CA1314486C - Axial flow compressor surge margin improvement - Google Patents
Axial flow compressor surge margin improvementInfo
- Publication number
- CA1314486C CA1314486C CA000483273A CA483273A CA1314486C CA 1314486 C CA1314486 C CA 1314486C CA 000483273 A CA000483273 A CA 000483273A CA 483273 A CA483273 A CA 483273A CA 1314486 C CA1314486 C CA 1314486C
- Authority
- CA
- Canada
- Prior art keywords
- slot
- axial flow
- flow compressor
- blades
- compressor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 230000006872 improvement Effects 0.000 title abstract description 24
- 230000004323 axial length Effects 0.000 claims description 6
- 239000012530 fluid Substances 0.000 claims description 6
- 238000011144 upstream manufacturing Methods 0.000 claims description 6
- 230000006735 deficit Effects 0.000 abstract description 13
- 230000008901 benefit Effects 0.000 abstract description 6
- 230000009467 reduction Effects 0.000 abstract description 6
- 238000011282 treatment Methods 0.000 description 7
- 238000006722 reduction reaction Methods 0.000 description 4
- 230000000712 assembly Effects 0.000 description 2
- 238000000429 assembly Methods 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- IJJWOSAXNHWBPR-HUBLWGQQSA-N 5-[(3as,4s,6ar)-2-oxo-1,3,3a,4,6,6a-hexahydrothieno[3,4-d]imidazol-4-yl]-n-(6-hydrazinyl-6-oxohexyl)pentanamide Chemical compound N1C(=O)N[C@@H]2[C@H](CCCCC(=O)NCCCCCC(=O)NN)SC[C@@H]21 IJJWOSAXNHWBPR-HUBLWGQQSA-N 0.000 description 1
- 206010011224 Cough Diseases 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/40—Casings; Connections of working fluid
- F04D29/52—Casings; Connections of working fluid for axial pumps
- F04D29/522—Casings; Connections of working fluid for axial pumps especially adapted for elastic fluid pumps
- F04D29/526—Details of the casing section radially opposing blade tips
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/66—Combating cavitation, whirls, noise, vibration or the like; Balancing
- F04D29/68—Combating cavitation, whirls, noise, vibration or the like; Balancing by influencing boundary layers
- F04D29/681—Combating cavitation, whirls, noise, vibration or the like; Balancing by influencing boundary layers especially adapted for elastic fluid pumps
- F04D29/685—Inducing localised fluid recirculation in the stator-rotor interface
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Structures Of Non-Positive Displacement Pumps (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
AXIAL FLOW COMPRESSOR SURGE MARGIN IMPROVEMENT
The casing 24 of an axial flow compressor 12 is provided with a plurality of axially extending cir-cumferentially spaced slots 30 in its internal cylindri-cal surface 32 adjacent the tips of at least one row of blades 26. A benefit in both stall margin improvement and a reduction in efficiency deficit may be achieved by positioning the leading edge of the slot 30 such that it leads the leading edge of the blade 26 by an amount termed the overhang or by reducing the closed to open ratio of the slots 30. A further reduction in effi-ciency deficit may be achieved by combining the overhang which individually gave the best stall margin improve-ment with a slot 30 closed to open ratio somewhat higher than the value which individually gave the best stall margin improvement.
AXIAL FLOW COMPRESSOR SURGE MARGIN IMPROVEMENT
The casing 24 of an axial flow compressor 12 is provided with a plurality of axially extending cir-cumferentially spaced slots 30 in its internal cylindri-cal surface 32 adjacent the tips of at least one row of blades 26. A benefit in both stall margin improvement and a reduction in efficiency deficit may be achieved by positioning the leading edge of the slot 30 such that it leads the leading edge of the blade 26 by an amount termed the overhang or by reducing the closed to open ratio of the slots 30. A further reduction in effi-ciency deficit may be achieved by combining the overhang which individually gave the best stall margin improve-ment with a slot 30 closed to open ratio somewhat higher than the value which individually gave the best stall margin improvement.
Description
~ 31 lL~8~
AXIAL FLOW COMPRRSSOR S~RGE MARGIN IMPROVEMENT
This invention relates to gas turbine engines and more particularly to axial flow compressors for such engines.
An axial flow compresso~ generally comprises one or more rotor assemblies that carry blades of aerofoil sec-tion, the rotor assemblies are carried within a casing within which are located stator blades~ The compressor is a multi-stage unit as the amount of work done (pressure increase) by each stage is small, a stage consists of a row of rotating blades followed by a row of stator blades. The reason for the small pressure increase across each stage is that the rate of diffusion and the deflection angle of the blades must be limited if losses due to air breakaway of the blades and subsequent blade stall are to be avoided.
