Abstract:
A method and apparatus for assembling a rotatable machine is provided. The machine includes a plurality of blades that extend radially outwardly from a rotor. The method includes determining a moment weight of each blade in a row of blades, determining a geometric parameter of each blade in the same row of blades, and determining a mapping order of each blade using the moment weight and the geometric parameter. The apparatus includes a computer system that includes a software product code segment for minimizing imbalance in a bladed rotor wherein the segment is configured to receive a moment weight value for each blade to be installed in said rotor, receive a geometric parameter value for each blade to be installed in said rotor, calculate a blade location on the rotor based on the received values, and generate a blade map based on the calculated location.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to gas turbine engines and, more particularly, to assembling rotating components of gas turbine engines. 
   At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly and a high pressure compressor which compress airflow entering the engine. A combustor ignites a fuel-air mixture which is then channeled through a turbine nozzle assembly towards low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. Gas turbines are used in different operating environments, such as, to provide propulsion for aircraft and/or to produce power in both land-based and sea-borne power systems. 
   During normal operation gas turbine engines may experience high rotational speeds. An imbalance of the rotor may cause vibration of the rotor and induce stresses to rotor bearings and support structures. Over time, continued operation with such stresses may lead to failure of the bearings, bearing support structure, and/or rotor components. Failure of a component within the engine system may damage the system and/or other components within the system, and may require system operations be suspended while the failed component is replaced or repaired. More particularly, when the component is a turbofan gas turbine engine fan blade, a blade-out condition may cause damage to a blade that is downstream from the released blade. 
   At least some known turbofan gas turbine engines include a fan base having a plurality of fan blades extending radially outwardly therefrom. To facilitate minimizing imbalance of the fan during operation, known fan assemblies are assembled in a controlled manner. For example, one control that may be used in assembling fan rotors is mapping each blade of the fan into specific slots in the fan base. Within other known fan assemblies a moment weight of each blade is determined and the determined moment weight is used to map each blade into specific fan base slots. However, because the geometry of adjacent blades may be different, during operation a rotor may still experience a shift in balance that is not associated with the moment weight of each blade. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method of assembling a rotatable machine is provided. The machine includes a plurality of blades that extend radially outwardly from a rotor. The method includes determining a moment weight of each blade in a row of blades, determining a geometric parameter of each blade in the same row of blades, and determining a mapping order of each blade using the moment weight and the geometric parameter. 
   In another aspect, a rotor assembly is provided. The rotor includes a disk that includes a plurality of circumferentially-spaced blade root slots defined therein, and a plurality of blades wherein each blade includes a root, a tip, and an airfoil therebetween, and wherein each blade is positioned within a pre-determined slot based on a blade map. The blade map is generated by a computer system configured to receive a moment weight value for each blade, receive a geometric parameter value for each blade, and determine a blade map based on the moment weight value and the geometric parameter value. 
   In yet another aspect, a computer system including a software product code segment for minimizing imbalance in a bladed rotor is provided. The segment is configured to receive a moment weight value for each blade to be installed in the rotor, receive a geometric parameter value for each blade to be installed in the rotor, calculate a blade location on the rotor based on the received values, and generate a blade map based on the calculated location. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an exemplary gas turbine engine; 
       FIG. 2  is a perspective view of an exemplary fan rotor and blading assembly that may be used with the gas turbine engine shown in  FIG. 1 ; 
       FIG. 3  is a block diagram of an exemplary process that may be used with the fan rotor and blading assembly shown in  FIG. 2 ; and 
       FIG. 4  is a simplified block diagram of an exemplary blade mapping computer system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic illustration of an exemplary gas turbine engine  10  including a rotor  11  that includes a low-pressure compressor  12 , a high-pressure compressor  14 , and a combustor  16 . Engine  10  also includes a high-pressure turbine  18 , a low-pressure turbine  20 , an exhaust frame  22  and a casing  24 . A first shaft  26  couples low-pressure compressor  12  and low-pressure turbine  20 , and a second shaft  28  couples high-pressure compressor  14  and high-pressure turbine  18 . Engine  10  has an axis of symmetry  32  extending from an upstream side  34  of engine  10  aft to a downstream side  36  of engine  10 . In one embodiment, gas turbine engine  10  is a GE90 engine commercially available from General Electric Company, Cincinnati, Ohio. 
   In operation, air flows through low-pressure compressor  12  and compressed air is supplied to high-pressure compressor  14 . Highly compressed air is delivered to combustor  16 . Combustion gases  38  from combustor  16  propel turbines  18  and  20 . High pressure turbine  18  rotates second shaft  28  and high pressure compressor  14 , while low pressure turbine  20  rotates first shaft  26  and low pressure compressor  12  about axis  32 . 
     FIG. 2  is an exploded perspective view of an exemplary composite blade  100  and fan rotor disk  102  that may be used with gas turbine engine  10 . A plurality of circumferentially-spaced blades  100  are supported by rotor disk or drum  102  through a dovetail slot  104 . Each blade  100  includes an airfoil  106  that extends between a dovetail root  108  and a blade tip  110  such that each blade  100  is supported through dovetail root  108  and dovetail slot  104  by rotor  102 . Blade  100  is representative of a plurality of circumferentially-spaced blades  100  that are each mapped into a specific slot  104  based on measured parameters of blade  100 . In the exemplary embodiment, each blade  100  includes a composite airfoil  106  that includes a plurality of layered composite plies (not shown). More specifically, each blade  100  includes a first plurality of structural and load carrying airfoil plies in airfoil  106  and a second plurality of root plies in root  108 . 
