FR3119195A1 - Measurement of the dynamic deformations of a moving blade - Google Patents

Abstract

The present invention relates to a blade (9) of a rotating impeller (8) of a turbomachine, typically a low pressure turbine impeller (7), comprising:- a blade (10) with an aerodynamic profile specific to spread out in an air stream; and - a heel (11), fixed to an outer radial end of the blade (10), the heel (11) comprising a platform (12) having an internal face (13) connected to the blade (10) and an external face (14) carrying at least one wiper (15);the blade (9) being characterized in that it further comprises a tongue (19) monolithic with the wiper (15) and extending axially from the wiper (15 ) away from the outer face (14) of the platform (12). Figure for the abstract: Fig. 1

Description

Measurement of the dynamic deformations of a moving blade

FIELD OF THE INVENTION

The present invention relates to the field of measuring dynamic deformations of a moving part. More specifically, the invention finds application in the measurement of dynamic deformations of a rotating part of a turbomachine, such as a moving wheel of a turbine.

STATE OF THE ART

A turbomachine generally comprises, from upstream to downstream in the direction of gas flow, a fan, a primary flow annular space and a secondary flow annular space which is externally with respect to the flow primary. The mass of air drawn in by the fan is therefore divided into a primary flow, which circulates in the primary flow space, and a secondary flow, which is concentric with the primary flow and circulates in the flow space. secondary. The fan (or propeller) can be faired and housed in a fan casing or in an unducted variant of the USF type (acronym for Unducted Single Fan, for unducted single fan). The fan blades can be fixed or have a variable pitch, the pitch being adjusted according to the phases of flight by a pitch change mechanism.

The primary flow space passes through a primary body comprising one or more compressor stages, for example a low pressure compressor (or booster) and a high pressure compressor, a combustion chamber, one or more turbine stages, for example a high pressure turbine and a low pressure turbine, and a gas exhaust nozzle. Typically, the high pressure turbine rotates the high pressure compressor via a first shaft, called the high pressure shaft, while the low pressure turbine rotates the low pressure compressor and the fan via a second shaft, called the low pressure shaft.

In a manner known per se, the turbines are made in the form of a succession of stages each comprising a wheel of moving blades (rotor) rotating in front of a wheel of fixed blades (stator, or distributors). Each mobile wheel comprises in particular a plurality of blades extending radially from the motor axis.

In operation, the moving blades resonate. Within the framework of the certification of the turbomachine, it is necessary to carry out an engine test of the stress analysis type (“stress survey” in English) to measure the vibratory stresses undergone by the blades and to demonstrate to the authorities that these stresses remain at acceptable levels for the mechanical strength of the blades.

The current practice consists in fixing extensometer type sensors on the blades to measure the dynamic deformations induced by the resonances of the blade. The blades being mobile, the measurements taken by the extensometers are transmitted to the test bench processors in real time using a telemetry system (by wireless means). However, the implementation and control of such a system is extremely complex and costly. In addition, the Applicant noticed that the telemetry system was sensitive to electromagnetic interference and to stresses from the entire turbomachine, which can significantly distort the measurements.

It has already been proposed to use a non-intrusive optical measurement system (known by the terminology of "tip timing" in English) comprising one or more optical probes fixed to a fixed part of the engine, opposite the part to be checked, typically in line with the tips of the blades of the impeller. In operation when the mobile wheel rotates, the vibrations of the blades result in a tangential deflection of their tip which is measured by the optical probes. Each optical probe determines the moment of passage of each blade when the blades cross its optical beam. When a blade resonates, the vibrations induce a periodic tangential movement of the blade (oscillations) which generates a time lag (delay or advance) with respect to a reference passage time (without vibration) in front of the probe. Then, the blade tip deflection (distance in millimeters) can be determined as a function of the radius between the blade tip and the axis of rotation and the rotational frequency of the rotating stage.

