Pre-swirl inlet guide vane for compressor

Abstract

Two sets of guide vanes are positioned in the combustion air flow path in the inlet duct of a rotary compressor of a gas turbine engine for controllably varying the air mass flow rate according to turbine load conditions. The upstream set which provides a fixed, initial degree of swirl relative to compressor rotational direction and axis and the controllably moveable downstream set which provides a final degree of swirl cooperate to provide controllable swirl over the range of about 0° to 32° in the inlet air incident upon the turbine blades. The two guide vane sets are separated by a distance sufficient to allow turbulence induced by the first set to fully decay before the second set is encountered.

What is claimed is: 
     
       1. In rotary apparatus for compressing a compressible fluid of the kind having a plurality of compressor blades mounted on a rotating hub positioned in a compressor housing, a preferred fluid flow path extending through the housing, the housing having a duct portion extending upstream of the compressor blades relative to the fluid flow path .[.and.]. .Iadd., with substantially all the fluid flowing through the duct being guided to the compressor blades, with the duct .Iaddend.determining, in part, the fluid flow path, the improvement comprising: means for controllably varying the fluid mass flow rate through the compressor including: (a) a first set of guide vanes .[.in.]. .Iadd.positioned substantially within ep the duct for imparting an initial degree of swirl to the fluid entering the duct relative to the axis and direction of rotation of the compressor hub; and   (b) a second set of guide vanes positioned .[.in.]. .Iadd.within .Iaddend.the duct upstream of the compressor blades, the vanes of the said second set being moveable about their axes, said second vane set being positioned a distance downstream of said first vane set along the preferred fluid flow path wherein at least about one first vane chord length separates the trailing edges of said first vane set from the leading edges of said second, moveable vane set, to permit substantial decay of the turbulence imparted to the flowing fluid by said first vane set prior to said swirling fluid reaching said second, moveable vane set, said second, moveable vane set for changing the degree of swirl in the fluid to a final degree of swirl incident upon the compressor blades corresponding to a desired compressor fluid mass flow rate.Iadd., said first vane chord length being measured at the widest part of said first vane, and said separation existing along substantially the entire axial length of said first and said second vanes.Iaddend..     
     
     
       2. Apparatus as in claim 1 wherein the separation distance is about 2-3 lengths. 
     
     
       3. In rotary apparatus for compressing a compressible fluid of the kind having a plurality of compressor blades mounted on a rotating hub positioned in a compressor housing, a preferred fluid flow path extending through the housing, the housing having a duct portion extending upstream of the compressor blades relative to the fluid flow path and determining, in part, the fluid flow path, the improvement comprising: means for controllably varying the fluid mass flow rate through the compressor including: (a) first set of guide vanes in the duct for imparting an initial degree of swirl to the fluid entering the duct relative to the axis and direction of rotation of the compressor hub; and   (b) a second set of guide vanes positioned in the duct upstream of the compressor blades, the vanes of the said second set being moveable about their axes, said second vanes set being positioned a distance downstream of said first vane set along the preferred fluid flow path sufficient to permit substantial decay of the turbulence imparted to the flowing fluid by said first vane set prior to said swirling fluid reaching said second, moveable vane set, said second, moveable vane set for changing the degree of swirl in the fluid to a final degree of swirl incident upon the compressor blades corresponding to a desired compressor fluid mass flow rate,     wherein said first vane set is positioned in a region of the duct having average streamline fluid velocities of less than about 30% of the average streamline velocities at the compressor blades, and wherein said second, moveable vane set is positioned in a region of the duct having average streamline fluid velocities of at least about 70% of the average streamline fluid velocities at the compressor blades.   
     
     
       4. Apparatus as in claim 3 wherein said first vane set is positioned in a region of the duct having average streamline fluid velocities less than about 10% of the average streamline velocities at the compressor blades. 
     
     
       5. Apparatus as in claim 3 wherein said second, moveable vane set is positioned in a region of the duct having average streamline fluid velocities of greater than about 80% of the average streamline fluid velocities at the compressor blades. 
     
