Patent Publication Number: US-2012039706-A1

Title: Compressor having a guide vane assembly with a radially variable outflow

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This application claims the priority of International Application No. PCT/DE2010/000186, filed Feb. 18, 2010, and German Patent Document No. 10 2009 009 715.5, filed Feb. 19, 2009, the disclosures of which are expressly incorporated by reference herein. 
    
    
     TECHNICAL FIELD  
     The present invention relates to a compressor. In addition, the present invention relates to an engine having a compressor. 
     Technical Problem 
     Such a compressor compresses a compression medium, wherein the pressure of the medium increases in the process. To achieve high pressures, the compressor has several stages, which are made up of rotors and stators arranged in an alternating manner or so-called guide vane assemblies. 
     Normally, the compressor has an inlet guide vane assembly in the flow direction, and a rotor (with rotor blades) connected downstream of the inlet guide vane assembly. A guide wheel, in turn, follows this rotor and the guide wheel is followed, in turn, by a rotor, etc. The blades of the guide vane assembly and rotors are arranged between a housing and a hub of the compressor. 
     To increase the aerodynamic stability of the compressor, the guide vane assemblies, in particular the inlet guide vane assembly, are designed to be adjustable in order to be able to change the outflow angle. This adjustment is achieved for the most part by rotating the guide vane assembly vanes. This rotation leads to the ratio of the flow surface that is effectively available at the compressor inlet and outlet to adapt to a changed pressure ratio of the compressor. 
     As a rule, the guide vane assembly vanes are rotated as a whole as a rigid body. During rotation, the outflow angle of the guide vane assembly is constantly changed radially in a first approximation. 
     A compressor is known, e.g., from Publication DE 36 24 951, which has a guide vane assembly featuring two individual guide vane assemblies arranged essentially in succession in the flow direction. Also in the case of these individual guide vane assemblies, the vanes can be rotated as a whole in order to change the outflow angle of the guide vane assembly. 
     Another possibility for changing the outflow angle is given in Publication EP 1 898 055, in which an assembly vane has an inner body bearing the load, which is encompassed by a shell. Arranged between the inner body and the shell are actuation mechanisms, which can change the shape of the shell. In the process, the assembly vane is changed as a whole in the radial direction. 
     Yet another possibility of changing the outflow angle is shown in Publication DE 102 56 008, in which a rear edge of a vane as viewed in the direction of flow direction can be moved relative to its forward edge on the basis of inflatable chambers. 
     Due to these known possibilities for changing the outflow angle, the compressor that is normally designed for full load operation may be switched to a partial load operation in which other flow conditions prevail. 
     In partial load operation of a compressor with such a design, however, because of the swirl distribution at the inlet guide vane assembly outlet, a strong mass flow displacement occurs at outlet of the first rotor, which takes place in the direction of the housing. The subsequent vane assemblies and in particular the subsequent rotor bear the brunt of this with hub portions that are subjected to very high aerodynamic stress. This results in a risk of a flow separation. If a flow separation occurs in one or more stages of the compressor, the result is a massive drop in power in the compressor. The compressor then tends to surge, because the flow no longer has adequate kinetic energy to overcome the increase in pressure. 
     Housing built-ins may have a stabilizing effect. However, the associated potential may only be utilized partially, because next of all flow separations may occur on the highly stressed hub portion of the next guide vane assembly and the next rotor, which again leads to the compressor surging. 
     Object of the Invention 
     Therefore, the object of the present invention is creating an improved compressor, which manages changes in the outflow angle on the guide vane assembly better than before, and an improved engine. A further goal is increasing the surge limit distance. 
     In accordance with a compressor according to the invention as defined in the claims, the guide vane assembly is divided in the direction of extension from the housing to the hub into two or more sections which can be radially adjusted relative to one another. In accordance with the compressor according to the invention as defined in the claims, the guide vane assembly leaves a clearance in the direction of extension from the housing to the hub, the clearance allowing a substantial amount of flow to pass. 
     With these types of designs, the inflow from the guide vane assembly to the subsequent rotor may be designed to be (radially) different along the direction of extension of a guide vane assembly vane. As a result, the outflow angle of the guide vane assembly may be changed more greatly on the housing side than on the hub side. This leads to a reduced displacement in the mass flow at the outlet of the rotor. And this, in turn, eases the load on the subsequent vane assembly and in particular on the subsequent rotor. As a result, the compressor has a greater surge limit distance. 
     The compressor according to the invention as defined in the claims makes a technically simple adjustability of the guide vane assembly sections possible. 
     The compressor according to the invention as defined in the claims makes a very specific response to desired flow conditions possible. 
