Abstract:
A turbine impeller including a rotor; a blade extending from the rotor from a first end of the blade; and a squealer tip provided at a second end opposite to the first end of the blade, wherein at least one perforated portion penetrates through the squealer tip.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2011-0129907, filed on Dec. 6, 2011 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field 
     Apparatuses consistent with one or more exemplary embodiments relate to a structure of a turbine impeller including a blade with a squealer tip for preventing thermal damage and for featuring high efficiency. 
     2. Description of the Related Art 
     A turbine is a device for producing power by using an energy generated as a high temperature and high pressure fluid flows in the turbine and expands. In the related art, the turbine includes one or more turbine impellers. Each turbine impeller includes a rotor located at the center and a plurality of blades extending in a long shape from a surface of the rotor. The rotor and the blades that are formed as a single body is accommodated in a shroud. The single body of the rotor and the blades rotates, and produces power. 
     Particularly, in case of an axial turbine, a fluid flows in a direction almost parallel to the rotating axis of a turbine impeller, and the fluid flowed into the turbine flows and contacts blades, thereby rotating the turbine impeller. Here, an end of a blade is located at a predetermined distance apart from the shroud to prevent the blade from being damaged and to allow smooth revolution. However, the fluid passing through the gap between the end of the blade and the shroud cannot contribute the production of energy via revolution of the turbine impeller at all. Therefore, the fluidic energy of the fluid through gap is wasted. 
     To prevent deterioration of efficiency of a turbine due to the fluid leaked through such a gap, a squealer tip is formed at an end of a blade close to a shroud. 
     The squealer tip is a protrusion which is formed at an end of a blade having a airfoil-like cross-sectional shape and has a predetermined height, where an airfoil-like groove is formed at an end of a blade having a squealer tip. 
     SUMMARY 
     One or more exemplary embodiments provide a turbine impeller including a blade which reduces thermal damage of the blade by preventing formation of hot spots in a squealer tip and around the blade and embodies high efficiency. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented exemplary embodiments. 
     According to an aspect of an exemplary embodiment, there is provided a turbine impeller includes a rotor; a blade extending from the rotor from a first end of the blade; and a squealer tip provided at a second end opposite to the first end of the blade, wherein at least one perforated portion penetrates through the squealer tip. 
     A first perforated portion of the at least one perforated portion may penetrate through a portion of a pressure surface of the blade closer to a leading edge than to a trailing edge. A fluid flows from outside of the blade into the squealer tip via the first perforated portion of the pressure surface of the blade, and a cross-sectional area of the first perforated portion of the pressure surface of the blade may decrease in a direction from the outside of the blade to an interior of the squealer tip. 
     A second perforated portion of the at least one perforated portion may penetrate through a portion of an absorbing surface of the blade closer to the trailing edge than to the leading edge. A fluid may flow from the interior of the squealer tip to outside of the blade via the second perforated portion, and a cross-sectional area of the second perforated portion may decrease in a direction from the interior of the squealer tip to outside of the blade. 
     Surfaces of the squealer tip contacting the perforated portion may include streamline shapes. 
     According to another aspect of an exemplary embodiment, there is provided a blade extending from a rotor of a turbine impeller including: a base portion provided at a first end attached to the rotor; a pressure side airfoil; a absorption side airfoil; a tip provided at a second end opposite of the first end of the blade including: a pressure side squealer tip; a suction side squealer tip; and a groove disposed between the pressure side and absorption side squealer tips, wherein a plurality of perforated portions penetrates through each of the pressure side and the absorption side squealer tips. 
     A cross-sectional area of each of the plurality of perforated portions of the blade may decrease in a direction from the pressure side airfoil to the absorption side of the airfoil. 
     Surfaces of the pressure and absorption side squealer tips contacting the plurality of perforated portions may include streamline shapes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a diagram partially showing a turbine impeller having a blade with thereat squealer tips in the related art; 
         FIG. 2  is a diagram showing the blade shown in  FIG. 1  viewed in a direction along a line II-II and showing flow of a fluid via a partial cross-section of the shroud; 
         FIGS. 3A ,  3 B, and  3 C are diagrams showing flows around at 20%, 40%, and 60% cross section along an axial axis from a leading edge to a trailing edge of the blade shown in  FIG. 1 , respectively. 
         FIG. 4  is a diagram partially showing a turbine impeller including a blade having thereat squealer tips; 
         FIG. 5  is a diagram showing the blade shown in  FIG. 4  viewed in a direction along a line V-V and showing flow of a fluid via a partial cross-section of a shroud which accommodates the blade; 
         FIG. 6  is a plan view of the blade shown in  FIG. 5   
         FIG. 7  is a diagram showing a modified example of the blade shown in  FIG. 4 , showing the blade viewed in the direction along the line V-V and flow of a fluid via a partial cross-section of the shroud accommodating the blade therein; and 
         FIG. 8  is a plan view of the blade shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. 
