US2944729A

US2944729A - Induction and discharge means for effective camber control

Info

Publication number: US2944729A
Application number: US649397A
Authority: US
Inventors: John R Foley; Charles B Smith
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1957-03-29
Filing date: 1957-03-29
Publication date: 1960-07-12
Anticipated expiration: 1977-07-12

Description

July '12, 1960 J. R. FOLEY ErAL INDUCTION AND DISCHARGE MEANS FOR EFFECTIVE CAMBER CONTROL Filed March 29. 1957 2 Sheets-Sheet 1 F'IGJ 5 m 3 I 6 YM a as L L i m U (z o s N M w R M EARHT I B T ,1 C 7A i 1.8 k W RE L NR a 7 HA 0 Jc 4 Y W a B a a Iliilll. 2 J MIH LP U T r s Q R Q G 5 WWW gm 2 Z Q a; 52 Hw Q P E July 12, 1960 J. R. FOLEY ETAL INDUCTION AND DISCHARGE MEANS FOR EFFECTIVE CAMBER CONTROL Filed March 29, 195'? 2 Sheets-Sheet 2 iNVENTORS JOHN RICHARD FOLEY ATTORNEY FIC3-3 States atent I John R. Foley, Manchester, and Charles B. Smith, Wind-' 7 sor, Conn., assignors to United'Airc'raft Corporation,

East Hartiord, (301111., a corporation oi Delaware Filed Mar. 29, 1957,Ser. No. 649,397 Claims. (Cl. 2 3tl:1'22) designed to be very effici'ent at design speed but are less efficient than possible at speeds below design speed,

known as part speed, and aboveidesignspeed, known as overspeed. Thisinvention teaches rematching fluid ma.- chines, such as axial flow compressors at speeds other than design speeds. V It is, an object of this invention to .vary the angle of fluid attack on the rotating blades of. a compressor rotor during periods of off-design operation bydischarging or inducting fluid through slots adjacent the trailingedge of the hollow vanes in the stator unit immediately upstream thereof, to vary the elfectivevane camber and hence to vary the angle of 'fluiddischarge through the vanes, to vary theangle of attack on the next succeeeding retor blades. i

' It is a further object of this invention to provide c'ooperation between the vanes of an upstream or forward Patented July 12, 1960' compressor'of the aircraft type utilizing our invention and diagrammatically illustrating its effect.

Fig. 2 is a view showing the correlation taught herein between the upstream and downstream stator stages in a fluid machine such as an axial flow compressor.

Fig. 3 is a graph with blade angle of attack plotted against'pressure ratio across the blade.

7 Figs. 4, 5, 6, and 7 are cross-sectional views of hollow stator vanes showing both upper surface and lower surface trailing edge slots, some of which are illustrated to be for purposes of fluid induction and others of which are illustrated to be for purposes of fluid discharge. Figs. 4 and 5 represent methods of increasing vane effective camber and fluid turning eifect While Figs. 6 and 7 represent methods of decreasing same.

Fig. 8 is a partial showing of a hollow compressor vane having trailing edge slots in both its upper and lower surfaces and illustrating means to determine which of saidslots is to be operative at a given time.

a Fig. 9 is a partial cross-sectional showing of a hollow compressor vane with a trailing edge slottherein illustrating fluid discharge normal to the vane surface which the slot is located.

Referring to Fig. 1,' We see hollow inlet guide or spin vanes 12 which are located at the inlet of'a fluid machine 1 0, such as an axial flow compressor, which are of airfoil cross section and which'comprise leading edge 14, trailing edge 16, lowerconcave surface 1.8,upper convex surface 20and which have trailing edge slots 22 in the concave surface thereof. Spin vanes 12 are substantially equally spaced circumferentially within compressor 10,

