US2382842A

US2382842A - Gas turbine

Info

Publication number: US2382842A
Application number: US468917A
Authority: US
Inventors: Joseph S Alford
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1942-12-14
Filing date: 1942-12-14
Publication date: 1945-08-14
Anticipated expiration: 1962-08-14

Description

Aug. 14, 1945. J, ALFQRD 2,382,842

GAS TURBINE Fi18d'D80*.-'l4, 1942 Inventor: Joseph S- AHoTd,

y czsAttcrhey.

Patented Aug. 14, 1945 rrso STATES PArE r orrics I are! Electric Company, a corporation or New York Application December 14, 19412, Serial No. 668,917

4 Claims.

The present invention relates to gas turbines. It is especially useful in connection with turbosuperchargers for aircraft wherein'the turbine is operated by exhaust gases from an internal combustion engine and it 'isthis application of my invention which I have elected to illustrate and describe, It is to be understood, however, that this is only by of example.

In connection with turbosuperchargers, it is known to provide means to effect circulation of cooling air across what may be termed the entrance side of the turbine wheel, i. e., the side of the wheel on which the nozzle box and nozzles are located, the cooling air beingsupplied adjacent to the center of the wheel and flowing radially outward along thesurface of the wheel.

In certain applications, it is important that air be prevented from leaking into and becoming mixed with the gases being supplied to the turbine buckets as this results in the burning of any unconsumed fuel in the gases, termed usually after-burning.

The object of my invention is to provide an improved construction and arrangement in va gas turbine for preventing leakage of cooling air supplied to the entrance side of the wheel into the gas stream as it flows from the nozzles to the buckets of the turbine wheel, and for a consideration of what I believe to be novel and my inven tion, attention is directed to the following speciiication and to the claims appended thereto.

In the drawing, Fig. l is a sectional view of a gas turbine (in the present instance the gas turbine oi a turbosupercharger) embodying my invention; Fig. 2 is a diagram, and Fig. 3 is a detail view of a modification.

Referring to the drawing, Figs. 1 and 2, 5-inchcates a bearing housing in which ls located a bear- Q ing, not shown, for the turbosupercharger shaft d. Overhung on the end of shaft 6 and suitably attached thereto by bolts l is a turbine wheel comprising a hub 8, a web Q, a rim ill and a ring of buckets it. Surrounding bearing housing 5 in spaced relation thereto is an annular nozzle box i2 which carries a ring of nozzles It which direct exhaust gases from the nozzle box to the ring of turbine buckets. The inlet conduit of the nozzle box is indicated at it). In the case of the usual turbosupercharger, there is provided also in connection with the nozzle box a wasteconduit in which is located'a; waste gate valve for regulating the flow of exhaust gases to the turbine wheel.

A turbosuper- 6, 19 42, and assigned to the same assignee as the instant application. At is a curved baflle plate located between bearing housing 6 and the nozzle box which serves side of the wheel. The arrows A indicate the di-= rection of air flow toward the wheel and the arrows B indicate the direction of the air away from the wheel. Usually, the cooling air is taken m from the slip stream of the aircraft, flowing down across the bearing housing to cool the bearing, thence along the entrance side of the wheel and out as indicated by the arrows B.

The construction so far described is a known 5 one and is to be taken as typical of any suitable gas turbine.

When such a gas turbine is operating, the gases are discharged through the nozzles against the turbine buckets at a high velocity. It, as indicated 20 at the upper portion of Fig. l, the radially inner ends or the'roots of the buckets H, or in other words the outer peripheral surface of rim ihlie radially beyond the radially inner ends or the roots of the nozzle partitions, gases issuing from the radially inner portion of the nozzles impinge against the outer radial portion of the rim tending to build up a pressure and efiect a flow of gases radially inward along the entrance side of the rim and web of the wheel. On the other hand, if the radially inner ends or roots of the nozzle partitions are radially beyond the radially inner ends or roots of the buckets as indicated at the lower portion of Fig. 1, then the exhaust gases in discharging across the space between the nozzle ring and the bucket ring have an ejector effect which tends to draw air from adjacent the entrance side oi the wheel rim into the gas stream, thus effecting entrainment of air with the gases.

The ideal situation would be one wherein the bucket ring is so located with respect to the nozzle ring that there would be a tendency neither for air to leak into the gas stream nor gases to discharge toward the entrance side of the wheel. In practice, however, this ideal cannot be obtained as because of the impossibility, due to tolerances in manufacture and expansion and contraction dur= ing operation, to maintain this condition. It is desirable to have as little leakage of gas inwardly along the inlet side of the wheel as possibleas any so such leakage detracts from the efilciency of the turbine and also effects heating of the wheel.

