CA2237611A1 - Optimization of turbomachinery harmonics - Google Patents
Optimization of turbomachinery harmonics Download PDFInfo
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- CA2237611A1 CA2237611A1 CA 2237611 CA2237611A CA2237611A1 CA 2237611 A1 CA2237611 A1 CA 2237611A1 CA 2237611 CA2237611 CA 2237611 CA 2237611 A CA2237611 A CA 2237611A CA 2237611 A1 CA2237611 A1 CA 2237611A1
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- tones
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- spinning mode
- turbomachine assembly
- harmonics
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Abstract
A turbomachine assembly (10) includes a number B of circumferentially spaced rotor blades (22), a number V of circumferentially spaced guide vanes (20) axially adjacent to the rotor blades (22), an annular chamber (30) surrounding the rotor blades (22), and an intake (12) and exhaust (24) for receiving and discharging air that passes through the annular chamber (30). When the turbomachine (10) is in operation, spinning mode tones are generated by the interaction of the rotor and guide vanes (22, 20). These tones are minimized by selecting a number of vanes (20) relative to the number of blades (22) so that selected tones propagate axial to the intake and exhaust of the turbomachine. A sound absorptive material (18) is then positioned so that the tones impinge upon it. Moreover, a tuned duct (32) is positioned in the path of the remaining tones. The turning vanes (26), placed within the tuned duct (32), cancel the remaining tones travelling through the duct.
Description
CA 02237611 1998-0~-13 W O 97/18396 PCT~US96/17223 OPTIMIZATION OF ImRBO~'H I ~:~Y E~ONICS
FIELD OF llH~ lNV~:NLlON
This invention relates generally to the field of turbomachinery. More specifically, this invention relates to a system for improved attenuation of the noise generated by the interaction of rotor blades and stationary guide vanes in industrial turbomachinery.
BACRGROUND OF TE~ Ihv~NLlON
The aerodynamic interaction of rotor blades and stationary guide vane wakes adds a significant contribution to the noise produced by turbomachinery. The rotor blade rotation causes this turbomachinery generated noise to be periodic. Correspondingly, the noise is heard as tonal or harmonic noise. This type of rotor/vane tonal noise, known in the art as spinning mode tones, has been studied extensively in aircraft applications and noise reduction strategies have been deduced. In particular, the Tyler/Sofrin Spinning Mode Theory has been used for many years to describe how spinning mode tones escape from ducts and propagate as noise. Aircraft engine designers have exploited this theory by selecting rotor blade and vane combinations that minimize the propagation of the spinning mode tones along the engine axis.
Unlike industrial turbomachinery, with intake and exhaust systems typically connected to an extensive duct system, conventional aircraft engines have short intake and 11--~t~ ' '5 c~L q,~4,c5c!~' CA 02237611 1998-O5-13J~L ~l~ ~iYiY r 1.~
W~ 396 P~flJW~iJ17~23 ~a~ duc~ that ~~e ccnt~guouo tc f~ p~ce. Becauoe c~ the ~ iculty o~ cor~troll~ n5 noi~ cnc~ it h~ c~ped into freo ~pac~l d~-~gn~rs of aircr~t ~ns~nea ~r.tem~t ~o co~ n the ~plnn l ~g ~od~ ~one~ within the en~lne and ~r~ant th~r proFaga.tion into ~he l~taX~ o~ ~xh~u~t. Quch dee~g~ d~lc~ t~o ~Lo~e ~y cr~t~s~g a ~honomesso~ lcnawn a~
"cut~ f, n o. by d~r~cting th~ n~ r~d~ tonell to l~p~nge on ~h~ w~ ci the intaric~ o~ the engine, wh~ ch 8 lin~d w~th a 3cu~d ~h~_yti~re mater~Al . Th~ techssic~us ~0 c~use~ the sFins~in~ moto tonea to decay be~oro exitin~ th~
~ngine. ~ onr~en~ly, ~he current ~tate o~ ~hs art t~actles away ~om F~ rpoJ~fully c~r-~c~ing Jpinn~ ng mcde tone out ~e ~ n'cake or eYh~u~t of a turbaenginl~ .
u.X. patent ~pecificat~t~n ~B 1, ~71, ~5 teache~ a is nolc~e a~atemant method and apparatu~ ~or a tur~ir~e ~ngine wherein ~he number o~ blades ~r~ ~rane~ are ~elected to attenuate ~hq~ e~ect o~ the ~ound produced upon a human ob~er. One em~o~i~ent o~ ch a3~ eng~n~ ha~ the num~er cf v~ne~ being twice the nu~r o~ ~ladeE~ time~ the 20 de~irQd hannon~c t~ be ~uppre~ed . German patent DE -A- 1 403 576 teachee the u8~ ol~ eound ~baorbing ~naterial in a turl~lne ~gine.
