Abstract:
A turbopump includes a turbine fed with hot gas, a pump driven by the turbine and fed with liquid fluid, and a hot gas exhaust pipe situated downstream from the turbine. The turbopump includes a bleed-and-injection circuit including a bleeder for bleeding the liquid fluid at the outlet from the pump, a heater for heating the liquid fluid as bled off in this way so as to transform it into gaseous fluid, and an injector for injecting the gaseous fluid into an interface region of the turbopump situated between the pump and the turbine, so as to optimize the flow and temperature conditions of the fluid entering into the turbine cavity in order to eliminate the vibratory phenomena that result from interaction between the fluid and the turbine disk.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a turbopump comprising a turbine fed with hot gas, a pump driven by the turbine and fed with liquid fluid, and a hot gas exhaust pipe situated downstream from the turbine. 
         [0002]    Such turbopumps are known, e.g. for feeding propellant to the combustion chamber of a rocket engine. 
         [0003]    By way of example, Document EP 1 672 270 in the name of the Applicant describes a turbopump in accordance with the precharacterizing portion of claim  1 . 
         [0004]    The turbine drives the pump (or more precisely the rotor portion of the pump) at speeds that can be very high and can reach several thousands of revolutions per minute. Consequently, the component elements of the turbopump are subjected to high levels of stress and of vibration. In certain circumstances, the frequencies of such vibration can correspond to resonant modes of certain elements of the turbopump, and in particular of certain parts of the turbine, which can lead to the parts concerned being damaged. Such vibration has a negative impact on the operation of the turbopump and on its lifetime. 
         [0005]    In particular, it has been observed that high levels of vibration affect the upstream parts of the turbine (first disk of the turbine that is close to the pump). If this vibration is not damped sufficiently, the vibratory phenomenon can become large, thereby leading to significant damage to the first disk of the turbine, or indeed to destruction of the turbine. 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0006]    The invention seeks to limit the vibration that occurs in the turbopump, in particular the vibration that affects the upstream parts of the turbine, i.e. the parts close to the pump. 
         [0007]    This object is achieved by the fact that the above-mentioned turbopump includes a bleed-and-injection circuit comprising bleed means for bleeding the liquid fluid at the outlet from the pump, heater means for heating the liquid fluid as bled off in this way so as to transform it into gaseous fluid, and injector means for injecting the gaseous fluid into an interface region of the turbopump situated between the pump and the turbine. 
         [0008]    Research has made it possible to have better understanding of the origin of the vibration affecting the upstream parts of the turbine. To clarify the explanations below, it is assumed that these upstream parts are constituted mainly by the first disk of the turbine. 
         [0009]    Even if particular care is given to the connection between the pump and the turbine, in particular in terms of sealing, small leaks of the pumped liquid fluid occur, such that small quantities of the liquid fluid coming from the pump penetrate into the upstream portion of the casing of the turbine, in particular in the region of the first disk of the turbine. 
         [0010]    Interaction has been revealed between this fluid coming from the pump and the first disk of the turbine. Energetic coupling occurs between this fluid coming from the pump, in which pressure pulses develop, and the first disk that starts vibrating at one of its resonant frequencies under the effect of these pressure pulses. In the absence of sufficient damping, this vibratory phenomenon can become large, thereby leading to significant damage of the disk or even to destruction of the turbine. The invention enables this vibration to be limited, thereby avoiding damage to the turbine. 
         [0011]    Tests have shown that by modifying the thermodynamic conditions (flow rate, temperature) of the fluid coming from the pump and entering into the upstream portion of the pump casing, it is possible to reduce the amplitude of the vibratory phenomenon. 
         [0012]    The inventors have had the idea of bleeding the liquid fluid at the outlet from the pump and of deliberately injecting it into the interface between the pump and the turbine after heating it. Thus, the bled-off and heated liquid fluid is injected in gaseous form into the interface between the pump and the turbine so as to mix in this location with the leakage liquid fluid, thereby causing a hotter fluid to enter into the turbine casing, thus having the effect of significantly reducing or even eliminating the phenomenon of interaction between the fluid coming from the pump and the first disk of the turbine that leads to vibration in the first disk of the turbine, as mentioned above. 