stator unit and a downstream or. rearward stator unit such that the air being inducted through the trailing edge slot intothe interior of one is conveyed .to the interior of the other forxdischarge through the trailing edge slots thereof; 7 It is a further object of'this invention to efiect better compressormatching by providing means to either dis; charge or induct air through trailing edge slots in hollow vanes during periods of oifldesign speed. operation and to determinefwhether"fluid flow through these slots is to be inducted or. discharged. 7 a l h I h It is a further object of this invention to provide matching means comprising discharge or induction slotslon and in eifect constitute first stage stator unit 25. Stator unit 25 performs the function of directing the air entering compressor 10 at the proper angle relative to rotating blades'28 of first stage rotor unit 27 to effect maximum efliciency and/or pressure rise therethrough, Blades 28 are substantially aligned axially within compressor 10 with spin'vanes 12. Slots-22 are radially extending and put the interior 24 of the spin vanes 12 into communication with the gas passage area26 of the fluid machine 10. 'Air is passing through the fluid machine in the direction indicated and, after passing through the area defined by the inner and outer shroud rings of stator 25 which extend circumferentially about the inner and outerends respectively of spin vanes 12in known fashion, and by convex and

concave surfaces

18 and 26 of spin vanes 12,'the fluid is then discharged toward the plurality both sides of the trailing edge of the hollow vanes in 'a stator unit together with means to determinewhichjof said two slots isxoperative at a given time. 1 h It is a further object to remove .the performance compromise at the design speedwhichis often accepted. to insure satisfactory performance at ofl-de'sign speeds; In short, a fluid machine, such as an axial flow compressor, could bedesigned for optimum performanceat design speed when utilizing our invention to correct off-speed mismatchi g. In the same vein, our inventionvZ ould per- 'mitides igningthe fluid machine for' optimumstarting perjangleof fluid discharge through stator'vanes and therefore the fluid angle of, attack onthe. succeeding rotor from the following specification and drawingsin which:

Fig. l is a schematic representation of an axial flow of first stage rotor blades 28. Blades 28 extend radially within fluid machine 10 and areattached to the periphery of a rotatable disc 29 in rotor 27 and are circumferentially'equaliy spaced thereabouts. The first stage compressor disc is adapted to rotate about the centerline of lfluid machine 10 and lies in a plane perpendicular therecase '33.

The vector diagram shown adjacent vanes 12 and blade 28 illustrate how the angle of attack 3% on or of rotating blades 28 is varied by use of trailing edge slots 22 in hollow vanes 12'. The vector lines shown as solid lines illustrate operating. conditions when no fluid is being discharged through trailing edge slots. 22. Vector 32 represents the velocity and angle of fluid discharge from-and relative to hollow v anes 12. Vector 34represents the velocity and angle of approach of fluid on blade 28 caused by blade rotation only. Vector 36 represents the vectorial sum of

vectors

32 and 34 which is the velocity and direction of fluid flow relative to blade 28. Angle 30 which is defined by vector '36 and chordline 38 of blade 28 is the angle of attack of the fluid passing through machine or compressor on rotating blades28.

It is a characteristic of axial flow compressor operation that the pressure rise through a rotor stage bears a relation to the angle of attack on the blades as illustrated in the graph shown in Fig. 3. Fig. 3 shows that pressure rise through a rotor stage increases with angle of attack up to a given angle a which is the critical angle and above which pressure ratio drops oflf with further increase of angle of attack. As the angle of attack exceeds the critical angle, the fluid flow along the upper surface 31 of blade 28 separates or loses contact therewith, thereby putting compressor 10 into stall and lowering the pressure rise through the compressor rotor stage and through the entire compressor.

It is further a Well-known characteristic of fluid machines such as axial flow compressors that at the forward stator and rotor stages during over-speed operation, the axial velocity of fluid flow, C which varies as air flow, is increased to a greater extent than the circumferential vector 34 which varies with r.p.m., and thereby decreases the angle of attack. During operation at part-speed, C decreases to a lesser extent than vector 34 and thereby decreases the angle attack, also. The converse occurs at rear stage stators during both over-speed and part-speed operation to increase the angle of attack so that it will be seen that for either over-speed and part-speed operation, the forward and rear stage stators and rotors present dilierent and opposite problems.

