Patent Publication Number: US-6705834-B1

Title: Axial flow turbine type rotor machine for elastic fluid operation

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/SE00/02151 filed Nov. 1, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to an axial flow turbine type rotor machine which is intended for elastic fluid operation. The turbine type machine includes a rotor having one or more axially spaced sections each comprising a circumferential array of radially extending drive blades, and a stator having two or more axially spaced sections each comprising a circumferential array of radially extending guide vanes. Each one of the stator sections is located on opposite sides of the rotor sections, and a flow path is formed between every two adjacent drive blades in each rotor section, and between every two adjacent guide vanes in each stator section. Each one of the flow paths has a certain length and extends between an entrance region and an exit region. 
     Turbine type machines of this type, for instance gas turbines of the above mentioned type, have in general a limited efficiency due to flow losses in the flow paths of the rotor and the stator. Big gas turbine motors, having a power output of some thousand kilowatts, often reach a maximum efficiency of above 90%. Mid size gas turbines motors, however, having a power output up to a few hundred kilowatts, reach a maximum efficiency of no more than 85%. This is considered to be too low efficiency for making gas turbines in this size range interesting for certain applications. 
     SUMMARY OF THE INVENTION 
     It is the main object of the invention to provide and axial flow turbine type rotor machine for elastic fluid operation, wherein the flow losses through the rotor and stator flow paths are substantially reduced and the efficiency of the turbine is substantially increased. 
     Characteristic features as well as further advantages of the invention will appear from the following detailed description of preferred embodiments of the invention and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a longitudinal sectional view through a turbine machine according to the invention. 
     FIG. 2 shows schematically a spread-out view of a number of drive blades of one rotor section and a number of guide vanes of one stator section of the turbine machine shown in FIG.  1 . 
     FIG. 3 shows, on a larger scale, a detail view of one guide vane and one drive blade of a turbine machine according to one embodiment of the invention. 
     FIG. 4 shows a detail view of a drive blade/guide vane arrangement in a turbine machine according to another embodiment of the invention. 
     FIG. 5 shows a spread-out view of the drive blade/guide vane arrangement shown in FIG.  4 . 
     FIG. 6 shows a drive blade/guide vane arrangement according to still another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     The turbine machine examples described below in detail are suitable mainly as gas turbine motors. Looking first at the example shown FIG. 1, the turbine machine comprises a stator housing  10  and a rotor  11 . The stator housing  10  is of a substantially cylindrical shape and is provided at one end with a number of gas inlet nozzles  12  communicating with a gas inlet  16  and a funnel shaped outlet diffusor  13  at the opposite end. The stator housing  10  is also provided with a number of guide vanes  14  which are arranged in an annular section  15  and which form a circumferential array. The guide vanes  14  are mounted on an inner ring structure  17  and are supported by their outer ends against a substantially cylindrical surface  18  of the stator housing  10 . The ring structure  17  is received in a peripheral space  19  in the rotor  11  and is arranged to co-operate with a cylindrical waist portion  20  on the rotor  11  to form a seal. 
     The rotor  11  comprises a forward part  22  and a rear part  23  and is journalled relative to the stator housing  10  by two bearings which are not illustrated. The rotor  11  comprises two axially spaced operating sections  26 ,  27  each carrying a circumferential array of drive blades  24 . The two operating sections  26 ,  27  are separated by the annular stator section  15 . An inner surface  28  formed by the rotor operating sections  26 , 27  as well as by the stator ring  17  tapers slowly towards the outlet diffusor  13  so as to make the gas flow expand as it passes through the turbine. 
     As shown in FIG. 2, between two adjacent guide vanes  14  in each array there is formed a stator flow path  29  having an entrance region A with a distance S A  between adjacent guide vanes  14  and an exit region B with a distance S B  between the guide vanes  14 . Both distances S A  and S B  are measured transversely to the stator flow path  29 . As clearly illustrated in FIG. 2, the distance S A  is considerably larger than distance S B , which means that the cross sectional area of the stator flow path  29  generally decreases from the entrance region A to the exit region B. 
     In a similar way, two adjacent drive blades  24  in each array define a rotor flow path  30  in which the width S C  at the entrance region C is larger than the width S D  at the exit region D, which means that each rotor flow path  30  has a decreasing cross sectional area towards the exit region D. 
     As illustrated in FIG. 3, the rotor flow path  30  comprises a radially widened region F located between the entrance region C and the exit region D. In the described example, this widened region F is formed by a concave portion  31  in the inner surface  28 . In this widened region F the radial extent R F  of the drive blade  24  is larger than the radial extent R D  of the drive blade  24  in the exit region D. This means that the cross sectional area of the flow path  29  is kept up in size close to the exit region D, which results in a lower gas velocity upstream of the exit region D and, hence, lower flow losses in the flow path  30 . 
     A similar arrangement is provided in each stator flow path  29  where a concave portion  32  is located in the ring structure  17  between the entrance region A and the exit region B and forms a widened region E. The radial extent of the guide vane  14  is larger in the widened region E than in the exit region B. It should be observed that the ring structure  17  is received in the waist portion  20  of the rotor  11 . 
     In FIG. 3, it is clearly shown that the concave portion  31  in the rotor  11  forms a radially widened region F in which the radial extent R F  of the drive blade  24  is larger than the radial extent R D  in the exit region D. The radial extent R C  in the entrance region C is even smaller than the radial extent R D  in the exit region D. 
     The arrangement of radially widened regions E and F in the stator flow paths  29  and rotor flow paths  30 , respectively, are effective in keeping down the fluid flow velocity through the flow paths  29 , 30  and, thereby, the flow losses. The radial extent of the drive blades  24  and the guide vanes  14  should be at least 5% larger in the widened regions E, F than in the exit regions B, D of the flow paths  29 ,  30  for obtaining a positive effect. In order to get a significant increase of the turbine efficiency, though, the difference in radial extent should be considerably larger than that. 