         [0013]    The invention applies not only when the propellant is a cryogenic propellant, but also when the propellant is non-cryogenic. Either way, changing the temperature of the leakage fluid as a result of being mixed with the heated fluid modifies the thermodynamic conditions of the fluid in the desired direction. 
         [0014]    Advantageously, the gaseous fluid is injected via a dynamic sealing system that is located in the interface region situated between the pump and the turbine. 
         [0015]    The sealing system needs to be dynamic since it is mounted on a rotary shaft—the shaft that is common to the turbine and to the pump—in order to provide sealing between a hot environment in which the fluid is gaseous (turbine end) and the cryogenic environment in which the fluid is liquid (pump end). 
         [0016]    The dynamic sealing system is situated in the interface region between the pump and the turbine. 
         [0017]    The rotor of the pump is driven in rotation by the turbine so as to pump the propellant for injection into the combustion chamber of a rocket engine. In the context of the invention, and as often happens in the field of space propulsion, the fluid used as cryogenic propellant is liquid hydrogen. 
         [0018]    Thus, advantageously, the turbine is fed with hot gas and the pump is fed with liquid hydrogen. 
         [0019]    Advantageously, the bleed-and-injection circuit includes a bleed pipe extending from the outlet from the pump to the inlet of a heat exchanger co-operating with the exhaust pipe, and an injection pipe extending from the outlet of the heat exchanger to the interface region, in particular from the outlet of the heat exchanger to the dynamic sealing system. 
         [0020]    Advantageously, the heat exchanger comprises a fluid flow chamber with a wall situated in the hot gas exhaust pipe. 
         [0021]    For the purpose of heating the bled-off liquid, this makes it possible to use heat energy that is already available in the hot gas exhausted by the turbopump. 
         [0022]    Advantageously, the flow chamber is coil shaped. 
         [0023]    A coil provides a large contact surface area with the hot gas exhausted into the pipe in which the coil is situated. 
         [0024]    Advantageously, the bleed-and-injection circuit includes means for controlling the flow of the liquid fluid in the bleed pipe. 
         [0025]    To perform this control, which may be in the form of regulating pressure and/or flow rate in a manner defined by testing, the quantity of fluid that is bled off is a quantity that is necessary and sufficient for obtaining the desired reduction in vibration. 
         [0026]    Advantageously, the means for controlling the flow of liquid fluid in the bleed pipe comprise means for adjusting the fluid pressure. 
         [0027]    Advantageously, the bleed-and-injection circuit includes a bypass pipe for bypassing the heat exchanger between the bleed pipe and the injection pipe, and means for sharing the liquid fluid between the bypass pipe and the heat exchanger. 
         [0028]    It is particularly advantageous to control the temperature of the gaseous fluid that is injected into the interface region between the pump and the turbine. This control over the temperature of the gaseous fluid is provided by the bypass pipe. The bypass pipe makes it possible to tap off liquid propellant prior to being injected into the heat exchanger in order to reinject it into the outlet from the heat exchanger, thereby causing it to be mixed with the fluid that has been vaporized in the heat exchanger and of temperature, if it is too high, that is lowered on coming into contact with the liquid fluid. 
         [0029]    Advantageously, the means for sharing the liquid fluid comprises an adjustable constriction on at least one of the elements constituted by the bypass pipe and a segment of the bleed pipe that extends between the bypass pipe and the heat exchanger. 
         [0030]    The adjustable constriction makes it possible to adapt the quantity of liquid fluid that is transformed into gaseous fluid at the outlet from the heat exchanger, and thus to control the temperature of the gaseous fluid that results from mixing between the gaseous fluid coming from the heat exchanger and the liquid fluid coming from the bypass pipe, which mixture is then injected into the dynamic sealing system; this is done while taking account of the temperature of the hot gas in the exhaust pipe and of the capacity of the heat exchanger. 
