Abstract:
A device for effecting heat transfer to rotating equipment, in particular gas turbines, is provided. A gas turbine ( 10 ) comprises a first rotating unit ( 11 ), i.e. an internal shaft and a second fixed unit ( 16 ), i.e. a housing. A third rotating unit ( 14, 17 ), i.e. rotor blades and plates connected to the rotor blades are disposed between the first unit ( 11 ) and the second unit ( 16 ). The first ( 11 ) and third ( 14, 17 ) units are rotatable around a common axis ( 12 ) and with respect to each other. At least one device ( 21 ) for improving heat transfer by convection is assigned to the first rotating unit ( 11 ), i.e. the internal shaft.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a system for affecting the heat transfer in rotating equipment. 
   BACKGROUND 
   Gas turbines used as propulsion units in aircrafts, for example, usually include a plurality of rotating blades arranged in series in the axial direction of the gas turbine. The rotating blades are surrounded by a stationary housing. A gap, which should have the smallest possible dimensions to avoid gas turbine efficiency losses, is formed between the rotating blades and the housing. 
   The rotating blades and the stationary housing have different temperature variations over time. Thus, as heat is generated during operation of the gas turbine, in particular in non-steady-state operation of the gas turbine, the rotating blades and the stationary housing expand to different degrees. This may result in enlargement of the gap between the rotating blades and the housing. 
   In rotating equipment, such as gas turbines, the different degrees of expansion of stationary units and rotating units should be compensated. This may be achieved by improving the heat transfer between the stationary units and the rotating units. Improved heat transfer between the stationary units and the rotating units equalizes the temperature variations over time and heat absorption, and thus ultimately the expansion of stationary and rotating units. For gas turbines this would mean that the rotating blades and housing expand equally or evenly even during non-steady-state operation of the gas turbine, whereby the size of the gap between the rotating blades and the housing is ideally no longer subject to fluctuations. 
   SUMMARY OF THE INVENTION 
   On this basis, an object of the present invention is to provide a novel system for affecting the heat transfer in rotating equipment. Furthermore, it is an object of the present invention to provide a corresponding gas turbine. 
   In accordance with an embodiment of the present invention, a system for affecting the heat transfer in rotating equipment (for example, a gas turbine) comprises a rotating first unit, a stationary second unit, and a rotating third unit situated between the first unit and the second unit. The first unit and the third unit rotate about a common axis, and the first unit and the third unit rotate relative to one another. At least one device is associated with the first rotating unit. and the at least one device is positioned to improve convective heat transfer in the rotating equipment. The different temperature variations over time of the units are thus improved. 
   In accordance with another embodiment of the present invention, a gas turbine comprises a rotating inner shaft, a stationary housing, and a rotor assembly. The rotor assembly includes a plurality of rotating blades, and the rotating blades, the rotor assembly, and the inner shaft rotate about a common axis and relative to one another. At least one device is associated with the inner shaft, and the at least one device is positioned to improve convective heat transfer in the gas turbine. 
   The gas turbine has a rotating inner shaft, a stationary housing, and a rotor assembly having a plurality of disks, each having a plurality of rotating blades, the rotating blades and the inner shaft rotating about a common axis at different speeds and possibly in different directions with respect to one another. At least one device for improving the convective heat transfer is associated with the inner shaft according to the present invention. The rotating blades and the housing thus expand more evenly even during non-steady-state operation of the gas turbine. The radial gap between the rotating blades and the housing is thereby reduced, which reduces efficiency losses of the gas turbine. 
   According to an advantageous refinement of the present invention, a plurality of rotating blades is arranged in series in the axial direction of the gas turbine. A component extending between the rotating blades and the inner shaft, namely a disk, is associated with each rotating blade. Two adjacent disks delimit a rotating chamber. A plurality of devices for improving convective heat transfer arranged in series in the axial direction are associated with the inner shaft, the devices extending radially from the inner shaft into the chambers delimited by the disks. The devices for improving convective heat transfer are designed as flexible elements whose external shape changes as they rotate. The devices improve, i.e., enhance the flow through the chambers, and thus increase the convective heat transfer in the rotating chambers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the present invention is explained on the basis of the drawing without being limited thereto. 