     However, the percentage of increase of the drive blade/guide vane radial extent in the widened regions depends on the relationship between the radial extent and the length of the respective drive blade or guide vane, such that a drive blade or guide vane having a short length but a large radial extent must be combined with a relatively smaller concave portion so as to avoid too large and abrupt area changes of the flow paths. 
     Employment of radially widened flow path regions according to the invention is particularly beneficial in turbines having drive blades and guide vanes with a small radial extent and a considerable length. In such turbines the radial extent of the drive blades and guide vanes in the widened regions may be 10-20% larger than the radial extent of the drive blades and guide vanes in the exit regions. 
     According to the invention, the radially widened regions of the flow paths through the rotor sections as well as the stator sections shall extend over at least 60%, preferably 80% of the flow path length, such that the fluid flow velocity is kept down during the main part of the flow path length. A low flow velocity gives low internal flow losses. At the very end of the flow paths, there is a reduction in cross sectional area which results in a rapid acceleration of the fluid flow. 
     In order to further reduce the internal flow losses and increase the efficiency of the turbine machine, the embodiment of the invention shown in FIGS. 4,  5  and  6  comprises a drive blade/guide vane arrangement which employs radially widened regions between the flow path entrance regions and exit regions. In this embodiment overlapping between the stator sections and the rotor sections is an essential part of the flow loss reduction. 
     In the embodiment of the invention illustrated in FIGS. 4 and 5, there are shown two stator sections with arrays of guide vanes  54 , and one rotor section with an array of drive blades  64 . Between two adjacent guide vanes  54  there is a stator fluid flow path  59  which has an entrance region A and an exit region B, and between adjacent drive blades  64  there are rotor flow paths  60  each having an entrance region C and an exit region D. Between the entrance region A and exit region B of each stator flow path  59  there is a radially widened region E, and between the entrance region C and the exit region D of each rotor flow path  60  there is a radially widened region F. 
     As in the previously described example, the distances between adjacent guide vanes  54  are characterized by a relatively large distance S A  in the entrance region A and a relatively small distance S B  in the exit region B. The distance between the guide vanes  54  decreases successively along the stator flow path  59 , but due to an increased radial extent of the guide vanes  54  in the widened region E the cross sectional area of the flow path is kept up in size to a point close to the exit region B. Accordingly, each guide vane  54  has radial extent R E  in the widened region E which is larger than the radial extent R B  in the exit region B. 
     In a similar way, the distance between adjacent drive blades  64  decreases successively from a large distance S C  in the entrance region C to a small distance S D  in the exit region D. The radial distance R F  in the widened region F, however, is larger than the radial distance R D  in the exit region D, which means that the cross sectional area of the rotor flow path  60  is kept up in size in the flow direction to a point close to the exit region D. This means in turn that the flow velocity is kept low during the main part of the rotor flow path  60  and is accelerated over a very short distance in the exit region D. 
     As described above in connection with the previous embodiment of the invention, the inner boundary of the flow paths through the stator end the rotor sections is defined by an inner surface  28 . This inner surface  28  is formed by the rotor operating sections  26 , 27  and by the stator section or sections  15  together. 
     A characterising feature of the stator and rotor sections according to this embodiment of the invention is that trailing end portions  62  of the drive blades  64  and trailing end portions  52  of the guide vanes  54  are extended in the flow direction beyond those parts of the stator and rotor sections that form parts of the inner flow path defining surface  28 . Moreover, the leading edges of the drive blades  64  as well as the leading edges of the guide vanes  54  are retracted in the flow direction a certain axial distance from the edge of the stator and rotor sections, respectively. An annular neck portion  65  on each rotor section and an annular neck portion  55  on each stator section is formed thereby. These annular neck portions  65 ,  55  on the stator sections and rotor sections, respectively, extend axially in the direction opposite the flow direction. And the extended trailing end portions  62  and  52  of the drive blades  64  and the guide vanes  54 , respectively, extend over the annular neck portions  55 , 65  of the downstream stator or rotor sections. 
     This arrangement of the extended trailing portions of the drive blades  64  and the guide vanes  54  in co-operation with the annular neck portions  65 ,  55  of the stator and rotor sections, respectively, serves to further lower the flow resistance through the flow paths and to improve the efficiency of the turbine. 
     As appears from FIG. 4, the portion of the inner surface  28  that is formed by a rotor section comprises a convex portion  68  followed in flow direction by a concave portion  69 , wherein the convex portion  68  is partly formed by the annular neck portion  65 . In a similar way, each one of the stator section parts of the inner surface  28  comprises a convex portion  58  and a concave portion  57 , wherein the convex portion  53  is partly formed by the annular neck portion  55 . 
     FIG. 4 also illustrates that in this embodiment of the invention the outer surface  18  which defines the flow paths  29 ,  30  is substantially cylindrical in shape, which means that all variations in the cross sectional areas of the flow paths are accomplished by the convex and concave portions on stator and rotor section parts of the inner surface  28 . 
     FIG. 6 shows an alternative design of the inner and outer flow path defining surfaces  18 ,  28 . Instead of locating all of the convex and concave portions on the inner surface  28 , the outer surface  18  of this alternative is formed with convex and concave portions  86 ,  87 ,  88 ,  89  which are located opposite the convex and concave portions  58 ,  57 ,  68 ,  69  on the inner surface  28 . By this arrangement further possibilities are obtained to give the flow paths optimum shapes in order to improve the fluid flow characteristics through the turbine. 
     Still an alternative design would be to have cylindrical inner surface  18  and locating all of the convex and concave portions  58 ,  57 ,  68 ,  69  on the outer surface  18 .