Advantageously, this system does not require wireless communication means since the optical probes are placed in the fixed frame of the engine (housing) so that the transmission of the measurements to the bench can be done by wire. However, this solution is only applicable to mobile stages whose blade tips are free, that is to say without a heel and/or platform, such as rotating fan, expansion or compression stages. . On the other hand, in the case of the turbine stages, the top of the blade is connected to a heel which prevents the direct measurement of a deflection of the blade (see ). Indeed, the obstacle that the beam of the optical probe can measure must be clear like a tip of a free blade

An object of the invention is to remedy the aforementioned drawbacks of the prior art and to propose a solution making it possible to measure the dynamic deformations of a rotary stage of a turbine, in particular of a low-pressure turbine, which is simple to put implemented and at a lower cost in comparison with the use of an extensometer.

For this purpose, according to a first aspect of the invention, a blade of a rotating mobile wheel of a turbomachine, typically of a mobile wheel of a low pressure turbine, comprising:
- a blade with an aerodynamic profile adapted to extend in an air flow;
- a heel, fixed to an outer radial end of the blade, the heel comprising a platform having an internal face connected to the blade and an external face carrying at least one wiper; And
- A monolithic tab with the wiper and extending axially from the wiper away from the outer face of the platform.

Certain preferred but non-limiting characteristics of the blade according to the first aspect are the following, taken individually or in combination:
- The outer face of the platform comprises two wipers, the tongue being monolithic with the two wipers and extending between the wipers;
- the or each wiper has a free top extending away from the platform, the tab having an outer face extending in the continuity of the top while being recessed with respect to said top;
- the outer face of the tab is recessed relative to the top of the or each wiper by a radial distance greater than or equal to 0.5 mm and less than or equal to 0.7 mm, for example equal to 0.6 mm;
- the tab has an internal face, extending opposite the external face of the platform, an intrados face and an extrados face extending from the internal face, a circumferential width of the tab measured between the intrados face and the upper surface decreasing from upstream to downstream;
- the intrados face and the extrados face of the tongue extend in the extension of an intrados wall and an extrados wall of the blade, respectively; and or
- a radial length, measured between an internal face and an external face of the tongue, is of the order of 1.4 mm.

According to a second aspect, the invention proposes a moving wheel of a turbomachine, in particular of a low pressure turbine, comprising at least one blade according to the first aspect.

According to a third aspect, the invention proposes a turbomachine comprising a mobile wheel according to the second aspect, in particular a mobile wheel of a low pressure turbine.

According to a fourth aspect, the invention proposes a non-intrusive measurement optical system for a moving wheel of a turbine engine according to the third aspect, said optical system comprising an optical probe, configured to be fixed on a stator part (16) and on the least one impeller vane.

According to a fifth aspect, the invention proposes a method for manufacturing a blade according to the first aspect, comprising the following steps:
- casting a raw casting, the raw part comprising a blade portion, a heel portion and casting feeds;
- machine the casting leads so as to form the tongue.

DESCRIPTION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

There is a partial perspective view of an optical measurement system according to a first embodiment of the invention;

There is a sectional view, along a radial plane passing through the axis of rotation of a rotary stage, of an optical measurement system according to a second example embodiment;

There is a sectional view along plan AA of the the optical measurement system according to the second embodiment;

There is a perspective view of a raw part intended to form a blade in accordance with one embodiment, before machining of the tongue;

There schematically and partially illustrates a turbomachine comprising a rotating stage in accordance with one embodiment of the invention; And

There , which has already been described, illustrates an optical probe and its beam in line with the heel of a conventional blade.

In all the figures, similar elements bear identical references.

DETAILED DESCRIPTION OF THE INVENTION

A turbomachine 1 according to the invention comprises, from upstream to downstream in the direction of gas flow, a fan 2, a compression section 3, 4 (if applicable, a low pressure compressor 3 and a high pressure compressor 4), a combustion chamber 5, a turbine section 6, 7 (if applicable, a high pressure turbine 6 and a low pressure turbine 7) and an exhaust nozzle (see ).

The invention will more particularly be described with reference to the moving wheels 8 of the turbine section 6, 7, typically of the low pressure turbine 7. However, the invention can easily be applied to any moving wheel of a turbomachine 1 comprising blades whose top is fixed to a heel and/or a platform.

