GB2316134A - Gas turbine blade tip clearance control device - Google Patents

Abstract

A gas turbine blade tip clearance control device consists of a thermally responsive hollow control ring 24 to which blade shroud segments 27 are attached. Contained within the control ring 24 are a plurality of perforated segments 29 each of which is provided with a separate fluid supply such that portions of the control ring may be expanded preferentially.

Description

2316134 -I l R7T, TC, jT S - c', L.

TT-PBIL' E'- J) r, 1 J1. -!'jrE This invention relates to g-?s turbine engines and more particularly o such engines having a turbine rotor of the unshrouded type.

It is well known that in order for an unshrouded type turbine to operate efficiently the clearance between the turbine blade tips and the adjacent shroud ring structure must be maintained within closely defined limits. The difficulties involved in maintaininj such clenrances have been well known for many years, and t-,e -problem has in fact become worse, as both the size and working temperature of g.s turbine engines has increased.

One of the main factors w-ich must be taken into account when designing a satisfactory arrangement is matching the respective diameters of the cpsing and the turbine at the different temperatures and speeds encountered during the working cycle of the enwine. ecount must also be taken of the differing coefficients of expansion of the materials involved together with the differing stresses imposed upon them together with their different thermal resmonse rate.

it. mu--t also be P.ppreciated tha.t wnilst strivin,7 to maintain the smallest POsTible r,?di-al cle-:)rp.nce between the resDective commonents the design must be such a.s to avoid any interference occuring between the respective components during the differing worlAing cycles to which the engine is subjected to.

In the past many differing desip.ns have been developed to overcome the aforementioned Droblems. In many such designs the shroud ring structure 'mi s been made radially moveable in an attempt to maintain turbine bl,-de tip clearance. Such. movement may be produced by either mechanical, electrical or mneumatic means w7ich are 9.d;,:a..oted to omerate in resronse to sensors arranged to monitor turbine blade t.:Lp clearance. Atern,,.tive types of system have also been devises in which the shroud ring structure is controlled in accordance with the thermal expansion and co--trRction of a control ring.

the Rforpmentioned 1,o,.r-vpr suffer . L - 4" th---- hp-,je nroved e-ith-er to be u--lstable,or their resr)on-e rate IRs no', been sufficiently r--ip-id. ly they h-ve not h:::d the;:bility to m,,int,in;,n adecu..te tip cleprance on 9.11 of the turbine rotor, i.e. tl-.e shroud ring 1-i:?s n,,-t re:rn.ined c.

W ire ulart.

An object of the nresent invention i!- to n-ovice ?. device ccn-rollino R-s turbine blne tip cler-rRrce 3 substantially eliminates the aforementioned problems.

According to the present invention a device for controlling the radial clearance between the blade tips of a gRs turbine engine rotor and a plurality of associated shroud segments comprises, a r4 hollow control ring having located within its hollow interior a plurality of hollow segments which are adapt ed to be supplied with fluid flow, a heat conducting path between the plurality of hollow segments and the control ring allowing the fluid to contiol the temperature of the ring. the fluid servinC to control the diameter of the control rin; by verying its temperrture, whereby the rWal movemen' of the hollow control ring and associated siroud menentR can be maintained substantially equal to that of the tips of the bl?des during at least a part of the engine cycle.

A plurality of sensors which monitor the bOde tip clearance may be troviied adjacent the shroud se,ents and the sensor are sdapt ed to indic-te changes in tip clearance such thpt t he fluil flow into the hollow segments may be adjusted by valve means such as to 2iep7ace the control ring and the associpted sproud sepments.

Alternatively lie fluil flow into the hollow segments mey be varied in accord-nce cith engine throttle movement or other engine parameters.

The fluid supplied to the control ring may comnrise a suvply of air bled from the high pressure compressor section of the J) engine.

Preferably eech of the plurality of hollow segments are perforated such that the fluid impinges upon the interior wall of the hollow control ring to adjust its temperature.

