Patent Application
20160169155
The present invention relates to the field of propulsion nozzles, and in particular the field of rocket engine nozzles. More specifically, the present invention relates to assembling a propulsion nozzle comprising first and second segments, said first and second segments being made of materials that are thermally dissimilar.
The term “propulsion nozzle” is used to mean a nozzle of a shape that is appropriate for producing thrust by accelerating a propulsive fluid in a direction opposite from the thrust direction. In the description below, the terms “upstream” and “downstream” are defined relative to the normal flow direction of the propulsive fluid through the nozzle, and the terms “inside” and “outside” indicate respectively the regions inside and outside the nozzle.
Propulsion nozzles may in particular be convergents, for fluids that are not compressible or that reach only subsonic speeds, or they may be convergent-divergent for propulsive fluids that are compressible and that reach supersonic speeds. Rocket engines normally have convergent-divergent propulsion nozzles located directly downstream from combustion chambers. The expansion of the hot combustion gas leaving the combustion chamber through the propulsion nozzle serves to convert the thermal energy of the gas into kinetic energy. Consequently, the propulsion nozzles of rocket engines are typically subjected to extreme thermal stresses, since they come directly into contact with such combustion gas.
Furthermore, in order to be able to increase the propelled payload, it is appropriate to lighten the nozzle as much as possible. To do this, one possibility is to use segments made of materials that differ as a function of the thermal and mechanical stresses acting on each segment. Thus, by way of example, an upstream segment of the nozzle may be made at least in part out of metal in order to better remove the heat that is transmitted to the walls of the nozzle by the combustion gas, while a downstream segment, and in particular a divergent segment of the nozzle, where the combustion gas is significantly less hot after expanding and accelerating beyond the speed of sound, may be made of a composite material that is lighter in weight for comparable mechanical strength.
The different thermal characteristics of such materials can nevertheless raise major drawbacks. In particular, the physical connection between the segments may be subjected to large thermal and mechanical stresses as a result of the dissimilar thermal properties of the materials of the two segments.
Thus, the different coefficients of thermal expansion may lead to major mechanical stresses on the connection between the two segments. Also, the difference between the thermal conductivities of the two materials can also give rise to large temperature differences in the proximity of the junction between the two segments.
In a first aspect, the present disclosure seeks to propose a device for connecting together a first segment and a second segment of a propulsion nozzle that are made of thermally dissimilar materials, which provides a mechanical connection that is very reliable between said nozzle segments even under high thermal stresses.
This object is achieved by the fact that the connection device includes at least one pin with a first axisymmetric surface that is to be housed in a radial orifice of the first nozzle segment and a second axisymmetric surface that is eccentric relative to said first axisymmetric surface, and at least one eccentric bushing presenting an inside axisymmetric surface complementary to the second axisymmetric surface of the pin and an outside axisymmetric surface, that is eccentric relative to said inside axisymmetric surface and that is to be housed in a radial orifice of the second nozzle segment. The radial orientation of the pin when housed in the orifices of the two nozzle segments in order to connect them together may avoid large temperature gradients even when the temperatures of the inside walls of the two nozzle segments are very different in the proximity of their junction. Furthermore, the eccentricity between the two axisymmetric surfaces of the pin, and also between the two axisymmetric surfaces of the bushing, make it possible to adjust the position of the first axisymmetric surface of the pin in a plane perpendicular to the pin relative to the outside position of the axisymmetric surface of the bushing, in order to connect together the two segments even if their radial orifices are not accurately in alignment, e.g. as a result of axial prestress that needs to be maintained between the two nozzle segments in order to ensure a constant mechanical connection between the nozzle segments.
In particular, the axes of symmetry of the inside and outside axisymmetric surfaces of the eccentric bushing may present substantially the same offset between them as between the axes of symmetry of the first and second axisymmetric surfaces of the pin. Thus, the eccentric bushing and the pin turning jointly enables the relative position of the radial orifices of the two segments to be adjusted only in a direction parallel to a central axis of the nozzle, without necessarily giving rise to a corresponding relative movement in a tangential direction.