     FIG. 3  is a flow diagram of an exemplary method  300  for assembling a rotatable machine such as turbine  10  (shown in FIG.  1 ). In the exemplary embodiment, the machine is a gas turbine engine that includes a rotor such as rotor  11 , shown in  FIG. 1 , that is rotatable about a longitudinal axis of symmetry of the engine. The rotor includes circumferentially-spaced slots for receiving the blades such that the blades extend radially between a blade root and a blade tip from the slots. 
   Method  300  includes determining  302  a moment weight of each blade that will be installed in the rotor. The moment weight may be determined by horizontally supporting a blade by its root in a device designed to measure moment weight. A moment weight is based not only on a pan weight of the blade but, also is based on a distribution of the weight of the blade along a radial distance extending between the blade root to the blade tip. In a rotating machine, an uneven distribution of moment weight of each blade spaced about the rotor may affect a balance condition of the rotor. 
   Some known rotors may experience a sudden shift in fan imbalance at high rotational speeds. Depending on the rotor, such a shift may occur at a certain fan corrected speed and may be associated with blade-to-blade airfoil geometry differences and/or aerodynamic balance. Specifically, the sudden shift in fan imbalance at high rotational speeds may adversely affect engine operation. Over time, a vibration caused by such imbalance may prematurely wear components within the engine and cause increased maintenance requirements. To facilitate minimizing imbalance due to the affects of blade-to blade airfoil differences, a measurement of the geometric parameter of each blade to be installed in the rotor is determined  304 . In the exemplary embodiment, such measurements are made directly during rotor assembly. In an alternative embodiment, the measurements may be made indirectly through the use of measurement devices that include sensors that detect and/or infer parameters of the blade. In another alternative embodiment, measurements of geometric parameters of a blade may be made post-assembly during a test phase. 
   Prior to positioning blades onto the rotor disk, a mapping order is determined  306 . A mapping order indicates a specific slot for each blade that will be assembled into the rotor. To determine  306  a mapping order, or blade map, a vector sum of the moment weight values and a vector sum of the geometric parameter values of each blade are combined. In the exemplary embodiment, blades are selected and mapped to a rotor slot that facilitates minimizing the vector sums of moment weight and aerodynamic or geometric parameters with each blade being evaluated individually for a particular slot position. In an alternative embodiment, the blades are selected based on the combination of the vector sums to provide offsetting corrections for each pair of blades positioned 180° apart on the rotor disk. Additionally, blades with offsetting aerodynamic or geometric parameters may be positioned adjacent to blades that have complementary aerodynamic or geometric parameters, to facilitate reducing undesirable shifts in balance due to high rotational speeds. Furthermore, aerodynamic or geometric parameters of blades that may aggravate a shift in balance may be positioned farther apart on the rotor disk to facilitate mitigating such effects. To facilitate determining  306  a mapping order, a computer including a program code segment configured to select and deselect blades may be utilized. Specifically, when blades are selected in complementary pairs, a first blade may be selected for positioning in a specific slot based on moment weight and aerodynamic or geometric parameters. A complementary second blade may then be selected for a slot located 180° apart from the first blade. The computer program iteratively selects the available blades in turn and matches them with complementary blades that will be positioned 180° apart from each selected blade. The computer selects blades in an order that facilitates minimizing a combination of the vector sum of the moment weight of all the blades to be positioned on the rotor disk and the vector sum of the geometric parameters of all blades to be positioned on the rotor disk. During the process of minimizing the combination of the vector sums, it may be necessary to deselect blades from blade pairs and reorder the blades selected. The computer system may then display the resultant blade map and generate a report detailing the selection process. Additionally, manual entry of blade parameters and recalculation of the blade map are supported. 
     FIG. 4  is a simplified block diagram of a blade mapping computer system  400 . As used herein, the term “computer” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set circuits (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer”. Computer system  400  includes a server system  412  including a disk storage unit  413  for data storage, and a plurality of client sub-systems, also referred to as client systems  414 , connected to server system  412 . In one embodiment, client systems  414  are computers including a web browser, such that server system  412  is accessible to client systems  414  via the Internet. Client systems  414  are interconnected to the Internet through many interfaces including a network, such as a local area network (LAN) or a wide area network (WAN), dial-in-connections, cable modems and special high-speed ISDN lines. Client systems  414  could be any device capable of interconnecting to the Internet including a web-based phone, personal digital assistant (PDA), or other web-based connectable equipment. A database server  416  is connected to a database  418  containing information regarding engine components. In one embodiment, centralized database  418  is stored on server system  412  and can be accessed by potential users at one of client systems  414  by logging onto server system  412  through one of client systems  414 . In an alternative embodiment database  418  is stored remotely from server system  412  and may be non-centralized. 
   The above-described blade mapping system is cost-effective and highly reliable means for determining a blade map using more than one blade parameter to facilitate assembling a rotatable machine. Each system is configured to receive a moment weight value for each blade, receive a geometric parameter value for each blade, calculate a blade location on the rotor based on the received values, and generate a blade map based on the calculated location. Accordingly, the blade mapping system facilitates assembly, operation, and maintenance of machines, and in particular gas turbine engines, in a cost-effective and reliable manner. 
   Exemplary embodiments of blade mapping system components are described above in detail. The components are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each blade mapping system component can also be used in combination with other blade mapping system components. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.