~ e~2 ~a~Jcy~ound ma~e~ial, no~ rel~ nt ~o ~he n c~ airc~ t ~nsJln~, bue rol~v~r~t to th~ curren~
25 iswont~n, conc~rn- duct ~yst-m~ uc~ ~y-~e~n~, such a~
tho-- ~n ~ nduJtri~ ch~ nen~, typicaLly h~v~ bends ~o ~ir-ct ~s-lcw. When pr~-curi2ed ai~ ~1 ow- ~hr~ugh ~uch 4~n~-, a p~-~ur- d~op occur~. ~o ~11~ ata thl~ prohlem.
~om dc~ gn- F~J~ t~o~ turnins vanc~ w~t~i~s th~ ~uct bends .
30 S~ch van~J ~ zo pro~our~ ~ro~ ~cro~ th~ b~nd~ ~nd ~rovlde ~mooth air ~lo~, thuJ ~ cins~ the a-rodyna~nic o~nc~ oi upctro-m o~ do~n~Jtre~m l-~h;~ery. ~owev~, e~-- p~ ~e~ st o~ th~ v~n~ ~ieh~ n ~hc ~nt- ha~ noc ~en u~d to ~ nr- t~ ~ound, ~ nu~ti on c~pability of ~he 3 s d~c~ .
AMENDED SHEET
A 22376 1 1 ' ~ r lY~ '~ cc! 41cb'4~'-c'o'~ ~ 1998-O5-13JL~L l'~U~
WO 9~~~ ~ u~96117~3 -- 2~ --Mcreolter, althcugh ~he ccm~in~tion ~ turn~ng ~ran~J and duct ~ndJ h~ not b~cn u-es~ to atten~late nolse oth-r me~nJ ha~ n uJad t~ att~nua~ noi~ within a ~uct. F~r exa~ , du~t branehe- h~ n u~d ~o S a~te~suat~ ~om~ ~ t~ ne~ . Such a d~ n c~ rect~ ~om~ of ~c~ nol~o throush a br~ch that ~cngthe:~- t~ ~ath c~ ~he ~n~ tr~ n~ thr~u~h ~he br~nch. l~y Yelecting the r ~ranch l-nst~, th- 5r~neh noi~e r~join~ tha main ~sct noi~ 180 degr~ OUt C~ pha~. Con~a~u-ntly, a 10 p~r~c~on o~ t~ no~ ~ can~ out . How~ver, ~dln~ t~e as~dlt~on~ to branc~ eh- ~ound i~ c-umb~r~oma as~d dQes AMEi~lDED SHE~T
_ _ _ CA 02237611 1998-0~-13 W O 97/18396 PCTrUS96/17223 not take advantage of the bends in the duct necessary to control the airflow.
SUMMARY OF THE lNv~NllON
In a typical turbomachine, there is a number B of circumferentially spaced rotor blades, a number V of circumferentially spaced guide vanes axially adjacent to the rotor blades, an annular chamber surrounding the rotor blades, and an intake and exhaust for receiving and discharging air that passes through the annular chamber.
When the turbomachine is in operation spinning mode tones are generated by the interaction of the rotor and guide vanes. According to the present invention, these tones are minimized by selecting the number of vanes V relative to the number of blades B such that the propagation path of substantially all of the harmonics of the spinning mode tones is substantially axial to the annular chamber intake and exhaust. A sound absorptive material is positioned perpendicular to the propagation path of the spinning mode tones such that the tones impinge thereon and are attenuated thereby. In a preferred embodiment, the sound absorptive material is placed in the intake of the turbomachine.
Such machines are usually coupled to ducts through which the air flows. In addition to the air flow, the spinning mode tones generated by the turbomachine tend to travel through these ducts. According to the present invention, a tuned duct is positioned in the path of the spinning mode tones. This tuned duct is connected to either the intake or the exhaust, or both, of the annular chamber and has a radial bend that forms a partial circle with an arc of ~ radians. A number of turning vanes are concentrically spaced within the bend, with each turning vane being spaced a distance D from each adjacent turning vane. The distance D is related to the arc ~ of the radial bend and the frequency of the spinning mode tones. The turning vanes, thus placed, effectively cancel a plurality _ CA 02237611 1998-0~-13 W O 97/18396 PCTrUS96/17223 of the harmonics of the spinning mode tones travelling through the duct. In a preferred embodiment, the relationship between the distance D and the arc ~ is chosen to cancel only the odd harmonics of the spinning mode S tones.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which ~orm a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed description of the preferred embodiment, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed.
