EP0214875A1 - Damping element limiting the angular deflection of turbo machine rotor vanes - Google Patents

Abstract

The limiting device comprises wedging means arranged radially between each pair of adjacent blades as high as possible on the stilt of each blade, the adjustment calculated between the wedging means and the two adjacent stilts being able to limit the angular movement of each blade around its longitudinal axis to its maximum value tolerated in autorotation.

Application to aviation turbojets.

Description

The technical sector of the present invention is that of turbomachinery and more specifically means for fixing and limiting the angular displacement of the rotor blades.

Such vanes are fixed in a known manner to the periphery of a rotor disc and traditionally comprise, under a platform and separated from it by a stilt, a foot in the shape of a fir tree or in dovetail coming to be housed in a corresponding groove of the rotor disc. For mounting reasons, when the blades are fins or peripheral heels, the designer is required to provide a large space between the foot of the blade and the bottom of the groove; This space is occupied by an axial shim which ensures correct positioning of the blade root in the grooves.

An assembly of this kind is shown for example in French patent 2,345,605 in the name of the applicant.

The vanes of this type are therefore susceptible at rest to a relatively large angular deflection on either side of the radial plane comprising the major axis of the blade, this deflection being maintained at a value given by the clearance calculated between the plates -forms of adjacent blades.

However, problems arise for the blades of a fan or of a low pressure compressor of a turbomachine, in particular of an aviation turbojet engine because the fan or low pressure compressor rotor located upstream of the turbojet engine, may be subjected to impacts. due to the ingestion of birds in flight and under the tangential force of the impact on the blade, it undergoes bending and is also subjected to a rotation around its major axis due to the large degree of freedom in rotation cleared at the foot of dawn as seen above.

If the mass of the ingested bird is large, the energy of the impact may be sufficient to lead to partial fragmentations of one or more blades, or even to their complete rupture, which also leads to destructures of the compressor stages downstream

This disadvantage is further accentuated for fan blades having fins at mid-height of the blade, because under the effect of the tangential force due to the shock, the adjacent fins overlap, which almost certainly leads to the destruction of the fan blades and consequently to the partial or total destruction of the downstream stages of the compressor, which can lead to complete shutdown of the turbojet engine and in the worst case, if the aircraft is a single jet engine, lead to loss of the device.

An example of this type of mounting is given by patent FR 2 286 282 which shows rotor blades the platform of which is placed on the edges of a cage, the latter being formed by two flanges, one upstream, the 'other downstream connected to each other by narrow axial bars arranged under the platforms in a space out of two left free between the stilts, the blade root being threaded in a groove of the disc and the cage screwed onto the rotor disc. Such a device where the blade root is not wedged in its groove has the drawbacks of allowing a significant rotation of the blade in the groove of the disc and of favoring significant vibrational phenomena between the blades and the cage on which rests platforms.

An attempt has therefore been made to eliminate these vibrations, in particular by placing beneath the blade platforms in the space left free between the stilts of the wedges plated under the platform, or by centrifugal force during the rotation of the rotor, thus that disclose the patents GB 670 665 or US 4,182,598 or even US 4,101,245, either by an elastic means as shown by the patent FR 2 527 260 in the name of the applicant.

However, if these devices fulfill an anti-vibration function by limiting the radial displacement of the blades, they generally do not prevent the angular movement of the latter under the effect of a shock. In addition, these devices cannot absorb the energy of the impact on a blade to transmit it and distribute it, for example over an entire disk sector where this energy would be dissipated.

One of the aims of the invention is therefore to limit in operation the angular movement of a blade of rotor of a turbojet engine, in particular of a fan or low pressure compressor blade and more particularly of a blade with side fins, in order to prevent the risk of overlapping of the fins under the effect of an accidental impact.

Another object of the invention is to provide a device which is able to withstand the energy of the shock suffered by a dawn, during an accidental ingestion of a bird in flight for example and to absorb this impact by making the 'force undergone by the disc-drum connection by a specific flange of the disc or the drum, according to a variant of the invention or by the two or three blades adjacent to that which has been impacted, according to another variant.

