Patent Publication Number: US-11396818-B2

Title: Triple-walled impingement insert for re-using impingement air in an airfoil, airfoil comprising the impingement insert, turbomachine component and a gas turbine having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to German patent Application No. 10 2020 103 657.4, filed on Feb. 12, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to impingement insert for re-using impingement air in an airfoil, an airfoil comprising the impingement insert, a turbomachine component and a gas turbine having the same, and more particularly to cooling of a turbomachine component or an airfoil comprising such an impingement insert. 
     Description of the Related Art 
     Turbomachines include various turbomachine components that benefit from cooling, resulting into increased operational life of the components. By cooling of turbomachine components an increase in efficiency of the turbomachine is also realized. 
     Certain turbomachine components have an airfoil, e.g. a blade or a vane. The airfoils enclose internal spaces and are cooled internally or from the inside by flowing cooling air through the internal space of the airfoil or through one or more cooling channels formed in the internal space of the airfoil. 
     The turbomachine component—hereinafter also referred to as the blade or vane—generally comprises of the airfoil (also referred to as an aerofoil) having an airfoil wall and an internal space defined by the airfoil wall. During operation of the gas turbine, the airfoil of the turbine section of the gas turbine are positioned in the hot gas path and are subjected to very high temperatures. Therefore, to provide cooling to the airfoil, one or more cooling channels are defined in the internal space of the airfoil. The entire internal space of the airfoil may form a cooling channel that generally extends in a longitudinal direction of the airfoil. 
     Alternatively, the airfoil may include at its inside one or more webs that extend from a pressure side to a suction side of the airfoil and thereby mechanically reinforce airfoil. The web, depending on the number of webs, divides the internal space of the airfoil into one or more cooling channels that extend along the longitudinal direction of the airfoil. 
     Cooling air generally flows along the longitudinal direction of the airfoil in such cooling channels after being introduced into the airfoil. Enhancement of such internal cooling of the airfoil would have beneficial effect on the efficiency of the gas turbine and/or on structural integrity of the airfoil. 
     It is commonly known to use impingement cooling of an inner surface of the airfoil, for example by using impingement inserts in the cooling channels.  FIG. 10  shows a conventional impingement insert  80 ′. The wall of the impingement insert  80 ′ defines a flow channel in which the cooling air  5  flows. The wall of the impingement insert  80 ′ includes a plurality of impingement cooling holes  85  facing an internal surface of the airfoil wall  101 . The cooling air from the flow channel is directed out of the impingement cooling holes  85 , in form of impingement cooling jets  86 , to impinge onto the internal surface of the airfoil wall  101 . The impinged air then flows in the space between the impingement insert  80 ′ and the airfoil wall  101 . This creates cross-flows  5   x  for impingement jets  86  that are downstream in the flow direction of the impinged air flowing in the space between the impingement insert  80 ′ and the airfoil wall  101 . This reduces the cooling efficiency in such downstream parts or regions of the airfoil wall  101 . Therefore, it is desirable to reduce such cross-flows. 
     Furthermore, for cooling of components of the gas turbine, a part of the air from the compressor section of the gas turbine is drawn and directed to different parts of the gas turbine to be used as cooling air. More cooling can be beneficial and can be achieved by drawing more air from the compressor. However, increase in an amount of air drawn from the compressor for cooling inadvertently results in decrease in the amount of air available for combustion—this may adversely affect the efficiency of the gas turbine. Therefore, it would be beneficial if cooling air that has been used once, e.g. for impingement cooling of a first surface, is reused for cooling another surface say a second surface, for example by being collected or extracted for being re-used, after having been used on the first surface, to form impingement jets that can impinge on the second surface. 
     Therefore, it is advantageous to enhance internal cooling of the airfoil. 
     SUMMARY OF THE INVENTION 
     The above objects are achieved by the subject matter of the independent claims, in particular by an insert for a turbomachine component for a gas turbine. Advantageous embodiments are provided in dependent claims. 
     Such turbomachine components that include an airfoil are exemplified hereinafter by a blade, however the description is also applicable to other turbomachine components that include an airfoil such as a vane, unless otherwise specified. 
     In a first aspect of the present technique, an impingement insert for a turbomachine component is presented. 
     The turbomachine component may be a component having an airfoil, e.g. a blade or vane of a turbine. One or more cooling channels may be formed in the airfoil of the turbomachine component. The impingement insert may be inserted or installed in such a cooling channel for providing impingement jets to an internal surface of the cooling channel i.e. the internal surface of the airfoil wall. Thus, the present technique also envisages the above described turbomachine component. 
     The impingement insert, hereinafter also referred to as the insert, includes a triple-walled structure or section, having a central wall, an inner peripheral wall and an outer peripheral wall. 
     The central wall, the inner peripheral wall and the outer peripheral wall may define four spatial divisions—a central channel formed at an inner surface of the central wall, an inner channel formed between an outer surface of the central wall and an inner surface of the inner peripheral wall, a middle channel formed between the outer surface of the inner peripheral wall and the inner surface of the outer peripheral wall, and an outer channel formed at an outer surface of the outer peripheral wall. 
     The central channel may be bound by a wall at the opposite side of the impingement insert. In other words, if the triple-walled section is present at a pressure side then the opposite side would be the suction side, and vice versa. The wall at the opposite side of the impingement insert may also have a triple-walled section, similar to the aspects of the present technique. When the wall at both sides of the impingement insert have a triple-walled section or structure, similar to the aspects of the present technique, then the common channel may be shared or common between the triple-walled sections or structures, in other words only one common channel may be present. Alternatively, the wall at the opposite side of the impingement insert may just be a single wall or may be a double-walled section or structure. 
     The impingement insert may include a plurality of impingement cooling holes formed in the outer peripheral wall and configured to eject impingement jets into the outer channel. The impingement jets may be formed of or formed from the cooling air of the middle channel. In other words, the cooling air of the middle channel is ejected out as impingement jets through the impingement cooling holes into the outer channel. 
     The impingement insert may include at least one supply duct fluidly connecting the central channel and the middle channel. The supply duct may supply cooling air from the central channel to the middle channel. The supply duct may have an inlet and an outlet. The inlet of the supply duct may be positioned at the central channel. The outlet of the supply duct may be positioned at the middle channel. The supply duct may run across or extend across the inner channel. Cooling air from the central channel may be delivered to the middle channel, across the inner channel, being confined within the supply duct, or in other words, the cooling air when being supplied from the central channel to the middle channel, via the supply duct, does not mix with, i.e. is isolated from, any air that may be present in the inner channel. 