Further mcre, each of the plurality of hollow segments is to provided with two fluid inlets each set of adiRcent fluid inlets . W 4 in adjacent hol7ow serments being CaDted to be supplied with fluid from a common supply.

ERch common fluid supply is provided with valve mepn, such thot fluid flow may be controlled in accordance with the bOde tip clearance monitored edjacent the hollow seeents which are supplied by the supply.

Preferably the blided rotor comprises a ges turbine engine high pressure turbine rotor.

For better understaWing thereof Rn embodiment o' tie invpntion will be more pert iculorly described by way of example only and with reference to the accempanying MwinCs in Mch 4 Figure 1 shows a diagrammatic side view of a gns turbine engine including an embodiment of the Dre!rent invention which is shown in this view in schematic form.

Figure 2 shows a cross-sectional view in greater detail ttken on line 2-2 at Figure 3.

Figure 3 shows a further enlRrged schematic view of the invention taken in direction of Arrow A at Figure 1.

Referring to Figure 1 of the drawings q. turbine engine shown generally at 10 comprises in flow series a fan 12, an 0 intermedin---te pressure compressor 13, a higl- pressure compressor 1L. combustion enuipment 15 a pressure turbine 16, an intermediate pressure turbine 17 and a low pressure turbine 18, the engine terminating in an ex.hA.ust -ozzle 19. The low pressure rotor system, the intermediate rres-ure rotor syster,,ctrd the pressure rotor systeTn,!re epch re-rectively mounted upon the low interr.-7d-iate, and high pressure engine -?in shafts 20, 21.22, ench of which z-te rota.tably supported in be2.rinr,s. A schematic view 23 c-' an embodiment c-' the present invention is arrantyed rpdially outw?rdly c.' the D-re!-sure turbine 16.

The view sl-oAn sche!,,,,'(lically in Figure in.rreter et-..- R- Figure 2. The device com.ur-se5z a 'hollow control rinz 2' which is mounted by Tnepns of a relatliv:-ly flexible axially extending portion 25 to the engine:7!in casing -Portion 26. It will be apprecipted ',hpt u-e of uch a mounting ensures the control ring 24 is rel.t-i'-vely unaffected by either movement, or c'.-ig-nge in tem.,oer-,3ture of tl- c-sing portion 26 ?s it is in 0.?rl.

mech2ncially isolnted from, it. C,-r-ied from the ridielly inner most rortilon of the control rinc. r-re the shroud cer-tier se--T.ent,.:

serve to carry the shroud eEr.e-ts one of is shown -t 27. The shroud sem:ren's 27 are iisposed adjacent the tips of the turbine bl?des one of which is showr it 28 and defines a seiling clep,.rRnce ',!-erebetween. The shroud cerrier:eo_merts one of w-ic- i,: s-own it 27. se--veR to -i,olnte 'te c-ntrol ring 24 from the 'hot ',irb-ne Epses. The control rinr --n,21---sociated structure is witi. -? continxus su7ply of rel;Rtively coal air bl-d from the compressor ecti-on of the engine.

Provided within the hollow control ring 24 is arranged a plurality of hollow segments one of wich is shown a. 29. The segments 29 are sized such as to define a gap 30 bet,,,reen their own outer surface and the hollow interior surface of the control ring 24. The segments 29 Are located within tl.-e hollow control ring 224 by means of upstgnding projections Y,-,n227 etc, formed unon their outer surf,?ces.

Figure 3 of the drawings shows further details of the hollow segments etc., however for t.e sa-ke of clarity the control ring 24 h?s been omitted from this view.

Two fluid supply tubes 33 are arranFred to coirnunic?te with each of the hollow segments. Each pair of fluid supply tubes are arranged to con-.r.unic?te with a common fluid. supply 34 which Tre e-ch supplied with hiL:+. pressure air from the hig,- rressure compressor sect'on of the engine 14. The flow of P:c, fl i- supply 7,4 ma., be adjusted individually by v91ve means not sl-own in'he dr.w-4ngs.