An additional object of the invention is to present a device which, in addition to the advantages mentioned above, allows the damping of vibrations undergone by the blades.

The invention also aims in an alternative embodiment to provide a simple means having the advantages cited and adapted to be adapted on existing rotor discs and requiring only modifications of detail of the rotor discs, easily executable in a maintenance workshop and does not require long and costly downtime of the turbojet.

The subject of the invention is therefore a device for limiting the auger deflection of turbine engine rotor blades of the type comprising a series of radial blades mounted on the periphery of a rotor disc, the blades comprising under a platform a separate stand of the platform by a stilt, the foot being received in a groove around the rotor disc, two adjacent grooves defining between them an ear of the disc.

According to the invention, the device comprises wedging means arranged between each pair of adjacent blades radially as high as possible on the stilt of each blade, the adjustment calculated between the wedging means and the two adjacent stilts being able to limit the angular movement of each blade around its longitudinal axis to its maximum value tolerated in autorotation.

According to an important characteristic, the wedging means are integral with an intermediate connecting means fixed on the rotor disc and able to absorb part of the force undergone by a blade during an accidental impact and to distribute it over a angular sector of the rotor.

According to another main characteristic of the invention, the intermediate connection means is constituted by an annular flange comprising a planar radial extension, the flange being arranged downstream of the disc and made integral with the latter and the wedging means are constituted by extensions of the radial extension of the flange, said extensions being of rectangular cross section arranged parallel to the axis of rotation of the rotor in the free spaces between each pair of adjacent stilts and produced in a single piece with said plane radial extension of the flange , the width of each of the extensions being substantially equal to that of the free space between the stilts.

• - la figure 1 montre une vue du montage d'une aube de soufflante sur un disque de rotor incorporant le dispositif de limitation de débattement selon un premier mode de réalisation dans lequel les efforts subis par une aube sont repris par les boulons de fixation disque-­bride, vu selon une coupe radiale du disque passant par une des oreilles de celui-ci.
• - la figure 2, montre une vue en perspective du montage de la figure 1, tandis que la figure 2a représente un secteur de 2 aubes à nageoires incluant le dispositif selon l'invention.
• - la figure 3 montre en coupe une variante du mode de réalisation précédent.
• - la figure 4 montre en coupe une deuxiéme variante dans laquelle les efforts subis par une aube sont transmis par l'anneau constituant le dispositif de limitation du débattement aux 2 ou 3 aubes adjacentes, ce qui permet de ne pas solliciter la liaison boulonnée.
• - La figure 5 montre en perspective arrière un deuxième mode de réalisation de l'invention dans lequel la limitation de débattement est effectuée par des cavaliers portés par les oreilles du disque.
• - la figure 6 montre en coupe au niveau d'une des oreilles du disque une variante de ce deuxième mode de réalisation incorporant des moyens d'amortissement des vibrations subies par les aubes.
• - la figure 7a présente en vue selon AA de la figure 6 les moyens d'amortissement de vibration et la figure 7b en présente une section rabattue suivant BB de la figure 7a.
• - la figure 8 montre une réalisation de moyens d'amortissement adaptables au mode de réalisation de la figure 5.

The invention will be better understood and variant embodiments explained in the additional description which follows and drawing boards representing embodiments of the invention without the latter being limited by the only boards shown, among which:

• - Figure 1 shows a view of the mounting of a fan blade on a rotor disc incorporating the movement limitation device according to a first embodiment in which the forces undergone by a blade are taken up by the disc fixing bolts- flange, seen in a radial section of the disc passing through one of the ears thereof.
• - Figure 2 shows a perspective view of the assembly of Figure 1, while Figure 2a shows a sector of 2 fin blades including the device according to the invention.
• - Figure 3 shows in section a variant of the previous embodiment.
• - Figure 4 shows in section a second variant in which the forces undergone by a blade are transmitted by the ring constituting the movement limitation device to the 2 or 3 adjacent blades, which makes it possible not to stress the bolted connection.
• - Figure 5 shows in rear perspective a second embodiment of the invention in which the limitation of travel is performed by jumpers carried by the ears of the disc.
• - Figure 6 shows in section at one of the ears of the disc a variant of this second embodiment incorporating means for damping the vibrations undergone by the blades.
• - Figure 7a shows a view along AA of Figure 6 the vibration damping means and Figure 7b shows a folded section along BB of Figure 7a.
• FIG. 8 shows an embodiment of damping means adaptable to the embodiment of FIG. 5.