     The supply duct may have an inlet at the central wall, preferably disposed at the inner surface of the central wall, and may have an outlet at the inner peripheral wall of the insert, preferably disposed at the outer surface of the inner peripheral wall. 
     The impingement insert may include at least one extraction duct. The extraction duct may fluidly connect the outer channel and the inner channel. 
     The extraction duct may include an inlet at the outer channel, and an outlet at the inner channel, for extracting cooling air from the outer channel into the inner channel. 
     Thus, the at least one extraction duct guides the air through the middle channel. Thus, the cooling air entering the impingement cooling holes from the middle channel is not mixed or is isolated from the air guided by the at least one extraction duct. 
     The extraction duct may extend between the outer peripheral wall and the inner peripheral wall across the middle channel. 
     The extraction duct may have the inlet at the outer peripheral wall, preferably disposed at the outer surface of the outer peripheral wall, and may have the outlet at the inner peripheral wall of the insert, preferably disposed at the inner surface of the inner peripheral wall, so that cooling air can flow from the outer channel into the inner channel through the extraction duct. Thus, the extraction duct functions to extract cooling air from the outer channel into the inner channel. 
     Thus, according to the present technique, the cooling air provided into the airfoil enters the impingement insert, particularly the triple-walled section of the impingement insert, flows into the central channel, then is supplied from the central channel to the middle channel via the supply duct. 
     From the middle channel, the cooling air then is ejected out into the outer channel as impingement jets onto the inner surface of the airfoil to provide impingement cooling, then is extracted by the extraction duct from the outer channel into the inner channel. 
     The extracted cooling air may have been used once in the outer channel to cool the inner surface of the airfoil wall facing the outer channel, or adjacent to or facing the outer surface of the outer peripheral wall. 
     Preferably, this extracted cooling air may then be used for some further processes such as providing impingement cooling to another part or section of the inner surface of the airfoil wall. 
     According to the present technique, in the impingement insert, a size of the inlet and/or the outlet of the extraction duct is larger than a size of the impingement cooling holes. 
     According to the present technique, in the impingement insert, a size of an inlet of the supply duct and/or an outlet of the supply duct is larger than a size of the impingement cooling holes. 
     According to the present technique, in the impingement insert, a size of an inlet of the supply duct and/or an outlet of the supply duct is larger than a size of the inlet and/or the outlet of the extraction duct. 
     The outer peripheral wall of the insert may have a corrugated shape. 
     The corrugated shape may comprise a plurality of recesses or troughs extending in a direction away from the inner peripheral wall, and one or more protrusions or ridges intervening the recesses or the troughs i.e. in an alternating way. One or more of the impingement cooling holes may be provided in at least one of the recesses or troughs. Preferably, all the recesses or troughs are provided with one or more of the impingement cooling holes. 
     The inlet of the extraction duct may be positioned at the one or more ridges or protrusions. 
     The triple-walled structure may comprise a main outlet for the cooling air. The main outlet may be an outlet of the inner channel. 
     The triple-walled structure may comprise at least one main inlet for the cooling air. The at least one main inlet may be is an inlet of the central channel. 
     The triple-walled structure may be configured such that the cooling air received into the central channel via the at least one main inlet is supplied to the middle channel via the at least one supply duct, then ejected from the middle channel into the outer channel as impingement jets via the impingement cooling holes, and then is extracted from the outer channel into the inner channel via the extraction duct. 
     The main inlet may be disposed at a top side and/or a bottom side of the central channel. The top side and the bottom side being spaced apart along a longitudinal direction of the impingement insert. In other words, the top side and/or the bottom side may be understood as sides or regions of the central channel that are spaced apart along a longitudinal direction of the impingement insert. The cooling air may enter the central channel along the longitudinal direction. 
     The main inlet may be disposed at a lateral side of the central channel. The lateral side may be extending parallel to a longitudinal direction of the impingement insert. The lateral side may be understood as extending parallel to a longitudinal direction of the impingement insert. The cooling air may enter the middle channel perpendicular to the longitudinal direction. 
     The extraction duct may be aerodynamically shaped with respect to a flow of the cooling air flowing through the middle channel. A cross-section of the extraction duct may have one of a round shape, oval shape and/or an elliptical shape. 
     The supply duct may be aerodynamically shaped with respect to a flow of the cooling air flowing through the inner channel. A cross-section of the supply duct may have one of a round shape, oval shape and/or an elliptical shape. 
     The impingement insert may include a downstream part. The downstream part may include a double-walled structure. The double-walled structure may have an inner wall and an outer wall, and may create three spatial divisions defining a downstream inner channel formed at an inner surface of the inner wall, a downstream outer channel formed at an outer surface of the outer wall, and a downstream middle channel formed between the inner surface of the outer wall and the outer surface of the inner wall. 
     The downstream part may also include a plurality of impingement cooling holes formed in the outer wall, which may be configured to eject impingement jets into the downstream outer channel. The impingement jets may be formed of or may be formed from cooling air of the downstream middle channel. 
     A main outlet of the triple-walled structure may be fluidly connected to a main inlet of the downstream part. The main inlet of the downstream part may be an inlet of the downstream middle channel. 
     The downstream part may include at least one downstream extraction duct extending between the outer wall of the downstream part and the inner wall of the downstream part across the downstream middle channel. The downstream extraction duct may include an inlet at the downstream outer channel, and an outlet at the downstream inner channel, for extracting cooling air from the downstream outer channel into the downstream inner channel. 
     In a second aspect of the present technique, a turbomachine component for a gas turbine is provided. 
     The turbomachine component may include an airfoil having an airfoil wall defining an internal space of the airfoil. At least one cooling channel may be formed in the internal space of the airfoil. An impingement insert may be inserted in the cooling channel. The impingement insert may be according to the first aspect of the present technique described hereinabove. The outer channel may be defined between the outer surface of the outer peripheral wall and an inner surface of the airfoil wall. 
     In the turbomachine component, the triple-walled section may include a main inlet formed at the central channel and a main outlet formed at the inner channel. 