It is an object of this invention to utilize trailing edge slots 22 in vanes 12 to vary theangle of attack 30' so as to effect maximum pressure rise through the compressor stage and the entire compressor by increasing the angle of attack toward the critical when the angle of attack is too small and by reducing the angle of attack on the blade when the angle of attack approaches too closely the critical or flow separation angle. Again referring to the graphic representation adjacent blade 28 of Fig. 1, it will be illustrated how discharge of fluid through trailing edge slots 22 of vane 12 serves to increase the effective camber and thereby increase the turning effect of vanes 12 upon fluid passing therethrough to decrease the angle of attack of the fluid on rotating blades 28. As fluid is discharged through slot 22 into the fluid stream passing between vanes 12, the vector of fluid discharge relative to vanes 12 is shifted to the dotted vector 32', since the eflective camber of vane 12 is increased thereby, which causes the shift of vector 36 to the dotted vector 36 thereby reducing the original angle of attack 30 on blade 28, to the angle defined between vector 36' and blade chordline 38. This action would be desirable in instances where the attack on blade 28 was close to or in excess of the critical angle of attack a as shown in Fig. 3 so that optimum pressure ratio will be obtained by reducing the angle of attack of blade 28 and to prevent flow separation from the upper surface 31 of blade 28 as explained supra.

Still considering Fig. 1, the fluid being passed through fluid machine or compressor 10 will eventually reach a rear stage stator 40, probably after passing through many stages of alternate stators and rotors. Rear stator stage 40 comprises a plurality of hollow vanes 42 which are substantially aligned with the rotor blades immediately upstream and downstream thereof. Vanes 42 comprise leading edge 44, trailing edge 46, concave surface 48, convex surface 50 and trailing edgeslots 52 which are radially extending adjacent trailing edge 46 and put vane interiors 54 into communication with fluid passage 26 external thereof. The fluid passing through compressor 10, after passing through rear stage stator 40, is then discharged toward rear stage rotor unit 56 which comprises a plurality of rotating blades 58. Referring to the vector diagram adjacent rear stage compressor blade 58, we see that 60 is the vector representing the angle and velocity of fluid flow from and relative to vane 42. Vector 62 represents the angle and velocity of approach of fluid relative to rotating blade 58 brought about by the rotation of the blade solely. Vector 64 represents the vectorial sum of vectors '68 and 62 to represent the velocity and angle of approach of the fluid relative to blade 58. Vector 64 and chordline 66 of blade 58 define the angle of attack 68 of fluid of or on rotating blade 58. Dotted vector lines are used to illustrate the effect showing etfec tive vane camber, effective vane fluid turning and blade angle of attack brought about by inducing air through trailing edge slots 52 in convex surface 50 into the interior 54 of hollow vane 42 from the gas passage 26. The induction of air through trailing edge slot 52 causes vector 60 to shift to dotted vector 60, which in turn causes vector 64 to shift to dotted vector 64' thereby increasing the angle of attack of the fluid on blade 58 to the angle 70 defined between blade chordline 66 and vector 64'. This would be desirable, as illustrated, when we wish to increase the angle of attack on a rotating blade to increase the pressure ratio through a particular rotor stage and the entire compressor such as is desirable on downstream rotor and stator stages during period of operation below design speed.

The characteristics ofan axial flow compressor when operating above design speed are such that the velocity of gas passing through the first stage vanes 12 is increased more than the rotational velocity 34 as previously described, thereby increasing the size of vector C the axial component of fluid velocity, in Fig. 1 to decrease the angle of attack of the fluid on blades 28. At periods of operation above design speed, called overspeed, it will be desirable to decrease the effective camber of inlet guide vanes 12 and the efiective fluid turning therethrough to increase the angle of fluid attack on rotating blades 28 while decreasing the eflective camber of and fluid turning through the stator units of the rear stages, such as 40, to decrease the angle of fluid attack on the rear stage blades, such as 58.

It will be obvious that by varying the size of our trailing edge slots, such as 22 and 52, we can regulate the amount of fluid passing therethrough'. Also, in certain fluid machine installations it is desirable to have the angle of attack on the succeeding rotating blades to a ldifierent degree at the blade tip than at the blade root and this can be accomplished by varying the width or size of the trailing edge slot to vary the flow therethrough at diflerent radial stages in the vane so as to have a different efl'ective vane camber and turning effect and, therefore, a diflerent angle of attack upon the blades of the next rotor stage. It is well known that in various installations the mismatching eflect, discussed previously with respect to changes in C and vector 34 of Fig. 1 at overspeed and part-speed operation, is different at the various vane radial stations, depending upon the basic design. Obviously, the slot size need not change uniformly, in fact, an advantage of our system is its great flexibility. If conditions dictate, a particular trailing edge slot could increase and/or decrease at various stages throughout its length either progressively, smoothly or irregularly as shown in vane 12 or smoothly as in vane '42 of Fig. 2. In addition to slot size variation, flow through trailing edge vane slots may, also be varied by the use of flow conducting ribs 53 and/or dams 55 in the vane interior, as shown in Fig. 2. 7