Referring to Figures 1 and 2, there is shown schematically a fan blade 1 with stilt 2 comprising a platform 3 whose heel 4 is mounted with play in a known manner in a groove 5 of the rotor disc 6. The feet 4 of the vanes 1, at a standstill, rest on the wedges 7 arranged at the bottom of the groove 5; the clearance between the upper faces 8 of the heel and the corresponding face 9 of the groove 5 as well as the clearance "e" between the stilt and the upper part of the groove allow the blade 1 in autorotation, an angular movement of about 4 degrees around the longitudinal diametral plane of the rotor, containing the long axis of the blade. In operation, the blade stub 4 has its faces 8 pressed by centrifugal force against the faces 9 of the upper part of the groove 5. As a result, the side faces 10 of the platforms 3 of the adjacent blades as well as the faces lateral 11 of the fins 12 are substantially in contact with one another.

To avoid that during an accidental impact in operation, on one of the blades 1, it is destabilized, enters into vibration and / or undergoes bending under the effect of the tangential force due to the impact, there is on the rotor disc the angular movement limitation device according to the invention.

In the embodiment of FIGS. 1 and 2, the device comprises wedging means constituted by teeth 13 carried by an intermediate connecting means 14. The latter is produced in the form of a downstream annular flange comprising a planar radial circular extension 14 on the inner periphery of which are made bores 15 which allow mounting downstream of the disc 6 and the flange 16 which connects the blower stage to the first rotor stage of the low pressure compressor. The disc 6, the flange 16 and the flange 14 are secured between by bolts 17 passing through the ears 18 of the disc, the bores of the flange and the bores 15 of the downstream flange constituting the intermediate connection means.

The teeth 13 constituting the wedging means are produced in the form of upstream extensions of the planar radial extension of the flange 14, these teeth having a substantially rectangular cross section and being arranged parallel to the axis of rotation of the rotor or, if the platform 3 is strongly inclined upstream, as shown in Figures 1 and 2, parallel to the underside of the platform. These teeth 13 positioned as high as possible on the stilt fit into the space left free between the stilts, the clearance between the stilts and the tooth being calculated as small as possible in order to limit the angular movement of the blade at its maximum permissible value in autorotation. The cross section of the teeth 13, the thickness of the flange 14 and the bore 15 made without play with the bolt 17 are dimensioned to give the flange a structure strong enough to transmit and resume by the bolts disc-flange connection, the force undergone by a blade during an accidental impact.

The flange 14 also fulfills a function of damping the vibrations undergone by the blades. To do this, it comprises on the periphery of its planar radial extension a frustoconical extension 19 inclined downstream comprising an inclined circular bearing 20 having a curvature corresponding to that of the lower downstream face 21 of the platform 3. When the flange is tightened on the disc 6 by the bolts 17, the face 20 of the flange comes to bear against, and exerts a pressure on the lower face 21 of the platforms 3, under the action of centrifugal forces thus ensuring the damping of vibrations undergone by the blades.

In addition, the travel limiting device provides a sealing function because it prevents recirculation between stilts.

Depending on the geometry of the disc and the drum and depending on whether the flange is arranged between the disc and the drum, or behind the flange of the drum, it will be made up of one or two semi-circular parts.

In the alternative embodiment of FIG. 3, the flange 14 is produced in a single annular piece and disposed between the disc 6 and the flange 16, its overall structure (teeth 13 of angular setting and damping by bearing support 20 under the platform) remaining identical with the previously described variant.