In the present application, the upstream and the downstream are defined with respect to the direction of normal flow of the gas in the turbine section 6, 7, through the turbomachine 1. Furthermore, the axis X of revolution of the mobile wheel 8 which is coaxial with the engine axis of the turbomachine 1. The axial direction corresponds to the direction of the axis X of the mobile wheel 8, a radial direction is a direction perpendicular to this axis and passing through it and a circumferential (or lateral) direction corresponds to a direction perpendicular to the X axis and not passing through it. Finally, we will use internal and external, respectively, in reference to a radial direction so that the internal part or face of an element is closer to the X axis than the external part or face of the same element.

A turbine impeller 8 comprises a disc configured to rotate around the X axis and a plurality of blades 9, extending radially from the disc between a foot, connected to the disc, and a heel 11.

Each blade 9 includes:
- A blade 10 with an aerodynamic profile adapted to extend in an air flow; And
- the heel 11, fixed on an outer radial end of the blade 10.

The heel 11 comprises a platform 12 having an internal face 13 connected to the blade 10 and an external face 14 carrying at least one wiper 15, for example two wipers 15.

The internal face 13 of the platform 12 is configured to radially delimit the flow of gases in the mobile wheel 8.

The wiper(s) 15 are configured to cooperate with a fixed part mounted on the facing casing 16 and comprising an abradable support or “abradable carrier” on which is fixed an annular element made of abradable material generally called an “abradable element”. On the , the fixed part and the casing 16 are shown as one and the same part for simplicity; however, it will be understood that the fixed part can be separate from the casing 16. The wiper or wipers 15 and the fixed part 16 together form a sealing element of the labyrinth seal type. In a non-limiting way, the abradable element can for example comprise a honeycomb structure.

The wipers 15 and the fixed part 16 being conventional, they will not be further described here.

In order to control the dynamic deformations of the blades 9 of the moving wheel 8 in a simple, efficient and inexpensive manner, the invention proposes a non-intrusive optical measurement system 17 for a moving wheel 8 of a turbomachine 1 comprising at least one probe optical 18, preferably several, fixed to the casing 16 of the mobile wheel 8, and to modify the heel 11 of at least one of the blades 9 in order to form a surface capable of being detected by the optical probe 18 in order to determine the deflections of the blades 9.

For this, at least one of the blades 9 further comprises a tongue 19, monolithic with the wiper(s) 15, which extends axially at a distance from the external face 14 of the platform 12. In the case where the platform comprises two wiper 15, tongue 19 is monolithic with the two wipers 15 and extends between said wipers 15.

Preferably, each blade 9 includes a tongue 19.

Despite the presence of the heel 11 between the blade 10 and the optical probe 18, the optical probe 18 can therefore control the dynamic deformations of the blade 9 by detecting the instant of passage of the tongue 19 to the right of the optical probe 18 following the conventional tip timing process described above.

In what follows, the invention will be described more particularly in the case where the platform 12 comprises two wipers 15. This is however not limiting, the platform 12 may comprise only one wiper 15 as indicated above.

The wipers 15 extend, in a manner known per se, in a circumferential direction. They each have a free vertex 20, extending away from the outer face 14 of the platform 12 and configured to come into contact with the abradable support.

The tongue 19 for its part extends between the two wipers 15 in an axial direction. The tongue 19 has an internal face 21, facing the external face 14 of the platform 12, an external face 22 extending in the continuity of the vertices 20, an intrados face 23 and an extrados face 24 each extending between the internal face 23 and the external face 24.

The optical probe or probes 18 are connected, in a conventional manner, to a processor of a test bench for the purpose of data processing. The connection can in particular be by wire.

Advantageously, the tongue 19 can be easily produced by taking advantage of the conventional manufacturing process for the blades 9 of the turbine.

More specifically, a turbine blade 9 is obtained by a foundry process during which a raw part is first produced. This raw part comprises in particular a raw heel 11 comprising casting feeds 25, as visible on the . These casting feeds 25 correspond to the portion of the raw part through which the material intended to form the blade 10 is injected. The profile of the casting feeds 25 therefore corresponds to the profile of the blade 10. Secondly, the raw part is machined in order to eliminate the casting leads 25.

