Abstract:
An blade row for use in a compressor is provided. The blade row has a plurality of inlet guide vanes. Each inlet guide vane has a meanline approximately equal to NACA standard A4K6 meanline, a thickness distribution approximately equal to NACA standard SR 63 thickness distribution, a stagger angle, and a lift coefficient between 0.0 and 0.8.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Embodiments of the invention relate to vanes for use in a compressor. More particularly, embodiments of the invention relate to the shape of inlet guide vanes in an axial compressor.  
           [0002]    Most axial compressors today have inlet guide vanes (IGVs) to modulate flow to the first stage, usually a first rotor stage, of the compressor. A variety of parameters define the shape and position of each IGV in a compressor. Among these parameters are the meanline of the IGV profile; the thickness distribution of the IGV profile; the lift coefficient, which is a multiplier of the meanline; and the stagger angle, which is the angle of the IGV relative to the axial direction of the compressor.  
           [0003]    By varying the IGV parameters, multiple IGV profile and stagger angle combinations are possible for any given IGV exit condition, the IGV exit condition being the angle at which a gas, usually air, exits the IGV.  
         SUMMARY OF THE INVENTION  
         [0004]    Examples of the invention include an inlet guide vane blade row for use in a compressor. The blade row has a plurality of inlet guide vanes. Each inlet guide vane has a meanline approximately equal to NACA standard A4K6 meanline, a thickness distribution approximately equal to NACA standard SR 63 thickness distribution, a stagger angle, and a lift coefficient between 0.0 and 0.8.  
           [0005]    Other examples of the invention include a compressor. The compressor has a housing, a shaft, a compressor stage, and a plurality of inlet guide vanes attached to the housing. Each inlet guide vane has a meanline approximately equal to NACA standard A4K6 meanline, a thickness distribution approximately equal to NACA standard SR 63 thickness distribution, a stagger angle, and a lift coefficient between 0.0 and 0.8.  
           [0006]    Other examples of the invention include methods of retrofitting a compressor with new inlet guide vanes, the compressor having existing inlet guide vanes and an existing inlet guide vane exit condition and the existing inlet guide vanes having an existing lift coefficient. The methods include designing the new inlet guide vanes such that the new inlet guide vanes have an exit condition substantially equal to the existing inlet guide vane exit condition, and the new inlet guide vanes have a new lift coefficient less than the existing lift coefficient. The methods further include removing the existing inlet guide vanes from the compressor; and installing the new inlet guide vanes in the compressor.  
           [0007]    These and other features of the invention will be readily apparent to those skilled in the art upon reading this disclosure in connection with the attached drawing figures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a partial sectional view of an example of an axial compressor in accordance with embodiments of the invention;  
         [0009]    [0009]FIG. 2 is a profile of a related guide vane;  
         [0010]    [0010]FIG. 3 is an example of a profile of a guide vane in accordance with embodiments of the invention;  
         [0011]    [0011]FIG. 4 shows an example of a comparison of two profiles;  
         [0012]    FIGS.  5 A- 5 L are a printout of profile information for an example of a guide vane in accordance with embodiments of the invention;  
         [0013]    [0013]FIG. 6 is a flow chart showing an example of a method of the invention;  
         [0014]    [0014]FIG. 7 shows an example of velocity vectors associated with a IGV having negative incidence;  
         [0015]    [0015]FIG. 8 shows an example of velocity vectors associated with a IGV having near optimum incidence;  
         [0016]    [0016]FIG. 9 shows an example of mach number vs. the distance along the blade of a IGV having high negative incidence;  
         [0017]    [0017]FIG. 10 shows an example of mach number vs. the distance along the blade of a IGV having near optimum incidence;  
         [0018]    [0018]FIG. 11 shows an example of flow factor vs. percent corrected speed for an uncambered IGV; and  
         [0019]    [0019]FIG. 12 shows an example of efficiency factor vs. percent corrected speed for an uncambered IGV. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    [0020]FIG. 1 is a partial sectional view of an example of an axial compressor in accordance with the invention. The compressor of FIG. 1 has a housing  100  to which IGVs  130 , first stator row  150 , and a plurality of stator rows  170  are attached. Hub  110  is attached to shaft  120 , both of which rotate about a centerline of shaft  120 . First rotor row  140  and a plurality of rotor rows  160  are attached to hub  110  and rotate therewith. In particular embodiments, IGVs  130  are movable during operation to achieve varying IGV angles.  
         [0021]    As minor changes in the IGV parameters can result in substantial changes in the efficiency with which the IGVs turn the compressor inlet air, optimization of the IGV parameters can result in a significant increase in compressor performance.  
         [0022]    Certain existing compressors were found to be operating at less than optimal efficiency due to less than optimal incidence loading at the IGVs. It was discovered that negative incidence results in incidence loading (losses resulting from inefficient turning of air flow) and that removing some of the negative incidence from the IGVs results in increased compressor airflow and efficiency (discussed further below with reference to FIGS.  7 - 12 ). One way in which the incidence loading can be optimized is to change the inlet angle of the IGVs, often referred to as “IGV angle”.  