       FIG. 1  is a diagram partially showing a turbine impeller having a blade  10  with thereat squealer tips  21  and  22  in the related art.  FIG. 2  is a diagram showing the blade  10  shown in  FIG. 1  viewed in a direction along a line II-II and showing flow of a fluid via a partial cross-section of the shroud  40 .  FIGS. 3A ,  3 B, and  3 C are diagrams showing flows around at 20%, 40%, and 60% cross section along an axial axis from a leading edge  13  to a trailing edge  14  of the blade  10  shown in  FIG. 1 , respectively. 
       FIG. 1  shows the blade  10  including the squealer tips  21  and  22  and a rotor  30 , where the blade  10  is located inside the shroud  40 . 
     A plurality of blades  10  are formed at the rotor  30 . The rotor  30  and the blades  10  are located inside the shroud  40 .  FIG. 1  shows a portion of the rotor  30  and only one of the blades  10  extending therefrom. Furthermore, the blade  10  is arranged, such that a tip of the blade  10  is a predetermined distance apart from the shroud  40 . 
     The blade  10  has an airfoil-like cross-section and has a long shape extending from the rotor  30  in a direction. The blade  10  includes a leading edge  13 , which is the front portion of each airfoil-like cross-section, located in the upstream of flow of a fluid, and initially contacts the fluid, and a trailing edge  14 , which is the rear portion of each airfoil-like cross-section and located where two portions of a fluid separated by the blade  10  are combined again. Furthermore, based on the leading edge  13  and the trailing edge  14 , side surfaces of the blade  110  includes a pressure surface  11 , at which a fluid passing around the blade  10  has a relatively high pressure, and an absorbing surface  12 , at which a fluid passing around the blade  10  has a relatively low pressure. 
     As shown in  FIG. 2 , a fluid flows in via a gap formed between the blade  10  and the shroud  40 . As the fluid passes a pressure surface squealer tip  21  formed on the pressure surface  11  and flows into the interior of the squealer tip  23 , flow separation takes place at a region A. Here, amount of additional fluid flowing into the region A decreases due to resistance resulted from the flow separation. At the same time, a high temperature and high pressure fluid forms a vortex, which does not move and stays at the region A, and thus a hot spot at which the blade  10  is locally heated is formed.  FIGS. 3A through 3C  provide detailed views thereof. 
     An excessive thermal stress applies to a portion of the blade  10  with the hot spot, thereby causing thermal damages to the blade  10 . Therefore, if there is no suitable cooling process, the blade  10  may be destroyed, and destruction of the blade  10  may cause serious defects not only to a turbine, but also to an engine including the turbine. Here, the region A is formed at a location in the interior  23  of the squealer tip relatively close to the pressure surface  11  and a leading edge  13 . 
     Furthermore, the fluid which flowed into the interior  23  of the squealer tip passes through a gap formed between the absorbing surface squealer tip  22 , which is formed on an absorbing surface  12 , and the shroud  40 . Another flow separation may likely occur in a region B. The flow separation is induced by a fluid which leaked from the interior  23  of the squealer tip over the absorbing surface squealer tip  22  and a fluid which moves from the leading edge  13  along the absorbing surface  12 . Like the region A as described above, the flow separation applies thermal stress to the blade  10 . Furthermore, the flow separation disturbs flow of a fluid flowing along the absorbing surface  12 , thereby deteriorating efficiency of a turbine. 
     Particularly,  FIGS. 3A and 3B  are diagrams showing flow of a fluid in regions corresponding to 20% and 40% cross section of  FIG. 1 , respectively.  FIGS. 3A and 3B  show that the fluid is relatively stagnant in the region A compared to the other regions. Furthermore,  FIGS. 3B and 3C  are diagrams showing flow of a fluid in regions corresponding to 40% and 60% of  FIG. 1 , respectively.  FIGS. 3B and 3C  show that the fluid is relatively stagnant in the region B compared to the other regions. In other words,  FIGS. 3A through 3C  show vortexes formed in the regions A and B as described above. Problems due to the formation of the vortexes are as described above. 
     Accordingly, the blade  10  including the squealer tips  21  and  22  has problems including thermal cracks due to formation of hot spots based on vortexes formed inside the squealer tips  21  and  22  and deterioration of efficiency due to flow separation formed on the absorbing surface  12 . 
     Hereinafter, exemplary embodiments will be described in detail with reference to the attached drawings. 
       FIG. 4  is a diagram partially showing a turbine impeller  100  including a blade  110  having thereat squealer tips  121  and  122 .  FIG. 5  is a diagram showing the blade  110  shown in  FIG. 4  viewed in a direction along a line V-V and showing flow of a fluid via a partial cross-section of a shroud  140  which accommodates the blade  110 .  FIG. 6  is a plan view of the blade  110  shown in  FIG. 5 . 