In the drawings:
FIGURE 1 illustrates, in simplified form, a cross section of a turbomachine and associated duct system and depicts a preferred embodiment of the spinning mode tone sound attenuation system of the present invention.
FIGURE 2 is a partial view of a turbomachine illustrating the rotor blades and guide vanes thereof.
DET~TT~Rn DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like numerals indicate like elements throughout, FIGURE 1 depicts an industrial turbine system 10 including the sound attenuation features of the present invention. Turbine CA 02237611 1998-0~-13 W O 97/18396 PCTrUS96/17223 system 10 includes an intake duct 12 for supplying an intake stream of high pressure gas, and an intake manifold 14 for supplying the gas to the turbine 16. The intake manifold 14 features an sound absorptive surface 18. The high pressure gas is routed through a set of circumferentially spaced intake guide vanes 20 and to a set of circumferentially spaced rotor guide blades 22, which are surrounded by an annular chamber 30. The high pressure gas then exits through the exhaust system 24.
The interaction of inlet guide vanes 20 with rotor blades 22 as well as other guide vane rotor blade sets (not shown) generate spinning mode tones. These spinning mode tones are periodic pressure patterns that spin about the turbine axis 34, and are perceived as noise to the human observer. These pressure pulses have zero or more lobes relative to the number and rotation speed of the rotor blades 22 as well as the number of inlet guide vanes 20. When the pressure pulse has zero lobes then a zeroth order spinning mode has occurred. The number of rotor blades 22 multiplied by the rotor speed is the fllnA~mental, or blade-pass frequency, of the spinning mode tones. When a combination of inlet guide vanes 20 and rotor blades 22 are selected such that the number of lobes in the spinning mode is zero then harmonics of the spinning mode tones propagate parallel to the turbine axis 34 and out of the turbine 16. The number of lobes can be determined by the equation:
N= ' m-B+k V';
where:
m is the harmonic and can take on any integer - 30 value from 1 to infinity;
B is the number of rotor blades;
k is an index that ranges over all integer values from - infinity to +infinity; and, V i8 the number of stationary guide vanes.
CA 02237611 1998-0~-13 W O 97/18396 PCT~US96/17223 Thus, N is equal to zero for a particular blade count B, a particular inlet guide vane count V, and a particular harmonic m.
Referring also to FIGURE 2, the zeroth order 8p; nn;ng mode can be forced to occur when there are an integer number of inlet guide vanes 20 relative to the number of rotor blades 22, or when an integer number times the number of inlet guide vanes 20 is equal to an integer number times the number of rotor blades 22, i.e. when I m*B
= ~k*V¦ and k and m are both integers. The zeroth order sp; nn; ng mode can be forced to occur at all harmonics of the blade-pass frequency when the number of inlet guide vanes 20 equals the number of rotor blades 22.
Alternatively, if the number of inlet guide vanes 20 selected is equal to twice the number of rotor blades 22 then the zeroth order spinning mode occurs only on even harmonics of the blade-pass frequency. In the preferred embodiment, twice the number of guide vanes 20 relative to the number of rotor blades 22 is selected. Thus, the even harmonics of the blade-pass frequency are propagated substantially along the turbine axis 34 and into the intake manifold 14.
A sound absorptive material 18 is placed perpendicular to the propagation path of the spinning mode tones. Preferably, as illustrated in FIGURE 1, this sound absorptive material 18 is attached to the inside of the intake manifold 14. As a result, the selected harmonics of the spinning mode tones impinge at a perpendicular incidence upon the face of the sound absorptive material 18. The sound absorptive material selected i5 preferably a bulk absorber with absorption coefficient of .99 or greater. For example, the bulk absorber selected may be fabricated from mineral wool, fiberglass, or ceramic fiber.
As a result of the harmonics impinging on the sound absorptive material, the sound levels of the zeroth order mode will be reduced by approximately 20 dB or greater. To a lesser degree, sound attenuation of modes other than the CA 022376ll l998-0~-l3 W O 97/18396 PCTrUS96/17223 zeroth order mode will occur, but the effectiveness will decrease as the sound propagates into the material at grazing incidence.