     The outer channel may be a closed chamber other than, i.e. besides, the impingement cooling holes of the outer peripheral wall and the inlet of the extraction duct, and optionally one or more film cooling holes that may be present in the airfoil wall. In other words, the outer channel may be a sealed space into which the cooling air may enter only by impingement cooling holes, i.e. no other air inlets into the outer channel are present, and from which the cooling air can flow out only via the inlet of the extraction duct or through one or more film cooling holes which may be present optionally, i.e. no other air outlets from the outer channel are present. 
     The middle channel may be a closed chamber other than, i.e. besides, the impingement cooling holes of the outer peripheral wall and the outlet of the supply duct. In other words, the middle channel may be a sealed space into which the cooling air may enter only via the supply duct, i.e. no other air inlets into the middle channel are present, and from which the cooling air may leave only via the impingement cooling holes, i.e. no other air outlets from the middle channel are present. 
     The inner channel may be a closed chamber other than, i.e. besides, the outlet of the extraction duct and the main outlet of the triple-walled section. In other words, the inner channel may be a sealed space into which the cooling air may enter only by the outlet of the extraction duct, i.e. no other air inlets into the inner channel are present, and from which the cooling air may leave only via the main outlet of the triple-walled section, i.e. no other air outlets from the inner channel are present. 
     The central channel may be a closed chamber other than, i.e. besides, the main inlet of the triple-walled section and the inlet of the supply duct. In other words, the central channel may be a sealed space into which the cooling air may enter only via the main inlet of the triple-walled section, i.e. no other air inlets into the central channel are present, and from which the cooling air may leave only via the supply duct, i.e. no other air outlets from the central channel are present. 
     The inner surface of the airfoil wall may include extraction guides protruding from the inner surface of the airfoil wall towards the outer surface of the outer peripheral wall. The cooling air after having impinged onto the inner surface of the airfoil wall is guided by the extraction guides towards the inlet of the of the extraction duct. 
     According to a third aspect of the present technique, a gas turbine is presented. The gas turbine includes a turbomachine component according to the second aspect of the present technique. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned attributes and other features and advantages of the present technique and the manner of attaining them will become more apparent and the present technique itself will be better understood by reference to the following description of embodiments of the present technique taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  shows part of an exemplary embodiment of a gas turbine in a sectional view and in which a turbomachine component of the present technique is incorporated; 
         FIG. 2  is a perspective view illustrating an exemplary embodiment of a turbomachine assembly that includes an exemplary embodiment of a turbomachine component according to the present technique, exemplified by a blade in accordance with the present technique; 
         FIG. 3  is a cross-sectional view along the line Y-Y in  FIG. 2  schematically depicting an exemplary location of an impingement insert of the present technique; 
         FIG. 4  schematically represents an exemplary embodiment of the impingement insert according to the present technique; 
         FIG. 5  schematically represents a part M, shown in  FIG. 4 , of the impingement insert of  FIG. 4 ; 
         FIG. 6  schematically represents another part N, shown in  FIG. 4 , of the impingement insert of  FIG. 4 ; 
         FIG. 7  schematically represents a section of another exemplary embodiment of the impingement insert of the present technique; 
         FIG. 8  schematically represents a larger section of the exemplary embodiment of the impingement insert of the present technique including the section of  FIG. 7 ; 
         FIG. 9  schematically represents a relative size and/or orientation and/or distribution of the impingement holes and an inlet of the extraction duct of the present technique; and 
         FIG. 10  illustrates a conventional impingement insert, for comparative understanding of the impingement insert of the present technique. 
     
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Hereinafter, above-mentioned and other features of the present technique are described in detail. Various embodiments are described with reference to the drawing, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be noted that the illustrated embodiments are intended to explain, and not to limit the invention. It may be evident that such embodiments may be practiced without these specific details. 
       FIG. 1  shows an example of a gas turbine  10  in a sectional view. The gas turbine  10  may comprises, in flow series, an inlet  12 , a compressor or compressor section  14 , a combustor section  16  and a turbine section  18  which are generally arranged in flow series and generally about and in the direction of a longitudinal or rotational axis  20 . The gas turbine  10  may further comprises a shaft  22  which is rotatable about the rotational axis  20  and which extends longitudinally through the gas turbine  10 . The shaft  22  may drivingly connect the turbine section  18  to the compressor section  14 . 
     In operation of the gas turbine  10 , air  24 , which is taken in through the air inlet  12  is compressed by the compressor section  14  and delivered to the combustion section or burner section  16 . The burner section  16  may comprise a burner plenum  26 , one or more combustion chambers  28  and at least one burner  30  fixed to each combustion chamber  28 . The combustion chambers  28  and the burners  30  may be located inside the burner plenum  26 . The compressed air passing through the compressor  14  may enter a diffuser  32  and may be discharged from the diffuser  32  into the burner plenum  26  from where a portion of the air may enter the burner  30  and is mixed with a gaseous or liquid fuel. The air/fuel mixture is then burned and the combustion gas  34  or working gas from the combustion is channeled through the combustion chamber  28  to the turbine section  18  via a transition duct  17 . 
     This exemplary gas turbine  10  may have a cannular combustor section arrangement  16 , which is constituted by an annular array of combustor cans  19  each having the burner  30  and the combustion chamber  28 , the transition duct  17  has a generally circular inlet that interfaces with the combustor chamber  28  and an outlet in the form of an annular segment. An annular array of transition duct outlets may form an annulus for channeling the combustion gases to the turbine  18 . 
     The turbine section  18  may comprise a number of blade carrying discs  36  attached to the shaft  22 . In the present example, two discs  36  each carry an annular array of turbine blades  38  are depicted. However, the number of blade carrying discs could be different, i.e. only one disc or more than two discs. In addition, guiding vanes  40 , which are fixed to a stator  42  of the gas turbine  10 , may be disposed between the stages of annular arrays of turbine blades  38 . Between the exit of the combustion chamber  28  and the leading turbine blades  38  inlet guiding vanes  44  may be provided and turn the flow of working gas onto the turbine blades  38 . 
     The combustion gas from the combustion chamber  28  enters the turbine section  18  and drives the turbine blades  38  which in turn rotate the shaft  22 . The guiding vanes  40 ,  44  serve to optimize the angle of the combustion or working gas on the turbine blades  38 . 
