Abstract:
A compressor scroll housing for use in conjunction with turbo-machinery, particularly applicable in aircraft. The scroll housing can include a plurality of scroll vanes arrayed around the scroll housing. Scroll vanes, integrally formed with the scroll housing, carry stress load on the scroll housing, including the load from fluid pressure within the scroll and carcass loading from the engine. The plurality of scroll vanes adapted for guiding flow of fluid from an inlet to an outlet while supporting the scroll housing. Chord length and cross sectional area of each scroll vane can be sized to maintain an equal stress in all scroll vanes. A method of making the scroll housing for use with an impeller connected to an engine is disclosed, as well as a method of operating turbo-machinery including supporting a load on the scroll housing with scroll vanes while maintaining an equal stress on each scroll vane.

Description:
GOVERNMENT RIGHTS  
       [0001]     This invention was made with Government support under contract number N00019-01-C-3002 awarded by the United States Government under the JSF program to Lockheed Martin. The Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to turbo-machinery that must be both powerful and that must carry structural loads in aircraft applications. More specifically, the present invention relates to apparatus and methods relating to a scroll housing for use with a compressor.  
         [0003]     In aviation applications, it is necessary to provide compressed air from the aircraft engines to the aircraft. Gas turbine engine aircraft may utilize an auxiliary power unit (APU) to provide air both when an aircraft is on the ground and when it is in flight. Air can be taken from an engine to pressurize or to otherwise condition the cabin air or, for example, to cool avionics equipment. In these aviation applications, there is a constant drive to both improve performance and to reduce the weight of components.  
         [0004]     In aviation applications, a centrifugal compressor can be used to compress air. In these cases, the compressor discharge scroll must also be capable of supporting a variety of loading stresses that will occur. Specifically, a compressor scroll must be able to support dynamic loading from the aircraft environment, and pressure loading from the pressurization of air that occurs from the compressor itself.  
         [0005]     U.S. Pat. No. 4,378,194 (the &#39;194) shows one method of supporting these loads. In the &#39;194 patent, there can be carcass loads that will develop between the forward and aft sections of the aircraft engine. The scroll housing surrounding the centrifugal compressor impeller is designed with a wall thickness that is great enough to handle these stress loads as well as the stress that will develop from air pressurized within the scroll. This is a common approach and one that works in some applications, although the weight of the heavy scroll wall and space restrictions limits the applicability of this approach.  
         [0006]     U.S. Pat. No. 3,963,369 discloses another centrifugal compressor that will withstand the stresses in an aviation environment. Through-bolts are installed through the diffuser, which surrounds the impeller. The bolts are laid out in a circular pattern surrounding the impeller. The through-bolts serve to transmit engine carcass loads through the compressor housing. The greater the design loads, the more through-bolts are used to carry the load. Bolts passing through the diffuser work in some applications, but their use is generally limited to applications in which their presence does not limit performance. As performance requirements push the need for greater airflow and reduced weight, through-bolts become a limiting factor in the design. The through-bolt design also has the problem of increased part count and tolerance buildup associated with the increased part count. Tolerance build up can occur when multiple parts must fit together in an assembly such as the through bolt compressor housing which has a plurality of through-bolts as well as at least two housing halves to be assembled.  
         [0007]      FIG. 1  shows a portion of a prior art turbo-machine including a scroll housing  100  designed so that all structural loads, including engine carcass loads, are carried solely by the scroll housing outer wall. In this design, the load path is contained in the scroll housing wall and does not cross the airflow path. This design requires a scroll housing wall thick enough to support all loading on the scroll housing  100 . A direct load path S 2  is required to maintain wall stresses comprising primarily tensile and shear components. In this prior art, as scroll wall  102  curvature between flanges  104  and  106  increases, bending stress becomes more predominant, and since bending is a less efficient means of supporting loads, material must be added to the scroll wall  102  in order to maintain adequate strength and stiffness, thus adding unwanted weight to the scroll housing  100 . The need to keep the scroll wall  102  relatively flat limits the size of the scroll flow path. As the scroll wall  102  gets more of a bulge, it must get thicker to remain stiff enough, thus the weight increases. So, minimizing weight leads to minimizing curvature, which puts limits on scroll size relative to the flange diameters of the scroll. If the size of the flanges  104 ,  106  are increased to minimize curvature, then weight and installation are adversely impacted. A scroll wall  102  is thick enough to carry all structural loading transmitted between a forward flange  104  and an aft flange  106 . The load path S 2  is entirely contained within scroll wall  102 . The scroll vanes  110  guide airflow A 2  but carry no structural load and are outside the load path S 2 . This design also requires at least two housing piece parts, leading to greater weight, cost, and tolerance buildup associated with fitted parts.  