     A turbine impeller  100  according to the present exemplary embodiment includes the blade  110  including the squealer tips  121  and  122  and a rotor  130 , where the turbine impeller  100  is located inside the shroud  140 . 
     A plurality of blades  110  are formed at the rotor  130 . The rotor  130  and the blades  110  are located inside the shroud  140 .  FIG. 4  shows a portion of the rotor  130  and only one of the blades  110  extending therefrom. Furthermore, the blade  110  is arranged, such that a tip of the blade  110  is a predetermined distance apart from the shroud  140 . 
     The blade  110  has an airfoil-like cross-section and has a long shape extending from the rotor  130  in a direction. The blade  110  includes a leading edge  113 , which is the front portion of each airfoil-like cross-section, located in the upstream of flow of a fluid, and initially contacts the fluid, and a trailing edge  114 , which is the rear portion of each airfoil-like cross-section and located where two portions of a fluid separated by the blade  110  are combined again. Furthermore, based on the leading edge  113  and the trailing edge  114 , side surfaces of the blade  110  includes a pressure surface  111 , at which a fluid passing around the blade  110  has a relatively high pressure, and an absorbing surface  112 , at which a fluid passing around the blade  110  has a relatively low pressure. 
     Same as the blade  10  in the related art as described above, squealer tips  121  and  122  are formed at the tip of the blade  110  close to the shroud  140 . 
     Furthermore, at least one perforated portions  121 _ 1  and  122 _ 1  penetrating through the squealer tips  121  and  122  are formed in the squealer tips  121  and  122 , respectively. 
     The perforated portion  121 _ 1  is formed in the pressure surface squealer tip  121 , and a fluid flows into the interior  123  of the squealer tip  121  from outside of the blade  110  via the perforated portion  121 _ 1 . The perforated portion  121 _ 1  formed in the pressure surface squealer tip  121  eliminates hot spots by forming a strong fluid flow toward a vortex, which is formed inside the interior  123  of the squealer tip  121  and forms hot spots. Therefore, the perforated portion  121 _ 1  may be formed at locations nearby a region of the interior  123  of the squealer tip  121  including a relatively large number of hot spots. Five ( 5 ) of the perforated portions  121 _ 1  formed in the present exemplary embodiment shown in  FIG. 4  are formed in a region of the pressure surface squealer tip  121  relatively close to the leading edge  113  than the trailing edge  114  of the blade  110 . However, the present exemplary embodiment is not limited thereto. 
     Furthermore, if a fluid flows from the leading edge  113  of the blade  110  along the absorbing surface  112 , flow separation takes place due to friction between the fluid and the absorbing surface  112  based on viscosity of the fluid. The flow separation usually occurs around the trailing edge  114 , which is in the downstream of a flow on the absorbing surface  112 , as described above. Since the flow separation deteriorates efficiency of a turbine, it is necessary to eliminate vortexes formed by the flow separation to improve efficiency of the turbine. 
     To this end, the perforated portion  122 _ 1  is formed in the absorbing surface squealer tip  122 , and a fluid flows from the interior  123  of the squealer tip  121  to the outside of the blade  110  via the perforated portion  122 _ 1 . The perforated portion  122 _ 1  formed in the absorbing surface squealer tip  122  eliminates vortexes formed around the absorbing surface  112  due to a flow separation. Another five ( 5 ) perforated portions  122 _ 1  formed in the present exemplary embodiment as shown in  FIG. 4  are formed in the absorbing surface squealer tip  122 . Particularly, the perforated portions  122 _ 1  may be formed in a region of the absorbing surface squealer tip  122  relatively close to the trailing edge  114  than the leading edge  113 , where vortexes are frequently formed around the region. 
     However, the present exemplary embodiment is not limited thereto, and a number, locations, and installation angles of perforated portions may vary. 
     The perforated portions  121 _ 1  and  122 _ 1  formed in the squealer tips  121  and  122  maintains the advantages of squealer tips  121  and  122  in preventing tip losses occurring at the tip of the blade  110  and resolves problems of squealer tips in the related art. Particularly, as a ratio between height of the blade  110  and a distance between the shroud  140  and the blade  110  increases, tip efficiency of the blade  110  decreases. The squealer tips  121  and  122  improve tip efficiency by reducing a distance between the shroud  140  and the blade  110 . However, if heights of the squealer tips  121  and  122  are reduced or grooves are formed in the squealer tips  121  and  122  to eliminate hot spots of the squealer tips  121  and  122 , a gap between the shroud  140  and the blade  110  increases, thereby deteriorating tip efficiency. On the contrary, since a perforated portion is formed in a squealer tip according to the present exemplary embodiment, hot spots may be removed without increasing the gap between the shroud  140  and the blade  110 , thereby contributing not only to elimination of hot spots, but also to improvement of tip efficiency. 
