Patent Publication Number: US-2012045318-A1

Title: Method and apparatus for air flow control

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to gas turbines. More particularly, the subject matter relates a guide vane in the gas turbine. 
     In a gas turbine, a compressor adds kinetic energy to a fluid, such as air, by increasing the fluid&#39;s tangential momentum. The kinetic energy from the compressor and thermal energy from the combustor is conveyed by a fluid, often air, to a turbine where the energy of the fluid is converted to mechanical energy. Several factors influence the efficiency of adding kinetic energy in the compressor. These factors may include air distribution within the compressor, pressure rise across the compressor, and loss sources in the compressor. One embodiment is a guide vane in the compressor which influences the distribution and magnitude of airflow into the compressor. The guide vane may be designed for high efficiency at a selected condition for the turbine, such as full load, high power output and/or fuel usage. The guide vane controls the air flow in the compressor, which determines the entitlement on kinetic energy that can be supplied to the rest of the gas turbine system. However, when operating at lower loads and reduced power output, the air flow distribution and aerodynamic loading from the guide vane causes less efficient gas turbine performance. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, an air flow control apparatus includes a guide vane to be positioned between an air inlet and a compressor rotor of a turbomachine. Further, the guide vane includes a geometry configured to control an air flow incidence on the rotor, the guide vane further having a substantially constant aspect ratio. In addition, a body of the guide vane includes a shape memory material configured to change a geometry of the guide vane in response to energy provided by a power source. 
     According to another aspect of the invention, a method for controlling air flow in a compressor includes flowing air from an inlet toward a guide vane and applying an energy to a shape memory material in the guide vane to change a geometry of the guide vane to control a distribution of air flow toward a rotor. 
     According to yet another aspect of the invention, a turbine compressor includes an air inlet, a rotor positioned downstream of the air inlet, and a guide vane positioned between the air inlet and the rotor, the guide vane comprising a shape memory material. The compressor also includes a power source coupled to the shape memory material to cause a change of a guide vane geometry. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a sectional side view of an embodiment of a gas turbine that includes a compressor with a guide vane and rotors; 
         FIG. 2  is a sectional view of the guide vane of  FIG. 1 ; 
         FIG. 3  is a sectional view of an embodiment of a guide vane in the shape of an airfoil; and 
         FIG. 4  is a perspective view of an embodiment of a guide vane as shape memory material changes the guide vane geometry. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a sectional side view of an embodiment of a gas turbine  100  disposed about a centerline axis  102 . The turbine  100  includes a guide vane  104  disposed in a compressor  106 . Air is compressed in the compressor  106  and is mixed with fuel that is burned in a combustor and expands in a turbine. The turbine then rotates in response to the expansion, driving the compressor  106  and producing a rotational power output. 
     A plurality of inlet guide vanes  104  (one shown) are disposed about the centerline axis  102  in front of one or more compressors  106 . As depicted, the compressor  106  includes an inner hub  108  and outer casing  110 , providing a flow path for air toward one or more combustors. The inlet guide vane  104  directs air flow from an inlet region  112 , as indicated by arrow  114 , downstream toward a first stage of the compressor  106 . In an aspect, the compressor  106  includes a plurality of stages. A first stage of the plurality of stages includes a rotor  116  and stator  118 . Similarly, a second stage includes a rotor  120  and stator  122  and a third stage includes a rotor  124  and stator  126 . The air flow  114  flows downstream, where the guide vane  104  creates a flow distribution or flow field through the plurality of compressor stages and into the combustor, indicated by flow arrow  128 . 
     In an embodiment, the guide vane  104  (also “inlet guide vane” or “IGV”) comprises a shape memory material (or “shape memory alloy”) that is in operable communication with the guide vane  104  to change the geometry of the guide vane  104  when an energy is applied to the shape memory material. For example, the shape memory material is embedded in or forms a portion of the interior and/or exterior of guide vane  104 . The shape memory material may include a flexible composite material with a conductor or wire embedded in the composite. The wire is operably coupled to a power source  130 , where the power source selectively applies energy, in the form of current and heat, to the wire. In one aspect, the power source  130  is coupled to a controller  132  to selectively apply current to the wires to change the geometry of the guide vane  104  based on turbine conditions. Conductive wire materials, such as nickel titanium (NiTi), produce a significant change in temperature when transmitting current. In an embodiment, a straight NiTi wire with a substantially straight shape is wound into a tight spiral and embedded in the composite. When a selected level of current is applied to the wire, the wire is heated to retain its previous, substantially straight shape. Accordingly, the composite shape memory material changes from a first shape to a second shape or geometry as the current carrying wire straightens. The power source  130  provides a selected level of current to the wire from a direct current (DC) source, such as a battery, a powerline-based alternating current (AC) source or any other suitable power source. A shape memory material may be described as having a shape memory property where the material remembers a plurality of different shapes based on a condition, such as an energy being applied to the material. For example, a shape memory material is configured to have one shape at low temperatures and a second shape at high temperatures. A material that shows a shape memory property during both heating and cooling may be called two-way shape memory material. As depicted, the guide vane  104  is an air foil defined by chord  134  and length  136  dimensions, wherein an aspect ratio (length/chord) is an expression of the relationship of the dimensions. In an embodiment, the aspect ratio of the guide vane  104  is substantially constant or fixed as the shape or geometry of the guide vane is changed by the shape memory material. 