During the manufacture of a blade 9 in accordance with the invention, the tongues 19 can in particular be produced during the machining of the casting feeds 25. More precisely, instead of completely eliminating the casting feeds 25, the invention proposes to machine the casting inlet extending between the wipers 15 in order to form the tongue 19 there. The casting inlets 25 extending on either side of the wipers 11 on the other hand can be machined conventionally and eliminated . The tongue 19 thus obtained is therefore monolithic with the wipers 15 and easy to produce at a lower cost. Advantageously, this embodiment makes it possible to minimize the impact on the manufacturing cost of the blade 9, the range for obtaining the raw part being unchanged.

In this embodiment, the intrados face 23 of the wiper 15 therefore extends in the extension of the intrados wall 26 of the blade 10 and the extrados face 24 of the wiper 15 extends in the extension of the extrados wall of the blade 10, since the tongue 19 is made from the casting inlet 25 of the blade 10 extending between the wipers 11. The circumferential width Ep (distance between the intrados 23 and extrados face of the wiper 15) is therefore variable in the circumferential direction, decreasing from upstream to downstream (in the direction of gas flow in the impeller 8).

In order to protect the tongue 19 against wear, the outer face 22 of the tongue 19 is recessed radially with respect to the tops 20 of the lips 15 to avoid any contact between the tongue 19 and the abradable support on the fixed part 16. The distance radial d of recess of the outer face 22 relative to the wipers 15 is chosen so as to be at least equal to the depth of wear of the abradable support, preferably equal to the depth of wear to which a margin is added. For example, the radial recess distance d is greater than or equal to 0.5 mm and less than or equal to 0.7 mm, for example equal to 0.6 mm.

Insofar as the wipers 15 are circumferential, the radial recess distance d is measured in a plane radial to the X axis, passing through the tab 19.

The characteristic dimensions of the tab 19 are as follows:
- The circumferential width Ep of the tongue 19;
- the axial length D of the tongue 19;
- the radial distance d of recess; And
- the radial length H of the tongue 19.

These dimensions are chosen so that the tongue 19 is thick enough to limit its bending induced by the centrifugal forces and to obtain an acceptable static stress for its mechanical strength, while remaining thin enough to limit the increase in the mass of the blade. 9 and its impact on the natural frequencies of blade 9. In fact, blade 9 must be representative of a standard turbine blade whose dynamic behavior is to be validated during a stress survey type test. For example, the maximum impact on the natural frequencies of the modes detectable by the non-intrusive measurement optical system 17 can be set at 1.1%. Furthermore, the impact on the mass of the blade 9 must be strictly less than 1%.

The axial length D of the tongue 19 is fixed by the distance between the wipers 15. For example, the axial length D of the tongue 19 can be equal to about twenty millimeters, for example 19.8 mm.

In the case where the tongue 19 is obtained by machining the casting feed 25 of the raw part intended to form the blade 9, the circumferential width Ep of the tongue 19 is at most equal to the circumferential width Ep of the blade 10. In one embodiment, the faces of the casting inlets 25 extending in the extension of the intrados 26 and extrados walls of the blade 10 may not be machined, so that the profile of the tongue 19 is identical to that of the blade 10. The circumferential width Ep of the tongue 19 is then fixed by the profile of the blade 10. For example, the circumferential width Ep of the tongue 19 can increase from 1.9 mm to 3.6 mm.

We have seen that the radial recess distance d is determined according to the depth of wear and possibly a predetermined margin. For example, the radial recess distance d is greater than or equal to 0.5 mm and less than or equal to 0.7 mm, for example equal to 0.6 mm.

The radial length H of the tongue 19 is optimized by taking into account the connecting radii between the tongue 19 and the wipers 15 in order to respect the compromise between the static stress acceptable for the mechanical strength and the impact on the natural frequencies. of dawn 9.

For example, with the axial length D, the circumferential width Ep and the radial recess distance d described above, the radial length H of the tongue 19 can be equal to 1.4 mm.

Finally, the optical probe 18 can be placed at a radial distance R from the outer face 22 of the tab 19 of between one millimeter and five millimeters inclusive. For this, the optical probe 18 can in particular be placed set back relative to the face of the abradable support which comes into contact with the wipers 15 (see ).