         [0023]    [0023]FIG. 2 shows the profile and position of IGV  230  having meanline  235  positioned such that the inlet angle relative to the axial direction of the compressor is A 1 . FIG. 3 shows the profile and position of IGV  330  having meanline  335  and angle A 2 . As can be seen from FIGS. 2 and 3, angle A 2  is reduced as compared to angle A 1 . In this example, A 1  is approximately 9° and A 2  is approximately  3 °.  
         [0024]    In the example shown in FIGS. 2 and 3, IGV  230  and IGV  330  have the same meanline, for example, National Advisory Committee for Aeronautics (NACA) meanline A4K6, but have different lift coefficients. The lift coefficient is a unitless multiplier of the meanline and determines the amount of bow or camber in the IGV profile. In this example, IGV  230  and IGV  330  have the same thickness distribution, for example the NACA series 63 (SR63) thickness distribution. IGV  330  has, for example, a lift coefficient of 0.4 and IGV  230  has, for example, a lift coefficient of 0.8. It was discovered that a lift coefficient of 0.4 results in less loss than a lift coefficient of 0.8. It is also believed that lift coefficients greater than 0.0 and less than 0.8 would result in improved efficiency compared to a lift coefficient of 0.8 for the example IGVs discussed above.  
         [0025]    [0025]FIG. 4 shows an IGV  432  having a given lift coefficient superimposed on an IGV  436  having a larger lift coefficient and more camber. FIG. 4 shows that IGV  432  and IGV  436  have the same trailing edge to help maintain the same IGV exit conditions.  
         [0026]    FIGS.  5 A- 5 L show coordinates for an example of a IGV of the invention that has been shown to provide improved efficiency as compared to existing IGVs in an existing compressor.  
         [0027]    In the case of an existing compressor, new IGVs can be designed to more efficiently turn the inlet air while still maintaining the IGV exit conditions (including air flow direction) of the original IGVs. It is important to maintain the IGV exit conditions of the original IGVs in order to avoid having to redesign and replace the compressor stages down stream of the IGVs.  
         [0028]    The efficiency and output of an existing compressor can be increased by retrofitting the IGVs of the invention to the compressor.  
         [0029]    An example of a method of retrofitting IGVs to an existing compressor is shown in FIG. 6. In  610 , the exit condition of the new IGVs are constrained to substantially equal the exit condition of the existing IGVs. This, as stated above, is to avoid having to redesign and replace the compressor stages down stream of the IGVs. In  620 , the lift coefficient of the new IGVs is defined to be less than the lift coefficient of the existing IGVs. In  630 , the existing IGVs are removed from the compressor and, in  640 , the new IGVs are installed in the compressor.  
         [0030]    Examples of the impact of incidence on flow are shown in FIGS.  7 - 10 . FIG. 7 shows an example of velocity vectors on an IGV having negative incidence. It can be seen in FIG. 7 that the stagnation point of the flow is on the suction surface of the IGV below the meanline pierce point. The meanline pierce point being defined as the point that the IGV profile meanline intersects the leading edge of the IGV. The stagnation of the flow at the stagnation point is illustrated by the very small arrow head size of the velocity vectors at that point. In addition, FIG. 7 illustrates the very high velocities (indicated by the velocity vectors having large arrow heads) experienced on the pressure surface side of the meanline pierce point. The wide range of velocities shown in the example of FIG. 7 illustrate the inefficiencies associated with negative incidence.  
         [0031]    [0031]FIG. 8 shows an example of near optimum incidence. In comparing FIG. 8 to FIG. 7, it can be seen that the range of velocities in FIG. 8 is smaller than the range of velocities in FIG. 7. Because there is less deceleration and acceleration of the flow in the example of FIG. 8 as compared to the example of FIG. 7, FIG. 8 illustrates a more efficient IGV. This efficiency results from the stagnation point being approximately at the meanline pierce point, or at least closer the meanline pierce point than in the example shown in FIG. 7.  
         [0032]    [0032]FIGS. 7 and 8 show the mach number of the flow over an IGV versus the distance along the blade of the IGV for IGVs having high negative incidence and near optimum incidence, respectively. FIG. 9 illustrates the large range (approximately 0 to mach 1.6) of flow velocities experienced in a high negative incidence situation such as, for example, that shown in FIG. 7. In contrast, FIG. 10 shows a velocity range of 0 to approximately mach 0.77 for an IGV having near optimum incidence such as, for example, the IGV shown in FIG. 8.  
         [0033]    [0033]FIGS. 11 and 12 show the flow factor and efficiency factor, respectively, versus percent corrected speed of the shaft of the compressor. As indicated, the flow factor and efficiency factor are relative to the base map at an IGV angle, or stagger angle, of 87°. As shown in the legends, plots are shown for various IGV angles between 42° and 91°. FIGS. 11 and 12 can be used in conjunction with the 87° base map to determine maps for IGV angles between 42° and 91°.  
         [0034]    While the invention has been described with reference to particular embodiments and examples, those skilled in the art will appreciate that various modifications may be made thereto without significantly departing from the spirit and scope of the invention.