Further, in certain fluid machine devices, for example to compensate for non-uniform compressor inlet airflow, it may be desirable to vary the angle of attack on the blades circumferentially about the periphery of the rotor carrying the rotating blades and this can be accomplished by varying the size or width of the trailing edge slots in adjacent vanes to accomplish the desired circumferential eflective vane camber and turning variation. For example, the fluid flow through the vane trailing edge slots 7 in the three oclock vanes would be made larger than the vane slot size in the nine oclock position.

The true merit of our invention lies in its flexibility, and whileinnumerable applications to utilize our teachings will occur to those skilled in the art, a few specific examples will now be given to illustrate this flexibility.

The condition of partial design speed operation is illustrated in Fig.1 and it is noted that fluid is induced into the interior of vanes 42 or rear stator stage 40 and discharged through trailing edge slots 22 of vanes 12 of forward stator unit or inlet guide vane unit 25. Fig.

2 illustrates a method for inducing fluid ino the interior 54 of vane 42, then conducting'the fluid to the interior 24 of ,vane .12 'tobe discharged through trailing edge slot 22 which comprises conduit 80 which has an on-oif valve'82 therein 'as wellas reversible fluid pump 84 therein. With valve 82 open and pump 84 inoperative, the high pressure fluid in gas passage 26 at rear stator stage 40 will pass through trailing edge slot 52 of vane 42 into the vane interior 54 and then through conduit 80 into the interior 24 of vanes '12 to be discharged through the trailing edge slot 22 thereof. If, no such flow was desired, valve '82 couldbe closed and, if a reverse flow was required, pump 84 could be used.

It can be shown graphically in the fashion illustrated in Fig. 1 that the eflect of increased vane camber or. fluid I turning can be accomplished either by discharging fluid from the hollow vane interior through a trailing edge slot 22 in the concavesurface '18 thereof (Fig. 4) or by inducing fluid into the vane interior-through such a slot in the convex surface 26 thereof (-Fig. 5). In Figs; 4

and 5, the fluid angle of attack on blade ZS is increased from the angle defined between vector 36 and chordline- 38 to the angle formed between phantom vector 36 to chordline 38. Effective camber and fluid turning can be decreased by the'lopposite action, that'is, discharging fluid through .an upper surface trailing edge slot as shown in Fig. 6 or inducing fluid through alower surface trailing edge slot as shown in Fig. 7. In 'Figs. 6 and 7, the

fluid angle of attack on 28 is decreased from the angle the same reference numerals are given to corresponding parts of the vec't'ordiagrams in Figs. 4 through 7 as are used in Fig. 1,. To give maximum flexibility to an axial flow compressor, it may be desirable'to provide, as illustrate d in Fig;

8, trailingedge slot 22 in concavesurface :18 thereofuand trailing edge slot 72 in convex surface '20 thereof so 'f't hat we may control whether eflective camber, efl'ective turn- 7 1 ing and, therefore, blade angle "of attack in the successive compressor rotor blades areincreased or decreased by a discharging action throughout or by an induction 7 action through either slot. For example, if we wish to discharge air through trailing edge slots, we may determine whether the camber, turning and blade angle of attack are increased or decreased by discharging the fluid through either the upper or lower vane surface. Valve 74 may be used to block off either lower surface trailing edge slot'22 or upper surface trailing edge slot 72 when fluid flow is desired through the other surface. Valve 74 may be of the flapper type and pivotable about shaft 76 and actuated by rotatable ring 78 which pivotally engages and pivots link 80,- which is attached to and therefore pivots valve 74 about rod 76.

Eperimental results haveshown that optimum eifective camber, fluid turning and blade angle of attack are attained during periods of fluid discharge through a trailing edge slot 22 when the fluid being discharged is discharged substantially normally or perpendicular to the vane surface in which it lies. Fig. 9' is intendedfto illustrate the fluid leaving the interior 24 of vane 12 normally or perpendicular to surface =18 thereof, that is, sothat angle ;0 isapproximately a right angle. I Trailing edge'slots should preferably be located as close to the va'netrailing edge as possible, however, strength and fabricationproblems may require compromises at times.