In Figure 4, there is shown another embodiment of the downstream annular flange comprising the wedging means according to the invention. In this version, the flange 14 'is not fixed to the disc by tightening bolts. It consists of a simple flat annular bearing 14 ′ carrying the teeth 13 and is centered on the external circular face 23 of the flange 16.

A circular groove 24 makes it possible, by a judicious adaptation of the manufacturing tolerances, to keep the flange 14 ′ axially clamped, between the two flanges of the disc-drum connection.

Thus, in this embodiment of the invention, the recovery of the force undergone by a blade is effected by the adjacent blades, the whole of the flange 14 ′ moving when the blade receiving the shock strikes the tooth. 13 neighbor.

Therefore, this embodiment allows the force to be absorbed on two or three blades because the forces are fully taken up by the adjacent blades without overloading the disc and the drum.

In Figure 5, there is shown schematically in perspective another embodiment of the invention seen downstream of the rotor disc. In this embodiment, the wedging means and the intermediate connecting means consist of jumpers 30 in the shape of a "U" arranged astride the upper part of each ear 18 of the disc, the base of the U constituting the means of intermediate link and being fixed to the lugs 18 by the bolts 17 of the 6-flange disc link 16 (not shown in FIG. 5), while the branches 31 of the U constitute the wedging means according to the invention.
It is already known to take up the forces undergone by the blades directly by the ears of the disc, these being machined so that the clearance between them and the stilts is low enough to limit the deflection of the blades.

However, precise machining of the cells is not easy to achieve when we want them to perform this function. In addition, when the device is implemented by ingestion, there is a great risk of seeing the ears of the disc deform, which leads to very expensive repairs.

The jumpers, as they are provided in the present invention make it possible to solve these problems because their machining is easier than that of the cells of the disc and because they allow a better limitation of the clearance because it is possible to position them very high on the ear of the disc, this being due to the dissociation of the function of limitation of clearance relative to the disc in comparison with the previous solution of direct limitation by the ears of the disc.

The base 30 of the rider is arranged on the upstream face of the ear 18, the lateral faces 32 of which are milled to the internal dimension of the rider. It can be seen in FIG. 5 that the usual inclination of the lateral faces 33 would allow, in the absence of a jumper, an angular movement 2 α at the stilt 2 of the blade 1.

The judicious choice of the thickness "e" of the branches 31 of the rider (FIG. 5) makes it possible to limit the angular movement of the blade 1 to a value at most equal to its maximum authorized value in self-rotation. The advantage of such a wedging means is that it can easily be adapted to an existing rotor disc, by simple machining of the lateral faces of the lugs 32 of the rotor disc 6, which can be easily carried out in a maintenance workshop without immobilization. excessive motor and without special or complex tools.
This embodiment of the angular movement limitation means according to the invention therefore constitutes an improvement which is simple to implement and inexpensive to the blower or low pressure compressor rotors of existing turbomachines.

To this type of jumpers can be added as shown in Figures 6, 7a, 7b, means for damping the vibrations undergone by the blades, these means being constituted by a flyweight 34 of generally cylindrical shape free to slide radially in a cylindrical sheath 35 of radial orientation carried by the rider 30, either by means of a fixing lug 36 secured to the rider by the tightening bolt 17 (FIG. 6), or that the sheath 35 and the rider 30 have been produced monobloc (figure 7a). The counterweight 34 has on its periphery a longitudinal groove 37 cooperating with a lug 38 of the sheath 35 to allow the counterweight only one degree of freedom in radial sliding so that the counterweight is pressed under the platform 3 by the centrifugal force during the rotation of the rotor and comes to exert on the platform a force antagonistic to the vibrations which it supports.

In another variant of use of the jumpers of FIG. 5, the vibration damping means can consist of a frustoconical flange 40 fixed by screws 42 on the flange 16 scalloped at 41 of the drum 22, the external diameter of the trunk of cone being shaped into a round 43 to come to bear against a corresponding rounding of the lower downstream face of platform 3 (figure 8).

This damping means can also be used in combination with the variant of FIG. 4 with a downstream flange limiting the travel centered on the external diameter of the flange 16.