The condition known as stall, or surge, occurs when the smooth flow oE air through the compressor is disturbed. Although the two terms "stall" and "surge" are often used synonymo-usly there is a difEerence which is mainly a matter of degree. A stall may affect only one stage or even group oE stages but a compressor surge generally refers to a complete flow breakdown through the compressor.
The value of airflow and pressure ratio at which a surge occurs is termed the "surge point". This point is a characteristic of each compressor speed, and a line which joins all the surge points, called the surge line, defines the maximum stable airflow which can be obtained at any ro-tational speed. A
compressor is designed to have a good safety margin (Region A) .~ ~
~ 31. A 4~
between the air flow and the pressure ratlo at which it will normally be operated (the working llne), and the airflow and pressure ratio at which a sure will occur.
la , 131~
For satiqfactory operation of a compressor stage, it is well known that it, and also the adjacent stages of the blades, must be carefully matched as each stage possesses its own individual airflow characteristics.
Thus it is extr~mely difficult to design a compressor to operate satisfactorily over a wide range of operating conditions such as an aircraft engine encounters.
Outside the design conditions, the gas flow around the blade tends to degenerate into a violent turbulence and the smooth pattern of flow through the stage or stages is destroyedO The gas flow through the compres-sor usually deteriorates and becomes a rapidly rotating annulus of pressurised gas about th~ tips of ~one com-pressor blade ~tage or gxoup of stagesO If a ~omplete breakdown of flow occurs through all the stages of the "- compressor such that all the stages of blades becomes ~stalledn the compressor will "surgen.
. ~ , The transition from stall to surge can be so rapid as to be unnoticed, or on the other hand, a stall may be so weak as to produce only slight vibration or poor acceleration or deceleration characteristics. A more severe compressor stall is indicated by a rise in turbine gas temperature, and vibration or "coughing" of the compressor. A surge is evident by a bang of varying severity from the engine compressor and a rise in turbine gas temperature.
3 It is necessary to use a system of airflow control to ensure the efficient operation of an engine over a wide speed range and to maintain the safety margin referred to above. A well known method of control is described in British Patent l,518,293 and consists of providing the compressor casing of such an engine with a circumferential row of slots inclined to the axis of rotation of the rotor blade row and disposed within its internal cylindrical surface adjacent to at least one blade row. The sl~s have an axial length substantially .
:13~486 greater than that of the blade row, and terminate downstream of the blade row.
An object of the present invention is to provide a form of compres~or casing treatment which optimises both the geometry and position of the slot re`lative to the blade, in order to obtain a stall marg~n-improvement without exces~ive loss of compressor efficiency.
10Accordingly the present invention provide~ an axial flow compressor, comprising a casing having an internal cylindrical surface, in which is mounted a rotor ! carrying at least one row of generally radially extending blades~ each of said blades having a leading edge which describes an arc upon rotation of said rotor and a trailing edge which describes an arc upon rotation of said rotor, one or more slots disposed within the internal cylindrical surface of the casing adjacent the ~ of at least one of said blade rows, each of -~aid slo~s having a leading end and a trailing end, c~aracterised in that the leading ends of the slots extend axially upstream of the arc described by the leading edges of the blades and the trailing ends of the slots lie in the same plane as, or axially upstream of, ~he arc describecl by the trailing edges of the blades.
) Preferably the base surface of each inclined slot is shaped to allow a smooth exit of high pressure fluid from the slot.
30Additivnally each slot is disposed such that its sidewalls are arranged at an angle to a radial line through the centre of the casing and so extend non-radially into the internal cylindrical surface of the casing with respect to the rotor axis, and the angle of inclination of the slot may be substantially equal to the exit angle of the fluid leaving the blades.
Tests have shown an improvement in surge margin can be obtained by altering the ratio ~f the distance 1 3 ~ 8 6 between the slots to the slot width, measured circumfer-entially around the compressor casing. This ratio is known as the closed to open ratio or (m/M) as shown in Figure 4. Improvements may also be made in the surge 5 margin by alte~ing the axial position of the slot such - that the leading edge of the slot leads the leading edge of the blade by an amount termed the overhang.
It was expected that the best overall improvement 10 in the compressor characteri~tics would be obtained by combining the m/M ratio with the overhang which indi-vidually provided the best surge margin improvement.
? Further test~ ~howed, however~ that this was not the case and that in fact the best overall impro~ement in 15 the compressor characteristics was obtained by combining the previous best known overhang with an (m~M) ratio somewhat higher.