The harmonics not absorbed by the sound ab~orptive material 18 will generally propagate out of the intake manifold 14 and out through the intake duct 12.
According to the present invention, a tuned duct section 32 is placed in the path of the remaining harmonics. To attenuate these harmonics, turning vanes are fixed in the tuned duct 32. As the rem~;nlng harmonics propagate back through the intake duct they will turn through the duct bend 28 and pass through the turning vanes 26. By controlling the spacing between these turning vanes 26 relative to the radius of the duct bend 28 the remaining harmonics (primarily the odd harmonics) can be effectively attenuated. The confined path of the remaining harmonics, defined by each of the turning vanes 26, forces the harmonics to travel increased distances for each of the larger radius turns. The harmonic at each path defined by the turning vanes 26 will be 180 degrees out of phase with the identical harmonic travelling through an adjacent path when the turning vane spacing is selected to be equal to:
l.SA.
~ ' where:
~ is the arc of the turn in radians; and, A is the wavelength of the fnn~m~ntal harmonic.
The turning vanes 26 will each be a partial circle defining the arc ~ and each successive turning vane 26 will increase in radius by:
n 1 ~A;
where n is the vane number.
The duct bend 28 and turning vane 26 combination will cancel all odd harmonics (1, 3, 5, etc.) while providing no benefit at the even harmonics (2, 4, 6 times, CA 02237611 1998-0~-13 etc.). However, tonal noise sources, such as spinning mode tones, typically have peak frequencies at the flln~mental harmonic with decreasing sound levels as the harmonics increase. By at least cancelling the odd harmonics, which include the fl~n~mental harmonic, a significant effect on the sound level is accomplished. Moreover, the sound absorptive material 18 will have effectively attenuated the even harmonics before they reach the duct bend 28. While the preferred radius of the duct is 1.5 radians, Applicant recognizes that manufacturing constraints may dictate that a 90 degree bend is used with a corresponding radius of ~/2.
The turning vanes 26 can be designed to also cancel some of the even harmonics by selecting the distance between turning vanes to be:
0.751 This design will provide partial cancellation at harmonics 1, 2, 3, 5, 6, 7, 9, 10 times, etc. of the blade-pass frequency. The partial cancellation will occur at all odd harmonics and every other even harmonic.
In the preferred embodiment, all of the components are optimized to provide a system that effectively cancels all harmonics of the spinning mode tones. In such an embodiment, the vane/blade ratio and sound absorptive material 18 are optimized to attenuate the even harmonics; whereas, the tuned duct 32 is optimized to attenuate the odd harmonics. To accomplish this system, the number of inlet guide vanes 20 selected is twice the number of rotor blades 22 selected. For example, in a turbomachine with nineteen rotor blades 22, thirty-eight inlet guide vanes 20 are selected. This combination directs the even harmonics substantially parallel to the turbine axis 34. A bulk absorber 18 is then placed in a path perpendicular to the even harmonics. This arrangement, while effectively attenuating the even harmonics, does very little to attenuate the odd harmonics.
CA 02237611 1998-0~-13 W O 97/18396 PCTnUS96/17223 Thus, the odd harmonics continue through the duct system 12. The tuned duct 32 placed in the path of the odd harmonics is optimized to attenuate these odd harmonics.
The effect of the entire system is to cancel substantially all of the harmonics of the spinning mode tones.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.
~ J3~S~
FIELD OF llH~ lNV~:NLlON
This invention relates generally to the field of turbomachinery. More specifically, this invention relates to a system for improved attenuation of the noise generated by the interaction of rotor blades and stationary guide vanes in industrial turbomachinery.
BACRGROUND OF TE~ Ihv~NLlON
The aerodynamic interaction of rotor blades and stationary guide vane wakes adds a significant contribution to the noise produced by turbomachinery. The rotor blade rotation causes this turbomachinery generated noise to be periodic. Correspondingly, the noise is heard as tonal or harmonic noise. This type of rotor/vane tonal noise, known in the art as spinning mode tones, has been studied extensively in aircraft applications and noise reduction strategies have been deduced. In particular, the Tyler/Sofrin Spinning Mode Theory has been used for many years to describe how spinning mode tones escape from ducts and propagate as noise. Aircraft engine designers have exploited this theory by selecting rotor blade and vane combinations that minimize the propagation of the spinning mode tones along the engine axis.