     In the case of the compressor according to the invention as defined in the claims, a guide vane assembly section which is not adjacent to the hub or housing may be adjusted relatively. Therefore, a subdivision into a plurality of relatively variable guide vane assembly sections in the radial direction is possible. As a result, many finely graduated flow differences between the housing and hub may be effected. 
     The compressor according to the invention as defined in the claims makes it possible to ease the load on the hub side in a very simple manner. 
     The compressor according to the invention as defined in the claims makes it possible to ease the load on the housing side in a very simple manner, if this should prove to be necessary. 
     The compressor according to the invention as defined in the claims makes it possible for particularly the first rotor behind the inlet guide vane assembly to experience an improved flow. 
     The compressors according to the invention as defined in the claims make a desired driving of a specific guide vane assembly section possible. 
     The engine according to the invention as defined in the claims utilizes these advantages of a compressor 
     The present invention will be described below more precisely on the basis of special embodiments. Drawings have been enclosed in order to better illustrate some aspects of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an operational diagram of a compressor with a radially constant change in the outflow angle, as known from the prior art. 
         FIG. 2  shows an operational diagram of a compressor according to the invention with radially variable change in the outflow angle. 
         FIG. 3  shows a schematic representation of a variation according to the invention with a shortened guide vane assembly vane and a clearance. 
         FIG. 4  shows a schematic representation of a variation according to the invention in the flow direction with a two-part guide vane assembly with a stationary part and an adjustable part with a shortened guide vane assembly vane and a clearance. 
         FIG. 5  shows an operational diagram of the design from  FIG. 3 . 
         FIG. 6  shows an operational diagram of the design from  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments of the present invention are described in the following making reference to the drawings as the case may be. 
     First of all, the general design of the compressor according to the invention will be described. 
     The compressor has an inlet guide vane assembly in the flow direction and a rotor which is connected downstream of the inlet guide vane assembly. A guide vane assembly, in turn, follows this rotor and the assembly is again followed by a rotor etc. The guide vane assembly and rotors are arranged between a housing and a hub of the compressor. The hub of the compressor in this case may be a rotary body of the rotor or a non-rotating support section, which is separate from the rotor body. Both design types are known from the prior art. 
     In a first embodiment, the compressor according to the invention has an adjustable guide vane assembly, which is divided (radially) into two sections in the direction of extension from the housing to the hub. These two guide vane sections may be adjusted relative to one another. The adjustment may be effected by rotation of an adjusting mechanism, as known from DE 36 24 951. However, the present invention is not restricted to a special type of adjusting mechanism. The adjustment may also be effected by changing the shell shape via actuator mechanisms, as known from EP 1 898 055, or via inflatable chambers, as known from DE 102 56 008. Additional adjusting mechanisms are likewise conceivable, the important thing is that a relative rotation of the guide vane sections may be realized radially. 
     A guide vane section may be adjusted from the housing side, while the other guide vane section may be adjusted from the hub side, for example, using microactuators. 
     In a second embodiment, the compressor according to the invention has a guide vane assembly in the so-called tandem design, which features two individual guide vane assemblies arranged essentially in succession in the flow direction, at least one of which can be adjusted independently of the other to change the outflow angle. However, both individual guide vane assemblies may be adjustable, as is known from DE 36 24 951. 
     Of these individual guide vane assemblies, one individual guide vane assembly is divided in the direction of extension from the housing to the hub into two sections which can be adjusted relative on one another, wherein both individual guide vane assemblies may also be respectively divided in the direction of extension from the housing to the hub into two sections which can be adjusted relative to one another. 
     In a third embodiment, the compressor according to the invention has an adjustable guide vane assembly for changing the outflow angle, which assembly is shortened in the direction of extension from the housing to the hub and leaves a clearance towards the hub. 
     In a fourth embodiment, the compressor according to the invention again has a guide vane assembly executed in a tandem design similar to the second embodiment. 
     One of the individual guide vane assemblies, preferably the rear individual guide vane assembly in the flow direction, is shortened in the direction of extension from the housing to the hub and leaves a clearance towards the hub. 
     In the third and fourth embodiment, the clearance has such a size that a substantial amount of flow is able to pass. The clearance may be, for example, ¼, half or ¾% of the total length between the housing and hub. The length of the clearance may also be selected as desired. 
     The functionality of the compressor according to the invention will be described in the following. 
     In the case of the compressors in the first and third embodiment, the guide vane assembly is divided radially into sections. In doing so, the outflow angle at the hub region may be adjusted to be different than at the housing region. In particular, by adjusting at the hub region, an outflow angle difference α1 may be set, which differs from the outflow angle difference α2 at the housing region. 