     The turbine section  18  drives the compressor section  14 . The compressor section  14  comprises an axial series of vane stages  46  and rotor blade stages  48 . The rotor blade stages  48  may comprise a rotor disc supporting an annular array of blades. The compressor section  14  may also comprises a casing  50  that surrounds the rotor stages and supports the vane stages  48 . The guide vane stages may include an annular array of radially extending vanes that are mounted to the casing  50 . The vanes are provided to present gas flow at an optimal angle for the blades at a given gas turbine operational point. Some of the guide vane stages may have variable vanes, where the angle of the vanes, about their own longitudinal axis, can be adjusted for angle according to air flow characteristics that can occur at different gas turbine operations conditions. The casing  50  may define a radially outer surface  52  of the passage  56  of the compressor  14 . A radially inner surface  54  of the passage  56  may be at least partly defined by a rotor drum  53  of the rotor which may be partly defined by the annular array of blades  48 . 
     The present technique is described with reference to the above exemplary gas turbine having a single shaft or spool connecting a single, multi-stage compressor and a single, one or more stage turbine. However, it should be appreciated that the present technique is equally applicable to two or three shaft gas turbines and which can be used for industrial, aero or marine applications. 
     The terms upstream and downstream refer to the flow direction of the airflow and/or working gas flow through the gas turbine unless otherwise stated. The terms forward and rearward refer to the general flow of gas through the gas turbine, unless otherwise stated. The terms axial, radial and circumferential are made with reference to the rotational axis  20  of the gas turbine, unless otherwise stated. 
     In the present technique, a turbomachine component including an airfoil  100  is presented—as shown for example in  FIGS. 2 and 3 . The turbomachine component of the present technique may be the blade  38  of the gas turbine  10 , described hereinabove, unless other specified. The turbomachine component of the present technique may be the vane  40 , 44  of the gas turbine  10 , described hereinabove, unless other specified. Hereinafter, for sake of simplicity and brevity and not intended to be a limitation unless otherwise specified, the turbomachine component has been exemplified, and has also been referred to, as a blade of the gas turbine, however it may be noted that the turbomachine component according to the present technique may also be another turbomachine component that includes an airfoil in accordance with the present technique. 
       FIGS. 2 and 3  schematically depict an example of a turbomachine component, exemplified by the blade  38  of the gas turbine  10 .  FIG. 2  schematically depicts an example of a turbomachine assembly. The assembly may include the turbine blades  38 , as the turbomachine component, arranged on the rotor disk  36 . The turbine blade  38  may include a platform  200 , an airfoil  100  and optionally a root  300 . The blade  38  may be fixed to or mounted onto the disk  36  via the root  300 . 
     In the turbomachine component, the airfoil  100  extends from the platform  200 . The platform  200  may include an upper surface  201  and a lower surface  210 . The airfoil  100  may extend from the upper surface  201  of the platform  200 . The upper surface  201  may extend circumferentially. Similarly, the lower surface  210  may extend circumferentially. The airfoil  100  extends radially outwards from the upper surface  201  of the platform  200 . The root  300  may extend radially downwards, opposite of the extension direction of the airfoil, from the lower surface  210  of the platform  200 . 
     The airfoil  100  includes an airfoil wall  101  that encloses an internal space  100   s  of the airfoil. The airfoil wall  101  may include a pressure side  102  (also referred to as pressure surface or concave surface/side) and a suction side  104  (also referred to as suction side or convex surface/side). The pressure side  102  and the suction side  104  meet each other at a leading edge  106  and a trailing edge  108  of the airfoil  100 . 
     The airfoil  100  may have a base part  100   b  adjoining the platform  200  and a tip part  100   a  spaced apart from the base part  100   b  along a longitudinal direction A of the airfoil  100 . 
     The internal space  100   s  of the airfoil  100  may form a cooling channel  70  bound by the airfoil wall  101 . 
     Alternatively, at least one web  60  may be disposed within the internal space  100   s  of the airfoil  100 . The web  60  may extend between the pressure side  102  and the suction side  104 . More precisely, each web  60  may extend between an inner surface  101   a  of the airfoil wall  101  of the airfoil  100  at the pressure side  102  of the airfoil  100  and an inner surface  101   a  of the airfoil wall  101  of the airfoil  100  at the suction side  104  of the airfoil  100 . It may be noted that although the example of  FIG. 3  shows two such webs  60 , for exemplary purposes, the airfoil  100  may have 1 or 3 or more webs  60 . Each of the webs  60  is connected to the pressure side  102  and the suction side  104 . More precisely, each of the webs  60  may be connected to an inner surface  101   a  of the airfoil wall  101  at the pressure side  102  and the inner surface  101   s  of the airfoil wall  101  at the suction side  104 . 
     The wall, i.e. the airfoil wall  101 , of the airfoil  100  that includes the pressure side  102  and the suction side  104  and defines the leading edge  106  and the trailing edge  108  may also be referred to as the external wall of the airfoil  100  or as primary wall of the airfoil  100 , besides being referred to as the airfoil wall  101 . The airfoil wall  101  defines the external appearance of the airfoil  100 , or in other words defines the airfoil shape. 
     Each of the web  60  may also be understood as formed by a wall in the airfoil  100 , however the wall forming the web  60  is different than the airfoil wall  101  and may be referred to as internal wall or secondary wall of the airfoil  100 . 
     As shown in the example of  FIG. 3 , the internal space  100   s  of the airfoil  100  may include at least one cooling channel  70  for flow of cooling air  5 . The cooling channels  70  may be understood as entire internal space  100   s  or as sub-divisions of the internal space  100   s  of the airfoil  100  created by the webs  60 . It may be noted that although the example of  FIG. 3  shows three such cooling channels  70 , for exemplary purposes, the airfoil  100  may have 1 or 2 or 4 or more of such cooling channels  70 . 
     The cooling air  5  may be provided into the cooling channel  70  from outside the airfoil  100 , for example by cooling air flow paths (not shown) formed in the root  300  of the blade  1 . Alternatively, or in addition to the above, the cooling air  5  may be provided into the cooling channel  70  from another, preferably adjacent, cooling channel  70  of the airfoil  100 , wherein the cooling air is made to make a U-turn at the tip part  100   a  or the base part  100   b  of the airfoil thereby flowing out of a first cooling channel  70  and then flowing into a second cooling channel  70  from a top or bottom side, with respect to direction A, of the cooling channel. 