The damping means (flanges 14, 14 'or 40) also fulfill a sealing function between the upstream part of the stilt of the fan blade and the compressor stage located downstream.

The various embodiments of the invention tested in a wind tunnel during bird ingestion tests have proved to be particularly effective in avoiding the overlapping of the fan fins under the effect of the shock, which has avoided the destruction of the 'blade subject to impact as well as downstream compressor stages.

The embodiment of FIG. 5 has the additional advantage of being adaptable to existing motors by simple machining of the ears of the disc and of greatly facilitating repair thereof during accidental ingestion.

Claims (8)

1 - Device for limiting the angular movement of vanes mounted on a turbomachine rotor disc of the type comprising a series of radial vanes (1) mounted on the periphery of a rotor disc (6), the vanes comprising under a platform (3) a foot separated from the platform by a stilt (2), the foot being received in a groove around the periphery of the rotor disc, two adjacent grooves defining between them an ear (18) of the disc, device characterized in that it comprises wedging means (13, 31) arranged between each pair of adjacent blades radially as high as possible on the stilt (2) of each blade, the adjustment calculated between the wedging means and the two adjacent stilts being able to limit the angular clearance of each blade around its longitudinal axis to its maximum value tolerated in autorotation, and in that the wedging means are carried by an intermediate connecting means (14, 30) fixed on the rotor disc and suitable for a absorb part of the force undergone by a blade during an accidental impact and distribute it over an angular sector of the rotor. 2 - Device according to claim 1, characterized in that the intermediate connecting means consists of an annular flange having a planar radial extension (14 14 '), the flange being arranged downstream of the rotor disc (6) and made integral of said disc and in that the wedging means consist of extensions (13) of the radial extension of the flange, said extensions being of cross section rectangular arranged parallel to the axis of rotation of the rotor in the free spaces between each pair of adjacent stilts and produced in a single piece with said planar radial extension (14, 14 ') of the flange, the width of each of the extensions (13) being substantially equal to that of the free space between two stilts. 3 - Device according to claim 2, for rotor disc cooperating with a downstream circular flange (16) fixed to the rotor disc by bolts (17) characterized in that the annular flange (14) is disposed between the disc (6) and the flange (16) and is secured to the disc-flange assembly by the bolts (17) cooperating without play with bores (15) of the flange regularly distributed around its periphery. 4 - Device according to claim 2 for rotor disc cooperating with a downstream circular flange (16) fixed to the rotor disc by bolts (17) and comprising on its external circular face (23) a circular groove of width "1", characterized in that the annular flange (14 ') has an internal circular bearing (25) of thickness "1" in that the flange (14') is centered on the external circular face (23) of the flange and in that that it is kept tight between the disc and the flange by cooperation of the bolts (17) and the adequate calculation of the clearance between the circular bearing surface of the flange and the corresponding groove in the flange. 5 - Device according to any one of claims 3 or 4 characterized in that the downstream flange (14) is separated into two semi-circular half-flanges. 6 - Device according to any one of claims 2 to 5 characterized in that the annular flange comprises on the periphery of its planar radial extension (14) a frustoconical extension (19) comprising an inclined circular bearing (20) bearing under the platform of each blade of the rotor to dampen the vibrations caused on the blades during an accidental impact. 7 - Device according to claim 1 characterized in that the wedging means and the intermediate connecting means consist of jumpers (30, 31) in the shape of "U" arranged astride the ears of the rotor disc and fixed on these by tightening bolts (17), the lateral thickness of the branches (31) of the U being dimensioned so as to limit the angular movement of each blade to its maximum value tolerated in autorotation. 8 - Device according to claim 7 comprising means for damping the vibrations caused on the blades during an accidental impact, characterized in that said means are constituted by a cylindrical counterweight (34) free to slide radially in a cylindrical sheath (35 ) of radial orientation, integral with the rider (30), the counterweight having a longitudinal groove (37) cooperating with a guide pin (38) of the sheath and being able to be pressed under the platform (3) of the blade by centrifugation during rotation of the rotor.

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