     Referring to  FIG. 5 , a fluid may form vortexes due to flow separation at the region A while the fluid is passing on the pressure surface squealer tip  121 , where the vortexes may be eliminated by flow of a fluid flowing in via the perforated portion  121 _ 1  formed in the pressure surface squealer tip  121 . In the same regard, vortexes that may be formed in the region B may be eliminated by flow of a fluid flowing out via the perforated portion  122 _ 1  formed in the absorbing surface squealer tip  122 . The faster the fluid flows via the perforated portions  121 _ 1  and  122 _ 1 , the more efficiently the vortexes may be removed. 
     The perforated portions  121 _ 1  and  122 _ 1  formed in the squealer tips  121  and  122  may have fluid inlets  121 _ 1   a  and  122 _ 1   a  that are larger than fluid outlets  121 _ 1   b  and  122 _ 1   b . In the words, the shape of the perforated portions  121 _ 1  and  122 _ 1  functions like nozzles, thereby accelerating flow of fluids flowing in the perforated portions  121 _ 1  and  122 _ 1 . The accelerated fluids may remove hot spots and vortexes more efficiently, thereby increasing effects of the exemplary embodiment. 
     Furthermore, inner surfaces of the perforated portions  121 _ 1  and  122 _ 1  of the squealer tips  121  and  122  may be smooth surfaces to prevent reduction of fluid pressure due to friction between the fluid and the inner surfaces. If the inner surfaces have high friction coefficients, pressure of the fluid is removed while the fluid flows in the perforated portions  121 _ 1  and  122 _ 1 , thereby further reducing speed of fluid flowing out of the fluid outlets  121 _ 1   b ,  122 _ 1   b . As a result, hot spots and vortexes may not be sufficiently removed. Furthermore, if the friction further increases, vortexes may be formed even by the fluids flowing in the perforated portions  121 _ 1  and  122 _ 1 , thereby increasing adverse effects of hot spots and vortexes. 
       FIG. 7  is a diagram showing a modified example of the blade  110  shown in  FIG. 4 , showing the blade  110  viewed in the direction along the line V-V and flow of a fluid via a partial cross-section of the shroud  140  accommodating the blade  110  therein.  FIG. 8  is a plan view of the blade  110  shown in  FIG. 7 . 
     Components of the modified example shown in  FIGS. 7 and 8  are identical to those shown in  FIGS. 4 through 6  except the perforated portions  121 _ 1  and  122 _ 1  formed in the squealer tips  121  and  122 . Therefore, descriptions and reference numerals regarding the components of the modified examples shown in  FIGS. 7 and 8  will be replaced with those regarding the components shown in  FIGS. 4 and 6  having the same shapes and functions. 
     In the present exemplary embodiment, surfaces of the squealer tips  121  and  122  contacting the spaces formed by the perforated portions  121 _ 1 ′ and  122 _ 1 ′ may be formed to have streamline shapes to reduce resistances received by a fluid passing through the spaces as much as possible. As shown in  FIGS. 5 and 6 , if portions of the squealer tips  121  and  122  close to the fluid inlets  121 _ 1   a  and  122 _ 1   a  and the fluid outlets  121 _ 1   b  and  122 _ 1   b  of the perforated portions  121  and  122  are formed to have acutely bent shapes, pressure of a fluid may be dropped when the fluid passes the fluid inlets and the fluid outlets. In other words, according to the present exemplary embodiment, surfaces of the squealer tips  121  and  122  contacting all spaces formed from the fluid inlets  121 _ 1   a ′ and  122 _ 1   a ′ to the fluid outlets  121 _ 1   b ′ and  122 _ 1   b ′ of the perforated portions  121 _ 1 ′ and  122 _ 1 ′ are formed to have streamline shapes to reduce pressure drops at the fluid inlets  121 _ 1   a ′ and  122 _ 1   a ′ and the fluid outlets  121 _ 1   b ′ and  122 _ 1   b ′ of the perforated portions  121 _ 1 ′ and  122 _ 1 ′ as shown in  FIGS. 7 and 8 . Therefore, drops of fluid pressure while a fluid flows in the perforated portions  121 _ 1 ′ and  122 _ 1 ′ may be reduced. 
     As described above, according to the one or more of the above exemplary embodiments, thermal damage of a blade may be reduced and power generation efficiency of a turbine may be improved. 
     It should be understood that exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
     While the exemplary embodiments have been particularly shown and described above, it would be appreciated by those skilled in the art that various changes may be made therein without departing from the principles and spirit of the present inventive concept as defined by the following claims.