 , the targets 7 extend substantially from a downstream surface 51 of the upstream lip 5 to an upstream surface 61 of the downstream lip 6. Thus, the targets 7 cover, in the axial direction, all the space available between the lips 5, 6 on the radially external surface 9, and the capacitive sensor 8 can detect the passage of the targets 7 regardless of the axial position at which it is located in the space defined between the two lips 5, 6.

Another aspect of the present disclosure relates to a blade 31 comprising targets 7 as defined previously. Such a blade can be used in a turbomachine component provided with an external casing 4 on an internal surface of which a capacitive sensor 8 is arranged, the capacitive sensor 8 then allowing the measurement of the radial clearance 11 between the blade tip and the capacitive sensor 8 as well as the measurement of the axial displacement 10 of the blade 31.

Another aspect of the present disclosure relates to a turbomachine 18 comprising a turbomachine component as described above. This may in particular be a compressor or turbine stage.

Another aspect of this disclosure, illustrated in FIG. 5 , relates to an aircraft 17 equipped with a turbomachine 18 as described in the preceding paragraph.

Claims (11)

Rotor blade (31) of a turbomachine component,
an axial direction being defined by an axis of rotation of the rotor, a radial direction being defined as any direction perpendicular to the axial direction and passing through the axis of rotation of the rotor,
a radially external surface (9) at the top of the blade (31) having an axially upstream lip (5) and an axially downstream lip (6) in a gas flow direction in the axial direction in the turbomachine component when the turbomachine component is in operation,
a plurality of targets (7) being arranged in relief on the radially external surface (9) of the blade between the axially upstream wiper and the axially downstream wiper of the blade, at least two of the targets (7) not being arranged in parallel directions. A blade according to claim 1, wherein a projection of the targets (7) onto the radially outer surface (9) extends substantially straight. Blade according to any one of claims 1 and 2, in which the targets (7) are parts projecting from the radially external surface (9) towards the radially internal surface of the external stator casing (4). Blade according to any one of claims 1 to 3, in which at least one of the targets (7) extends substantially in the axial direction. Blade according to any one of claims 1 to 4, in which a maximum thickness (16) of the targets (7) in the radial direction is at least 2.5 millimeters. Blade according to any one of claims 1 to 5, in which at least one of the targets (7) has a first surface (13) in direct contact with the radially external surface (9) of the blade, the first surface (13) extending substantially in the radial direction. Turbomachine component comprising:

• an external stator casing (4), and
• a rotor provided with a blade (31) according to any one of claims 1 to 6, the rotor being movable relative to the stator,

the turbomachine component further comprising a capacitive sensor (8) arranged on a radially internal surface of the external casing (4), the capacitive sensor (8) being arranged so as to allow the measurement of a distance between the capacitive sensor (8) and each target (7) at least during a passage of the target (7) opposite the capacitive sensor (8) in the radial direction. A turbomachine component according to claim 7, the turbomachine component being selected from a compressor stage or a turbine stage. A turbomachine component according to any one of claims 7 and 8, wherein the capacitive sensor (8) comprises a cylindrical electrode. A turbomachine (18) comprising a blade according to any one of claims 1 to 6 or a turbomachine component according to any one of claims 7 to 9. Aircraft (17) comprising a turbomachine (18) according to claim 10.