Mounting assembly for a divergent master petal of a variable geometry nozzle

Abstract: Compression bar (11,12) for divergent master petals (6) of variable geometry nozzles, of the type which exhibit a system of command constituted by three ring-like pieces (7,8,9), the external ring piece (9) being divided into two half-rings (9a,9b), which binds the two half-rings and the corresponding divergent master petal, and which may be formed by two bars (11,12) joined at one end by means of specific or universal joints to the external ring (9), and joined between themselves, by means of a cylindrical articulation (33,37) considerably perpendicular to the plane which contains both bars (11,12) and by a divergent master petal-binding transition piece (16) joined to the two bars (11,12) by means of cylindrical articulations (34,42,36,41) with sufficient looseness to absorb the changes in distance between the ends of the two bars (11,12).

Description: The invention relates to gas turbine engines and in particular to a mounting assembly for a divergent master petal of a variable geometry nozzle. BACKGROUND OF THE INVENTION Gas turbine engines for aircraft achieve thrust by discharging hot gas through an exhaust nozzle. A variable area convergent/divergent nozzle is necessary in order to achieve a good efficiency for multi-mission application. The maximum efficiency is obtained with an independent control of exhaust nozzle throat and exit areas. With this, the maximum expansion of the gases and therefore maximum thrust is achieved at all times. One of the goals of the designers is to increase the aircraft manoeuvrability, especially in those flight conditions in which the aerodynamic control surfaces begin to lose their efficiency. A way of achieving this goal is by directing the gas flow from the axial direction, so as to achieve a thrust component which is directed up, down or sideways. At present, there are several solutions with two-dimensional convergent/divergent nozzles, such as the one disclosed in U.S. Pat. No. 4,763,840. However, these nozzles can only orient the gas in one direction (generally pitch) and they are heavier than the axisymmetric convergent/divergent nozzles. There are different systems of 3-D thrust vectoring convergent/divergent nozzles. All these systems can be classified into three major groups: Those that orientate the whole exhaust nozzle upstream of the convergent section. Due to the fact that the alteration of the geometry is done upstream of the throat, perturbations are induced in the turbine. Moreover, a highly complicated sealing device is required. Those that orientate the flow at the outlet itself of the exhaust nozzle, more downstream of this. With this system there is an efficiency reduction and the weight increases as this system requires an additional device. Those that orientate the divergent segment of the exhaust nozzle. With this system the perturbation upstream of the turbine is minimized. The increase in weight is less than in the previous case, due to the fact that the nozzle itself orientates the flow without the help of any other additional device. Within this third group, the most common embodiment includes, as shown in US Pat. No. 5,082,182, a convergent section that consists of a plurality of master petals and a plurality of slave petals in order to provide an adequate sealing. The throat area is governed by the well-known cam+roller mechanism. The control of the throat area requires a number of linear actuators. Downstream of this convergent section there is a divergent section consisting of the same plurality of divergent master petals and a plurality of slave petals in order to provide an adequate sealing. The divergent master petals are connected to convergent master petals by universal linkage. The linkage permits the lateral and radial motion of the divergent master petals, thus allowing orientation of the gas flow. The divergent master petals are linked to an external ring by load struts. The connection of the strut to the divergent master petal is carried out via a spherical linkage, while the connection to the external ring is made via a cylindrical linkage. Both outlet area and flow orientation is controlled by the external ring. This external ring requires at least three linear actuators. With this embodiment two independent actuator systems are required, internal and external. Another variable geometry nozzle is disclosed in EP 0557229B1. This one is characterised by fact that it controls the throat area, outlet area and flow orientation with only one set of linear actuators. That implies a reduction in cost and a more simple design of the actuator system. This single system consists of three rings, concentric among themselves and with the axis of the turbine, and having a plurality of linear actuators linked by their upstream ends to the structure of the turbine. The rings mentioned above are connected together and to the structure of the turbine via