Abstract:
A thermally loaded, cooled component thermally coupled to a cooling system configured to receive a gaseous cooling introduced in a forced manner from outside that flows through the cooling system so as to absorb and transport heat away from the component as a result of thermal contact with the component. The component includes at least one Helmholtz resonator configured to improve thermal contact between the cooling medium and the component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Swedish Patent Application No. 01040/10, filed Jun. 25, 2011, which is hereby incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to the field of cooling of thermally loaded components. 
       BACKGROUND OF THE INVENTION 
       [0003]    An effective cooling of gas-turbine components which come into contact with the hot gas of the turbine, such as rotor blades, stator blades or combustor parts, is an important element for controlling the service life and the performance of the machine. Thus, for example air, which is tapped off at the compressor and guided to the hottest points of the gas turbine, is directed through the rotor and the casing. In this way, hot regions of the rotor and of the casing are also cooled, which particularly in the case of the latest generations of high-performance gas turbines is absolutely necessary for these components for achieving the desired service life. In this sense, the tapped-off air fulfills two tasks: it reduces the metal temperatures in the rotor and casing to an acceptable level and then cools components which are exposed to the hot gas, such as turbine blades and combustor parts. The same also applies to other cooling media such as steam which has to be produced specially for cooling purposes or is tapped off from an already existing steam cycle of a combined cycle power plant or from a separate steam boiler. The tapped-off cooling medium is either lost—in an open cooling system—or is returned to the steam cycle—in a closed cooling cycle, wherein, however, some energy losses typically arise. 
         [0004]    When designing cooling systems, it is the aim 
         [0005]    to reduce the amount of cooling medium which comes from the compressor, from the steam generator, or from another source for the cooling medium; and 
         [0006]    to increase the cooling efficiency of the cooling medium, which for example flows through internal cooling passages. 
         [0007]    As an example for such cooling, a turbine blade  10  is shown in  FIG. 1 . Sub- figure 1   a ) shows the longitudinal section through the turbine blade  10  and sub- figure 1   b ) shows the cross section in the plane A-A from  FIG. 1   a ). The turbine blade  10  has a lower part  13  and a blade airfoil  11  which is connected thereto in the radial direction and terminates in a blade tip  12 . The blade airfoil  11  customarily has a leading edge  21 , a trailing edge  22 , and also a pressure side  24  and a suction side  25  between the two edges. A plurality of cooling passages  14 ,  15 ,  16  and  17  extend inside the blade airfoil  11  in the radial direction. A cooling medium from the lower part  13  of the blade enters (arrow) the cooling passage  15  and  16 , flows towards the blade tip  12 , is deflected there by 180° within the limits of a flow reversal  18 , and in the cooling passage  14  flows back towards the lower part  13  of the blade and through small cooling passages to the trailing edge  22 . The cooling medium which enters the cooling passage  16  finds its way through passages  19  into the adjacent cooling passage  17 , and from there discharges outwards through outlet openings  20 ,  23  in order to cool the blade, for example in the manner of film cooling, on the outer side. 
         [0008]    When designing the thermally loaded component (in this case, the turbine blade), the cooling capacity is customarily intensified by provision being made in the cooling passages for different types of obstacles, or by openings or slots of different configuration being arranged between adjacent cooling passages or opposite walls which are to be cooled. These geometric elements are to create either local turbulences in the flow of cooling medium or to increase convection in a local region in order to increase the heat transfer between a hot internal wall of the component and the colder medium. Even if a highly-complex cooling system is provided inside the component which is to be cooled, which in the case of production can be associated with high costs, certain regions, such as corners inside the component which with regard to effective cooling still constitute a challenge, and which on account of local effects such as oxidation, creep or premature crack development may constitute a service-life problem, still remain. 
         [0009]    The cooling system generally comprises one or more inlets for entry of the cooling medium into the hot component, and one or more outlets for discharge of the cooling medium. Depending upon the process of heat transfer between the cooling medium and the hot walls of the component, the cooling system comprises different cavities which are interconnected by means of passages or slots. On account of the different configuration, dimensions, temperatures and pressures in these cavities and passages, different acoustic resonances occur in the cooling system. In general, each cavity and each passage has a different acoustic resonance. When designing the cooling system, attention is paid to keeping the Mach numbers in the flow of the cooling medium through the cooling system within specific upper and lower limits in order to avoid flow separation and regions of poorer heat transfer which are associated therewith. 