       FIG. 1  shows a schematic cross section of a detail of a gas turbine according to the present invention; 
       FIG. 2  shows a detail of  FIG. 1  in a cross section rotated 90° from the plane of the drawing with respect to  FIG. 1 ; 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a gas turbine  10  according to the present invention. Gas turbine  10  has a rotating inner shaft  11 ,  FIG. 1  showing an axis of rotation  12  of inner shaft  11  and a wall  13  of the same. Gas turbine  10  also has a plurality of rotating blades  14  arranged in series in the axial direction. A stationary series of guide vanes  15  is positioned between each adjacent series of rotating blades  14 . A stationary housing  16  delimiting gas turbine  10  to the outside is adjacent to rotating blades  14  and guide vanes  15 . 
   Rotating blades  14  rotate about the same axis of rotation  12  as inner shaft  11 . As mentioned previously, guide vanes  15  and housing  16  are stationary, i.e., non-rotating. A gas turbine having a rotating inner shaft  11  is a medium-pressure or high-pressure component. 
   As apparent from  FIG. 1 , a disk  17  extending toward inner shaft  11  is associated with each rotating blade  14 . Disks  17  are fixedly attached to rotating blades  14  and rotate together with rotating blades  14  about axis of rotation  12 . Disks  17  are fixedly connected to one another by a shroud  18 . Shroud  18  also rotates together with rotating blades  14  and disks  17  about axis of rotation  12 . 
   Each pair of adjacent rotating disks  17  delimits a chamber extending between inner shaft  11  and shroud  18 . Such a chamber is labeled with reference number  19  in  FIG. 1 . Chambers  19  therefore delimit a defined volume. Chambers  19  rotate about axis of rotation  12 . 
   In such a gas turbine  10 , a gap is formed between an outer wall  20  of rotating blades  14  and housing  16 . This gap should be as small as possible to avoid efficiency losses. It is important to note in this context that the gap between rotating blades  14  and housing  16  should have the smallest possible dimensions during the entire operation of gas turbine  10 . However, since the rotating units of gas turbine  10 , in particular rotating blades  14  and rotating disks  17 , have temperature variations over time that are different from those of the stationary units, in particular those of stationary housing  16 , the gap between rotating blades  14  and housing  16  is subject to changes in the gas turbines of the related art. 
   Specifically, during acceleration, housing  16  according to the related art expands more rapidly under the effect of heat than rotating blades  14  do. In particular, the thermal portion of the gap between rotating blades  14  and housing  16  increases during acceleration of gas turbine  10 . However, an increased gap impairs the efficiency of the gas turbine. An increase in the gap should therefore be avoided. 
   According to the present invention, devices  21  for improving the convective heat transfer within chambers  19  and thus between rotating blades  14  and stationary housing  16  are associated with rotating inner shaft  11  of gas turbine  10 . Devices  21  are fixedly attached to inner shaft  11  and rotate together with inner shaft  11  about axis of rotation  12 . According to  FIG. 1 , devices  21  for improving the convective heat transfer protrude into chambers  19  delimited by disks  17 . 
   It should be pointed out here again that disks  17  rotate together with rotating blades  14  about axis of rotation  12 . Rotating blades  14  and disks  17  therefore have the same direction of rotation and rotational speed with respect to axis of rotation  12 . Devices  21  for improving convective heat transfer are fixedly attached to inner shaft  11 . Devices  21  therefore rotate together with inner shaft  11  about axis of rotation  12 . Inner shaft  11  and devices  21  for improving convective heat transfer therefore rotate at the same speed and in the same direction with respect to axis of rotation  12 . 
   However, rotating inner shaft  11  has a different speed and/or different direction of rotation compared to rotating blades  14  and thus rotating disks  17  and rotating chambers  19 . Therefore, inner shaft  11  rotates together with devices  21  relative to rotating blades  14  and thus relative to rotating chambers  19  delimited by disks  17 . 
