WO2019110889A1

WO2019110889A1 - Improved device for clamping heat shields for rocket engine diverging nozzle section

Info

Publication number: WO2019110889A1
Application number: PCT/FR2018/052974
Authority: WO
Inventors: Alain Pyre
Original assignee: Arianegroup Sas
Priority date: 2017-12-06
Filing date: 2018-11-26
Publication date: 2019-06-13
Also published as: FR3074540A1; FR3074540B1

Abstract

Assembly for a rocket engine diverging nozzle section, comprising a rocket engine diverging nozzle section having an outer wall and an axis of revolution, a plurality of heat shield blocks which are made of a thermally insulating material and are designed to be placed against the outer wall, at least one cable (10) that has two ends (10a, 10b) and is designed to be wound about a circumference of the diverging nozzle section so as to press the plurality of heat shield blocks against the outer wall, the cable (10) having a coefficient of thermal expansion lower than that of the diverging nozzle section along its circumference, a clamping device (20) designed to keep the two ends (10a, 10b) of said at least one cable (10) face to face; the assembly further comprising at least one cable payout unit (40) through which the cable (10) can slide and which is designed to urge a portion of the cable (10) to follow a predetermined path having a certain length; the cable payout unit (40) being designed such that, when the temperature increases, said length also increases, but to a lesser extent than the length of the circumference of the diverging nozzle section.

Description

Improved thermal protection clamping device for rocket motor divergent

FIELD OF THE INVENTION

The invention relates to the field of space launchers, and more particularly divergents equipping the engines of space launchers.

STATE OF THE PRIOR ART

The divergents are subjected to extremely large heat fluxes that may cause them to reach particularly high temperatures, and, as a result, may compromise their mechanical integrity, so it is essential to provide protection devices. thermal to protect the divergents.

These thermal protection devices are generally arranged around the diverging, and pressed against an outer face thereof with the aid of holding cables. To provide sufficient thermal protection, it is necessary that the thermal protections remain sufficiently tight against the divergent throughout the flight. Consequently, the cables allowing the tightening of the thermal protections must remain sufficiently tight, regardless of the thermal stresses existing during the flight. However, the cables must not be excessively tight in order not to damage the thermal protections and / or to unacceptably force the diverging ones. Moreover, these cables must be made of a material resistant to strong thermal stresses in flight, in order to maintain their mechanical properties, and thus ensuring sufficient tightening of the thermal protections throughout the flight. However, the coefficients of thermal expansion of the cables and the divergent are different from each other. Similarly, the temperatures of the cables and the divergent can vary greatly during the flight phase. At the beginning of flight for example, the divergent heats faster than the cables, which has the consequence of increasing the tightening of the cables. During flight, the cables may be hotter than the diverging. Nevertheless, since the coefficient of thermal expansion of the cables is very low compared to that of the divergent, the expansion of the divergent remains greater than that of the cables, so that the tightening of the latter also increases. Therefore, in case of high thermal gradients, when the expansion of the divergent is greater than that of the cable or cables, they are likely to break. There is therefore a need for a device to ensure a sufficient clamping of the thermal protections, whatever the thermal stresses.

PRESENTATION OF THE INVENTION

The present disclosure relates to a set for rocket engine divergent, comprising:

a diverging rocket motor having an outer wall and an axis of revolution,

a plurality of thermal protection blocks made of thermally insulating material, configured to be arranged against the outer wall,

at least one cable having two ends and configured to be wound around a circumference of the divergent so as to press the plurality of thermal protection blocks against the outer wall, the cable having a coefficient of thermal expansion less than that of the divergent, according to its circumference,

- A clamping device configured to maintain the two ends of said at least one cable vis-à-vis;

the assembly further comprises at least one cable reserve, through which the cable can slide, and configured to constrain a portion of the cable to follow a predetermined path having a given length; the cable reserve being made such that, as the temperature increases, said length also increases, but to a lesser extent than the length of the divergent circumference.

The thermal protection blocks may consist of different types of thermally insulating materials. They may be distributed on the outer wall of the divergent, being arranged against each other, so as to cover at least part of the surface of the outer wall, preferably the entire surface. To optimize their thermal protection function, and withstand dynamic stresses during flight, these blocks must be pressed against the outer wall of the diverging. This is possible thanks to at least a cable wrapped around the outer wall of the divergent, so as to perform at least one turn of the circumference thereof. In this way, the thermal protection blocks are sandwiched between the outer wall of the divergent and the at least one cable. The cable may have a circular section or any other shape.