~ ~. The present invention will now be more particularly 20 described, by way of example only, and with reference to t~he àccompanying drawings, in which:
Figure l shows a pictorial side elevation of a gas turbine engine having a broken away compressor casing 25 portion di~closing a diagrammatic embodiment of the present invention.
Figure 2 illustrates in more detail the casing treatment shown in the broken away portion of Figure l.
3o Figure 3 shows a view in the direction of arrows D-D at Figure 2.
Figure 4 is a cross-sectional view of the slots in 35 the direction of arrows K-X in Figure 3.
Figure 5 is a graph of surge margin improvement (line W) and efficiency deficit (line X) plotted against the clo~ed to open ratio (m/M~ for a zero overhang 1314~86 casing treatment.
Figure 6 is a graph of surge margin improvement (line Y) and efficiency deficit (line Z) plotted against 5overhang for a~.slotted casing treatment having a closed to open ratio of 0.58.
Figure 7 is a graph of pres6ure ratio against mass flow for a typical compxe~sor, clearly illu~trating the 10surge line, the working ].ine and the safety margin between the two (region A). - -, . . .
?Figures 8, 9 and 10 illustrate three alternative shapes of slot.
Referring to Figure 1 of ~he drawings, a gas turbine en~ine shown generally at 10 comprises in flow serie~ a low pressure compressor 12, a high pressure co~pressor 1~, combustion equipment 16, a high pressure Z0 tur~ine 18, a low pressure turbine 20 and.exhaust nozzle ~~. The low pressure compressor 12 and low pressure turbine 20, and the high pressure compressor 14 and high pressure turbine 18 are each rotatably mounted upon a co-axially arranged shaft assembly not shown in the 25 drawing~. A diagrammatic view of an embodiment of the present invention i8 shown within the broken portion of the low pressure compressor casing 24.
Figure 2 of the drawings shows a cross-sectional 30 view in greater detail of that shown diagrammatically at Figure 1 and comprises a portion of low pressure com pressor blade 26 having a leading edge 26(a) and a trailing edge 26(b) on one sta~e of the low pressure compressor 12. A compressor casing 24 is arranged 35 radially outwardly of the low pressure compressor 12, a portion of which is shown at 28. A circumférentially extending array of inclined slot-~, one of which is shown at 30, are provided within the internal cylindrical surface 32 of the compressor casing portion 28. Bach .. ~
~3~186 slot 30 has a depth B and an axial length C and is shaped and positioned such that the leading end 30(a) of the slot 30 extends axially upstream of the arc de~
scribed by the blade leading end 26(b).
Referring to Figure 3, the skew angle~ ~ of the inclined slot is arranged to be substantially the same as the gas outlet angle of the compressor blade 26. The gas outlet angle being that angle at which the compres-sor gas leaves the row of compressor blades, and isusually substantially 35~ Thi~ angle is obviously also the same angle as that of the gas inlet angle of the adjacent down~tream stator blade row Inot shown).
Dimension H defines the axlal length of the ~blade 26 measured between its leading edge 26(a3 and its trailing edge 26(b) along an axis parallel to the centreline of the compressor I-I.
~ As will,be seen from Figure~2 of the drawings the bas`~ 34 of each slot 30 is substantially flat except for t~e tralfi~g end 30(b) which is tapered at an angle arranged to be approximately 45 to the compressor longitudinal axis. It will be appreciated however that alternative surfacas may be incorporated, for example, the slots 30 may be formed with a concaved bottom ) surface or with a taper at both ends in order to effect a smoother passage of air through the slots 3n. The longitudinal sidewalls 36 of each slot 30 are inclined to the radial plane as shown in Figure 4.
3o Figure 4 of the drawings shows a cross-sectional view taken on line KK of Figure 3. The slots 30 extend non radially into the compressor casing 28 at an angle 0 relative to a radial axis R of the compressor 12. This angle 0 being so arranged that the slots 30 collect pressurised gas from the compressor blade 26. The direction of travel of the compressor blade 26 being indicated by arrow S. The slot closea to open ratio is illustrated by dimensions m and M respectively.
.
13~448~
It has been found that the slots 30 provided within the low pressure casing 28 can provide a degree of control or in fact eliminate a "stall" and thus substan-tially reduce the likelihood of "surge" occurring.
The following results are given as examples of the '' benefit3 obtain2ble Eor a set of blades as tested.
The sl~t axial length C wa~ arranged to be equal to the axial length ~ of the blade 26 measured at its radially outermost portion approximately 12mm (0.47 inches). The optimum overhang A of the slot 30 was i , "
found to be equal to approximately 23% of the bladeR 26 axial length H measured at its radially outermost portion. It is reasonable to expect similar ~enefits will be achieved on blade~ of other dimensions 7 n which the overhang A of the slot 2~ is similarly arranged to be approximately equal to 23% of the blades axial -le~th.