Arr-axiged. bet,.,reen et?ch adj!?cent Pair of ends of hollow seginents 29 R-re Provided sensors 35 whici 7pss.1-1 .irouj?h apertures rrovided within the control ring 24. The:ensors are P-rr2ned to monitor the cealing cleprance between ne, turbine bldes 28 and adjp-cent shroud segments 27. The sensors 35 may comprise either electrical optical, or pneumetic devices which are 2R adatted. to provide an electric;.:;,l sign21 upon a. c-i2.nge in -'the dimension of the blade tip clearance occuring. The electrical Sig-1-.als may therefnre be utilised in adjusting the valve controlling 'the fluid flow witlin the Y-.e-..bers 34, such tha.t the flows may be varied in accordmnce with diferring bl,de tip -JO cleprance conditions to vary the size of the control rinp, 2,4 and -ence displace the sli-oud segments 27.

Alternatively the fluid flow into the control ring 24 -ray r,?ried by u-e of control!,e.--ns which are adp-,oted to re-,-,ct in a.ccordnce with the enFin,- throttlp settings, however it is - U 3 5 cone;iderel '.h:%t J may also be nece-s-?ry to provide 'the bl,ie tip clearance sen,ors 35 to encure -,.IL-r.u:Rte tilD clearance under,-. 11 creratinp- conditions.

6 - As previously stated during the oDerfting cycle of a ga.s turbine engine its components are subjected to changes in both temperature and mechanical stress,both of which c7.a.nge the tip clearance between the turbine blade 28 and the adjacent shroud segments 27. However it is believed thpt by carefully controlling the degree of expansion or contraction to w,ich the control ring ?4 ip subjected it is possible to maintain the tip cleararce within reasonable lim.its during critical n.arts of the eilgine cycle.

Obviously the engine is designed slich that its blade tip clearances are at their minimum size when it is in the cruise condition. However it is also iT-n-port?nt that the engine is running 9s efficiently cs possible n,----t-icul,-rly during the "t,?'&'-.e-off" and "climb" engine conditions.

Cn engine "star'.-ur)?' and subseauent "g--ound.-i.ile" the turbine bla-es,,rill expand due to both thermal expansion and centrifugal 1 0a--4 cearances between nni this tends to close up the rdJal the bl,-n-e tirs 28 anj the shroud segments 227; however sucIn a reduction in clearance can be simply allowed for in the design 2C of th-e engine by suitable sizinrof the rel?tive parts and corr.a't4tble material selection as it is --el:gt-ively unim-:)ortant if the-re Rre large clearances when the engine is cold and stationary.

Various changes in the tu--bine bl-?e tip diameter will P1so occur during other phases of engine operation, such as during acceleration to "t.-,ke-off" Dower; acceleration from "cruise" to "cli!-b" Pn.d --n 19nding from "approach" to "reverse thrust".

-,,irin,- 'ihee phases the shroud se,;,-ents 27 Rnd engine casinE irde-nzo som.e exnnrsior. due to t'-.e=il effects and prer-ure.

However such expansion wouli not P.ro..e to be sufficient to maint-in -7,0 adequate tip clearance without the rrovision of the control ring device.

-'atc'.ine,. the rp-siecti,.,e grc,,rtl-, r%'t".es of the turbine shroud eg:.-.en's 27 to thnt of the turbine bles 28 sui'- zs to r.,int2,in n ac-elptable tip clearpnce (,urir- the "take-off" a.nd "climb" a.' re engine -ycle is achieved by -:tc'-in,- the r-te of expansion of control ring 24 to that of the turbine roor disc Pi.nd bi,de structure.