     
       6. Apparatus as in claim 1 or 3 wherein said second, moveable vane set is positioned upstream of and adjacent to the compressor blades. 
     
     
       7. Apparatus as in claim 1 or 3 wherein the duct has a predominantly radial inlet portion and a predominantly axial exit portion, the fluid flow path undergoing a substantial angular change in direction through the compressor inlet, and wherein said first vane set is located in said inlet portion and said second moveable vane set is located in said exit portion. 
     
     
       8. Apparatus as in claim 1 or 3 wherein the individual guide vanes in said first vane set are configured to impart about +10° to +15° of swirl to the incoming fluid relative to the axis and direction of rotation of the compressor hub. 
     
     
       9. Apparatus as in claim 8 wherein said first vane set and said second, moveable vane set cooperate to provide final fluid swirl of from about 0° to +32° at the inlet to the compressor blades, relative to the axis and direction of rotation of the compressor hub. 
     
     
       10. Apparatus as in claim 1 or 3 wherein the individual guide vanes in said second, moveable vane set are moveable to change direction in the fluid incident thereupon by about -20° to +20°, the direction of rotation of the compressor hub establishing the positive direction. 
     
     
       11. Apparatus as in claim 1 or 3 wherein said first vane set is essentially fixed. 
     
     
       12. In an air-breathing, variable load recuperated gas turbine engine of the kind having a rotary compressor section for compressing the air for combustion, a combustor for combusting the compressed air with fuel to produce combustion gases, a turbine for recovering mechanical work from the combustion gases, and apparatus for recovering heat valves from the combustion gases and heating the compressed air prior to combustion using the recovered heat values, the compressor further including a plurality of compressor blades mounted on a rotating hub positioned in a compressor housing, the compressor housing having a preferred air flow path extending therethrough, and also having a duct portion extending upstream of the compressor blades relative to the air flow path, the duct determining, in part, the air flow path, the improvement comprising: means for controllably varying the air mass flow rate through the compressor and to the combustor to maintain highest possible turbine section inlet temperatures over varying turbine load conditions, the air mass flow rate varying means including (a) a first set of guide vanes in the duct for imparting an initial degree of swirl to the fluid entering the compressor housing inlet relative to the axis and direction of rotation of the compressor hub; and   (b) a second set of guide vanes positioned in the duct upstream of the compressor blades, the vanes of said second set being moveable about their axes, said second vane set being positioned a distance downstream of said first vane set along the fluid flow path wherein at least about one first vane chord length separates the trailing edges of said first vane set from the leading edges of said second, moveable vane set, to permit substantial decay of the turbulence imparted to the flowing fluid by said first vane set prior to said swirling fluid reaching said second, moveable vane set,     said second, moveable vane set for changing the degree of swirl in the fluid to a final degree of swirl corresponding to a predetermined turbine load condition,   wherein said first vane set is positioned in a region of the duct having average streamline fluid velocities of less than about 30% of the average streamline velocities at the compressor blades, and   wherein said second, moveable vane set is positioned in a region of the duct having average streamline fluid velocities of at least about 70% of the average streamline fluid velocities at the compressor blades.   
     
     
       13. A method of throttling the compressible fluid mass flow rate through a rotary compressor of the kind having a plurality of compressor blades on a rotating hub and having an inlet region including a duct determining, in part, the preferred flow path of the incoming fluid to the compressor blades .Iadd.with substantially all the fluid flowing in the duct being guided to the compressor blades, .Iaddend.the method comprising the steps of: (a) imparting a first, initial degree of swirl to the incoming fluid relative to the axis and direction of rotation of the compressor;   (b) removing turbulence in the swirling fluid induced by said initial swirl imparting step; and   (c) imparting a second, controllably variable degree of swirl to the swirling fluid to change the degeee of swirl in the fluid to a desired final value prior to admitting the fluid to the compressor blades, steps (a)-(c) being accomplished .[.in.].ep  .Iadd.substantially within .Iaddend.the duct, wherein said removing step includes performing said first swirl imparting step using a first set of guide vane at a location along the preferred fluid flow path a distance of at least one first vane chord length upstream of the location where said second variable swirl imparting step is performed to allow the induced turbulence to decay naturally.Iadd., said first vane chord length being measured at the widest part of said first vane, and said distance existing along substantially the entire axial length of said first vane relative to said variable swirl step location.Iaddend..     
     