To ensure the clamping of the thermal protection blocks against the outer wall of the diverging, the cable must be sufficiently tight. This is possible thanks to the clamping device. The cable is wrapped around the divergent so that its two ends are vis-à-vis, close to each other, after being wound in one or more turns around the diverging. Both ends of the cable are then held in this position by the clamping device. The clamping device can be any system allowing the locking of the two ends of the cable and the maintenance of the clamping of the cable around the diverging, for example a system comprising plates taking the ends of the cable sandwich, or other.

By cable reserve, it comprises a device made so that the cable follows a predetermined path within the reserve. In other words, within the cable pool, it does not follow the circumference of the divergent rectilinearly, but can be wound or folded so as to form back and forth on both sides of the reserve of cable. The length of the cable on this predetermined path within the cable pool is therefore greater than the length that the cable would have had in the absence of a reserve of cable, if it had simply been wound around the divergent over its entire circumference .

The length of the cable, due to the presence of the cable pool, allows it to expand sufficiently to accompany the expansion of the divergent. This is made possible by the fact that the cable is free to slide along its predetermined path inside the cable pool, and can therefore accompany the increase in the circumference of the divergent under the effect of thermal stresses. Specifically, the cable has a coefficient of thermal expansion less than the coefficient of thermal expansion of the divergent. Therefore, when the temperature increases in the absence of a reserve of cable, the cable is very tight around the diverging. On the other hand, in the presence of the reserve of cable, the cable can slide the along its predetermined path when the divergent expands under the effect of an increase in temperature. This allows a balancing of the tensions between the divergent and the reserve; thus the final tension is less than if there was no reserve of cable.

The presence of the cable reserve therefore ensures a sufficient cable clamping around the divergent subjected to strong thermal fluctuations, limiting or avoiding the risk of rupture of the cable.

In certain embodiments, the predetermined path comprises at least one round trip or a loop between two supports of the cable reserve; and the average coefficient of thermal expansion of the measured cable reserve from one support to the other is less than the coefficient of thermal expansion of the divergent circumference.

The supports may be studs machined in the cable pool, around which the cable can pass along its predetermined path, and against which it can bear when it is stretched. Thus, along its predetermined path, the cable bypasses a first support in one direction, then bypasses a second support in an opposite direction, thus making a round trip. The coefficient of thermal expansion of the cable portion disposed between two supports is less than the coefficient of thermal expansion of the divergent circumference. Thus, the number of round trips of the cable in the cable pool can be determined in such a way as to obtain an optimum tightening of the cable around the divergent, making it possible to ensure sufficient clamping around it in the event of large temperature increases. , while limiting or avoiding the deterioration of the thermal protections and the divergent.

In some embodiments, the supports have a shape inscribed in a cylinder and are configured for the cable to pass against them along its predetermined path.

The cable reserve may have the form of a plate, and the supports may be cylinders protruding from the plate. Alternatively, the cable pool may comprise two plates separated from each other by the cylindrical supports, the cable passing against these supports between the two plates. In this case, one end of the cylindrical supports is fixed to the first plate, and the opposite end cylindrical supports is fixed to the second plate. According to this alternative, the cable passes between the two plates along its predetermined path bypassing the cylindrical supports. The presence of these two plates prevents the cable from getting out of the cable pool, by sliding along a cylindrical support for example. When the cable pool has two cylindrical supports, they can each be arranged at a distal end of the plate. Thus, along its predetermined path, the cable bypasses a first support disposed at one end of the plate, then bypasses a second support disposed at the opposite end, bearing against these supports, and thus achieving a round trip. The cylindrical supports have the advantage of being easy to achieve, and allow the cable to slide against them when it expands, without deteriorating.

In some embodiments, the cable is made of carbon fiber.

This material has the advantage of maintaining a high stiffness at high temperatures, for example 1700 K.

In some embodiments, the cable pool is made of carbon.

The cable pool, that is to say the plate or plates that it has and the cylindrical supports, are made of carbon. The use of carbon allows the cable pool to withstand high thermal stresses in flight. Moreover, the cable pool can thus expand in the same proportions as the carbon fiber cable.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will be better understood on reading the detailed description given below of various embodiments of the invention given by way of non-limiting examples. This description refers to the pages of annexed figures, in which:

FIGS. 1A and 1B schematically represent an assembly for rocket engine divergent according to the present invention;

- Figure 2 shows schematically a cable and a cable reserve of the assembly of Figure 1;

- Figure 3 shows schematically a cable reserve of the assembly of Figure 1;

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS An assembly for rocket engine divergent according to the present invention will be described with reference to Figures 1 to 3. Figure IA shows an assembly comprising a rocket engine divergent 1 having an outer wall 2, a set of blocks thermal protectors 3 distributed on the outer wall 2 of the divergent, and a set of cables 10 wound around the divergent, and for pressing the thermal protection blocks 3 against the outer wall 2 of the diverging. In this nonlimiting example, the cables 10 are circular section cables, whose diameter d is between 3 and 10 mm.