     The cooling channel  70  may extend along the longitudinal direction A of the airfoil  100 , as shown in the example of  FIGS. 2 and 3 . As shown in the example of  FIG. 3 , each cooling channel  70  of the airfoil may be defined by one or more of the webs  60  and the pressure side  102  and the suction side  104 . The example of  FIG. 3  shows a first cooling channel  70  defined by one of the webs  60 , a part of the pressure side  102 , a part of the suction side  104  and the leading edge  106 . The example of  FIG. 3  also shows a second cooling channel  70  defined by one of the webs  60 , a part of the pressure side  102 , a part of the suction side  104  and the trailing edge  108 . Furthermore, the example of  FIG. 3  shows a third cooling channel  70  defined by two adjacent webs  60  facing each other, a part of the pressure side  102 , and a part of the suction side  104 . The third cooling channel may be understood as the cooling channel between the first and the second cooling channels, and may also be present in a plurality. 
       FIG. 3  also shows a schematic representation of one or more impingement inserts  800  according to the present technique inserted or positioned or formed in the cooling channel  70 . The impingement insert  800  according to the present technique is explained hereinafter with reference to  FIGS. 4 to 9 . A conventional impingement insert  80 ′ is shown in  FIG. 10  for comparative understanding. 
     The impingement inserts  800  (hereinafter also referred to as the insert  800 ) may generally be understood as a component inserted in the cooling channel  70 , or as a component formed, e.g. by additive manufacturing, in the cooling channel  70  and that includes one or more impingement holes  85  for ejecting impingement jets  86  of cooling air towards the inner surface  101   a  of the airfoil wall  101 , preferably towards the pressure side  102  and/or the suction side  104  of the airfoil  100  and/or towards the leading edge  106  and/or towards the trailing edge  108  of the airfoil  100  for the purpose of impinging onto the inner surface  101   a  (hereinafter also referred to as the target surface) of the airfoil  100  to provide cooling of the target surface. 
     The impingement insert  800  may be inserted in the cooling channel  70  of the turbomachine component, which may be the blade  38  or the vane  40 ,  44 , of the gas turbine  10  to provide impingement cooling to the inner surface  101   a  of the airfoil wall  101  that forms the cooling channel  70  in the airfoil  100  of the turbomachine component of the gas turbine  10 . 
     Hereinafter, referring to  FIG. 5  in combination with  FIG. 4 , an exemplary embodiment of the impingement insert  800  of the present technique has been explained. 
     The impingement insert  800 , hereinafter also referred to as the insert  800 , includes a triple-walled structure or section  1 . In  FIG. 4  section  1  presents an exemplary embodiment of such a triple-walled section. 
     Generally, the phrase ‘triple-walled’ section or structure may be understood as a section or structure or a part of a structure i.e. a part of the insert  800  having three walls, that are substantially parallelly disposed with respect to each other. 
     To explain further, when positioned within the airfoil  100 , a side or part or region of the impingement insert  800  may be disposed adjacent to the pressure side  102  of the airfoil  100  as shown in  FIG. 3 , and may be referred to as a pressure side of the impingement insert  800 . The pressure side of the impingement insert  800 , may also be understood in other words, as a side of the impingement insert  800  for providing impingement jets  86  towards the pressure side  102  of the airfoil  100 . 
     Similarly, when positioned within the airfoil  100 , a side or part or region of the impingement insert  800 , different than the pressure side of the impingement insert  800 , may be disposed adjacent to the suction side  104  of the airfoil  100 , as shown in  FIG. 3 , and may be referred to as of a suction side of the impingement insert  800 . The suction side of the impingement insert  800 , may also be understood in other words, as a side of the impingement insert  800  for providing impingement jets  86  towards the suction side  104  of the airfoil  100 . 
     In the impingement insert  800 , the term ‘triple-walled’ includes that the suction side and/or the pressure side of the impingement insert  800 , each has three walls, namely a central wall  80 , an outer peripheral wall  82  and an inner peripheral wall  81 , as shown in  FIG. 4 . Simply put, only the suction side, or only the pressure side, or both the suction side and the pressure side, of the impingement insert  800  according to the present technique has three walls—the central wall  80 , the inner peripheral wall  81  and the outer peripheral wall  82 . The ‘triple-walled’ section, as used in the present technique, may not include a section, for example a section of the conventional impingement insert  80 ′ shown in  FIG. 10 , that has only one wall or only two walls at the suction side and the only one wall or only two walls at the pressure side. 
     To explain further, the pressure side of the impingement insert  800  may comprises three walls—a central wall  80  of the pressure side, an inner peripheral wall  81  of the pressure side and an outer peripheral wall  82  of the pressure side—hence forming an example of the triple-walled section. Alternatively, or in addition to the above, the suction side of the impingement insert  800  may comprises three walls—a central wall  80  of the suction side, an inner peripheral wall  81  of the suction side and an outer peripheral wall  82  of the suction side—hence forming an example of the triple-walled section. In short at least one of the pressure side and the suction side of the impingement insert comprises the triple-walled section, and the other of the pressure side and the suction side of the impingement insert may comprise a single wall or may comprise a double-walled section, or may comprise the triple-walled section as explained above. 
     When both the pressure side and the suction side of the impingement insert comprise the triple-walled section, then the two triple-walled section may be symmetrical, with respect to a camber of the airfoil. When both the pressure side and the suction side of the impingement insert comprise the triple-walled section, then the two triple-walled section may be mirror image of each other, with respect to a camber of the airfoil. 
     In the triple-walled section of the present technique, the outer peripheral wall  82  has been referred to as ‘outer peripheral’ because it forms an external appearance of the impingement insert  800 . The inner peripheral wall  81  has been referred to as ‘inner peripheral’ since it is positioned inwards of the outer peripheral wall  82  with respect to the central wall  80  or with respect to a center (not shown) of the impingement insert  800  or with respect to center (not shown) or central axis (not shown) of the cooling channel  70  defined in the airfoil  100 , as shown in  FIG. 3 . 