     In the case of the compressors in the second and fourth embodiments, the guide vane assembly has a suitably designed clearance at the hub region. In this case, the outflow angle at the housing region may be changed, wherein hardly a change is effected in the vicinity of the hub. In particular, an outflow angle difference α1 of approximately zero can be achieved at the hub region, which differs from the outflow angle difference α2 at the adjusted housing region. 
       FIGS. 1 and 2  show a comparison of operational diagrams of a compressor with a radially constant change in the outflow angle as known from the prior art, and a compressor according to the invention with radially variable change in the outflow angle. 
     The white arrows show the change in the outflow angle from full load at the design point to partial load. The outflow angle progression effected in the present invention is clear to see, in which the change in the outflow angle increases radially from the hub side to the housing side. 
     According to the invention, a radially different change in the outflow angle is effected at the inlet guide vane assembly (inlet guide wheel). 
     As a result, the inflow from the guide vane assembly to the subsequent rotor may be designed to be (radially) different along the direction of extension. In particular, the outflow angle of the guide vane assembly may be changed more greatly on the housing side than on the hub side. This leads to a reduced displacement in the mass flow at the outlet of the rotor. And this, in turn, eases the load on the subsequent vane assembly and in particular on the subsequent rotor. As a result, the compressor has a greater surge limit distance. 
     As a result, the present invention provides a clear improvement in the surge limit in the partial load range. This is responsible for a clear improvement over the prior art. 
     In the case of the design according to the invention, the problem of flow separation mentioned in the foregoing is minimized as a result. 
       FIG. 3  shows a schematic representation of a variation according to the invention with a shortened guide vane assembly vane and a clearance according to, for example, the third embodiment explained in the foregoing. An adjustable guide vane assembly is shortened in such a way linked on the housing that an area remains free on the hub (clearance). In this area, the flow is not actively influenced by this guide vane assembly vane. In the representation, the free area in the radial direction is slightly shorter than the length of the guide vane assembly vane. 
       FIG. 4  shows a schematic representation of a variation according to the invention in the flow direction with a two-part guide vane assembly with a stationary part and an adjustable part with a shortened guide vane assembly vane and a clearance according to, for example, the fourth embodiment explained in the foregoing. In the flow direction in front of the adjustable guide vane assembly vane, which is designed in a similar manner as in  FIG. 3 , an individual guide vane assembly is upstream resulting in a tandem design. 
       FIG. 5  shows operational diagram of the design in  FIG. 3 . It is clear to see the outflow angle progression effected in the present invention, in which the outflow angle remains unchanged from the hub (N) up to point  1  (outflow angle in the design point is equal to the outflow angle with partial load). Starting at point  1 , the change in the outflow angle increases continuously toward the housing side. 
       FIG. 6  shows an operational diagram of the design in  FIG. 4 . In contrast to the previously described variation ( FIG. 6  and  FIG. 4 ), the outflow angle in the region between hub N and point  1  is arbitrary. The desired guide wheel outflow angle is effected by the stationary part. The adjustable part of the two-part guide vane assembly effects the change in the outflow angle increasing from point  1  towards the housing. 
     Point  1  preferably lies between 10% and 90% of the channel height (channel height is defined as r−r Hub ).
         r Housing −r Hub          

     In the case of the first and second embodiment described in the foregoing, both guide wheel sections are adjustable relative to one another. However, a design is also conceivable in which only one of the two guide wheel sections is adjustable and the other guide wheel section is rigid. It is also possible to achieve a radially different outflow angle in this case. 
     In the case of the first and second embodiment described in the foregoing, two guide wheel sections are adjustable relatively to one another. However, three or more guide wheel sections may be designed to be radially adjustable relative to one another. The drive of the inner guide wheel sections that are not adjacent to the housing/hub may be designed such that a first guide vane assembly section has a transmission device on the hub and/or housing which passes energy from the adjusting drive through it in order to adjust a second (inner) guide vane assembly section relative to the first one. 
     In the case of the third and fourth embodiment, the compressor according to the invention has an adjustable guide vane assembly for changing the outflow angle, which is shortened in the direction of extension from the housing to the hub and leaves a clearance toward the hub. If so desired, a design is also conceivable in which a shortened guide vane assembly is arranged in the hub region and leaves a clearance remaining towards the housing. The shortened guide vane assembly may be fastened on the housing, for example, by means of thin braces (e.g., one thin brace per guide vane assembly vane), if the flow resistance due to this thin brace can be tolerated. 
     In the case of the embodiments described in the foregoing, the inlet guide vane assembly is designed such that it may achieve a radially different outflow angle. A corresponding design may also be provided on every guide vane assembly in front of every subsequent rotor so that a radially different outflow angle can be achieved on every subsequent rotor.