~,.
~ n '`à ~first,test, with a casing treatment having zero overhang, there was found to be a definite advan-tage in improved surge margin by reducing the closed to open ratio (m/M) to as low a value as 0.42. This is clearly illustrated in Figure 5 (line W). However, as ) indisated in this Figure (line X) the efficiency deficit increases with reducing closed to open ratio. At the best recorded closed to open ratio of 0042, giving the maximum surge margin improvement of 63~, the deficits in flow (not shown) and efficiency were in the region of 1.1% and 1.4~ respectively.
A second test showed that for a casing treatment having a given m/M ratio a further benefit in surge margin improvement was obtainable by'' altering the slot overhang such that the leading edge of the slot leads the leading edge of the blade. The greatest benefit was obtained with an overhang of between 2.54mm and 4.6mm (0.1" and 0.18n) and have a surge maxgin improvement of 13~86 64%.
It was reasonable expected that the best overall improvement in surge margin would be achieved by com-bining the previously best overhang from Test 2 with thebest open to closed ratio frorn Test 1.
A third test, however, showed that this was not the case and that the same maximum improvement in surge margin was obtained by combining the previou~ best overhang with a closed to open ratio ~omewhat higher than Test 1 and that this combination gave a r~duced -i deficit in flow and eficiency.
The advantage of the overhang is that it gives the same (i.e. maximum) surge margin improvement at higher - m/M value with a corresponding reduction of the flow and efficiency deficits.
,~ .
~ The optimum combination was found to be one having ~n--m7M ra~io of 0.58 and an overhang of approximately 2.8mm (0.11 inches). Figure 6 is a graph of stall margin improvement (line Y) and efficiency deficit (line Z) plotted against overhang for a slotted casing treat-ment having a closed to open ratio of 0.58. The rise in ) stall margin improvement is clearly illustrated by line Y; there being a rapid rise in improvement between zero and 2.5mm (0.10 inches) overhang whilst the maximum improvement is achieved between 2.8mm (0.11 inches) and 3 4.6mm ~0.18 inches) overhang. The corresponding reduc-tion in efficiency deficit is clearly illustrated by line Z which has a rapid reduction in deficit between zero overhang and 2.5mm (0.1 inches) overhang, the minimum value being reached with an overhang between 2.54mm (0.1 inches~ and 4.6mm (0.18 inches). Region C
marked on the graph indicates the optimism performance conditions. That is to say for a slot having a closed to open ratio of 0.58 and an overhang of approximately 2.8mm (0.11 inches~ a stall margin improvement of 64~
. . .
.
~31~86 can be obtained with an efficiency deficit of just 0.3%
and a rPduction in flow (not shown) of just 1%.
Whilst there i8 no actual increase in ~tall margin improvement be~ween the ~econd and third teqts (both 64%) the thir~ te~t has the advantage of sub~tantial reductions in both the eficiency deficit and flow defect over the ~econd.
.. . -- .
AXIAL FLOW COMPRRSSOR S~RGE MARGIN IMPROVEMENT
This invention relates to gas turbine engines and more particularly to axial flow compressors for such engines.
An axial flow compresso~ generally comprises one or more rotor assemblies that carry blades of aerofoil sec-tion, the rotor assemblies are carried within a casing within which are located stator blades~ The compressor is a multi-stage unit as the amount of work done (pressure increase) by each stage is small, a stage consists of a row of rotating blades followed by a row of stator blades. The reason for the small pressure increase across each stage is that the rate of diffusion and the deflection angle of the blades must be limited if losses due to air breakaway of the blades and subsequent blade stall are to be avoided.
The condition known as stall, or surge, occurs when the smooth flow oE air through the compressor is disturbed. Although the two terms "stall" and "surge" are often used synonymo-usly there is a difEerence which is mainly a matter of degree. A stall may affect only one stage or even group oE stages but a compressor surge generally refers to a complete flow breakdown through the compressor.
The value of airflow and pressure ratio at which a surge occurs is termed the "surge point". This point is a characteristic of each compressor speed, and a line which joins all the surge points, called the surge line, defines the maximum stable airflow which can be obtained at any ro-tational speed. A
compressor is designed to have a good safety margin (Region A) .~ ~
~ 31. A 4~
between the air flow and the pressure ratlo at which it will normally be operated (the working llne), and the airflow and pressure ratio at which a sure will occur.
la , 131~
For satiqfactory operation of a compressor stage, it is well known that it, and also the adjacent stages of the blades, must be carefully matched as each stage possesses its own individual airflow characteristics.