Figure IB shows a partial section of the assembly of Figure IA, along the IA-IA section plane. As represented in FIGS. 1A and 1B, the assembly comprises several successive rows of blocks 3 distributed in a vertical direction of the divergent 1, against its outer wall 2. Each row of blocks 3 is held and pressed against the outer wall 2 by At least one cable 10. In the example of FIG. 1A, two cables are arranged around each row of blocks 3, but more cables can be provided. Each thermal protection block 3 has an inner face 31, configured to be disposed against the outer wall 2 of the diverging portion 1, and an outer face 32, opposite to the inner face 31. The thermal protection blocks are made of thermally insulating material. For example and without limitation, the blocks 3 comprise an expanded cork type material, which also gives it satisfactory properties of lightness, flexibility and resistance to shock and moisture.

The divergent 1 may further comprise a plurality of stiffeners 4 which extend circumferentially on the outer wall 2; for example and without limitation, the stiffeners 4 extend substantially parallel to each other, regularly. Each thermal protection block 3 is configured to be pressed against the outer wall 2, despite the presence of the stiffeners 4. The blocks 3 comprise for example notches 33, in which the stiffeners 4 can be inserted.

In addition, the thermal protection blocks 3 comprise, on their outer face 32, grooves 34 extending in a circumferential direction, in which the cables 10 may housing. The grooves 34 may extend in a plane perpendicular to the axis of revolution of the divergent, or inclined relative to this axis, so that the cables 10 are arranged helically around the divergent, when they are housed in the grooves 34. The cables can thus press the blocks 3, and tighten the latter against the outer wall 2, without risking to move along the vertical direction of the divergent 1 during flight.

Figure 2 illustrates a single cable 10 with a clamping device 20, for clamping the cable 10 around the diverging 1, and two cable reserves 40. The cable 10 has a first end 10a and a second end 10b. The clamping device comprises a first locking element 20a and a second locking element 20b. The first locking element 20a makes it possible to block the first end 10a of the cable 10, and the second locking element 20b makes it possible to block the second end 10b of the cable 10. Thus, when the cable 10 is stretched around the divergent 1, so to press and tighten the blocks 3 against the outer wall 2, the ends 10a and 10b of the cable 10 remain blocked by the clamping device 20. The tightening of the cables 10 can thus be maintained during the flight. The clamping device 20 may be any system for locking the two ends of the cable 10a and 10b and maintaining the clamping of the cable around the diverging, for example a tensioner, or other. In addition, the first and second locking members 20a, 20b can be fixed and tightened to each other by a screw / nut system, for example, to tension the cable 10 around the diverging portion 1.

Figure 2 illustrates two cable reserves 40. Nevertheless, different numbers are possible: a reserve of cable, three or more.

FIG. 3 schematically represents a reserve of cable 40 in a view perpendicular to the axis of revolution of divergent 1. Thus, the left-right direction on the sheet of FIG. 3 corresponds to the circumferential direction of divergent 1, and the up-down direction on the sheet of FIG. 3 corresponds to the direction of the axis of revolution of the divergent 1. Therefore, in the rest of the description, the lower and upper ends of the cable reserve 40, and the part central disposed between the lower and upper ends, are considered along the axis of revolution of the divergent 1.

The cable pool 40 comprises a plate 41 and a plurality of pads 42 projecting from the plate 41. Alternatively, the cable pool may comprise two plates 41 separated from each other by the pads 42 , the plate assembly 41 and pads 42 forming a single block. In this case, one end of the pads 42 is fixed to the first plate 41, and the opposite end of the pads 42 is fixed to the second plate 41. According to this alternative, the pads 42 are sandwiched between the two plates 41 , the cable 10 thus passing between these two plates 4L or the plates 41 may be carbon, and the pads 42 may be cylindrical. When the cable 10 is tightened around the diverging portion 1, the cable 10 follows the circumference of the divergent portion 1, as illustrated in FIG. 1A, and passes into the cable reserve 40, itself disposed around the divergent portion 1, against the outer surface of it (more exactly, against the surface of the blocks of thermal protections 3). By passing through the cable pool 40, the cable 10 follows a predetermined path. In this example, a stud 42 is disposed in the central portion of the cable reservoir 40 at each end, in the circumferential direction of the diverging portion 1, of the cable reserve 40. L _e denotes the distance between these pads 42 in the direction In addition, in this example, three pads 42 are arranged at the lower end of the cable pool 40, and three pads 42 are arranged at the upper end of the cable pool 40. Preferably, a distance H, along the axis of revolution of the divergent 1, between a stud 42 disposed at the lower end of the cable reserve 40, and a stud 42 disposed at the upper end of the cable reserve 40, is included between 40 and 70 mm, preferably between 50 and 65 mm, more preferably between 58 and 62 mm.

