Abstract:
A gas turbine includes an annular combustion chamber and an outer wall of an annular combustion chamber. A straining ring is arranged on the outer wall of the annular combustion chamber and enables oscillations of the outer wall to be damped via friction. The effects of combustion oscillations produced by damaging vibrations of the annular combustion chamber are thus reduced. A method is further for damping an oscillation of an outer wall of an annular combustion chamber.

Description:
This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/EP01/11511 which designated the United States of America and which claims priority on European Patent Application number EP 00122554.9 filed Oct. 16, 2000, the entire contents of which are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention generally relates to a gas turbine with a compressor, with an annular combustion chamber and with a turbine part. The invention also generally relates to a method for the damping of oscillations of an annular combustion chamber of a gas turbine. 
     BACKGROUND OF THE INVENTION 
     DE 43 39 094 A describes a method for the damping of thermoacoustic oscillations in the combustion chamber of a gas turbine. During the combustion of fuels in the combustion chamber of a stationary gas turbine, an aircraft or the like, the combustion processes may result in instabilities or pressure fluctuations which, under unfavorable conditions, excite thermoacoustic oscillations which are also called combustion oscillations. These not only constitute an undesirable sound source, but may lead to inadmissibly high mechanical loads on the combustion chamber. Such thermoacoustic oscillation is actively damped in that the location of the heat release fluctuation associated with combustion is controlled by the injection of a fluid. 
     SUMMARY OF THE INVENTION 
     An object of an embodiment of the invention is to specify a gas turbine with an annular combustion chamber which is particularly robust with respect to combustion oscillations. A further object of an embodiment of the invention is to specify a method for damping the oscillation of an annular combustion chamber of a gas turbine. 
     According to an embodiment of the invention, the object directed at a gas turbine may be achieved by a gas turbine with a compressor, with an annular combustion chamber and with a turbine part being specified. The annular combustion chamber preferably includes an outer wall with an outer surface, and the annular combustion chamber is preferably surrounded on its outer surface by a tension ring. 
     Conventional measures against the action of combustion oscillations were all measures which attempted actively or passively to reduce the combustion oscillation itself in terms of its amplitude. Here, active measures are, for example, the antiphase modulation of supplied fuel or antiphase acoustic irradiation by means of a loud speaker. Passive measures attempt, by a change in the acoustic boundary conditions of the combustion chamber, to achieve acoustic detuning, in such a way that combustion oscillations of specific frequencies are damped. The active measures contain a high outlay in terms of apparatus and are not always effective. The passive measures, as a rule, can damp only specific frequency ranges. It is virtually impossible, precisely in an annular combustion chamber, to calculate and forecast acoustic resonances at which a stable combustion oscillation builds up. 
     The proposed gas turbine is distinguished by an entirely novel attempt to reduce the effects of a combustion oscillation. The annular combustion chamber is surrounded by a tension ring which clamps around the outer wall of the annular combustion chamber. By such a tension ring, the harmful vibration of the annular combustion chamber can then be damped by the oscillation energy being dissipated to the tension ring. Moreover, the tension ring affords the possibility of damping any frequency ranges particularly efficiently by the setting of a defined pretension. Thus, a higher tension force is selected for the controlled damping of higher oscillation frequencies than for the damping of low frequencies. 
     By an automated tension force setting by way of a suitable drive, even an in-situ change in the tension force may take place during the operation of the gas turbine. Thus, in each case, oscillation modes just occurring in the annular combustion chamber wall are damped particularly efficiently by the setting of the tension force in the tension ring. 
     a) Preferably, the outer surface has a cylindrical contact face, on which the tension ring lies. By such a cylindrical contact face, the tension ring comes to lie in a slip-free manner. Since the tension ring force acts radially inward, there is otherwise the risk of the tension ring slipping off on a sloping bearing face. Also preferably, the cylindrical contact face is formed by a rib running in the circumferential direction. 
     b) Preferably, the tension ring is constructed from at least two tension ring segments along its circumferential direction. This allows a simplified mounting of the tension ring. Also preferably, the tension ring segments are connected by use of a tension device. This tension device serves for setting a pretension in the tension ring and consequently, in particular, also for setting a tension force particularly suitable for dissipating the energy of specific oscillation forms. 
     c) Preferably, the tension ring has a recess such that it lies on the rib so as at least partially to surround the rib by way of the recess. This leads to a further-improved bearing protection for the tension ring. 
     d) Preferably, the tension device has a pull rod which engages into a pull lug, a pretensioning force being set between the pull rod and the pull lug by means of a spring. Also preferably, the pull lug is arranged displaceably in long holes. 