linkage elements and guide devices which allow the joint axial displacement of the three rings in equal magnitude, with respect to the structure of the turbine, as well as a relative rotary movement of the intermediate and external rings between themselves and with respect to the internal ring, thereby allowing the external ring to be inclined in any direction with the centre of rotation in the axis of the turbine. The convergent master petals are connected at a point in their upstream segment to the internal ring by cylindrical linkages, tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and located in a theoretical plane perpendicular to such longitudinal axis. The master petals of the divergent section are subdivided transversely into at least two segments that are connected to each other by a cylindrical linkage perpendicular to that of a linkage between the master petals of the convergent and divergent sections. The divergent master petals are connected at a point in their upstream segment to the convergent master petals by cylindrical linkages, parallel to the linkages between the internal ring and the master convergent petals. The downstream segment is connected to the external ring via a load strut that is linked to that segment by a spherical linkage and to the external ring by a cylindrical linkage, tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and located in a theoretical plane perpendicular to such longitudinal axis. The invention is related to said load strut. The external ring is connected to downstream ends of the linear actuators by spherical linkages. The external ring is divided in two half rings that are connected to each other by a cylindrical linkage, perpendicular to the theoretical axis of the engine. The linkage allows a relative rotary movement of the external half rings between themselves achieving the outlet control or allowing the external ring to be inclined in any direction with the centre of rotation in the axis of the turbine as a unique ring, orienting the flow in any direction. In patent EP 0557229B 1 the master petals are distributed in such a way that half of them are connected to one of the two external half rings via a load strut, an the other half of them are connected to the other external half ring. The above distribution of the petals limits the control of the outlet area due to petal interferences and sealing problems. If two of the master petals are located in the linkage between the two external half rings the limitation of outlet area control is smaller. This new distribution of the petals needs a different load strut. The new load strut must allow said divergent master petals to be connected to the two external half rings at the same time. SUMMARY OF THE INVENTION The object of the present invention is to provide a load strut arrangement that allows to connect a divergent master petal to both external half rings at the same time. The invention resides in an assembly according to claim 1. A preferred embodiment of the invention is defined in the dependent claims 2 and 3. If the two external half rings move as a unique external ring, the load strut has to work in the same way as a load strut that connects a divergent master petal to a single external ring. If a relative rotary movement takes place between the two external half rings, the theoretical symmetric plane of the load strut has to be the same as the bisector plane formed by the two external half rings, the linkage with the divergent master petal remaining in said plane. Accordingly, the device of the present invention comprises two bars that are connected to each other at a downstream point by a cylindrical linkage. Each bar is connected at an upstream point, by a spherical or universal linkage, to an external half ring. The position of the two bars with regard to each other is fixed by the linkages and the position of the external half rings, forming a unit. This unit has one single degree of freedom, just as the conventional load struts. Said degree of freedom is the rotation about the axis formed by the theoretical line through the two spherical or universal linkages. In order to join the two bars to the master divergent petal, a transition part is necessary. This part is connected to each bar by means of a cylindrical linkage. This linkage is substantially parallel to the linkage between the mentioned bars. The three cylindrical linkages have to be substantially coplanar. In such a way, when there is a relative motion between the two external half rings, there is a relative motion between the two bars and then the distance between the two cylindrical linkages of the transition part changes slightly. Due to the alignment of the three cylindrical linkages, the mentioned variation is a function of (1-cos) of the rotation angle, this angle being very small. The cylindrical linkage clearances allow this slight variation of the distance. The load strut that is the object of the invention comprises the two bars and the transition part. The linkage between the load strut and the divergent master petal can be the same as for a conventional load strut. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective of a exhaust nozzle related with the invention. Figure 2 is a perspective of a detail of the nozzle when a load strut according to a preferred embodiment of the invention appears. Figure 3 is an exploded perspective showing the load strut according to a preferred embodiment of the invention. Figure 4 is a view showing sealing problems in a nozzle in accordance with the patent EP 0557229B1. Figure 5 is a view showing that there are no sealing problems in a nozzle in accordance with the patent EP 0557229B1 using the load strut of the preferred embodiment of the invention. Figure 6 is a view showing a nozzle in accordance with the patent EP 0557229B1 using the load strut of the preferred embodiment of the invention orienting the flow. DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 represents, in a schematic and partially cross-sectional perspective view, an exhaust nozzle that has a load strut 1 in accordance with a preferred embodiment of the invention, with arrow 33 showing the direction of the flow. As with traditional exhaust nozzles, the nozzle represented in figure 1 includes a casing 2, a convergent section 3 and a divergent section 4. The convergent section 3 consists of a plurality of convergent master petals 5 and convergent slave petals 34. In the same way, the divergent section 4 consists of a plurality of divergent master petals 6 and divergent slave petals 31. The variation in the throat area, defined by the downstream end contour of the convergent petals, the outlet area, defined by the downstream end contour of the divergent petals, and the vectoring of the thrust are controlled by a system consisting of three rings 7,8,9, concentric with each other and with the axis of the turbine. The external ring 9 is divided in two external half rings. Only one of the two external half rings is represented in figure 1. The position of the rings 7,8,9 is controlled by a plurality of linear actuators 10 which are linked by their upstream ends to the casing 2. If the vectoring of the thrust is not required the intermediate ring 8 can be removed. The rings 7,8,9 are also linked to each other by devices that allow axial displacement of the set of three rings, in equal magnitude, with respect to the casing 2 of the turbine, as well as a relative rotary movement of the intermediate ring 8 and external half ring 9 between themselves and with respect to the internal ring 7, in such a way that it allows the external half rings 9 to incline in any direction, and a relative rotary movement of the external half rings 9 between themselves. Figure 2 represents a perspective of a detail of the nozzle when the load strut 1 according to a preferred embodiment of the invention is present. The load strut comprises two bars 11,12. Each bar is connected at its upstream end, by a spherical or universal linkage 13,14, to a external half ring and they are connected to each other, at their respective downstream ends, by a cylindrical linkage 15, this cylindrical linkage 15 being perpendicular to a theoretical plane 32 that contains both bars 11,12. The mentioned plane is formed by the centre of the spherical linkages 13,14 and the cylindrical linkage 15. Thus, the relative position of the two bars 11,12 is fixed by the linkages 13,14,15 and the position of the external half rings 9, forming a unit. This unit has one single degree of freedom, just as a conventional load strut 19. Said degree of freedom is the rotation about the axis formed by the theoretical line through the two spherical or universal linkages 13,14. The transition part 16 is connected by a cylindrical linkage 17,18 to each bar 11,12. These linkages 17,18 are substantially parallel to the linkage 15. The three cylindrical linkages 15,17,18 have to be substantially coplanar. The linkage between the transition part 16 and the divergent master petal can be the same as for a conventional load strut 19. The convergent master petals 5 are connected at an upstream point to the internal ring 7, by cylindrical linkages 20, tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and located in a theoretical plane perpendicular to said longitudinal axis. The master divergent petals 6 are subdivided transversely into at least two segments. The upstream segment 21 is connected to the master convergent petal by a cylindrical linkage 23, tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and located in a theoretical plane perpendicular to said longitudinal axis. The downstream segment 22 is connected to the upstream segment 21 by a cylindrical linkage 24 perpendicular to the base of the master divergent petal. The divergent master petal 6 is connected to the load strut 1 or 19 by two intermediate bars 25,26. These intermediate bars 25,26 are connected