Thus it is extr~mely difficult to design a compressor to operate satisfactorily over a wide range of operating conditions such as an aircraft engine encounters.
Outside the design conditions, the gas flow around the blade tends to degenerate into a violent turbulence and the smooth pattern of flow through the stage or stages is destroyedO The gas flow through the compres-sor usually deteriorates and becomes a rapidly rotating annulus of pressurised gas about th~ tips of ~one com-pressor blade ~tage or gxoup of stagesO If a ~omplete breakdown of flow occurs through all the stages of the "- compressor such that all the stages of blades becomes ~stalledn the compressor will "surgen.
. ~ , The transition from stall to surge can be so rapid as to be unnoticed, or on the other hand, a stall may be so weak as to produce only slight vibration or poor acceleration or deceleration characteristics. A more severe compressor stall is indicated by a rise in turbine gas temperature, and vibration or "coughing" of the compressor. A surge is evident by a bang of varying severity from the engine compressor and a rise in turbine gas temperature.
3 It is necessary to use a system of airflow control to ensure the efficient operation of an engine over a wide speed range and to maintain the safety margin referred to above. A well known method of control is described in British Patent l,518,293 and consists of providing the compressor casing of such an engine with a circumferential row of slots inclined to the axis of rotation of the rotor blade row and disposed within its internal cylindrical surface adjacent to at least one blade row. The sl~s have an axial length substantially .
:13~486 greater than that of the blade row, and terminate downstream of the blade row.
An object of the present invention is to provide a form of compres~or casing treatment which optimises both the geometry and position of the slot re`lative to the blade, in order to obtain a stall marg~n-improvement without exces~ive loss of compressor efficiency.
10Accordingly the present invention provide~ an axial flow compressor, comprising a casing having an internal cylindrical surface, in which is mounted a rotor ! carrying at least one row of generally radially extending blades~ each of said blades having a leading edge which describes an arc upon rotation of said rotor and a trailing edge which describes an arc upon rotation of said rotor, one or more slots disposed within the internal cylindrical surface of the casing adjacent the ~ of at least one of said blade rows, each of -~aid slo~s having a leading end and a trailing end, c~aracterised in that the leading ends of the slots extend axially upstream of the arc described by the leading edges of the blades and the trailing ends of the slots lie in the same plane as, or axially upstream of, ~he arc describecl by the trailing edges of the blades.
) Preferably the base surface of each inclined slot is shaped to allow a smooth exit of high pressure fluid from the slot.
30Additivnally each slot is disposed such that its sidewalls are arranged at an angle to a radial line through the centre of the casing and so extend non-radially into the internal cylindrical surface of the casing with respect to the rotor axis, and the angle of inclination of the slot may be substantially equal to the exit angle of the fluid leaving the blades.
Tests have shown an improvement in surge margin can be obtained by altering the ratio ~f the distance 1 3 ~ 8 6 between the slots to the slot width, measured circumfer-entially around the compressor casing. This ratio is known as the closed to open ratio or (m/M) as shown in Figure 4. Improvements may also be made in the surge 5 margin by alte~ing the axial position of the slot such - that the leading edge of the slot leads the leading edge of the blade by an amount termed the overhang.
It was expected that the best overall improvement 10 in the compressor characteri~tics would be obtained by combining the m/M ratio with the overhang which indi-vidually provided the best surge margin improvement.
? Further test~ ~howed, however~ that this was not the case and that in fact the best overall impro~ement in 15 the compressor characteristics was obtained by combining the previous best known overhang with an (m~M) ratio somewhat higher.
~ ~. The present invention will now be more particularly 20 described, by way of example only, and with reference to t~he àccompanying drawings, in which:
Figure l shows a pictorial side elevation of a gas turbine engine having a broken away compressor casing 25 portion di~closing a diagrammatic embodiment of the present invention.
Figure 2 illustrates in more detail the casing treatment shown in the broken away portion of Figure l.
3o Figure 3 shows a view in the direction of arrows D-D at Figure 2.
Figure 4 is a cross-sectional view of the slots in 35 the direction of arrows K-X in Figure 3.
Figure 5 is a graph of surge margin improvement (line W) and efficiency deficit (line X) plotted against the clo~ed to open ratio (m/M~ for a zero overhang 1314~86 casing treatment.
Figure 6 is a graph of surge margin improvement (line Y) and efficiency deficit (line Z) plotted against 5overhang for a~.slotted casing treatment having a closed to open ratio of 0.58.
Figure 7 is a graph of pres6ure ratio against mass flow for a typical compxe~sor, clearly illu~trating the 10surge line, the working ].ine and the safety margin between the two (region A). - -, . . .