         [0031]    Advantageously, the bleed-and-injection circuit includes means for adjusting flow rate in the injection pipe. 
         [0032]    Advantageously, the turbopump includes a helium feed circuit for injecting helium into at least one of the elements constituted by the pump and by the turbine, with helium injection advantageously taking place via the dynamic sealing system. 
         [0033]    The helium flow circuit serves to provide sealing between the pump while cooling down the engine and the turbopump prior to igniting the engine. By means of the above-described provision, advantage is taken of a portion of this circuit for the purpose of injecting the anti-vibration gaseous fluid. 
         [0034]    The use of this pre-existing helium flow system presents the advantage of avoiding any need to incorporate an additional flow system for passing the flow of gaseous fluid and then for injecting it into the interface region of the turbopump situated between the pump and the turbine, with injection taking place in particular via the dynamic sealing system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    Other characteristics and advantages of the invention appear on reading the following description of a preferred embodiment of the invention, given by way of example and with reference to the accompanying drawings. 
           [0036]      FIG. 1  is a section view showing a conventional turbopump (shown in simplified manner to facilitate understanding the invention). 
           [0037]      FIG. 2  is a section view of the same turbopump provided with the fluid recirculation system in an embodiment of the invention. 
           [0038]      FIG. 3  is a detail view of the interface region between the pump and the turbine of the turbopump, shown in the zone into which, in accordance with the invention, the gaseous fluid coming from the fluid that has been bled off is injected. 
           [0039]      FIG. 4  is a diagrammatic view of a heat exchanger in an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]      FIG. 1  is a simplified view of a turbopump  10  comprising at least a pump  14  and a turbine  12  connected together by a common rotary shaft  13 ,  13 ′. This type of turbopump  10  is used in particular in liquid-propellant rocket engines in order to bring the propellants up to the pressure at which the propellants are injected into a combustion chamber of such an engine. In very diagrammatic manner, there can be seen the rotor  14   a  of the pump  14  and the rotary disk  12   a  of the turbine  12 . Reference  1  designates the casing of the turbopump, which includes a pump casing portion and a turbine casing portion. 
         [0041]    Rotation of the turbine  12  causes the shaft  13 ,  13 ′ to rotate, thereby driving the rotor of the pump  14  in rotation for the purpose of pumping a liquid from a feed  22 . By way of example, the turbine  12  is driven by a gas generator on board the rocket engine. This applies to turbopumps in which the turbine is actuated by the expansion of hot gas  20  generated by the gas generator. 
         [0042]    Nevertheless, the turbine  12  of this type of turbopump could also be an expander cycle turbine. This applies to turbopumps in which the turbine is driven by the expansion of a propellant in the gaseous state after it has been heated via the wall of the combustion chamber. 
         [0043]    The hot gas  20  that has driven the turbine  12  in rotation is exhausted via a hot gas exhaust pipe  16 . The hot gas that drives rotation of the turbine may for example be gaseous hydrogen (expander cycle) or a mixture of gaseous hydrogen and steam (gas generator cycle). 
         [0044]    By way of example, the pumped liquid fluid may be a propellant, and in particular liquid hydrogen, that the pump  14  raises to pressure at its outlet  21  for the purpose of injecting the propellant into a combustion chamber of an engine (not shown) associated with the turbopump. 
         [0045]    The hot and gaseous environment of the turbine  12  is sealed from the cryogenic and liquid environment of the pump  14  by a dynamic sealing system  18  that co-operates firstly with the shaft  13 ,  13  and secondly with the casing  1  of the turbopump. In spite of this sealing, a small leak of liquid hydrogen is liable to flow from the pump environment  14  to the turbine environment  12 , as represented by arrows f. This leakage liquid reaches the turbine casing portion upstream from the first disk of the turbine. It thus becomes mixed, in a zone Z marked in  FIG. 1 , with the hot gas leaving the upstream cavity  1 A of the turbine. 
         [0046]    Bearings  13 A and  13 ′A support the shaft  13 ,  13  in rotation relative to the casing  1  of the turbopump. 