     The statements according to features a) to c) may also be combined with one another in any way. 
     According to an embodiment of the invention, an object directed at a method may be achieved by a method for the damping of oscillations of an annular combustion chamber of a gas turbine being specified, in which, by the setting of a tension force on a tension ring running around the outer circumference of the annular combustion chamber, a dissipation of oscillation energy of the annular combustion chamber as a result of friction on the tension ring and consequently the damping of the oscillation are induced. 
     The advantages of such a method may arise correspondingly from the above statements relating to the advantages of the gas turbine. 
     Preferably, the tension force is set so as to be tuned to a prevailing oscillation frequency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail, by way of example, with reference to the drawing in which, partially diagrammatically and not true to scale, 
         FIG. 1  shows a gas turbine, 
         FIG. 2  shows an outer wall of an annular combustion chamber with a tension ring, 
         FIG. 3  shows a tension ring segment with a securing lug, 
         FIG. 4  shows, in cross section, a tension ring seated on a rib, 
         FIG. 5  shows the connection of two tension ring segments, 
         FIG. 6  shows a further connection of two tension ring segments, 
         FIG. 7  shows a tension device, and 
         FIG. 8  shows a bridge of the tension device. 
       Identical reference symbols have the same significance in the various figures. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows diagrammatically a gas turbine  3  in a longitudinal section. The gas turbine  3  is directed along an axis  5  and has, connected one behind the other, a compressor  7 , an annular combustion chamber  9  and a turbine part  11 . Air  13  is sucked in and highly compressed by the compressor  7 . The highly compressed air  13  is delivered to the annular combustion chamber  9 . There, it is burnt, with fuel being added. The hot exhaust gas  15  which occurs is delivered to the turbine part  11 . The annular combustion chamber  9  has an outer wall  23  with an outer surface  25 . On the outer surface  25  runs in the circumferential direction a rib  29  which has, lying radially on the outside, a cylindrical contact face  28 . A tension ring  27  surrounding the annular combustion chamber  9  lies on the cylindrical contact face  28 . 
     During combustion, flame instabilities may occur in the annular combustion chamber  9  and result, in turn, in pressure pulsations in the annular combustion chamber  9 . The pressure pulsations reflected by the annular combustion chamber wall are also reflected back to the combustion location. There, if the phase relationship is correct, they may reinforce flame instabilities in such a way that the build-up of a stable combustion oscillation by means of the fed-back system occurs. This combustion oscillation may be so considerable that damaging vibrations are built up in the gas turbine  3 . 
     In particular, the annular combustion chamber  9  is exposed to these vibrations. The vibrations are also transmitted to the ribs  29  and lead to a friction of the tension ring  27  on the cylindrical contact face  28 . Oscillation energy of the annular combustion chamber oscillation is thereby converted into heat and the oscillation is consequently damped. Moreover, the tension ring  27  requires no external supporting points, that is to say there is no need for any external compensation of thermally induced relative movements. 
     This is particularly important if external supporting points were to assume, even only temporarily, a markedly different temperature level from that of the structure to be damped. In this case, it would not be possible to compensate the expansion differences at a justifiable outlay. The friction of the tension ring  27  on the rib  29  occurs due to the fact that the neutral fibers of the rib  29 , on the one hand, and of the tension ring  27 , on the other hand, lie on different diameters. If, then, excitations to oscillation and consequently elastic deformations, for example ovalizations, of the outer wall  23  occur during operation, the tension ring  27  follows this deformation, the radius of curvature of the contact face  28  changing cyclically. 
     In the event of a reduction in the radius of curvature, there is a prolongation of the outer material fibers of the rib  29  which lie nearer to the contact face  28 . In contrast to this, the marginal fibers of the tension ring  27  which lie near the contact face  28  are compressed in the longitudinal direction. 
     The superposition of the two effects results in a relative movement which is counteracted by a frictional resistance at the contact face  28 . Since the strength of the components involved is sufficiently high, the frictional resistance is overcome, energy being extracted from the oscillating system as a result of the friction on the contact face  28 . This leads to the desired damping of the oscillation of the outer wall  23 . 