The predetermined path of the cable 10 in the cable pool 40 is determined by the pads 42. The cable 10 passes along each pad 42 bypassing and bearing against them. More specifically, the cable 10 first bypasses a stud 42 disposed in the central portion of the cable reserve 40, then back and forth between the lower end and the upper end of the cable reserve 40, successively bypassing the studs on each of these ends. In this example, the cable pool 40 is configured such that the cable travels three times back and forth. More generally, the number N of round trips is optimized so that, thanks to the total length of the cable 10, the increase of the tension of the cable 10 remains moderate, which makes it possible to avoid excessive tightening of the cable. cable 10 in case of large temperature increases. The length of the cable 10, due to the presence of the cable reserve 40, and the number N of back and forth, allows it to expand sufficiently to accompany the expansion of the divergent 1. This is made possible by the fact that the cable 10 is free to slide along the pads 42 inside the cable pool 40, and can therefore accompany the increase in the circumference of the divergent under the effect of thermal stresses.

The minimum number N of round trips and the distance H between the ends of the reserve must be calculated according to the expansion coefficients of the divergent, the cable and the cable reserve, the temperatures reached in the divergent and in the cable pool, the circumference of the divergent, and also depending on the voltage or the maximum elongation (e) considered admissible for the cable 10 when the latter expands with temperature. In the case of a carbon fiber cable, for example, an elongation of the order of 1% of the cable, relative to its initial length at ambient temperature, may cause the cable to break. In order to avoid such a break, a margin of 10% with respect to the elongation at break of the cable 10 can be fixed. It is therefore necessary to determine the minimum minimum number N of round trips, and the distance H between the ends of the reserve, to maintain a lengthening of the cable less than 0.90%, depending on the above parameters.

Different cases are possible. A first case corresponds to a case in which the divergent has reached an equilibrium temperature in operation (approximately 1000 K) but in which the thermal protection blocks 3 and the cables 10 have not yet heated. In this case, for a distance H = 60 mm, the optimal number N of round trips is N = 6. In fact, for lower numbers, the cable 10 is stretched by the divergent 1 with a deformation greater than its deformation rupture, which can cause the rupture thereof. This value of N = 7 thus makes it possible to obtain at least 10% margin with respect to the elongation at break of the cable 10.

A second case corresponds to a subsequent situation in which the heat flow also strongly heats (at 1500 K for example) the thermal protection blocks 3 and the cable 10. In this case, for a distance H = 60 mm , the number N of round trips can be N = 4 or more, in order to keep at least 10% of the margin with respect to the elongation at break of the cable 10.

Although the present invention has been described with reference to specific embodiments, it is obvious that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the revendications. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

1. A set for rocket engine divergent, comprising:

a rocket engine divergent (1) having an outer wall (2) and an axis of revolution,

a plurality of thermal protection blocks (3) made of thermally insulating material, configured to be arranged against the outer wall (2),

at least one cable (10) having two ends (10a, 10b) and configured to be wound around a circumference of the divergent (1) so as to press the plurality of thermal protection blocks (3) against the outer wall ( 2), the cable (10) having a coefficient of thermal expansion smaller than that of the divergent (1), according to its circumference,

- a clamping device (20) configured to maintain the two ends (10a, 10b) of said at least one cable (10) vis-à-vis;

the assembly being characterized in that it further comprises at least one cable reserve (40), through which the cable (10) can slide, and configured to constrain a portion of the cable (10) to follow a predetermined path having a certain length; the cable reservoir (40) being constructed such that, as the temperature increases, said length also increases, but to a lesser extent than the length of the circumference of the divergent (1).

2. The assembly of claim 1, wherein the predetermined path comprises at least one round trip or loop between two supports (42) of the cable pool (40); and the average coefficient of thermal expansion of the cable pool (40) measured from one support (42) to the other is less than the coefficient of thermal expansion of the circumference of the divergent (1).

3. The assembly of claim 2, wherein the supports (42) have a shape inscribed in a cylinder and are configured so that the cable (10) passes against them along its predetermined path.

4. An assembly according to any one of claims 1 to 3, wherein the cable (10) is carbon fiber.

5. An assembly according to any one of claims 1 to 4, wherein the cable pool (40) is carbon.