         [0047]    There follows a description of an embodiment of the invention, with reference to  FIG. 2 . 
         [0048]    In the description below, reference is made, by way of example, to using a hot gas mixture of hydrogen and steam as the fluid flowing through the turbopump for rotating the turbine, and to using hydrogen in liquid form as the liquid fluid being pumped. Nevertheless, other types of fluid could be envisaged, e.g. depending on the type of propellant concerned. 
         [0049]    In the invention, and as shown in  FIG. 2 , a bleed-and-injection circuit C is added to the  FIG. 1  turbopump. This circuit has bleed means  30  that in the embodiment shown comprise a bleed pipe  30  bleeding liquid hydrogen at the outlet  21  from the pump  14 . This liquid hydrogen is at a high outlet pressure, e.g. about 185 bars. The fluid bled through this bleed pipe  30  then reaches the inlet  32  of a heat exchanger  34 , while it is still in liquid form, and it leaves the heat exchanger at  36  in gaseous form. The outlet  36  from the heat exchanger  34  is connected to an injection pipe  50  that leads into the dynamic sealing system  18  situated at the interface between the pump  14  and the turbine  12 . Specifically, the dynamic sealing system has two gaskets that are axially spaced apart in the longitudinal direction of the shafts  13 ,  13 ′, and injection takes place between these two gaskets. 
         [0050]    Specifically, the heat exchanger  34  co-operates with the hot gas exhaust pipe  16  so as to enable it to be heated by the gas coming from the turbine exhaust. More precisely, the heat exchanger  34  is situated in a segment of the pipe  16 . 
         [0051]    The temperature of the liquid hydrogen at the net to the heat exchanger may for example be about 40 K. At the outlet from the heat exchanger  36 , the hydrogen is gaseous as a result of being heated in the heat exchanger. 
         [0052]    In the example shown, pressure regulator means  38  are situated on the liquid hydrogen bleed pipe  30 . The pressure regulator means  38 , e.g. a constriction of variable section, serves to reduce the pressure of the liquid hydrogen flowing in the pipe  30 , e.g. to take it to a pressure of about 110 bars downstream from the constriction. 
         [0053]    Provision could be made for all of the liquid hydrogen downstream from the pressure regulator means  38  to reach the inlet of the heat exchanger. Nevertheless, in the example shown, a bypass pipe  40  serves to bypass the heat exchanger  34  so that a portion of the fluid that has been bled off can pass directly from the bleed type  30  to the injection pipe  50 . Under such circumstances, only a portion of the liquid hydrogen at low pressure is injected into the heat exchanger  34  in order to be heated, while the remaining portion passes directly into the injection pipe  50  without being heated. It can be understood that the relative proportions of heated hydrogen and of non-heated hydrogen determine the temperature of the gaseous fluid that results from mixing them together and that is injected into the region of the dynamic sealing system  18 . 
         [0054]    In order to adjust these proportions, the fluid bleed and injection circuit has means for sharing the liquid hydrogen between the heat exchanger and the bypass pipe. These means may comprise flow sharing means between the bypass pipe  40  and the segment  31  of the bleed pipe  30  that extends between the bypass pipe  40  and the inlet  32  of the heat exchanger. They may merely comprise a flow rate limiter situated on the bypass pipe  40  or on the segment  31 . In the example shown, flow rate adjustment means  39  of the adjustable section constriction type are provided on the segment  31 , and flow rate adjustment means  42  of adjustable section constriction type are provided on the bypass pipe  40 . 
         [0055]    The adjustable constriction  38  serves to adjust the pressure at the inlet to the heater device. The constrictions  39  and  42  serve to adjust the proportion of the fluid that is heated and vaporized in the heat exchanger compared with the proportion that remains liquid and cold, thus making it possible to adjust the temperature of the fluid injected by the pipe  50 , e.g. in order to obtain a temperature of about 300 K. Under all circumstances, the proportions are such that the fluid leaving the pipe  50  is in gaseous form. 