Such matching is achieved by supplying relatively hot pressurised air from the h-i7h nressure compressor 14 via supply sources 34 such that it passes into the hollow segments 29 and passes through the perforations 36 to impinge upon the internal wall of the hollow control ring 24 such that it expands at substantially the same rate as the turbine 28 and its associated disc etc., the blade tip clearance will therefore remain substantially consistent by virtue of the fact that the shroud segments 27 move in accordance with the control ring 34.

ltrnen the engine ultimptely assures the cruise condition the air flow through the ducts 33 may be significantly reduced, and it is considered that alterngtive supply sources 34 may be terminated comDleltel.

It will be PrTrecipted tli-?t during engine operation each j: tip clearRnce sensor will corstpntly monitor the blade tip cle.--rp..nce in its 4-,.-,rediate locPlity and by means of 9. control system not s'no-wr in the drawings demand const,-.nt::r'.,u.tment c.' l'low t - "ai-n a subst,-nI u d - llhroi-,7h tU-e ducts 3 3 t. o -, n.. i nt ia ly constant bleAe tlip cle-ir-3.nce. By varying. flows of fluid through 2,3 the different Dairs of ducts 33 it is therefore practicable to disT)','.ace a portior of the control ring 24. This c!n hpve rprt.cula- advantages in that under certain operating conditiDns slight eccentricities of turbine to casing or ovality could occur.

Obviously by use of the present invention this problem is tantially overcome.

27, subst It will be aucreci-?ted that tiis spec ific-?t ion oes no', 97ive a comprehensive description of either the npce.-sary control system or cearance sensor 'nowever such devicps are repdily Pvailpble or are not beyond the ability of -:. person skililed in the art RO to desigr.

Claims (9)

1. What We Claim Is:1. A device for controlling the radial clearance between

   the blade tips of a gas turbine engine rotor and a plurality of associated shroud segments comprises, a hollow control ring having located within its hollow interior a plurality of hollow segments which are adapted to be supplied with fluid flow, a heat conducting path between the plurality of hollow segments and 'he control ring allowing the fluid to control the temT)erature of the ring. the fluid serving to control the diameter of the contro ring by varying its temperature, whereby the radial movement of the hollow control ring and associated shroud segments can be maintained substantially equal to that of the tips of the blades during at least a portion of the engine cycle.
2. 2. A device as claimed in claim 1 in which a ulur!ility of sensor which monitor the blade tip clearance are provided adjacent the shroud segments, and the sensors are adapted to indicate charges in tin clearance such that fluid flow into the hollow segments ray be adjusted by valve means such Ps the dispIRce the control ring. and the P.ssociated shroud segments.
3. 3. A device as claimed in cl,-im 1 in wl---ich the luid flow into the hollow segments is varied in accordance with engine throttle movement or ot.-r engine parameters. fluid
4. 4. A device as claimed in any preceding claim in which the J trol ring comprises a supply of air bled from supplied to the con, the high pressure compressor section of t 1 he engine.
5. 5. A device:a.53 cl,:..-,ned in claim 1 in w'--icl-i the plurplity of hollow egments are -.nerfor:.ted such 'Ilaat the fluid im-pinges uron tle interior wall of the hollow control rin,7 tc adjust its temp.T-Pture.
6. 6. A device as elpimed in claim 1 in wich ep..ch of the DlurRlity of hollow segments is provided with two fluid inlets, each set of adjacent fluid inlets in adjacent segments being adapted to be supplied with fluid from a. common supply.
7. 7. A device as cl!?imed in claim 6 in which each common supply is provirled with valve meRns such th-t the fluid T-.i.y be controlled tored adjacent the n --ccord?r.ce vith the blade tip clearance r.r.onit hollow segments wn;-ci:-e supplied by --un-on suprl,,.
8. 8. A device s cla-4-Pd in cl.?im 1 in w,ich tne '--'.,ded rotor corp.,?r-ises.,. turbine engine hif7h pressure turbine rotor.

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9. 9. A device for controlling the radial clear2nce between -the blade tips of a gas turbine engine turbine rotor and a plurality W of associited shroud segments as claimed in any preceding claim t and substantially as hereinbefore described by way of example only and with reference to the accompanying drawings.

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