?Figures 8, 9 and 10 illustrate three alternative shapes of slot.
Referring to Figure 1 of ~he drawings, a gas turbine en~ine shown generally at 10 comprises in flow serie~ a low pressure compressor 12, a high pressure co~pressor 1~, combustion equipment 16, a high pressure Z0 tur~ine 18, a low pressure turbine 20 and.exhaust nozzle ~~. The low pressure compressor 12 and low pressure turbine 20, and the high pressure compressor 14 and high pressure turbine 18 are each rotatably mounted upon a co-axially arranged shaft assembly not shown in the 25 drawing~. A diagrammatic view of an embodiment of the present invention i8 shown within the broken portion of the low pressure compressor casing 24.
Figure 2 of the drawings shows a cross-sectional 30 view in greater detail of that shown diagrammatically at Figure 1 and comprises a portion of low pressure com pressor blade 26 having a leading edge 26(a) and a trailing edge 26(b) on one sta~e of the low pressure compressor 12. A compressor casing 24 is arranged 35 radially outwardly of the low pressure compressor 12, a portion of which is shown at 28. A circumférentially extending array of inclined slot-~, one of which is shown at 30, are provided within the internal cylindrical surface 32 of the compressor casing portion 28. Bach .. ~
~3~186 slot 30 has a depth B and an axial length C and is shaped and positioned such that the leading end 30(a) of the slot 30 extends axially upstream of the arc de~
scribed by the blade leading end 26(b).
Referring to Figure 3, the skew angle~ ~ of the inclined slot is arranged to be substantially the same as the gas outlet angle of the compressor blade 26. The gas outlet angle being that angle at which the compres-sor gas leaves the row of compressor blades, and isusually substantially 35~ Thi~ angle is obviously also the same angle as that of the gas inlet angle of the adjacent down~tream stator blade row Inot shown).
Dimension H defines the axlal length of the ~blade 26 measured between its leading edge 26(a3 and its trailing edge 26(b) along an axis parallel to the centreline of the compressor I-I.
~ As will,be seen from Figure~2 of the drawings the bas`~ 34 of each slot 30 is substantially flat except for t~e tralfi~g end 30(b) which is tapered at an angle arranged to be approximately 45 to the compressor longitudinal axis. It will be appreciated however that alternative surfacas may be incorporated, for example, the slots 30 may be formed with a concaved bottom ) surface or with a taper at both ends in order to effect a smoother passage of air through the slots 3n. The longitudinal sidewalls 36 of each slot 30 are inclined to the radial plane as shown in Figure 4.
3o Figure 4 of the drawings shows a cross-sectional view taken on line KK of Figure 3. The slots 30 extend non radially into the compressor casing 28 at an angle 0 relative to a radial axis R of the compressor 12. This angle 0 being so arranged that the slots 30 collect pressurised gas from the compressor blade 26. The direction of travel of the compressor blade 26 being indicated by arrow S. The slot closea to open ratio is illustrated by dimensions m and M respectively.
.
13~448~
It has been found that the slots 30 provided within the low pressure casing 28 can provide a degree of control or in fact eliminate a "stall" and thus substan-tially reduce the likelihood of "surge" occurring.
The following results are given as examples of the '' benefit3 obtain2ble Eor a set of blades as tested.
The sl~t axial length C wa~ arranged to be equal to the axial length ~ of the blade 26 measured at its radially outermost portion approximately 12mm (0.47 inches). The optimum overhang A of the slot 30 was i , "
found to be equal to approximately 23% of the bladeR 26 axial length H measured at its radially outermost portion. It is reasonable to expect similar ~enefits will be achieved on blade~ of other dimensions 7 n which the overhang A of the slot 2~ is similarly arranged to be approximately equal to 23% of the blades axial -le~th.
~,.
~ n '`à ~first,test, with a casing treatment having zero overhang, there was found to be a definite advan-tage in improved surge margin by reducing the closed to open ratio (m/M) to as low a value as 0.42. This is clearly illustrated in Figure 5 (line W). However, as ) indisated in this Figure (line X) the efficiency deficit increases with reducing closed to open ratio. At the best recorded closed to open ratio of 0042, giving the maximum surge margin improvement of 63~, the deficits in flow (not shown) and efficiency were in the region of 1.1% and 1.4~ respectively.
A second test showed that for a casing treatment having a given m/M ratio a further benefit in surge margin improvement was obtainable by'' altering the slot overhang such that the leading edge of the slot leads the leading edge of the blade. The greatest benefit was obtained with an overhang of between 2.54mm and 4.6mm (0.1" and 0.18n) and have a surge maxgin improvement of 13~86 64%.