       SUMMARY OF THE INVENTION 
       [0010]    An aspect of the invention is to provide a thermally loaded, cooled component which avoids the described disadvantages of known components and is characterized by intensified cooling, which is associated with lower cost, in critical regions. 
         [0011]    In an embodiment, the present invention provides a thermally loaded, cooled component thermally coupled to a cooling system configured to receive a gaseous cooling introduced in a forced manner from outside that flows through the cooling system so as to absorb and transport heat away from the component as a result of thermal contact with the component. The component includes at least one Helmholtz resonator configured to improve the thermal contact between the cooling medium and the component. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    Exemplary embodiments are explained in more detail with reference to the drawings, in which: 
           [0013]      FIG. 1  shows two sub-figures  1   a ) and  1   b ) the longitudinal section and the cross section through a turbine blade with internal cooling; 
           [0014]      FIG. 2  shows an enlarged detail of the turbine blade from  FIG. 1   a ), which shows a corner region which is critical for cooling; and 
           [0015]      FIG. 3  shows the region of a turbine blade, comparable to  FIG. 2 , in which by a corresponding modification of the cooling passages interconnected Helmholtz resonators are arranged according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In one embodiment, at least one Helmholtz resonator is in hydraulic communication with the cooling system and is excited into vibrations by means of the flowing cooling medium itself. 
         [0017]    In another embodiment, the at least one Helmholtz resonator is integrated into the cooling system. 
         [0018]    In another embodiment, a plurality of Helmholtz resonators are arranged next to each other, and in the Helmholtz resonators are hydraulically interconnected in each case by means of a connecting passage for forming an acoustic heat pump. 
         [0019]    In another embodiment, the Helmholtz resonator(s) is (are) integrated into the component, and in that the Helmholtz resonator(s) is (are) arranged in the component in regions with particularly high thermal loading. 
         [0020]    In a further embodiment the component is part of a heat-generating electric device, especially a generator, a motor or a high-energy electronic system. 
         [0021]    In another embodiment the component is part of a heat engine, especially a steam or gas turbine. 
         [0022]    In accordance with another embodiment the component is a turbine blade, the turbine blade has a cooled blade airfoil, through the interior of which flows a gaseous cooling medium, and one or more Helmholtz resonators, which are acted upon by the flowing cooling medium, are formed in the interior of the blade airfoil. 
         [0023]    In another embodiment, the blade airfoil the turbine blade has a plurality of cooling passages which extend in parallel in the radial direction, and in that the Helmholtz resonator(s) is (are) integrated into the cooling passages. 
         [0024]    In another embodiment, the blade airfoil has a leading edge and a trailing edge, and the Helmholtz resonator(s) is (are) arranged in the region of the leading edge. 
         [0025]    The present invention provides a locally improved cooling effect by acoustic vibrations being excited in the cooling medium in the corresponding region in the cooling system. Within the scope of the subsequently explained exemplary embodiment, consideration is given to a thermo-acoustic model in which a network of coupled, discrete, non-linear vibrating cavities inside the cooling system is taken as a starting point. The vibrations can be excited by means of the flowing cooling medium itself. It is also conceivable, however, to excite the acoustic vibrations in another way, such as by temperature differences or the like. Depending upon requirement, shape and dimension of a specific cavity can be adapted to the required dimensions of a specific Helmholtz resonator, as becomes clear from a comparison of  FIG. 2  (prior art) and  FIG. 3  (exemplary embodiment according to the invention). 
         [0026]    Reproduced in  FIG. 3  is the region of the blade tip of a turbine blade  30 , in which in comparison to  FIG. 2 , in the especially thermally loaded corners  32 , the cooling passage  17  is redesigned so that at least two Helmholtz resonators (cavities)  26  and  28  are formed and hydraulically interconnected by means of a connecting passage  31 . The Helmholtz resonator  26  is connected to the adjacent flow of the cooling medium by means of a constriction  27 , and the Helmholtz resonator  28  is correspondingly connected by means of a slot  29 . The configuration and the dimensions of the slot  29  have to be determined with regard to the flow velocity of the cooling medium (arrows) which flows past it. 
         [0027]    By selecting suitable dimensions of the cavities and also of the constrictions of the Helmholtz resonators  26  and  28  with regard to the flow parameters of the cooling medium, different intensities of acoustic vibrations can be excited between adjacent resonators. Resulting from this is the phenomenon of the acoustic heat pump, in which heat from the resonator with the lower vibration amplitude is pumped towards the resonator with the higher vibration amplitude. 
         [0028]    The transporting of heat between adjacent cavities, which are interconnected by means of a connecting passage ( 31  in  FIG. 3 ), can be estimated by means of the following equation: 
         [0000]    
       