Unlike industrial turbomachinery, with intake and exhaust systems typically connected to an extensive duct system, conventional aircraft engines have short intake and 11--~t~ ' '5 c~L q,~4,c5c!~' CA 02237611 1998-O5-13J~L ~l~ ~iYiY r 1.~
W~ 396 P~flJW~iJ17~23 ~a~ duc~ that ~~e ccnt~guouo tc f~ p~ce. Becauoe c~ the ~ iculty o~ cor~troll~ n5 noi~ cnc~ it h~ c~ped into freo ~pac~l d~-~gn~rs of aircr~t ~ns~nea ~r.tem~t ~o co~ n the ~plnn l ~g ~od~ ~one~ within the en~lne and ~r~ant th~r proFaga.tion into ~he l~taX~ o~ ~xh~u~t. Quch dee~g~ d~lc~ t~o ~Lo~e ~y cr~t~s~g a ~honomesso~ lcnawn a~
"cut~ f, n o. by d~r~cting th~ n~ r~d~ tonell to l~p~nge on ~h~ w~ ci the intaric~ o~ the engine, wh~ ch 8 lin~d w~th a 3cu~d ~h~_yti~re mater~Al . Th~ techssic~us ~0 c~use~ the sFins~in~ moto tonea to decay be~oro exitin~ th~
~ngine. ~ onr~en~ly, ~he current ~tate o~ ~hs art t~actles away ~om F~ rpoJ~fully c~r-~c~ing Jpinn~ ng mcde tone out ~e ~ n'cake or eYh~u~t of a turbaenginl~ .
u.X. patent ~pecificat~t~n ~B 1, ~71, ~5 teache~ a is nolc~e a~atemant method and apparatu~ ~or a tur~ir~e ~ngine wherein ~he number o~ blades ~r~ ~rane~ are ~elected to attenuate ~hq~ e~ect o~ the ~ound produced upon a human ob~er. One em~o~i~ent o~ ch a3~ eng~n~ ha~ the num~er cf v~ne~ being twice the nu~r o~ ~ladeE~ time~ the 20 de~irQd hannon~c t~ be ~uppre~ed . German patent DE -A- 1 403 576 teachee the u8~ ol~ eound ~baorbing ~naterial in a turl~lne ~gine.
~ e~2 ~a~Jcy~ound ma~e~ial, no~ rel~ nt ~o ~he n c~ airc~ t ~nsJln~, bue rol~v~r~t to th~ curren~
25 iswont~n, conc~rn- duct ~yst-m~ uc~ ~y-~e~n~, such a~
tho-- ~n ~ nduJtri~ ch~ nen~, typicaLly h~v~ bends ~o ~ir-ct ~s-lcw. When pr~-curi2ed ai~ ~1 ow- ~hr~ugh ~uch 4~n~-, a p~-~ur- d~op occur~. ~o ~11~ ata thl~ prohlem.
~om dc~ gn- F~J~ t~o~ turnins vanc~ w~t~i~s th~ ~uct bends .
30 S~ch van~J ~ zo pro~our~ ~ro~ ~cro~ th~ b~nd~ ~nd ~rovlde ~mooth air ~lo~, thuJ ~ cins~ the a-rodyna~nic o~nc~ oi upctro-m o~ do~n~Jtre~m l-~h;~ery. ~owev~, e~-- p~ ~e~ st o~ th~ v~n~ ~ieh~ n ~hc ~nt- ha~ noc ~en u~d to ~ nr- t~ ~ound, ~ nu~ti on c~pability of ~he 3 s d~c~ .
AMENDED SHEET
A 22376 1 1 ' ~ r lY~ '~ cc! 41cb'4~'-c'o'~ ~ 1998-O5-13JL~L l'~U~
WO 9~~~ ~ u~96117~3 -- 2~ --Mcreolter, althcugh ~he ccm~in~tion ~ turn~ng ~ran~J and duct ~ndJ h~ not b~cn u-es~ to atten~late nolse oth-r me~nJ ha~ n uJad t~ att~nua~ noi~ within a ~uct. F~r exa~ , du~t branehe- h~ n u~d ~o S a~te~suat~ ~om~ ~ t~ ne~ . Such a d~ n c~ rect~ ~om~ of ~c~ nol~o throush a br~ch that ~cngthe:~- t~ ~ath c~ ~he ~n~ tr~ n~ thr~u~h ~he br~nch. l~y Yelecting the r ~ranch l-nst~, th- 5r~neh noi~e r~join~ tha main ~sct noi~ 180 degr~ OUt C~ pha~. Con~a~u-ntly, a 10 p~r~c~on o~ t~ no~ ~ can~ out . How~ver, ~dln~ t~e as~dlt~on~ to branc~ eh- ~ound i~ c-umb~r~oma as~d dQes AMEi~lDED SHE~T
_ _ _ CA 02237611 1998-0~-13 W O 97/18396 PCTrUS96/17223 not take advantage of the bends in the duct necessary to control the airflow.