         [0008]      FIG. 2  shows a portion of another prior art turbo-machine including a scroll housing  200  where bolts, passing through the diffuser, carry all the structural loads including engine carcass load. The through-bolt design requires diffuser vanes that are wide enough to accommodate the through-bolts. In many gas turbine engines the diffuser vanes are not large enough to accommodate the through-bolts. Through-bolts  202  carry all structural load, indicated by load path S 3 , between a forward flange  204  and an aft flange  206 . Scroll vanes  210  guide air and can carry some of the pressure load S 4  generated by airflow A 3  within scroll housing  200  itself. Scroll vanes  210  are outside the structural load path S 3 , and the scroll wall  212  will carry no structural load.  
         [0009]     As can be seen, there is a need for an improved scroll discharge housing for a centrifugal compressor and a method of making the scroll housing for use with an impeller. There is a need for a compressor discharge scroll housing design that maximizes performance while minimizing weight and part count. There is also a need for a compressor discharge scroll housing that allows for optimum air flow performance while being designed to withstand essentially all the stresses associated with pressure and engine carcass loads.  
       SUMMARY OF THE INVENTION  
       [0010]     In one aspect of the present invention, there is provided a scroll housing for use in conjunction with a fluid compressor. The compressor has an inlet adapted to receive a flow of fluid. The scroll housing can include a scroll shaped outer wall, an outlet and a plurality of scroll vanes integrally formed with the scroll-shaped outer wall. The aft flanges, and plurality of scroll vanes connect the forward and aft flanges and the plurality of scroll vanes are adapted for guiding the flow of fluid from the inlet to the outlet while supporting the scroll housing.  
         [0011]     In another aspect of the invention, a compressor includes a scroll housing, the compressor comprising an impeller, the scroll housing having a scroll shaped outer wall; an inlet adapted for receiving a fluid from the impeller; and a plurality of scroll vanes integrally formed with the scroll shaped outer wall, wherein the plurality of scroll vanes are adapted for guiding the flow of fluid from the inlet to an outlet, and wherein the plurality of scroll vanes are further adapted for supporting said scroll housing.  
         [0012]     In a still further aspect of the invention, a turbo-machine includes a scroll housing, a scroll shaped outer wall, and a forward flange and an aft flange formed on said scroll shaped outer wall. A plurality of scroll vanes integrally formed with the scroll shaped outer wall and the forward and aft flanges, each of the scroll vanes including a leading edge and a trailing edge, and the scroll vanes adapted for guiding the airflow through the scroll housing while the scroll vanes support the scroll housing.  
         [0013]     In yet another aspect of the invention, a scroll housing for use in combination with an air compressor comprises a scroll shaped outer wall, a forward flange and an aft flange formed on the scroll shaped outer wall. A plurality of scroll vanes can be integrally formed with the scroll shaped outer wall and with the forward and aft flanges, each of the plurality of scroll vanes including a leading edge and a trailing edge, each of the plurality of scroll vanes guiding a flow of air through the scroll housing while supporting the scroll housing.  
         [0014]     In another aspect of the invention, a method is disclosed of making the scroll housing for use with an impeller connected to an engine, wherein the method includes determining the optimum size and shape characteristics for the scroll housing. The method also includes calculating loads on a scroll shaped outer wall of the scroll housing, and designing a plurality of scroll vanes to support the scroll shaped outer wall based on calculating the loads. The method includes casting the scroll housing and scroll vanes as one piece.  
         [0015]     In yet another aspect of the invention a method of operating the turbo-machinery is disclosed that includes providing an airflow with an impeller and guiding airflow through a scroll housing using a plurality of scroll vanes integrally cast with the scroll housing while supporting a load on a scroll housing with scroll vanes and maintaining an equal stress on each scroll vane.  
         [0016]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a sectional view of a portion of a prior art turbo-machine;  
         [0018]      FIG. 2  is a sectional view of a portion of an alternative prior art turbo-machine;  
         [0019]      FIG. 3  is a sectional view of a portion of a turbo-machine including a compressor, according to one embodiment of the present invention;  
         [0020]      FIG. 4  is a cross sectional view of the compressor scroll and diffuser of  FIG. 3 ;  
         [0021]      FIG. 5  shows detail of a scroll vane of the compressor scroll of  FIG. 4 ;  
         [0022]      FIG. 6  is a perspective view of a compressor scroll as seen from the outside, also according to the present invention.  