         
           
             
               
                 Q 
                 . 
               
               = 
               
                 
                   ( 
                   
                     
                       S 
                        
                       
                           
                       
                        
                       δ 
                     
                     4 
                   
                   ) 
                 
                  
                 
                     
                 
                  
                 
                   
                     1 
                     + 
                     
                       σ 
                     
                   
                   
                     1 
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                     σ 
                   
                 
                  
                 
                   v 
                   c 
                 
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                   p 
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             , 
           
         
       
     
         [0029]    wherein S refers to the circumference of the surface of the connecting passage ( 31 ), δ represents the thermal penetration depth, σ is the Prandt1 number, and p c  and v c  are the amplitude of the acoustic vibration and the velocity in the connecting passage ( 31 ). The velocity v c  can be calculated to: 
         [0000]    
       
         
           
             
               
                 v 
                 c 
               
               = 
               
                 
                   Δ 
                    
                   
                       
                   
                    
                   p 
                 
                 
                   ω 
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                    
                   ρ 
                    
                   
                       
                   
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                     l 
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             , 
           
         
       
     
         [0030]    wherein Δp is the difference of the vibration amplitudes of the adjacent resonators, ρ refers to the density of the cooling medium, φ represents the angular frequency of the acoustic system, and l c  is the effective length of the connecting passage ( 31 ) which is influenced by losses at both ends of the passage. 
         [0031]    With a corresponding design and arrangement of the Helmholtz resonators, heat can be “pumped out” from the critical region, which amounts to intensified cooling of this region. 
         [0032]    The present invention is not limited to the analytical methods which are described above. Rather, other procedures and methods can also be used in order to achieve improved cooling in an acoustic way in a cooling system with gaseous cooling medium, especially air, of a thermally loaded component. Thus, the necessary acoustic resonance can be produced by modifying an existing geometry of a cooling passage or of a forum. 
         [0033]    The acoustic resonances in the cooling system can be based on 
         [0034]    the shapes of standing waves transversely to the cooling passage or along the cooling passage for low Mach numbers, and specifically 0.2, and/or 
         [0035]    the shapes of transient waves transversely to the cooling passage or along the cooling passage for higher Mach numbers above 0.3, and/or 
         [0036]    the shapes of rotating waves along the cooling passage, and also 
         [0037]    the superposition of these types for improving the cooling effect. 
         [0038]    In addition to the configuration and the geometric dimensions, the temperature and the pressure must also be taken into consideration in order to achieve the cooling capacity which is improved in an acoustic way. 
         [0039]    The methods for acoustically intensified cooling which are described here can be used with gas turbines both in the intended operating range or outside the operating range, but can also be used with any other machine or device which requires cooling, such as a generator, jet-engine, any type of piston machine, electric motors or actuators. The acoustic resonances, however, taken individually, can also be used as the central element of a cooling process. Such a design can also be used with other components of a gas turbine, such as for cavities of the rotor or of the casing. 
       LIST OF DESIGNATIONS 
       [0040]      10 ,  30  Turbine blade 
         [0041]      11  Blade airfoil 
         [0042]      12  Blade tip 
         [0043]      13  Lower part of blade 
         [0044]      14 ,  15 ,  16 ,  17  Cooling passage 
         [0045]      18  Flow reversal 
         [0046]      19  Through-opening 
         [0047]      20 ,  23  Outlet opening 
         [0048]      21  Leading edge 
         [0049]      22  Trailing edge 
         [0050]      24  Pressure side 
         [0051]      25  Suction side 
         [0052]      26 ,  28  Helmholtz resonator 
         [0053]      27  Constriction 
         [0054]      29  Slot 
         [0055]      31  Connecting passage 
         [0056]      32  Corners (especially thermally loaded)