SUMMARY OF THE lNv~NllON
In a typical turbomachine, there is a number B of circumferentially spaced rotor blades, a number V of circumferentially spaced guide vanes axially adjacent to the rotor blades, an annular chamber surrounding the rotor blades, and an intake and exhaust for receiving and discharging air that passes through the annular chamber.
When the turbomachine is in operation spinning mode tones are generated by the interaction of the rotor and guide vanes. According to the present invention, these tones are minimized by selecting the number of vanes V relative to the number of blades B such that the propagation path of substantially all of the harmonics of the spinning mode tones is substantially axial to the annular chamber intake and exhaust. A sound absorptive material is positioned perpendicular to the propagation path of the spinning mode tones such that the tones impinge thereon and are attenuated thereby. In a preferred embodiment, the sound absorptive material is placed in the intake of the turbomachine.
Such machines are usually coupled to ducts through which the air flows. In addition to the air flow, the spinning mode tones generated by the turbomachine tend to travel through these ducts. According to the present invention, a tuned duct is positioned in the path of the spinning mode tones. This tuned duct is connected to either the intake or the exhaust, or both, of the annular chamber and has a radial bend that forms a partial circle with an arc of ~ radians. A number of turning vanes are concentrically spaced within the bend, with each turning vane being spaced a distance D from each adjacent turning vane. The distance D is related to the arc ~ of the radial bend and the frequency of the spinning mode tones. The turning vanes, thus placed, effectively cancel a plurality _ CA 02237611 1998-0~-13 W O 97/18396 PCTrUS96/17223 of the harmonics of the spinning mode tones travelling through the duct. In a preferred embodiment, the relationship between the distance D and the arc ~ is chosen to cancel only the odd harmonics of the spinning mode S tones.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which ~orm a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed description of the preferred embodiment, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed.
In the drawings:
FIGURE 1 illustrates, in simplified form, a cross section of a turbomachine and associated duct system and depicts a preferred embodiment of the spinning mode tone sound attenuation system of the present invention.
FIGURE 2 is a partial view of a turbomachine illustrating the rotor blades and guide vanes thereof.
DET~TT~Rn DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein like numerals indicate like elements throughout, FIGURE 1 depicts an industrial turbine system 10 including the sound attenuation features of the present invention. Turbine CA 02237611 1998-0~-13 W O 97/18396 PCTrUS96/17223 system 10 includes an intake duct 12 for supplying an intake stream of high pressure gas, and an intake manifold 14 for supplying the gas to the turbine 16. The intake manifold 14 features an sound absorptive surface 18. The high pressure gas is routed through a set of circumferentially spaced intake guide vanes 20 and to a set of circumferentially spaced rotor guide blades 22, which are surrounded by an annular chamber 30. The high pressure gas then exits through the exhaust system 24.
The interaction of inlet guide vanes 20 with rotor blades 22 as well as other guide vane rotor blade sets (not shown) generate spinning mode tones. These spinning mode tones are periodic pressure patterns that spin about the turbine axis 34, and are perceived as noise to the human observer. These pressure pulses have zero or more lobes relative to the number and rotation speed of the rotor blades 22 as well as the number of inlet guide vanes 20. When the pressure pulse has zero lobes then a zeroth order spinning mode has occurred. The number of rotor blades 22 multiplied by the rotor speed is the fllnA~mental, or blade-pass frequency, of the spinning mode tones. When a combination of inlet guide vanes 20 and rotor blades 22 are selected such that the number of lobes in the spinning mode is zero then harmonics of the spinning mode tones propagate parallel to the turbine axis 34 and out of the turbine 16. The number of lobes can be determined by the equation:
N= ' m-B+k V';
where:
m is the harmonic and can take on any integer - 30 value from 1 to infinity;
B is the number of rotor blades;
k is an index that ranges over all integer values from - infinity to +infinity; and, V i8 the number of stationary guide vanes.
CA 02237611 1998-0~-13 W O 97/18396 PCT~US96/17223 Thus, N is equal to zero for a particular blade count B, a particular inlet guide vane count V, and a particular harmonic m.