It will be obvious to those skilled in the art that, while trailing edge vane slots are discussed herein, the principles taught are equally applicable to rotating blades and to vanes in a cascade, the latter beingat least one stationary vane located in a fluid passage.

We claim: v V 1. In a fluid machine, a stator unit comprising aplurality of radially extending, stationary, hollow vanes arranged in a circumferential pattern and each having a slot adjacent the trailing edge thereof, a rotor unit comprising a plurality of blades located downstream of and aligned with said vanes and extending radially from the periphery of a rotatable disc mounted for rotation to pump fluid between said vanes and blades, means connected to said vanes to pass fluid through said slots so as to vary the angle of attack of said first mentioned fluid on said blades, and means connected to said vanes to vary fluid flow along the radial stations of any of said ranged in a circumferential pattern and each having a slot adjacent the trailing edge in the concave surface thereof, a rotor unit comprising a plurality of blades located downstream of and aligned with said vanes and extending radially from the periphery of arotatable disc mounted for rotation to pump lfl'did between said vanes and-blades, and means connected to said vanes to suck fluidthrough said slots so as to decrease the angle of attack'of said first mentioned fluid on saidblades.

'3. An axial flow compressor comprising a duct type housing and alternate stator and rotor units located within said housing, said rotor units comprising a plurality of radially extending blades attached to the periphery of a disc lying in a plane perpendicular to the compressor centerline andadapted to rotate about said compressor centerline to pass fluid through said compressor such that the fluid pressure increases at successive stator and rotor unit stages, said stator units comprising a plurality of radially extending hollow vanes substantially aligned with said blades and lying in 'a plane parallel to the plane of said blades and spaced axially therefrom, slots located adjacent the trailing edge of at least some of said vanes in upstream and downstream stator units, .and means connected to said vanes to pass fluid through the slots of at least one upstream and one downstream stator unit in opposite directions to vary the fluid angle of attack upon the blades of the rotors immediately downstream thereof to improve the match of said stators and rotors at over-deslgn speed operation and to reverse the flowthru said slots at under-design speed operation.

4. An axial flow compressor comprising a duct type housing and alternate stator and rotor units located within said housing, said rotor units comprising a plurality of radially extending blades attached to the periphery of a disc lying in a plane perpendicular to the compressor centerline and adapted to rotate about said compressor centerline to pass fluid through said compressor such that the fluid pressure increases at successive stator and rotor unit stages, said stator units comprising a plurality of radially extending hollow vanes substantially aligned with said blades and lying in a plane parallel to the plane of said blades and spaced axially therefrom, a convex surface slot and a concave surface slot located adjacent the trailing edge of at least some of said vanes in upstream and downstream stator units, and means. connected to said vanes to pass fluid through the vane slots and vane interiors, and meansconnected to said vanes to determine whether the fluid will pass through the convex surface or in said housing, said rotor units comprising a plurality of radially extending blades attached to the periphery of a disc lying in a plane perpendicular to the compressor centerline and adapted to rotate thereabout to pass fluid through said compressor and progressively build up pressure in successive rotor and stator stages, said stator units comprising a plurality of radially extending hollow vanes substantially aligned with said blades and lying in a plane parallel to the plane of said blades and spaced axially therefrom, slots located adjacent the trailing edge of at least some of said vanes in upstream and downstream stator units, and means connected to said vanes to conduct fluid into the interior of the vanes of an upstream stator unit through said slots in said upstream stator unit vanes to the interior of the vanes of a downstream stator unit to be discharged through said slots in said downstream stator unit vanes normal to the vane surface in which said slot is located to vary the fluid angle of attack upon the blades of the rotors immediately downstream of said upstream and said downstream stator unitsto improvethe match of said stators and rotors at olfdesign speeds.

i 3 References .Cited in the file of this patent UNITED STATES PATENTS 2,344,835 Stalker Mar. 21, 1944 2,599,470 Meyer June 3, 1952 2,649,243 Stalker Aug. 18, 1953 2,720,356 Erwin Oct. 11, 1955 2,749,025 Stalker d. June 5, 1956 2,759,663 Stalker Aug. 21, 1956 2,825,532 Kadosch et al. Mar. 4, 1958 2,851,216 Scanlan et al. Sept. 9, 1958 2,885,856

Pedersen .5. May 12, 1959