The simplicity of manufacturing the blades 9 comprising the tongue 19, the low impact on the manufacturing cost and the reliability of the measurements obtained with one or more optical probes 18 make it possible to produce a moving wheel 8 of which all or part of the blades 9 include such a tongue 19. In one embodiment, all of the blades 9 of the impeller 8 may include a tongue 19, which makes it possible to control the dynamic deformations of the entire impeller 8.

In comparison, in the case where the measurement of the dynamic deformations was carried out using extensometers, only part of the blades 9 of a mobile wheel 8 could be instrumented, which reduced the quantity of information likely to be obtained. In addition, many extensometers were damaged during the measurements, which inevitably led to a loss of information. Finally, the Applicant realized that the telemetry was sensitive to electromagnetic interference and to the stresses of the turbomachine 1 and that this sensitivity had the effect of polluting the results. It was therefore necessary to reprocess the data obtained (application of filters, performance of additional tests, etc.), thus increasing the cost of the tests and their complexity.

In the context of the invention, the data measured by the optical probes 18 being able to be transmitted by wire to the test bench, they are much less sensitive to electromagnetic disturbances and are not impacted by the vibrations of the turbomachine 1.

It will be noted that the tests can be carried out on the turbine engine 1 directly or, as a variant, only on the moving wheel (outside the turbine engine).

Claims (11)

Blade (9) of a rotating impeller (8) of a turbine engine, typically a low pressure turbine impeller (7), comprising:
- a blade (10) with an aerodynamic profile adapted to extend in an air flow; And
- a heel (11), fixed to an outer radial end of the blade (10), the heel (11) comprising a platform (12) having an internal face (13) connected to the blade (10) and an external face ( 14) carrying at least one wiper (15);
the blade (9) being characterized in that it further comprises a tongue (19) monolithic with the wiper (15) and extending axially from the wiper (15) at a distance from the external face (14) of the platform (12). Blade (9) according to Claim 1, in which the external face (14) of the platform (12) comprises two wipers (15), the tongue (19) being monolithic with the two wipers (15) and extending between the wipers (15). Blade (9) according to one of Claims 1 or 2, in which the or each wiper (15) has a free top (20) extending at a distance from the platform (12), the tongue (19) having a external (24) extending in the continuity of the top (20) being recessed with respect to said top (20). Blade (9) according to Claim 3, in which the outer face (24) of the tongue (19) is recessed relative to the top (20) of the or each wiper (15) by a radial distance (d) greater or equal to 0.5 mm and less than or equal to 0.7 mm, for example equal to 0.6 mm. Blade (9) according to one of Claims 1 to 4, in which the tongue (19) has an internal face (21), extending opposite the external face (14) of the platform (12), an intrados (23) and an extrados face (24) extending from the internal face (21), a circumferential width (Ep) of the tab (19) measured between the intrados face (23) and the extrados face (24) being decreasing from upstream to downstream. Blade (9) according to Claim 5, in which the intrados face (23) and the extrados face (24) of the tongue (19) extend in the extension of an intrados wall (26) and of an extrados wall of the blade (10), respectively. Blade (9) according to one of Claims 1 to 6, in which a radial length (H), measured between an internal face (13) and an external face (14) of the tongue (19), is of the order of 1.4mm. Movable wheel (8) of a turbomachine, in particular of a low-pressure turbine (7), comprising at least one blade (9) according to one of Claims 1 to 7. Turbomachine (1) comprising a mobile wheel (8) according to claim 8, in particular a mobile wheel (8) of a low pressure turbine (7). Non-intrusive measurement optical system (17) for a moving wheel (8) of a turbomachine according to claim 9, said optical system (17) comprising an optical probe (18), configured to be fixed on a stator part (16) and at least one vane (9) of the moving wheel (8). Method of manufacturing a blade (9) according to one of Claims 1 to 7, comprising the following steps:
- casting a raw casting, the raw part comprising a blade portion (10), a heel portion (11) and casting feeds (25);
- Machining the casting feeds so (25) to form the tongue (19).