Referring also to FIGURE 2, the zeroth order 8p; nn;ng mode can be forced to occur when there are an integer number of inlet guide vanes 20 relative to the number of rotor blades 22, or when an integer number times the number of inlet guide vanes 20 is equal to an integer number times the number of rotor blades 22, i.e. when I m*B
= ~k*V¦ and k and m are both integers. The zeroth order sp; nn; ng mode can be forced to occur at all harmonics of the blade-pass frequency when the number of inlet guide vanes 20 equals the number of rotor blades 22.
Alternatively, if the number of inlet guide vanes 20 selected is equal to twice the number of rotor blades 22 then the zeroth order spinning mode occurs only on even harmonics of the blade-pass frequency. In the preferred embodiment, twice the number of guide vanes 20 relative to the number of rotor blades 22 is selected. Thus, the even harmonics of the blade-pass frequency are propagated substantially along the turbine axis 34 and into the intake manifold 14.
A sound absorptive material 18 is placed perpendicular to the propagation path of the spinning mode tones. Preferably, as illustrated in FIGURE 1, this sound absorptive material 18 is attached to the inside of the intake manifold 14. As a result, the selected harmonics of the spinning mode tones impinge at a perpendicular incidence upon the face of the sound absorptive material 18. The sound absorptive material selected i5 preferably a bulk absorber with absorption coefficient of .99 or greater. For example, the bulk absorber selected may be fabricated from mineral wool, fiberglass, or ceramic fiber.
As a result of the harmonics impinging on the sound absorptive material, the sound levels of the zeroth order mode will be reduced by approximately 20 dB or greater. To a lesser degree, sound attenuation of modes other than the CA 022376ll l998-0~-l3 W O 97/18396 PCTrUS96/17223 zeroth order mode will occur, but the effectiveness will decrease as the sound propagates into the material at grazing incidence.
The harmonics not absorbed by the sound ab~orptive material 18 will generally propagate out of the intake manifold 14 and out through the intake duct 12.
According to the present invention, a tuned duct section 32 is placed in the path of the remaining harmonics. To attenuate these harmonics, turning vanes are fixed in the tuned duct 32. As the rem~;nlng harmonics propagate back through the intake duct they will turn through the duct bend 28 and pass through the turning vanes 26. By controlling the spacing between these turning vanes 26 relative to the radius of the duct bend 28 the remaining harmonics (primarily the odd harmonics) can be effectively attenuated. The confined path of the remaining harmonics, defined by each of the turning vanes 26, forces the harmonics to travel increased distances for each of the larger radius turns. The harmonic at each path defined by the turning vanes 26 will be 180 degrees out of phase with the identical harmonic travelling through an adjacent path when the turning vane spacing is selected to be equal to:
l.SA.
~ ' where:
~ is the arc of the turn in radians; and, A is the wavelength of the fnn~m~ntal harmonic.
The turning vanes 26 will each be a partial circle defining the arc ~ and each successive turning vane 26 will increase in radius by:
n 1 ~A;
where n is the vane number.
The duct bend 28 and turning vane 26 combination will cancel all odd harmonics (1, 3, 5, etc.) while providing no benefit at the even harmonics (2, 4, 6 times, CA 02237611 1998-0~-13 etc.). However, tonal noise sources, such as spinning mode tones, typically have peak frequencies at the flln~mental harmonic with decreasing sound levels as the harmonics increase. By at least cancelling the odd harmonics, which include the fl~n~mental harmonic, a significant effect on the sound level is accomplished. Moreover, the sound absorptive material 18 will have effectively attenuated the even harmonics before they reach the duct bend 28. While the preferred radius of the duct is 1.5 radians, Applicant recognizes that manufacturing constraints may dictate that a 90 degree bend is used with a corresponding radius of ~/2.
The turning vanes 26 can be designed to also cancel some of the even harmonics by selecting the distance between turning vanes to be:
0.751 This design will provide partial cancellation at harmonics 1, 2, 3, 5, 6, 7, 9, 10 times, etc. of the blade-pass frequency. The partial cancellation will occur at all odd harmonics and every other even harmonic.
In the preferred embodiment, all of the components are optimized to provide a system that effectively cancels all harmonics of the spinning mode tones. In such an embodiment, the vane/blade ratio and sound absorptive material 18 are optimized to attenuate the even harmonics; whereas, the tuned duct 32 is optimized to attenuate the odd harmonics. To accomplish this system, the number of inlet guide vanes 20 selected is twice the number of rotor blades 22 selected. For example, in a turbomachine with nineteen rotor blades 22, thirty-eight inlet guide vanes 20 are selected. This combination directs the even harmonics substantially parallel to the turbine axis 34. A bulk absorber 18 is then placed in a path perpendicular to the even harmonics. This arrangement, while effectively attenuating the even harmonics, does very little to attenuate the odd harmonics.