     Alternatively, the terms ‘inner peripheral’ and ‘outer peripheral’ may be understood as follows—the outer peripheral wall  82  of the impingement insert  800  is referred to as ‘outer peripheral’ since it is disposed towards the airfoil wall  101  i.e. near the pressure side  102  or the suction side  104  of the airfoil  100 , when the impingement insert  800  is located within the airfoil  100 . The outer peripheral wall  82  is located between the inner surface  101   a  of the airfoil wall  101  and the inner peripheral wall  81  of the triple-walled section. 
     Simply put, when moving from an outside of the impingement insert  800  into the impingement insert  800  from a lateral side of the impingement insert  800 , first appears the outer peripheral wall  82  of the impingement insert  800  and then the inner peripheral wall  81  of the impingement insert  800  and finally the central wall  80 . Similarly, when the impingement insert  800  is located in the airfoil  100 , when moving from an outside of the airfoil  100  into the airfoil  100  from a lateral side (e.g. the pressure side or suction side of the airfoil) of the airfoil  100 , first appears the airfoil wall  101 , then the outer peripheral wall  82  of the impingement insert  800 , then the inner peripheral wall  81  of the impingement insert  800 , and then the central wall  80  of the impingement insert  800 . 
     As shown in  FIGS. 4 and 5 , the central wall  80  has an inner surface  80   a  and an outer surface  80   b , the inner peripheral wall  81  has an inner surface  81   a  and an outer surface  81   b , and the outer peripheral wall  82  has an inner surface  82   a  and an outer surface  82   b . The inner surface  81   a  of the inner peripheral wall  81  faces the outer surface  80   b  of the central wall  80 . The inner surface  82   a  of the outer peripheral wall  82  faces the outer surface  81   b  of the inner peripheral wall  81 . The space between the inner and the outer peripheral walls  81 ,  82  is referred to as middle channel  502 . The middle channel  502  is defined or present between the inner surface  82   a  of the outer peripheral wall  82  and the outer surface  81   b  of the inner peripheral wall  81 . The space between the central wall  80  and the inner peripheral wall  81  is referred to as inner channel  501 . The inner channel  501  is defined or present between the inner surface  81   a  of the inner peripheral wall  81  and the outer surface  80   b  of the central wall  80 . 
     The outer surface  82   b  of the outer peripheral wall  82  is configured to face the inner surface  101   a  of the airfoil wall  100 , when the impingement insert  800  is positioned within the airfoil  100 . 
     As shown in  FIGS. 4 and 5 , in the impingement insert  800 , the central wall  80 , the inner peripheral wall  81  and the outer peripheral wall  82  of the triple-walled section define four spatial divisions—a central channel  500  formed at the inner surface  80   a  of the central wall  80 , the inner channel  501  formed between the outer surface  80   b  of the central wall  80  and the inner surface  81   a  of the inner peripheral wall  81 , the middle channel  502  formed between the inner surface  82   a  of the outer peripheral wall  82  and the outer surface  81   b  of the inner peripheral wall  81 , and an outer channel  503  formed at the outer surface  82   b  of the outer peripheral wall  82 . 
     Simply put, the inner channel  501  is defined between the central wall  80  and the inner peripheral wall  81 , and the middle channel  502  is defined between the inner and the outer peripheral walls  81 ,  82 . The inner channel  501  and the middle channel  502  are adjacent to each other separated by the inner peripheral wall  81 . The main channel  500  is at the central wall side of the inner channel  501 , and the outer channel  503  is at the outer peripheral wall side of the middle channel  502 . The inner and middle channels  501 ,  502  may be disposed between the central and the outer channels  500 ,  503 . 
     As shown in  FIGS. 4 and 5 , when the impingement insert  800  is positioned within the airfoil  100 , the space between the airfoil wall  101  and the outer peripheral wall  82  may be referred to as the outer channel  503 . More precisely, the space between the airfoil wall  101  and the outer surface  82   b  of the outer peripheral wall  82  may be referred to as the outer channel  503 . Even more particularly, the space between the inner surface  101   a  of the airfoil wall  101  and the outer surface  82   b  of the outer peripheral wall  82  may be referred to as the outer channel  503 . 
     To explain further, as shown in  FIGS. 4 and 5 , when moving from a center (not shown) of the impingement insert  800  towards an outside of the impingement insert  800 , first appears the central channel  500 , then the central wall  80  of the triple-walled section, then the inner channel  501 , then the inner peripheral wall  81  of the triple-walled section, then the middle channel  502 , then the outer peripheral wall  82  of the triple-walled section, then the outer channel  503 . On continuing further, finally the inner surface  101   a  of the airfoil wall  100  would appear, if the impingement insert  800  were positioned or located within the airfoil  100 . 
     As shown in  FIGS. 4 and 5 , the impingement insert  800  includes a plurality of impingement cooling holes  85  formed as through-holes in the outer peripheral wall  82  and configured to eject impingement jets  86  into the outer channel  503 . The impingement jets  86  are formed of or formed from the cooling air  5  of the middle channel  502 . In other words, the cooling air  5  of the middle channel  502  is ejected out as impingement jets  86  through the impingement cooling holes  85  into the outer channel  503 . The cooling air  5  is ejected out via the impingement cooling holes  85  in form of impingement jets  86  towards the inner surface  101   a  of the airfoil wall  100 , if the impingement insert  800  were positioned or located within the airfoil  100 . 
     As shown in  FIGS. 4 and 5 , the impingement insert  800  includes at least one supply duct  7 . The supply duct  7  may be understood as a pipe or tube that extends between the central wall  80  and the inner peripheral wall  81  across the inner channel  501 , i.e. from the central wall  80  to the inner peripheral wall  81  across the inner channel  501 . A cross-section of the supply duct  7  may be circular, or oval, or polygonal. The cross-section of the supply duct  7  may be aerodynamically shaped which may be oriented accordingly to any flow of cooling air  5  that occurs across or past the supply duct  7 . 
     As shown in  FIGS. 4 and 5 , the supply duct  7  has an inlet  7   a  that may be disposed in the central channel  500 , e.g. at the inner surface  80   a  of the central wall  80 . The supply duct  7  has an outlet  7   b  that may be disposed in the middle channel  502 , e.g. at the outer surface  81   b  of the inner peripheral wall  81 . In other words, the supply duct  7  fluidly connects the central channel  500  and the middle channel  502 , so that cooling air  5  can flow from the central channel  500  into the middle channel  502  through the supply duct  7 . The cooling air  5  passes from the central channel  500  to the middle channel  502  by flowing in a confined way, confined in the supply duct  7 , through the intervening inner channel  501 . 