It was reasonable expected that the best overall improvement in surge margin would be achieved by com-bining the previously best overhang from Test 2 with thebest open to closed ratio frorn Test 1.
A third test, however, showed that this was not the case and that the same maximum improvement in surge margin was obtained by combining the previou~ best overhang with a closed to open ratio ~omewhat higher than Test 1 and that this combination gave a r~duced -i deficit in flow and eficiency.
The advantage of the overhang is that it gives the same (i.e. maximum) surge margin improvement at higher - m/M value with a corresponding reduction of the flow and efficiency deficits.
,~ .
~ The optimum combination was found to be one having ~n--m7M ra~io of 0.58 and an overhang of approximately 2.8mm (0.11 inches). Figure 6 is a graph of stall margin improvement (line Y) and efficiency deficit (line Z) plotted against overhang for a slotted casing treat-ment having a closed to open ratio of 0.58. The rise in ) stall margin improvement is clearly illustrated by line Y; there being a rapid rise in improvement between zero and 2.5mm (0.10 inches) overhang whilst the maximum improvement is achieved between 2.8mm (0.11 inches) and 3 4.6mm ~0.18 inches) overhang. The corresponding reduc-tion in efficiency deficit is clearly illustrated by line Z which has a rapid reduction in deficit between zero overhang and 2.5mm (0.1 inches) overhang, the minimum value being reached with an overhang between 2.54mm (0.1 inches~ and 4.6mm (0.18 inches). Region C
marked on the graph indicates the optimism performance conditions. That is to say for a slot having a closed to open ratio of 0.58 and an overhang of approximately 2.8mm (0.11 inches~ a stall margin improvement of 64~
. . .
.
~31~86 can be obtained with an efficiency deficit of just 0.3%
and a rPduction in flow (not shown) of just 1%.
Whilst there i8 no actual increase in ~tall margin improvement be~ween the ~econd and third teqts (both 64%) the thir~ te~t has the advantage of sub~tantial reductions in both the eficiency deficit and flow defect over the ~econd.
.. . -- .
Claims (9)
1. An axial flow compressor, comprising, a casing, having an internal cylindrical surface;
a rotor;
at least one row of generally radially extending blade , each of which are mounted on the rotor and having a leading edge and a trailing edge, the leading edges of said blades describing an arc upon rotation of said rotor and said blades trailing edges describing an arc upon rotation of said rotor;
one or more slots, each of which are disposed within the internal cylindrical surface of the casing adjacent the tips of at least one of said blade rows and having a leading end and a trailing end; wherein the leading end of each slot extending axially upstream of the arc described by the leading edges of the blades and the trailin and of each slot lies in the same plane as or axially upstream of the arc described by the trailing edges of the blades.
a rotor;
at least one row of generally radially extending blade , each of which are mounted on the rotor and having a leading edge and a trailing edge, the leading edges of said blades describing an arc upon rotation of said rotor and said blades trailing edges describing an arc upon rotation of said rotor;
one or more slots, each of which are disposed within the internal cylindrical surface of the casing adjacent the tips of at least one of said blade rows and having a leading end and a trailing end; wherein the leading end of each slot extending axially upstream of the arc described by the leading edges of the blades and the trailin and of each slot lies in the same plane as or axially upstream of the arc described by the trailing edges of the blades.
2. An axial flow compressor according to claim 1 in which a pair of sidewalls are provided in each slot, said sidewalls being arranged at an angle to a radial line through the centre of the casing and extend non-radially into the internal cylindrical surface of the casing.
3. An axial flow compressor as claimed in claim 1 in which each slot is inclined at an angle relative to the longitudinal axis of the compressor such that the angle of inclination is substantially equal to the angle of the fluid leaving the blades.
4. An axial flow compressor as claimed in claim 1 in which the amount by which the leading ends of the slots extend axially upstream of the arc described by the leading edges of the blades is substnatially equal to 20% of the blades axial length.
5. An axial flow compressor as claimed in claim 4 in which the ratio of the distance between the slots to the slot width (m/M) is substantially 0.58.
6. An axial flow compressor as claimed in claim 1, including means for enabling a smooth exit of high pressure fluid from each slot.
7. An axial flow compressor as claimed in claim 6, in which the means for enabling a smooth exit of high pressure fluid from each slot comprises a base surface which reduces in depth towards the trailing end.
8. An axial flow compressor as claimed in claim 6 in which the means for enabling a smooth exit of high pressure fluid from each slot comprises a base surface which reduces in depth towards the leading end and the trailing end.