         [0023]      FIG. 7  is a flowchart of the method of making a compressor discharge scroll housing according to one embodiment of the present invention; and  
         [0024]      FIG. 8  is a flowchart of the method of utilizing a compressor discharge scroll housing according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.  
         [0026]     The present invention is directed to an integral, one-piece scroll housing that includes scroll vanes designed to support all the loads typically transmitted by a scroll housing of compressors used in aircraft. These scroll vanes allow for a scroll housing design that can be optimized for performance in terms of both airflow and strength.  
         [0027]     The scroll housing of the present invention provides a one-piece design where scroll vanes can carry all structural loading including engine carcass load. The present invention does not require diffuser through bolts or a thick scroll housing outer wall to carry structural loading. This is in contrast to the prior art, which require either a plurality of through bolts or a scroll housing outer wall having a thickness great enough to carry all structural loading.  
         [0028]     Referring now to  FIG. 3 , a compressor  10  can include an impeller  12  which can create a flow A of a fluid such as air. The compressor  10  can be disposed between a forward engine housing  14  and an aft engine housing  16 . Airflow A from impeller  12  can travel radially outwardly through a diffuser  20 . Airflow A can leave diffuser  20  and travel radially into the scroll housing  24 . Scroll housing  24  may include an air flow path cross sectional area  25  which increases in cross sectional area in the direction of flow A around scroll housing  24 . Scroll housing  24  may include a scroll shaped outer wall  26  and a forward flange  28  connecting compressor  10  to the forward engine housing  14 . Scroll housing  24  may also include an aft flange  30  connecting compressor  10  to the aft engine housing  16 . Forward and aft flanges  28 ,  30  can be connected to forward and aft engine housings  14 ,  16 , respectively, by a plurality of fasteners such as studs or bolts  32 .  
         [0029]     Scroll vanes  34  may guide airflow A from diffuser  20 , across inlet  33 , and into scroll housing  24 . Vanes  34  may be integrally formed with scroll housing  24 , and can include a leading edge  36  and a trailing edge  38  ( FIG. 5 ). As can be seen, trailing edge  38  can be tilted with respect to plane  2 - 2  of the impeller  12 , at an angle B. With trailing edge  38  tilted at angle B, aft flange  30  can be radially outward from forward flange  28 .  
         [0030]      FIG. 3  shows that load path S from loading L from aft housing  16  to forward housing  14  cuts across airflow A. For example, if aft engine housing  16  applies a compressive force L to aft flange  30 , that compressive force would carry through scroll vane  34  and into forward flange  28 . Forward flange  28  and aft flange  30  carry the load L, which is transmitted from one of forward flange  28  and aft flange  30  to the other flange (forward flange  28  or aft flange  30 ) through scroll vane  34 .  
         [0031]      FIG. 4  shows a cross section of compressor  10  taken through the plane of impeller  12 . Airflow A from impeller  12  can enter diffuser  20 . Diffuser vanes  42  can guide airflow A through diffuser  20  and into scroll housing  24 . There can be a plurality of scroll vanes  34 A through  34 T in this embodiment of the invention. Other embodiments of the present invention may have other numbers or configurations of scroll vanes  34 . Scroll vanes  34 A-T can start with a smallest cross-section vane  34 A and proceed to largest cross-section vane  34 T. Cross-sectional area  40  of each scroll vane  34 A-T can be designed to carry the local load experienced by that vane. For example, vane  34 A can be relatively small because the pressure of airflow A at the trailing edge  38 A of vane  34 A is relatively small, and because the scroll shaped outer wall  26  is relatively thicker adjacent this vane  34 A. As viewed from  FIG. 4 , proceeding clockwise about scroll shaped outer wall  26 , scroll vanes  34  get progressively larger as air flow pressures increase and as the distance, D in  FIG. 5 , of scroll shaped outer wall  26  from trailing edges  38  of scroll vanes  34  gets larger. Maximum vane loading can typically occur in those vanes  34  near the compressor outlet  46  where pressure from airflow A and distance from scroll shaped outer wall  26  can be maximum. It will be understood that cross sectional area  40  of each scroll vane  34 A-T may be designed to carry the local loading experienced by that scroll vane  34 A-T. Scroll housing  24  and scroll vanes  34  may be designed such that each scroll vane  34 A-T experiences an equal level of stress, individual scroll vane  34  can be sized according to local loading thus minimizing material weight.  
         [0032]     Referring now to  FIG. 5 , for each scroll vane  34 A-T, the distance from leading edge  36  to its trailing edge  38  is the chord length C for that vane  34 . Chord length C and scroll vane  34  cross sectional area  40  can increase for scroll vanes  34  in areas of high loading. The distance D is from trailing edge  38  of scroll vane  34  to scroll shaped outer wall  26 . Distance D can vary for each scroll vane  34 , and in the embodiment shown increases in the clockwise direction of scroll shaped outer wall  26  as shown. In an exemplary embodiment, scroll vanes  34  get progressively larger as air flow path cross sectional area  25  within scroll shaped housing  26  gets larger.  