     With continued reference to the embodiment of  FIG. 1 , the guide vane  104  geometry changes when a selected level of current is directed to the embedded wire. For example, the profile or geometry of the guide vane  104  is in the form of a first shape that is designed for a full load and increased power turbine condition and a second shape that is designed for a reduced load or turn down turbine condition. The full-load condition occurs at a time when an increased power is needed from the turbine and a low-load or turn-down condition occurs during off-peak times when less power is needed. Therefore, the first shape creates an air flow distribution that enables improved combustion, efficiency and power production at the full-load condition. The second shape creates an air flow distribution that is most efficient for the lower power condition, such as during off peak power demands. In aspects, turbine combustion efficiency is increased when a radial distribution of air flow has improved uniformity through the compressor. Specifically, overall efficiency improves as the variable geometry of the guide vane  104  causes a substantially uniform air flow incidence on a rotor blade at a plurality of turbine load conditions. Air flow incidence is the relationship or alignment of air flow from the guide vane to the rotor blade. Substantially uniform air flow may be described as a radial distribution of air across the span of an airfoil (guide vane or rotor blade) that causes improved efficiency for a turbine condition. In an embodiment, the guide vane  104  changes an angle of the vane with respect to air flow from the inlet, depending on the turbine condition. Further, efficiency is also affected by the amount of air flow through the compressor  100 . The amount of air flow varies depending on the amount of fuel injected into the combustor and the associated turbine load condition. In aspects, various power and fuel usage scenarios provide various operating conditions, where the variable geometry of guide vane  104  is adjusted to improve turbine efficiency. In an embodiment, the guide vane  104  comprises a single member or piece. In other embodiments, the guide vane  104  comprises a plurality of members. 
     In some embodiments, the entire structure of guide vane  104  includes the shape memory material, where wires are embedded throughout a composite-based structure. Such structures allow the entire geometry of the guide vane  104  to change based on current conditions. In other embodiments, selected portions or regions of the guide vane  104  structure include the shape memory material. For example, a trailing edge of the guide vane  104  comprises the shape memory material, thereby enabling the profile or geometry of the trailing edge to selectively change based on turbine conditions. In another embodiment, the leading edge changes geometry based on current selectively applied to a shape memory material located in the leading edge of the guide vane. In aspects, the shape memory material of the guide vane  104  include an alloy, flexible carbon fiber composites, conductive wires and/or nanoparticles, where the shape memory material changes shape when energy is applied to the material or selected portions of the material. The energy applied to the material may include current, voltage, electromagnetic waves, heat or other suitable energy. Although the guide vane  104  of the present embodiment is shown with a particular type of gas turbine engine  100 , the guide vane may be used with any known turbine engine type, including but not limited to steam turbines, gas turbines and aeroderivative turbines. In some embodiments, it is noted that the depicted air flow through compressor  106  comprises any suitable fluid, including air, oxygen, gas fuel, liquid fuel or any combination thereof. Further, the variable geometry guide vane  104  may be positioned between various stages of the compressor  106 . As discussed herein, the guide vane  104  is also referred to as an air flow control apparatus. 
       FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 , showing a profile of the guide vane  104 , in the shape of an airfoil  200 . The airfoil  200  includes a leading edge  202  and trailing edge  204 . The airfoil  200  includes a shape memory material, such as a flexible composite, that forms at least a portion of the airfoil wall  206 . Conductors, such as wires  208 , are embedded in the airfoil wall  206 . As depicted, the wires  208  are embedded in the flexible composite wall  206  of trailing edge  204 , therefore forming a trailing edge shape memory region. In an embodiment, the airfoil  200  is a substantially hollow structure, wherein a cavity  210  is surrounded by the airfoil wall  206 . As previously discussed, the shape memory material, which includes the composite wall  206  and wires  208 , changes the geometry of trailing edge  204  as current is applied to the wires  204 . In some embodiments, the shape memory material and airfoil  200  change geometry based upon the time of day, wherein the time corresponds to a condition and an expected power output. For example, a hypothetical turbine engine experiences a low load condition from 8 PM to 8 AM and experiences a full load condition from 8 AM to 8 PM. Accordingly, the airfoil  200  has a first shape designed for improved efficiency at the full load condition and a second shape designed for improved efficiency at the low load condition, where the shape change material enables the change between the first and second shapes. In one embodiment, a controller including a processor, memory, software, firmware, inputs and outputs are coupled to a power source to control the geometry changes that correspond to scheduled or pre-programmed conditions, such as the low and full load times discussed above. In another embodiment, a feedback loop runs on the controller  132  which receives sensed turbine parameters, wherein sensed turbine parameters are used to determine the geometry of the airfoil  200 . For example, sensors determine temperature and the amount of unwanted combustion byproducts in the combustor. Thus, the sensed temperature and byproduct parameters are used to determine the improved airfoil and guide vane geometry for turbine power production for the sensed conditions and send a corresponding current level to the shape memory material. In embodiments, the shape memory material changes the airfoil  200  geometry in one or more dimensions or regions and/or overall vane profile. For example, a shape memory material and wires are configured to cause span-wise and/or chord-wise expansion and contraction of the guide vane. In addition, the shape memory material is configured to cause rotation of at least a portion of the guide vane. For example, wires are embedded in the airfoil walls, causing change in span and a rotation of the vane tip about a fixed root of the guide vane. 
       FIG. 3  is a sectional view of an embodiment of a guide vane in the shape of airfoil  300 . The airfoil  300  includes a leading edge  302  and trailing edge  304 . The airfoil  300  includes airfoil walls  306 , wherein at least a portion of the walls  306  comprise a shape memory material. The shape memory material includes leading edge wires  308  and trailing edge wires  309  embedded in a flexible composite material of the airfoil walls  306 . The airfoil  300  is substantially hollow with a cavity  310 , providing flexibility to the airfoil. Thus, the airfoil  300  geometry changes when an energy is applied to the flexible shape memory material of the wall. As depicted, leading edge wires  308  and trailing edge wires  309  are embedded in the wall  306 , forming a shape memory region in both the leading and trailing edge portions ( 302 ,  304 ) of the airfoil  300 . Accordingly, based on a turbine condition, a selected current is applied to leading edge wires  308  and/or trailing edge wires  309  to cause a shape change of the leading edge  302  and/or trailing edge  304 , respectively. Thus, in some embodiments, the shape memory material in the guide vane  300  enables substantially uniform air flow incidence on a rotor blade for a plurality of turbine load conditions. The substantially uniform incidence causes an even radial distribution of air flow span-wise across the rotor blade, wherein the substantially uniform incidence causes improved compressor and combustor efficiency at selected turbine load conditions. Further, the shape memory material in guide vane  300  provides improved overall turbine efficiency as compared to a static guide vane geometry is designed for improved combustion and efficiency at one condition, but is less efficient at a second condition. 
       FIG. 4  is a perspective view of an embodiment of a guide vane  400 . The guide vane  400  is shown in a first shape  402  and a second shape  404 . As discussed above, shape memory material in the guide vane  400  enables a geometry change as energy, in the form of current, is applied to the shape memory material. In an embodiment, the shape or geometry change causes a rotation of the guide vane  400 , as indicated by arrow  406 . To facilitate rotation  406 , a vane root  408  or vane tip  410  is attached to the compressor. For example, if the vane root  408  is attached to an inner wall, hub or casing of the compressor, the vane tip  410  rotates  406  relative to the root  408  when a current is applied to shape change material. Attaching either the root  408  or tip  410  to the compressor enables relative rotation  406  of the root  408  and/or tip  410 , as show in  FIG. 4 . The rotation of the guide vane  400  provides improved incidence of air flow on the rotor at a full load condition when in first shape  402  as well as for a low load condition in second shape  404 . In embodiments, the shape of the guide vane  400  is different than an airfoil. In embodiments with alternative guide vane shapes, the shape change material and guide vane  400  are configured to cause a geometry change based on a condition to improve turbine efficiency. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.