Patent Publication Number: US-2012034101-A1

Title: Turbine blade squealer tip

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to turbine blades, and more particularly to tip sealing systems for turbine blades. 
     BACKGROUND 
     Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures. In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures. 
     Typically, turbine blades are formed from a root portion at one end and an elongated portion forming an airfoil that extends outwardly from a platform coupled to the root portion at an opposite end of the turbine blade. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge. The tip of a turbine blade often has a tip seals to reduce the gap between ring segments and blades in the gas path of the turbine. The tip seals are often referred to as squealer tips and are frequently incorporated onto the tips of blades to help reduce pressure losses between turbine stages. These features are designed to minimize the gap between the blade tip and the ring segment. The material at the tip is exposed to the hot gas path because there is not a ceramic thermal barrier coating on the squealer tips. Squealer tips are integrally cast with the turbine blade. Turbine engines are being run at higher and higher temperatures in an effort to create increasing amounts of power from the engines. These higher temperatures are creating increased thermal stress levels on the turbine airfoils. 
     The inner aspects of most turbine blades typically contain an intricate maze of cooling channels forming a cooling system. The cooling channels often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature. However, centrifugal forces and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots. Localized hot spots, depending on their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade. 
     SUMMARY OF THE INVENTION 
     A turbine blade having a squealer tip coupled to a radially outer end of the turbine blade that is usable in a gas turbine engine is disclosed. The squealer tip may be configured such that the squealer tip requires less cooling fluids than conventional squealer tips, therefore increasing the efficiency of the turbine engine in which the squealer tip is used. In at least one embodiment, the squealer tip may use about 1.5 percent less cooling fluids than conventional turbine blades. In addition, the squealer tip may also be configured to be used in turbine engines that are designed to operate at higher operating temperatures than conventional turbine engines. The squealer tip may be formed from a material that is different than the material forming the turbine blade. 
     The turbine blade may be formed from a generally elongated blade having a leading edge, a trailing edge, a tip wall at a first end, a root coupled to the blade at an end generally opposite the first end for supporting the blade and for coupling the blade to a disc, and at least one cavity forming a cooling system in the blade. The squealer tip may be coupled to the tip at the first end. The squealer tip may be formed from a material selected from the group consisting of oxide dispersion strengthened alloys and FeCrAl alloys. The oxide dispersion strengthened alloys may include, but are not limited to, PM2000 and ODM 751, and the FeCrAl alloy may include, but are not limited to, APMT. 
     The squealer tip may be formed from a plurality of segmented tips extending radially outward and spaced apart from each other to relieve thermal stress at the tip. To relieve thermal stress in the squealer tip, the squealer tip may be formed from two rails extending radially outward and spaced apart from each other. The two rails may be formed from outer and inner rails that each form a continuous ring. 
     The squealer tip may be attached to the tip using a joining method such as transient liquid phase bonding. Alternatively, the squealer tip may be attached to the tip with an additive manufacturing process. The additive manufacturing process may be a selective laser melting process or a direct metal laser sintering process. 
     An advantage of this invention is that the squealer tip may enable turbine blade tips to be exposed to higher temperatures without an increased risk of failure. 
     Another advantage of this invention is that the squealer tip may be made with materials that would reduce cooling requirements at the tip and improve blade clearance while increasing the operating efficiency of the turbine engine by about ½ percent. 
     Yet another advantage of this invention is that the squealer tip may be formed from segmented tips to alleviate thermal stress in the squealer tip. 
     These and other embodiments are described in more detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention. 
         FIG. 1  is a perspective view of a turbine blade having features according to the instant invention. 
         FIG. 2  is top view of the turbine blade. 
         FIG. 3  is a detailed, side view of a squealer tip. 
         FIG. 4  is a partial side of a squealer tip being formed in a mechanical attachment system. 
         FIG. 5  is a partial side view of a squealer tip attached to a tip of the turbine blade. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1-5 , this invention is directed to a turbine blade  10  having a squealer tip  12  for use in turbine engines. The squealer tip  12  may be configured such that the squealer tip  12  requires less cooling fluids than conventional squealer tips, thereby increasing the efficiency of the turbine engine in which the squealer tip  12  is used. In at least one embodiment, the squealer tip  12  may use about 1.5 percent less cooling fluids than conventional turbine blades. In addition, the squealer tip  12  may also be configured to be used in turbine engines that are designed to operate at higher operating temperatures than conventional turbine engines without an increased risk of failure. 
     The squealer tip  12  may be attached to a radially outward tip  14  of a turbine blade  10 . The turbine blade  10  may be formed from a generally elongated airfoil  16  having a leading edge  18 , a trailing edge  20 , the tip  14  at a first end  24 , a root  26  coupled to the blade  10  at an end  28  generally opposite the first end  24  for supporting the blade  10  and for coupling the blade  10  to a disc, and one or more cavities forming a cooling system in the blade  10 . The cooling system may have any appropriate configuration within internal aspects of the elongated blade  16 . 
     The squealer tip  12  may be coupled to the tip  14  at the first end  24 . The squealer tip  12  may be formed from a material having high temperature oxidation and corrosion properties. The squealer tip  12  may be formed from materials that are different from the turbine blade  10 . The material may be, but is not limited to, an oxide dispersion strengthened alloy, such as, but not limited to, PM2000 and ODM 751. The material may also be an advanced dispersion strengthened powder metallurgy FeCrAl alloy, such as, but not limited to Kanthal APMT. These materials are capable of withstanding temperatures in excess of 1200 degrees Celsius in an uncoated condition. 
     The squealer tip  12  may be configured such that the squealer tip  12  is formed from a plurality of segmented tips  32  extending radially outward and spaced apart from each other, as shown  FIG. 3 . The tips  32  may include channels  34  between each adjacent tip  32 . The segments tips  32  may be aligned with each other or otherwise positioned. The channels  34  may extend any appropriate depth into the squealer tip  12  but not completely through the squealer tip  12  and into the tip  14  of the turbine blade  10 . The channels  34  may be square, rectangular, or have any other appropriate cross-sectional configuration. 
     In one embodiment, as shown in  FIG. 2 , the squealer tip  12  may be formed from two rails  36 ,  38  extending radially outward and spaced apart from each other. The rails  36 ,  38  may be formed from inner and outer rails  36 ,  38  that each form a continuous ring. 
     The squealer tip  12  may be formed using powder manufacturing systems that enable easy buildup of different structures on the tip  14  of the turbine blade  10 . The squealer tip  12  may be manufactured using an additive manufacturing technique such as selective laser melting (SLM), direct metal laser sintering (DMLS) or via the attachment of a preform by techniques such as transient liquid phase (TLP) bonding. Such a system enables multiple rails, such as rails  36 ,  38 , to be formed, which may have increased efficiencies. In particular, these manufacturing systems enable the formation of the inner and outer rails  36 ,  38  that follow the exterior shape of the turbine blades  10 . 
     As shown in  FIGS. 4 and 5 , the squealer tip  12  may be attached to the tip  14  via a mechanical attachment system  36 . The mechanical attachment system  36  may be any cavity having a ledge under which the squealer tip  12  may be attached. As shown in  FIG. 4 , a powder may be placed in a cavity and sintered therein to build the squealer tip  12 . As shown in  FIG. 5 , the squealer tip  12  may extend radially outward from the tip  14 . The mechanical attachment system  36  may be a dovetail attachment system  38 , as shown in  FIG. 5 . 
     The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.