         [0056]    In the example shown, the injection pipe  50  also has means  44  for adjusting the rate at which gaseous hydrogen is injected, e.g. a constriction of adjustable section. These adjustment means are situated in the downstream portion of the pipe  50 , downstream from the connection node  43  between the bypass pipe  40  and the outlet from the heat exchanger. By way of example, this ensures that the gaseous hydrogen is injected into the dynamic sealing system  18  at a flow rate of about 7 grams per second (g/s). 
         [0057]      FIG. 3  shows the dynamic sealing system  18  in detail. 
         [0058]    This figure is a diagram showing the location of the end  50 A of the injection pipe  50  as described above with reference to  FIG. 2 . As can be seen, this end  50 A leads into the region of the dynamic sealing system  18  in order to inject gaseous hydrogen into that location. More particularly, the injection at the outlet from the end  50 A takes place at a location referred to as the “inter-ring” location  52  of the dynamic sealing system  18 . This inter-ring location  52  is situated between two sealing gaskets, respectively referenced  55  and  55 ′, that are held by two flanges, respectively referenced  51  and  51 ′, and by a spacer  53 . The gaseous hydrogen from the injection pipe  50  is injected between the two gaskets  55  and  55 ′ via holes  53 ′ that are pierced radially through the spacer  53 . 
         [0059]    A small leakage flow of liquid hydrogen  54  comes from the environment of the pump and flows towards the environment of the turbine. 
         [0060]    This small flow of liquid hydrogen  54  is vaporized as it comes into contact with the gaseous hydrogen. Thus, all of the leakage fluid is vaporized. 
         [0061]    The mixing between the leakage liquid fluid and the gaseous fluid injected into the inter-ring location  52  takes place in the downstream region of the inter-ring location  52 , where “downstream” is in the flow direction of the gaseous fluid injected by the pipe  50 . Specifically, mixing takes place in the gaps between the spacer  53  and the shafts  13 ,  13 ′. The pressure at which the gaseous hydrogen is injected into the inter-ring location  52  is of the order of 35 bars, for example. 
         [0062]      FIG. 4  is a diagrammatic view of the heat exchanger  34  situated in the hot gas exhaust pipe  16 . This heat exchanger  34  is preferably held by attachments  35  that withstand thermal expansion. 
         [0063]    The heat exchanger  34  is in the form of a coil. It could have other shapes appropriate for a heat exchanger. 
         [0064]    Nevertheless, and byway of example, when the heat exchanger  34  is in the form of a coil, it presents: a thickness of about 1 millimeter (mm), and it is helically wound so as to form a plurality of turns. 
         [0065]    The temperature inside the hot gas exhaust pipe  16  usually lies in the range about 600 K to about 700 K. 
         [0066]    The injection pipe  50  uses a portion of the helium flow circuit in the turbopump. In the example shown, the turbopump includes a helium feed connected to the dynamic sealing system  18  that provides sealing for the pump during the stage prior to igniting the engine that the turbopump  10  is to feed; this stage is known as the stage of cooling down the engine. No propellant leak between the pump  14  and the turbine  12  is acceptable during this stage. 
         [0067]    As can be seen in  FIG. 2 , the injection pipe  50  includes the terminal segment  67  of the pipe for feeding the dynamic sealing system with helium. Thus, a portion of the helium flow circuit is reused for making a portion of the bleed-and-injection circuit of the invention. It should be observed that the segment  67  includes a check valve  66  that is situated upstream from its connection to the injection pipe  50  so as to prevent hydrogen coming from the pipe  50  penetrating into the helium delivery circuit. 
         [0068]    The gaseous hydrogen is introduced into the helium feed circuit of the turbopump  10  after its engine has been ignited, once the pressure at the outlet from the pump reaches a sufficient value. The gaseous helium and hydrogen thus coexist in the same circuit for a few seconds. Once this time has elapsed, only gaseous hydrogen flows in the segment  67 . 
         [0069]    It should be observed that flexible portions may be provided on the above-described pipes (in particular the bleed pipe  30  and the injection pipe  50 ) in order to absorb relative movements between these pipes  30  and  50  within the turbopump  10 .