     Thus, the supply duct  7  functions to supply or provide cooling air  5  from the main channel  500  into the middle channel  502 . 
     As shown in  FIG. 4  and, the impingement insert  800  includes at least one extraction duct  9 . The extraction duct  9  may be understood as a pipe or tube that extends between the outer peripheral wall  82  and the inner peripheral wall  81  across the middle channel  502 , i.e. from the outer peripheral wall  82  to the inner peripheral wall  81  across the middle channel  502 . A cross-section of the extraction duct  9  may be circular, or oval, or polygonal. The cross-section of the extraction duct  9  may be aerodynamically shaped which may be oriented accordingly to any flow of cooling air  5  that occurs across or past the extraction duct  9 , explained later with reference to  FIG. 9 . 
     As shown in  FIGS. 4 and 5 , the extraction duct  9  has an inlet  9   a  that may be disposed in the outer channel  503  e.g. at the outer surface  82   b  of the outer peripheral wall  82 . The extraction duct  9  has an outlet  9   b  that may be disposed in the inner channel  501  e.g. at the inner surface  81   a  of the inner peripheral wall  81 . In other words, the extraction duct  9  fluidly connects the outer channel  503  and the inner channel  501 , so that cooling air  5  can flow from the outer channel  503  into the inner channel  501  through the extraction duct  9 . The cooling air  5  passes from the outer channel  503  to the inner channel  501  by flowing in a confined way, confined in the extraction duct  9 , through the intervening middle channel  502 . 
     Thus, the extraction duct  9  functions to extract cooling air  5  from the outer channel  503  into the inner channel  501 . 
     It may be noted, that in the present technique the terms ‘inlet’ and ‘outlet’ and like terms, have been used with reference to cooling air. In other words, an ‘inlet’ may mean ‘inlet for cooling air’ and similarly, an ‘outlet’ may mean ‘outlet for cooling air’, unless otherwise stated. 
     The inlet  7   a  of the supply duct  7  may be flush with the inner surface  80   b  of the central wall  80 . Alternatively, the inlet  7   a  of the supply duct  7  may be protruding from the inner surface  80   b  of the central wall  80 . Alternatively, the inlet  7   a  of the supply duct  7  may be recessed inward in the central wall  80  from the inner surface  80   b  of the central wall  80 . 
     The outlet  7   b  of the supply duct  7  may be flush with the outer surface  81   b  of the inner peripheral wall  81 . Alternatively, the outlet  7   b  of the supply duct  7  may be protruding from the outer surface  80   b  of the inner peripheral wall  81 . Alternatively, the outlet  7   b  of the supply duct  7  may be recessed inward in the inner peripheral wall  81  from the outer surface  81   b  of the inner peripheral wall  81 . 
     The inlet  9   a  of the extraction duct  9  may be flush with the outer surface  82   b  of the outer peripheral wall  82 . Alternatively, the inlet  9   a  of the extraction duct  9  may be protruding from the outer surface  82   b  of the outer peripheral wall  82 . Alternatively, the inlet  9   a  of the extraction duct  9  may be recessed inward in the outer peripheral wall  82  from the outer surface  82   b  of the outer peripheral wall  82 . 
     The outlet  9   b  of the extraction duct  9  may be flush with the inner surface  81   a  of the inner peripheral wall  81 . Alternatively, the outlet  9   b  of the extraction duct  9  may be protruding from the inner surface  81   a  of the inner peripheral wall  81 . Alternatively, the outlet  9   b  of the extraction duct  9  may be recessed inward in the inner peripheral wall  81  from the inner surface  81   a  of the inner peripheral wall  81 . 
     Thus, as shown in  FIGS. 4 and 5 , in the present technique, the triple-walled section  1  structurally implements a flow scheme by which the cooling air  5  from the central channel  500  is supplied to the middle channel  502  via the supply duct  7 , from the middle channel  502  is ejected as impingement jets  86  via the impingement cooling holes  85  into the outer channel  503  for impinging onto the inner surface  101   a  of the airfoil wall  100 , and then is extracted from the outer channel  503  into the inner channel  501  via the extraction duct  9 . 
     As shown in  FIG. 4 , the triple-walled section  1  may include a main inlet  5   a  for the cooling air  5 . The main inlet  5   a  may be an inlet of the central channel  500 . The main inlet  5   a  may be the only inlet of the triple-walled section  1 . 
     The cooling air  5  that circulates through the triple-walled section  1  may enter the triple-walled section  1  via the main inlet  5   a . In other words, the cooling air  5  that circulates through the triple-walled section  1  may enter the central channel  500  first via the main inlet  5   a , then flow to the middle channel  502  via the supply duct  7 , and then flows to the outer channel  503  via impingement cooling holes  85 , and thereafter flows to the inner channel  501  via the extraction duct  9 . 
     As schematically depicted in  FIG. 4 , the main inlet  5   a  may be disposed at a top side or at bottom side of the central channel  500 . It may be possible to have a main inlet on both the bottom and top of the central channel  500 . The top side and the bottom side may be understood as sides or regions of the central channel  500  that are spaced apart along the longitudinal direction A (also shown in  FIGS. 2 and 3 ) of the impingement insert  800 . The top side and the bottom side of the central channel  500  may correspond to or coincide with the tip part  100   a  and the base part  100   b  of the airfoil  100  shown in  FIG. 2 . The top side and the bottom side of the impingement insert  800  may be spaced apart along the longitudinal direction A which may be understood to be same as a longitudinal direction of the impingement insert  800 . The cooling air  5  may enter the central channel  500  along the longitudinal direction A. 
     The longitudinal direction A may also be understood as the radial direction with respect to the rotational axis of the gas turbine. 
     Alternatively, or in addition to the above, the main inlet  5   a  may be disposed at a lateral side of the central channel  500 . The lateral side may be understood as extending parallel to the longitudinal direction A of the impingement insert  800 . The cooling air  5  may enter the central channel  500  perpendicular to the longitudinal direction A. 