     
       14. A method of throttling the compressible fluid mass flow rate through a rotary compressor of the kind having a plurality of compressor blades on a rotating hub and having an inlet region including a duct determining, in part, the preferred flow path of the incoming fluid to the compressor blades, the method comprising the steps of: (a) imparting a first, initial degree of swirl to the incoming fluid relative to the axis and direction of rotation of the compressor;   (b) removing turbulence in the swirling fluid induced by said initial swirl imparting step; and   (c) imparting a second, controllably variable degree of swirl to the swirling fluid to change the degree of swirl in the fluid to a desired final value prior to admitting the fluid to the compressor blades, steps (a)-(c) being accomplished in the duct, wherein said second, variable swirl imparting step is carried out in a region of average streamline fluid velocities of at least about 70% of the average streamline fluid velocities at the compressor blades, and   wherein said first swirl imparting step is carried out in a region of average streamline fluid velocities of less than about 30% of the average streamline flow velocities of the compressor blades.     
     
     
       15. The method as in claims 13 or 14 wherein said second, variable swirl imparting step is accomplished by variable angle guide vane means positioned in the fluid flow path, and wherein said first set of guide vanes is positioned in the duct upstream of the variable guide vane means. 
     
     
       16. The method as in claim 13 or 14 wherein about +10° to +15° of swirl relative to the axis and direction of rotation are imparted to the incoming fluid in said first swirl imparting step, measured immediately upstream of the location in the fluid flow path where the second, variable swirl imparting step is carried out. 
     
     
       17. The method as in claim 13 or 14 wherein said second, variable swirl imparting step changes the direction of the incident fluid from about -20° to +20°. 
     
     
       18. The method as in claim 13 or 14 wherein said second, variable swirl imparting step together with said first swirl imparting step provide a final swirl of between about 0° to +32° prior to admitting the fluid to the compressor blades. 
     
     
       19. The method as in claim 13 or 14 wherein the duct has a predominately radial inlet portion and a predominately axial exit portion, said first swirl imparting step being carried out in the inlet portion and said second, variable swirl imparting step being carried out in the exit portion. 
     
     
       20. An improved method of throttling inlet air flow rate to the combustor in a recuperated gas turbine engine of the type having a rotary compressor with a plurality of compressor blades on a rotating hub and with an inlet region including a duct determining, in part, the flow path of the incoming air to the compressor blades, for maintaining a highest possible turbine inlet temperature over variable load conditions, the improvement comprising the steps of: (a) imparting a first, initial degree of swirl to the incoming air relative to the axis and direction of rotation of the compressor;   (b) removing turbulence in the incoming air induced by said preliminary swirl imparting step; and   (c) imparting a second, variable degree of swirl to the incoming air to change the degree of swirl in the air to a final desired value corresponding to a predetermined turbine load condition prior to admitting the air to the compressor blades, said steps (a)-(c) being accomplished in the duct,   wherein said removing step includes performing said first swirl imparting step using a first set of guide vane and at a location along the preferred fluid flow path a distance of at least one first vane chord length upstream of the location where said second variable swirl imparting step is performed to allow the induced turbulence to decay naturally,   wherein said second, variable swirl imparting step is carried out in a region of average streamline fluid velocities of at least about 70% of the average streamline fluid velocities at the compressor blades, and   wherein said first swirl imparting step is carried out in a region of average streamline fluid velocities of less than about 30% of the average streamline flow velocities of the compressor blades.