   Because devices  21  for improving convective heat transfer protrude into rotating chambers  19  and have a different direction of rotation and/or rotational speed relative to rotating chambers  19 , an intensive flow is generated through rotating chambers  19 , increasing the convective heat transfer in rotating chambers  19  and therefore ultimately causing a more rapid temperature change over time of rotating disks  17 . This allows the different temperature variations over time of stationary housing  16  and rotating blades  14 , and thus the different expansion characteristics of stationary housing  16  and rotating blades  14 , to be better equalized. Rotating blades  14  and stationary housing  16  thus expand more evenly over the entire range of operation of gas turbine  10  according to the present invention. In particular, during the non-steady-state operation of gas turbine  10 , a change in the gap between rotating blades  14  and housing  16  is reduced. This allows the efficiency of gas turbine  10  to be markedly improved, in particular during non-steady-state operation, which results in fuel savings and improvement in the surge limit of the compressor in gas turbine  10 . 
   Devices  21  for improving the convective heat transfer attached to rotating inner shaft  11  may be designed as elements of any desired shape. However, the design of devices  21  shown in  FIG. 2  is preferred. 
   Thus, in the exemplary embodiment of  FIG. 2 , devices  21  for improving convective heat transfer are flexible elements made for example of flexible metal or plastic. First sections  22  of devices  21  are fixedly anchored in wall  13  of inner shaft  11 . Second sections  23  opposite first sections  22  of devices  21  protrude into rotating chambers  19 . Because devices  21  are designed as flexible elements in the exemplary embodiment illustrated here, they may stretch under the effect of centrifugal force. In other words, this means that the external shape of devices  21 , designed as flexible elements, changes as they rotate. Devices  21  may also be designed as metal strips or metal wires or metallic elements of any desired shape. The flexible elements may also protrude into chambers  19  to different depths. The length of the above-described device may be changed, i.e., adjusted, via a mechanism integrated into the shaft. Also conceivable are rigid elements which are suitable for deflecting axially flowing air into the chamber due to their shape and which have a radial dimension that is not greater than the hubs of the disks, so that they are installable on the shaft, i.e., may be pushed through the hubs. 
   Therefore, it is within the scope of the present invention to increase the convective heat transfer in the rotating chambers of a gas turbine or a propulsion unit or another rotating device. This allows the different temperature variations over time of rotating units of a gas turbine  10 , namely rotating blades  14  and rotating disks  17  attached to rotating blades  14 , and stationary units, namely stationary housing  16 , to be equalized. For this purpose, the above-mentioned devices  21  for improving convective heat transfer are associated with inner shaft  11  of gas turbine  10 . 
   Devices  21  therefore rotate together with inner shaft  11  about axis of rotation  12 . Devices  21  for improving convective heat transfer and inner shaft  11  rotate at the same speed and in the same direction of rotation. Disks  17  associated with rotating blades  14  form chambers  19 . Rotating blades  14  and disks  17  also rotate at the same speed and in the same direction about axis of rotation  12 , but relative to inner shaft  11  and devices  21 . However, the rotary motions of devices  21  and of chambers  19  delimited by disks  17  differ with respect to their rotational speed and/or the direction of rotation. Devices  21  for improving convective heat transfer protruding into chambers  19  therefore move with respect to chambers  19  and disks  17 , ensuring an intensive flow through chambers  19  and ultimately increasing the convective heat transfer in the rotating chambers. 
   Although the present invention has been described using the example of a gas turbine, it is not limited to this specific application. Rather, the present invention is applicable wherever heat transfer is to be influenced in rotating devices. Therefore, the area of application is not limited to gas turbines and other propulsion units in aeronautics, although this application is preferred and is particularly advantageous. 
   LIST OF REFERENCE NUMERALS 
   
       
       gas turbine  10   
       inner shaft  11   
       axis of rotation  12   
       wall  13   
       rotating blade  14   
       guide vane  15   
       housing  16   
       disks  17   
       shroud  18   
       chamber  19   
       wall  20   
       device  21   
       section  22   
       section  23