     As compared with methods which bring about a suppression of the causal combustion oscillation, the damping via the tension ring  27  leads to a damping of all the oscillation modes in the outer wall  23 . Moreover, specific oscillation modes can be damped in a controlled manner by the setting of a circumferential pretension in the tension ring  27 . The construction of the tension ring  27  is explained in more detail with reference to the following figure. 
       FIG. 2  shows part of an outer wall  23  of an annular combustion chamber  9 . The outer wall  23  is surrounded by a tension ring  27 . The tension ring  27  is constructed from individual tension ring segments  27   a ,  27   b ,  27   c ,  27   d ,  27   e . Two of the tension ring segments  27   a ,  27   b  are connected via a tension device  31 . The tension device  31  has a bridge-like strap  33 . Two pairs of pull rods  37  lead through this bridge-like strap. A pair of pull rods  37  is in engagement in each case with a pair of pull lugs  35 . The pull rods  37  are held in a strap  33  in each case so as to be pretensionable via a plurality of nuts  41  and cup springs  39  located between these. A superbold nut  42  in each case closes off a cup spring column. Each pull lug  35  has a long hole  43 , by which it is connected displaceably in the circumferential direction to one of the tension ring segments  27   a ,  27   b  via a jointed pin  36 . The more detailed construction of the tensioning device  31  is also illustrated, enlarged, in FIG.  7 . 
     Further segment connections are illustrated in more detail in the following figures. 
       FIG. 3  shows a tension ring segment  27   d . The tension ring segment  27   d  has, at one end, a recess  81 , by which it can be connected to an adjacent tension ring segment via bolts  83 . On the other side of the tension ring segment, it is likewise possible to have a connection to an adjacent tension ring segment via a narrowing  85  of the tension ring segment thickness and a bore  87 . These two types of connection are explained in more detail later. The tension ring segment  27   d  has an engagement groove  89  which is in engagement with a guide bracket  91  during the mounting of the tension ring segment  27   d . The guide bracket  91  allows a positive guidance of the tension ring segment  27   d  along the circumference during mounting. In the lower part of the outer wall  23 , the guide brackets  91  prevent the tension ring segment  27   d  from pivoting away during mounting. This measure is, of course, also used in the other tension ring segments in the lower part of the outer wall  23 . 
       FIG. 4  shows, in a cross section, how the tension ring  27  is seated on the rib  29 . The tension ring  27  has a recess  30  on its underside. The recess  30  is formed by two webs  71  located on the underside of the tension ring  27  on the outside in the axial direction and running in the circumferential direction. The webs  71  engage around the rib  29 . The rib  29  is in this case formed from two axially spaced rib webs  29   a  which run around in a circumferential direction and between which is fastened, offset upward in the radial direction, a u-shaped carrying part  29   b  which is open downward in the radial direction. The u-shaped carrying part  29   b  has the contact face  28  on its radially outer surface. The tension ring  27  has a width of about 70 mm in the axial direction. The height of the tension ring  27  in the radial direction, including the extensions  71  enclosing the rib  29 , amounts to about 80 mm, while the radial height H 1  of the tension ring  27  without the extensions  71  amounts to about 60 mm. 
       FIG. 5  shows a segment connection, designed as a coupling member  51 , between two tension ring segments  27   d ,  27   e . The coupling member  51  has two elongately rectangular side parts  101 . The side parts  101  are connected to a central bolt  103 . A tension ring segment  27   d  is inserted with its thick narrowing  85  between the side parts  101  between one end of the side parts  101 . A coupling bolt  105  leads through the side parts  101  and through the bore  87  of the tension ring segment  27   d.    
     The tension ring segment  27   e  is fastened on the other side of the coupling member  51  in the same way. The coupling member  51  allows a rotatability of the tension ring segments  27   d ,  27   e  in relation to one another and also allows a simple releasability of this connection point. The coupling member  51  is inserted, in particular, via a parting line of the outer wall  23 , in order to make it possible to open the annular combustion chamber  9 , instead of demounting the tension ring  27 . 
       FIG. 6  shows a further connection between two tension ring segments  27   b ,  27   d . The tension ring segments are in this case inserted one into the other in the circumferential direction and are secured by means of continuous connecting bolts  111 . 
       FIG. 7  shows once again, in detail, the tension device  31  already described. Additionally illustrated is a long hole for the bridge  121  which spans the annular combustion chamber  9  and which connects the tension ring segments  27   a ,  27   b . The bridge  121  is illustrated in detail in FIG.  8 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.