         [0033]     Scroll housing  24 , including all scroll vanes  34 A-T, forward and aft engine flanges  28  and  30 , and scroll shaped outer wall  26 , can be formed as one piece, i.e., integral. Typically, scroll housing  24  can be formed as a casting. Scroll housing  24  can be formed, for example, by sand casting. Scroll vanes  34  may be used as-cast. Certain portions, such as forward and aft flanges  28 ,  30 , may require machining. Unlike the prior art, which uses a scroll housing thick enough to support all loading, or through-bolts to withstand pressure loads and engine carcass loads, scroll vanes  34  of the present invention can carry most, if not all, of the structural loading experienced by compressor  10 . For example, scroll vanes  34  can typically carry 70 to 100% of the load, and more typically can carry 98-100% of the load, including engine carcass load and pressure load. In practice, scroll vanes  34  may be designed to carry 100% of the load plus any safety factors that might be applied, whereas scroll shaped outer wall  26  may carry, at most a small percent of the actual load. For example, scroll shaped outer wall  26  may typically carry less than 30% of the load, and more typically may carry less than 2% of the load. In aircraft applications, scroll housing  24  may be cast from a material such as titanium.  
         [0034]      FIG. 6  shows the exterior of scroll housing  24  as seen from the side. As can be seen in this view, forward and aft engine flanges  28  and  30  may be circular and can extend around scroll shaped outer wall  26 . Surfaces  28   a  and  30   a  of forward and aft engine flanges  28  and  30 , respectively, can be machined flat surfaces that will allow scroll housing  24  to mate with adjacent engine housings  14  and  16  shown in  FIG. 3 .  
         [0035]     Referring now to  FIGS. 5 and 7 , a method  300  of making a one-piece (integral) scroll housing  24  is shown. Scroll shaped outer wall  26 , and plurality of scroll vanes  34 A-T formed integrally therewith, may be designed by a step  310  of optimizing scroll housing  24  to allow for the required performance of compressor  10  with respect to parameters such as air flow speed, temperature, pressure, and air volume. The optimum characteristics for scroll shaped outer wall  26  can be based on one or several operating modes such as, for example, on ground and in-flight operation of compressor  10 . The next step  320  may involve calculating the total loading on scroll housing  24 . In step  320 , the total loading that will occur from engine carcass loads and from airflow pressure load and from other loading, such as shock loading, can be calculated. The loading can be calculated and localized, according to step  330 , across scroll shaped outer wall  26 , and then scroll vanes  34 A-T can be designed in step  340  with a chord length C, distance D to scroll shaped outer wall  26  and cross sectional area  40  sufficient to carry the calculated localized loading. It will be obvious that additional calculations based on, for example, a desired safety factor or life factor, can also be included in determining the required cross sectional area  40  of each scroll vane  34 A-T. Once a design for scroll housing  24  is complete, the next step can be casting step  350  to cast scroll housing  24  as a single piece. The casting step  350  can be, for example, investment or sand casting. Thereafter the next step  360  can be machining mating surfaces  28   a  and  30   a.    
         [0036]      FIG. 8  shows a method  400  of operating compressor  10 . Method  400  includes the step  410  of providing airflow from impeller  12 . Then the method  400  includes a step  420  of guiding the airflow into and through scroll housing  24  using scroll vanes  34 A-T. Step  430  may involve supporting, via scroll vanes  34 A-T, a load applied to scroll housing  24  as air flows through scroll housing  24 . As the load is applied to scroll housing  24 , step  440  may involve maintaining an equal stress on each scroll vane  34 A-T. That is to say, the stress in each scroll vane  34  is designed to be substantially equal to the stress in every other scroll vane  34  as load is applied. By equalizing the stress each scroll vane  34  experiences according to step  440 , the total weight requirement of scroll housing  24  may be minimized. In step  450 , air may be outlet from scroll housing outlet  46 .  
         [0037]     Though shown and described herein with respect to use in an aircraft, it will be understood that scroll housing compressor  10  of the present invention may also be used in other applications. It will also be understood that though the embodiment shown has a scroll with scroll vanes  34 A-T getting larger in a clockwise direction, the size, location and orientation of each vane can be determined to meet stress loading on the scroll housing. Also it will be understood that the number of scroll vanes used can vary depending upon design requirements.  
         [0038]     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.