     As shown in  FIG. 4 , section  2  and also shown in part ‘N’ and  FIG. 6 , the impingement insert  800  may include a downstream part  2 . The downstream part  2  may include a double-walled structure. The double-walled structure may have an inner wall  281  and an outer wall  282 , and may create three spatial divisions defining a downstream inner channel  2501  formed at an inner surface  281   a  of the inner wall  281 , a downstream outer channel  2503  formed at an outer surface  282   b  of the outer wall  282 , and a downstream middle channel  2502  formed between the inner surface  282   a  of the outer wall  282  and the outer surface  281   b  of the inner wall  281 . 
     The downstream part  2  may also include a plurality of impingement cooling holes  285  formed in the outer wall  282 , which may be configured to eject impingement jets  286  into the downstream outer channel  2503 . The impingement jets  286  may be formed of or may be formed from cooling air of the downstream middle channel  2502 . 
     A main outlet  5   b  of the triple-walled structure may be fluidly connected to a main inlet  2   a  of the downstream part  2 . The main inlet  2   a  of the downstream part may be an inlet of the downstream middle channel  2502 . 
     The downstream part  2  may include at least one downstream extraction duct  29  extending between the outer wall  282  of the downstream part  2  and the inner wall  281  of the downstream part  2  across the downstream middle channel  2502 . The downstream extraction duct  29  may include an inlet  29   a  at the downstream outer channel  2503 , and an outlet  29   b  at the downstream inner channel  2501 , for extracting cooling air from the downstream outer channel  2503  into the downstream inner channel  2501 . 
     As shown in  FIG. 4 , the impingement insert  800  may also have a third section  3 , which may not be a triple-walled section. The third section  3  may be a double-walled section, as explained for  FIG. 6 , or simply have one wall as shown in  FIG. 4 . One or more walls of the third section  3  may have impingement cooling holes  85  formed therein, and may form impingement jets  86  ejected out towards the inner surface  101   a  of the airfoil wall  101  positioned adjacent to the third section  3 . The impingement jets  86  comprise the cooling air  5  that flowed out of the main outlet  2   b  of the second section  2  and into the third section  3 . 
     Further aspects of the present technique have been discussed hereinafter with respect to  FIGS. 7 and 8 . 
     As shown in  FIGS. 7 and 8 , the outer peripheral wall  82  may have a corrugated shape. The corrugated shape includes a plurality of troughs  82   t  or indented regions  82   t  or recesses  82   t  that extend in a direction away from the inner peripheral wall  81 . One or more ridges  82   r  or protruded regions  82   r  or protrusions  82   r  may intervene the troughs  82   t  i.e. in an alternating way. One or more of the impingement cooling holes  85  may be placed or formed or located or disposed or provided in at least one of the troughs  82   t . Preferably all the troughs  82   t  are provided with one or more of the impingement cooling holes  85 . 
     As shown in  FIGS. 7 and 8 , the inlet  9   a  of the extraction duct  9  may be positioned at the one or more ridges  82   r.    
     Similarly (not shown), in addition to the above or as an alternative, the outer wall  282  may have a corrugated shape. The corrugated shape may include a plurality of troughs or indented regions or recesses that extend in a direction away from the inner wall. One or more ridges or protruded regions or protrusions may intervene the troughs i.e. in an alternating way. One or more of the impingement cooling holes  285  may be placed or formed or located or disposed or provided in at least one of the troughs. Preferably all the troughs are provided with one or more of the impingement cooling holes  285 . 
     Furthermore, as shown in  FIGS. 7 and 8 , when the impingement insert  800  is positioned in the airfoil  100 , the inner surface  101   a  of the airfoil wall  101  may include extraction guides  99  protruding from the inner surface  101   a  of the airfoil wall  101  towards the outer surface  82   b  of the outer peripheral wall  82 . The extraction guides  99  may be configured, for example shaped and/or sized, e.g. by having inclined surfaces, to guide the cooling air  5  from the outer channel  503  towards the inlet  9   a  of the of the extraction duct  9  or into the inlet  9   a  of the of the extraction duct  9 . 
     Further aspects of the present technique have been discussed hereinafter with respect to  FIG. 9 . 
     According to the present technique, a size of the inlet  9   a  and/or the outlet  9   b  of the extraction duct  9  may be larger than a size of the impingement cooling holes  85 . 
     According to the present technique, in a non-depicted embodiment, a size of the inlet  7   a  and/or the outlet  7   b  of the supply duct  7  may be larger than a size of the impingement cooling holes  85 . 
     According to the present technique, in a non-depicted embodiment, a size of the supply duct  7  may be larger than a size of the extraction duct  9 . 
     Here, ‘size’ may be understood as cross-sectional area. 
     Furthermore, as shown in  FIG. 9 , since in the present technique the cooling air  5  flows, via the supply duct  7 , into the middle channel  502  and since the extraction ducts  9  are located across the middle channel  502 , the cooling air  5  flows across or past the external surfaces of the extraction duct  9 . Thus, the extraction duct  9  may be aerodynamically shaped with respect to a direction of the cooling air  5  flowing through the middle channel  502 . 
     As shown in  FIG. 9 , the cross-section of the extraction duct  9  may be oval or elliptical in shape. Preferably, having the long axis or the longer axis of the shape aligned with or parallel to the flow direction of the cooling air while flowing through the middle channel  502 . 
     Furthermore, as shown in  FIG. 9 , there may be multiple extraction ducts  9 , and the extraction ducts  9  may be distributed, preferably evenly or uniformly, with respect to a distribution of the impingement cooling holes  85  on the outer peripheral wall  82 . In other words, the inlets  9   a  of the extraction ducts  9  may be distributed at the outer surface  82   b  of the outer peripheral wall  82 , preferably, evenly or uniformly amongst the impingement cooling holes  85  of the outer peripheral wall  82 . As shown in example of  FIG. 9 , each inlets  9   a  of the extraction ducts  9  may be surrounded by plurality of impingement cooling holes  85 , for example 4 impingement cooling holes  85  are depicted in  FIG. 9 . 
     Similarly, there may be multiple supply ducts  7 . The outlets  7   b  of the supply ducts  7  may be distributed on the inner peripheral wall  81 , preferably evenly or uniformly, with respect to a distribution of the impingement cooling holes  85  on the outer peripheral wall  82 . In other words, the outlets  7   b  of the supply ducts  7  may be distributed at the outer surface  81   b  of the inner peripheral wall  81 , preferably, evenly or uniformly corresponding to the impingement cooling holes  85  of the outer peripheral wall  82 . 
     While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope of the appended claims. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.