In order to retain the pin after it has been put into place between the two nozzle segments, the connection device may further include at least one axial retention member for axially retaining said pin, possibly associated with members for fastening said axial retention member to one of said nozzle segments.
At least some of said axisymmetric surfaces may in particular be cylindrical, thereby facilitating fabrication and facilitating installation of the bushing and of the pin. Nevertheless, it is also possible to envisage using other axisymmetric shapes, e.g. frustoconical shapes.
The present disclosure also relates to a propulsion nozzle including first and second nozzle segments made of thermally dissimilar materials, each having a radial shoulder bearing against a corresponding radial shoulder of the other one of said segments, together with a plurality of radial orifices facing corresponding orifices in the other one of said segments, and a plurality of the above-mentioned connection devices, with the first axisymmetric surface of the pin of each of them being housed in one of said radial orifices of the first segment, and the respective eccentric bushing is housed in the corresponding radial orifice of the second segment, the second axisymmetric surface of the pin co-operating with the inside axisymmetric surface of the eccentric bushing. The connection devices may thus maintain axial prestress between the two segments so as to maintain a strong mechanical connection between the segments, even under high levels of vibration.
In order to retain the eccentric bushings inside the radial orifices of the second nozzle segment after the two segments have been assembled together, each eccentric bushing may be retained between an outer surface of the first nozzle segment and a shoulder in the radial orifice of the second nozzle segment in which the eccentric bushing is housed.
The present disclosure also relates to a rocket engine with such a propulsion nozzle.
A second aspect of the present disclosure relates to a method of connecting together a first segment and a second segment of a propulsion nozzle that are made of thermally dissimilar materials, each of said segments including a plurality of radial orifices. The method includes at least the following steps:
Firstly inserting eccentric bushings in the radial orifices of the second nozzle segment, each bushing presenting an inside axisymmetric surface, and an outside axisymmetric surface that is eccentric relative to said inside axisymmetric surface.
Thereafter, causing a radial shoulder of the first segment to press against a radial shoulder of the second segment, said radial orifices of the first segment being put into register with corresponding orifices among the radial orifices of the second segment.
Finally, inserting pins in the radial orifices, each pin presenting a first axisymmetric surface that is to be housed in a radial orifice of the first nozzle segment and a second axisymmetric surface of the same connection part, that is eccentric relative to the first axisymmetric surface and complementary to the inside axisymmetric surface of one of said eccentric bushings. The first axisymmetric surface of the pin is aligned with the radial orifice of the first nozzle segment by turning the pin and the eccentric bushing in the corresponding radial orifice of the second segment.
Thus, thanks to the eccentricity of the pin and of the bushing, it is possible to adapt the geometry of the connection device formed by each bushing-and-pin pair to different relative positions in the axial direction of the nozzle of the radial orifices of the first segment relative to the radial orifices of the second segment, thus at least maintaining prestress between the two segments in that direction.
In order to obtain accurate prestress between the two elements, the prestress may be applied by external tooling while bringing the radial shoulder of the first segment to bear against the radial shoulder of the second segment. By way of example, the external tooling may comprise traction fingers or clamps. Nevertheless, as an alternative, it is also possible to envisage applying the prestress by turning the pin and the eccentric bushing in the corresponding radial orifice of the second segment.
The method may also include an additional step of putting into place at least one axial retention member for axially retaining said pins, in order to retain them in the radial orifices of the nozzle segments.
The invention may be well understood and its advantages appear better on reading the following detailed description of an embodiment given by way of nonlimiting example. The description refers to the accompanying drawings, in which:
Because of the greater thermal conductivity of the metal material of the throat 103a, and because it is subjected to regenerative cooling by the propellant flowing through the ducts 104, the temperature of the throat 103a in the proximity of its junction with the divergent portion 103b may be substantially lower than the temperature of the divergent portion 103b in the same zone. Furthermore, the metal of the throat 103a normally presents a coefficient of thermal expansion that is substantially different from that of the composite material of the divergent portion 103b. This gives rise to particular stresses for the mechanical connection between these two segments 103a and 103b.