CA 02237611 1998-0~-13 W O 97/18396 PCTnUS96/17223 Thus, the odd harmonics continue through the duct system 12. The tuned duct 32 placed in the path of the odd harmonics is optimized to attenuate these odd harmonics.
The effect of the entire system is to cancel substantially all of the harmonics of the spinning mode tones.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.
~ J3~S~
Claims (10)
1. A turbomachine assembly (10) having a number v of circumferentially spaced rotor blades (22); a number v of circumferentially spaced inlet guide vanes (20) axially adjacent to said rotor blades (22); and an annular chamber (30) surrounding said rotor blades (22) and said inlet guide vanes (20) and having an intake for receiving.
air and an exhaust for discharging air, said rotor blades (22) and inlet guide vanes (20) generating spinning mode tones when said turbomachine assembly (10) is in operation; characterized by:
a tuned duct (12) having a radial bend (28) forming a partial circle with an arc of ~ radians, said tuned duct (12) connected to at least one end of said annular chambers (30);
a plurality of turning vanes (26) concentrically paced a distance D within said radial bend (28) of said tuned duct (12);
said distance D relative to said arc ~ being effective to substantially cancel a plurality of harmonics of the spinning mode tones.
air and an exhaust for discharging air, said rotor blades (22) and inlet guide vanes (20) generating spinning mode tones when said turbomachine assembly (10) is in operation; characterized by:
a tuned duct (12) having a radial bend (28) forming a partial circle with an arc of ~ radians, said tuned duct (12) connected to at least one end of said annular chambers (30);
a plurality of turning vanes (26) concentrically paced a distance D within said radial bend (28) of said tuned duct (12);
said distance D relative to said arc ~ being effective to substantially cancel a plurality of harmonics of the spinning mode tones.
2. A turbomachine assembly (10) as in claim 1, further characterized by said distance D being substantially equal to;
where, .lambda. is the wavelength fundamental harmonic of the periodic sound wave, and n is an integer ranging from 1 to 2.
where, .lambda. is the wavelength fundamental harmonic of the periodic sound wave, and n is an integer ranging from 1 to 2.
3. A turbomachine assembly (10) as in claim 1, further characterized by said arc ~ having a length substantially aqual to 1.5 radians.
4 . A turbomachine assembly (10) as in claim 1, further characterized by said vane number V being selected relative to said blade number B to create a propagation path of spinning mode tones in a patch such that substantially all of at least selected harmonica of the spinning mode tones are oriented substantially axial to said annular chamber intake and exhaust.
5 . A turbomachine assembly (10) as in claim 4, further characterized by a sound absorptive material (18) having a face disposed within said propagation path of said spinning mode tones and said face being positioned perpendocilar to the propagation path of said spinning mode tones to absorb the tones impinging thereon.
6. A turbomachine assembly (l0) as in claim 5, further characterized by said sound absorptive material is one of mineral wool, finerglass, and ceramic fiber.
7. A turbomachine assembly (10) as in claim 1, further characterized by said vane number V being one.
substantially equal to an integer multiple of said blade number B.
substantially equal to an integer multiple of said blade number B.
8. A turbomachine assembly (10) as in claim 7, further characterized by said integer multiple being one.
9. A turbomachine assembly (10) as in claim 1, further characterized by said integer multiple being two.
10. A turbomachine assembly (10) as in claim 1, further characterized by said selected harmonics being substantially all even harmonics of the spinning mode tones.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/557,641 | 1995-11-14 | ||
| US08/557,641 US5709529A (en) | 1995-11-14 | 1995-11-14 | Optimization of turbomachinery harmonics |
| PCT/US1996/017223 WO1997018396A1 (en) | 1995-11-14 | 1996-10-28 | Optimization of turbomachinery harmonics |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2237611A1 true CA2237611A1 (en) | 1997-05-22 |
Family
ID=29406026
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2237611 Abandoned CA2237611A1 (en) | 1995-11-14 | 1996-10-28 | Optimization of turbomachinery harmonics |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2237611A1 (en) |
-
1996
- 1996-10-28 CA CA 2237611 patent/CA2237611A1/en not_active Abandoned
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