9. An axial flow compressor according to claim 1 in which each slot has a base surface which is at a constant depth.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8415605 | 1984-06-19 | ||
| GB8415605 | 1984-06-19 | ||
| GB8511464A GB2245312B (en) | 1984-06-19 | 1985-05-07 | Axial flow compressor surge margin improvement |
| GB8511464 | 1985-05-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1314486C true CA1314486C (en) | 1993-03-16 |
Family
ID=26287887
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000483273A Expired - Lifetime CA1314486C (en) | 1984-06-19 | 1985-06-06 | Axial flow compressor surge margin improvement |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1314486C (en) |
| DE (1) | DE3521798C2 (en) |
| FR (1) | FR2669687B1 (en) |
| IT (1) | IT1235237B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114576205A (en) * | 2022-03-14 | 2022-06-03 | 中国航发湖南动力机械研究所 | Efficient self-circulation processing casing with mode conversion |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6231301B1 (en) * | 1998-12-10 | 2001-05-15 | United Technologies Corporation | Casing treatment for a fluid compressor |
| DE10135003C1 (en) * | 2001-07-18 | 2002-10-02 | Mtu Aero Engines Gmbh | Compressor housing structure in axially, through-flowing moving blade ring for use in pumps |
| DE10205363A1 (en) * | 2002-02-08 | 2003-08-21 | Rolls Royce Deutschland | gas turbine |
| FR2882112B1 (en) * | 2005-02-16 | 2007-05-11 | Snecma Moteurs Sa | HEAD SAMPLING OF HIGH PRESSURE COMPRESSOR MOBILE WHEELS FROM TURBOREACTOR |
| DE102007037924A1 (en) * | 2007-08-10 | 2009-02-12 | Rolls-Royce Deutschland Ltd & Co Kg | Turbomachine with Ringkanalwandausnehmung |
| DE102008006739A1 (en) * | 2008-01-30 | 2009-08-13 | Daimler Ag | Compressor system for a fuel cell assembly, fuel cell assembly and method of control |
| DE102008011644A1 (en) * | 2008-02-28 | 2009-09-03 | Rolls-Royce Deutschland Ltd & Co Kg | Housing structuring for axial compressor in the hub area |
| DE102011006273A1 (en) | 2011-03-28 | 2012-10-04 | Rolls-Royce Deutschland Ltd & Co Kg | Rotor of an axial compressor stage of a turbomachine |
| DE102011006275A1 (en) | 2011-03-28 | 2012-10-04 | Rolls-Royce Deutschland Ltd & Co Kg | Stator of an axial compressor stage of a turbomachine |
| DE102011007767A1 (en) | 2011-04-20 | 2012-10-25 | Rolls-Royce Deutschland Ltd & Co Kg | flow machine |
| FR2989742B1 (en) * | 2012-04-19 | 2014-05-09 | Snecma | UPRIGHT CAVITY COMPRESSOR HOUSING OPTIMIZED |
| FR3109959B1 (en) * | 2020-05-06 | 2022-04-22 | Safran Helicopter Engines | Turbomachine compressor comprising a fixed wall provided with a shaped treatment |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3893787A (en) * | 1974-03-14 | 1975-07-08 | United Aircraft Corp | Centrifugal compressor boundary layer control |
| GB1518293A (en) * | 1975-09-25 | 1978-07-19 | Rolls Royce | Axial flow compressors particularly for gas turbine engines |
| GB2017228B (en) * | 1977-07-14 | 1982-05-06 | Pratt & Witney Aircraft Of Can | Shroud for a turbine rotor |
| JPS6318799Y2 (en) * | 1980-12-02 | 1988-05-26 | ||
| US4479755A (en) * | 1982-04-22 | 1984-10-30 | A/S Kongsberg Vapenfabrikk | Compressor boundary layer bleeding system |
-
1985
- 1985-06-06 CA CA000483273A patent/CA1314486C/en not_active Expired - Lifetime
- 1985-06-13 IT IT8521142A patent/IT1235237B/en active
- 1985-06-18 FR FR858509205A patent/FR2669687B1/en not_active Expired - Lifetime
- 1985-06-19 DE DE3521798A patent/DE3521798C2/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114576205A (en) * | 2022-03-14 | 2022-06-03 | 中国航发湖南动力机械研究所 | Efficient self-circulation processing casing with mode conversion |
| CN114576205B (en) * | 2022-03-14 | 2023-11-28 | 中国航发湖南动力机械研究所 | Efficient self-circulation processing casing with mode conversion |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2669687B1 (en) | 1994-07-01 |
| DE3521798C2 (en) | 1993-12-09 |
| DE3521798A1 (en) | 1992-08-27 |
| IT8521142A0 (en) | 1985-06-13 |
| IT1235237B (en) | 1992-06-26 |
| FR2669687A1 (en) | 1992-05-29 |
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