Thus, in a conventional connection using radial flanges together with bolts, during operation of the rocket engine, the bolts suffer firstly from high levels of shear stress because of the difference of thermal expansion between the two adjacent segments of the nozzle, and secondly from nonuniform heating that tends to expand the bolts and thus to loosen the connection. Such a connection is thus normally unsuitable for this application.
The pin 106 and the bushing 107 may be seen more clearly in
The second axisymmetric surface 106b of the pin 106 is housed with a small radial clearance inside the inside axisymmetric surface 107a of the bushing 107, in such a manner as to allow relative rotation between these two parts, but without allowing significant relative movement in a direction perpendicular to the axis of rotation. In analogous manner, the first axisymmetric surface 106a of the pin 106 and the outside axisymmetric surface 107b of the bushing 107 are also housed with a small radial clearance respectively inside of the orifice 108 of the ring 109 and inside the corresponding radial orifice 110 of the ring 111.
In order to avoid of the pins 106 being able to escape from the radial orifices 108, the assembly also includes an axial retention member in the form of an annulus 117 fastened by screws 119 to the ring 109 of the throat 103a. Axial projections 117a from the annulus 117 engage in an annular groove 118 around an inside end 106c of each pin 106 projecting from the orifice 108, in order to retain each pin 106.
The connection shown in
In a first step, the bushings 107 are received inside the radial orifices 110 of the ring 111 of the divergent portion 103b, each coming into abutment against the shoulder 112 of the corresponding orifice 110. Thereafter, the divergent portion 103b is caused to press against the throat 103a as shown in
Thereafter, while this prestress F is being maintained between the opposite radial shoulders 113 and 114 of the throat 103a and of the divergent portion 103b, the pins 106 are inserted through the remaining orifices 110. For the purpose of bringing each pin 106 into exact alignment with the corresponding orifice 108 in the ring 109, the pin 106 and the bushing 107 may be turned in the orifice 110 in the manner shown in
h=s
1 sin α+s2 sin β
in which the angles α and β are the angles of rotation respectively of the pin 106 and of the bushing 107 starting from the position shown in
If the offsets s1 and s2 are substantially equal, and if the adjustment is purely vertical, as in the example shown, then the angles of rotation α and β will be substantially identical, and the value of the adjustment distance h will comply with the following formula:
h=2s1 sin α
After insertion of the pins 106 through the orifices 110 that are not occupied by the fingers 116 and into the corresponding orifices 108, the fingers 116 are removed and the pins 106 that have been installed take up the prestress F. The three orifices 110 now released of the fingers 116 may still receive respective pins 106, with their inside ends 106c being put into in alignment with the corresponding orifices 108 in the same manner. Each connection device 105 is self-locking, in the sense that the dimensions of the pin 106 and of the bushing 107, and the coefficients of friction between the various contacting surfaces, are such that neither the prestress F nor the additional stresses during operation of the rocket engine 1 may cause them to turn any more in order to relax the prestress.
Finally, the annulus 117 is put into place, engaging the annular grooves 118 of the pins 106 in order to retain them, and it is fastened to the ring 109 by means of screws 119.
The member for axially retaining the pins may be of a form other than the annulus 117 in this first embodiment. Thus, according to a second embodiment as shown in
Although in the first and second embodiments the ring of the downstream nozzle segment, i.e. of the divergent portion, surrounds the ring of the upstream nozzle segment, this arrangement may also be inverted. In a third embodiment, as shown in
Although the present invention is described above with reference to a specific embodiment, it is clear that various modifications and changes may be applied to those embodiments without going beyond the general ambit of the invention as defined by the claims. Furthermore, individual characteristics of the various embodiments mentioned may be combined in additional embodiments. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1356554 | Jul 2013 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2014/051700 | 7/2/2014 | WO | 00 |