to the divergent master petal 6 by spherical linkages 27,28. The intermediate bar located downstream 26 is connected to the load strut 1 or 19 by a spherical linkage 29 and he intermediate bar located upstream 25 is connected to the load strut 1 or 19 by a cylindrical linkage 30. Figure 3 is an exploded perspective showing the load strut according to a preferred embodiment of the invention. The load strut comprises two bars 11,12 and a transition part 16. Bar 11 has at one end a lug 35, that is designed to receive a spherical linkage 13. That linkage joins said bar 11 with one external half ring 9a. The other end has two lugs 36,37. One of the lugs 37 is connected to the lug 38 of the other bar 12 by a cylindrical linkage 15. In the same way, the other bar has at one end a lug 40, that is designed to receive a spherical linkage 14. That linkage joins said bar 12 with the other external half ring 9b. The other lug 36 of the bar 11 is connected to the lug 41 of the transition part 16 by a cylindrical linkage 17. In the same way, the other lug 39 of the bar 12 is connected to the lug 42 of the transition part 16 by a cylindrical linkage 18. The design of the bars 11,12 could be made in such way that both bars would be equal. Therewith it is possible to reduce cost of design, manufacturing and maintenance. Figure 4 shows a relative rotation between the two external half rings 9a, 9b in accordance with the patent EP 0557229B1. The divergent master petal 6a rotates clockwise and the divergent master petal 6b rotates counter-clockwise. These rotations cause a big gap between the divergent master petals 6a,6b that the divergent slave petal 31 has to cover. With a small angle of rotation the gap is to big and there is a sealing problem. Figure 5 shows the same rotation between the two external half rings 9a, 9b as figure 4, in accordance with the patent EP 0557229B1, but using the load strut 1 according to the preferred embodiment of the invention. In the same way as above, the divergent master petal 6a rotates clockwise and the divergent master petal 6b rotates counter-clockwise, but now there is a further divergent master petal 6c that remains at same position. Thus, the gap between the divergent master petals 6a,6b is distributed between two divergent slave petals 31a,31b, without sealing problems. A bigger relative rotation between the two external half rings 9a,9b is necessary to produce sealing problems. The variation range of the nozzle outlet area is bigger due to a bigger allowable relative rotation between the two external half rings 9a, 9b When there is a relative movement between the two external half rings 9a, 9b, there is a relative movement between the two bars 11,12 and then the distance between the two cylindrical linkages 17,18 of the transition part 16 changes slightly. However, the cylindrical linkage clearances allow this slight variation of the distance. Figure 6 shows the rotation of the two external half rings 9a, 9b together relative to the internal ring 7. In such a case, there is no relative movement between the two external half rings 9a, 9b and hence between the two load strut bars 11,12. Then, the load strut 1 works as a conventional load strut 19.

Claims: A mounting assembly for a divergent master petal of a variable geometry nozzle of a gas turbine engine, the assembly comprising a load strut (1), an external ring (9) composed of two external half rings (9a, 9b) joined by linkage and a divergent master petal (6), characterised in that the load strut (1) is linked to both half rings (9a, 9b) and to the divergent master petal (6). A mounting assembly according to claim 1, characterised in that the load strut comprises two bars (11, 12), a first one (11) of said bars being connected at an upstream end by a spherical or universal linkage (13) to a first external half ring (9a) and a second one (12) of said bars being connected at an upstream end by a spherical or universal linkage (14) to a second external half ring (9b), the bars (11, 12) further being connected to each other at a downstream end by a cylindrical linkage (15) which is substantially perpendicular to a theoretical plane (32) that contains both of said bars (11,12); the strut further comprising a transition part (16) arranged to be joined at one end with the divergent master petal (6) and connected at the other end to both of said bars (11, 12) by cylindrical linkages (17,18), substantially parallel and coplanar to the linkage (15) between the bars (11, 12). A mounting assembly according to claim 2, characterised in that at least some of the three cylindrical linkages (15, 17, 18) have enough clearance so as to allow for a distance variation between the ends of the two bars (11, 12).

Inventors: ELORRIAGA JAVIER, IKAZA DANIEL, MARTIN LUIS, ELORRIAGA, JAVIER, IKAZA, DANIEL, MARTIN, LUIS
Applicants: TURBO PROPULSORES IND, INDUSTRIA DE TURBO PROPULSORES, S.A.
Application year: 1997
Main classification: F02K1
IPC codes: F02K1