According to one embodiment of my invention, Iprovide a sealing ring 58 adjacent to rim id which provides a sealing chamber l9.- I then locate the nozzle box with respect to the turbine wh'eel so that for a portion of the circumference, the radially inner ends of the buckets are radially yond the radially inner ends of the nomle tions while roranother portion, the radially inner to direct the flow of cooling air to the entrance ends of thenozzle partitions are radially beyond the radially inner ends of the buckets. With this arrangement, there is a tendency over a portion of the circumference for gases to be discharged into the sealing chamber lawhileover another portion of the circumference there is a tendency for the sealing gases to be entrained with the main gas stream. The arrangement is such that sumcient gases leak into the sealing chamber it) so that it is entirely filled with gases and a pressure built up therein higher than the air pressure on the radially inner side of the sealing ring iii. As a result, air is prevented from leaking past the sealing rin and being entrained into the gases issuing from the nozzles, any entrainment from sealing chamber i9 being in the form of gases which have leaked into it. With the eccentric arrangement between the nozzle ring and the bucket ring the pressure in the annular sealing chamber is i substantially higher than would obtain it the bucket and nozzle rings were concentric. This is in part due to the building up of pressure in the inner part of some of the nozzle passages which face portions of the rim l0. As the gases h'it said rim portions their velocity energy is substantially converted into pressure energy, causing a substantial flow of gases into the annular chamber I9. On the other hand, no such building up or pressure in the inner part of the nozzle passages takes place over those portions of the nozzle ring which are located radially beyond th'e rim of the bucket wheel. of the blades and nozzles produces a pressure effeet and an ejector effect over equal areas but under different pressure differentials In Fig. 2, the circle 9 indicates the circle of the roots of buckets ll and the circle 2 indimtes the circle of the roots. of the nozzle partitions. Circles l and 2 may be termed the root circles of the bucket ring and nozzle ring, respectively. similar points are indicated at l and 2 in Fig. i. As will be seen, these circles are eccentric with respect to each other and during operation such eccentricity will be maintained to a greater or lesser extent.

In Fig. 3 is shown an embodiment of my invention wherein instead of providing a gas belt by means of an eccentric arrangement oi the wheel with respect to the nozzles, I utilize the usual concentric arrangement and. obtain a gas belt by providing a number of circumferentially spaced passages 20 which connect the interior of the nozzle box to space l9, leakage through passages 26 serving to maintain sealing chamber is filled with as.

My invention finds especial utility in instances where a portion of a nozzle ring is blanked off as in the case of partial admission, that is, where the nozzle ring occupies less than 360, or in the case where a cruising valve is employed to ren- 1 der a part of the nozzles inactive since this pro: vides an inactive are adjacent to an active arc wherein the discharge of gases from the active arc has an ejector action on the adjacent inactive arcbe arranged to have a close clearance with the wheel rim l 0, thus serving m minimize leakage of hot gases from sealing chamber 19 into the cooling air stream that flows radially outward along th face ofthe wheel.

' In accordance with the provisions 0! the patent statutes, I have described the principle of operation oi my invention, together with'the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

i. In combination, a nozzle box having nozzles, a turbine wh'eel having a ring of buckets which receive actuating fluid from the nozzles, the root circles of the nozzle ring and the bucket ring being eccentric. an axially extending sealing ring supported on and sealed to thenozzle box and forming a close clearance with the wheel rim and defining with the adjacent portions of the nozzle box and. wheel rim a sealing chamber radially 111-.

ward of the nozzle ring and adjacent to the rim of the wheel.

In other words, the eccentricity 2. in combination, a nozzle box having nozzles, a turbine wheel having a rins oi buckets which receive actuating fluid from the nozzles, an axially extending sealing ring carried by and sealed to the nozzle box and forming a close clearance with the wheel rim and defining with adj aoent portions of the nozzle box and wheel rim a sealing chamber radially inward of the nozzle rinse.' and adiacent to the rim or the wheel, and passages connecting said chamber to the interior of the nozzle box whereby there is maintained in said chamber a positive gas pressure.

3. In combination, a turbine wheel having a rim and a ring of buckets carried by the rim, an an nular nozzle box located at one side of the turbine wheel provided with nozzles for directly-l;

gases to the ring or buckets, means for eflectlng flow of cooling air along the surface of the wheel, a' sealing ring carried by the nozzle box having an edge which has close clearance with the wheel rim and defining with the adjacent surface or the nozzle box an annular sealing chamber, and passages in the nozzle box wall for flow of gases Irom the nozzle box to said chamber for maintaining positive gas pressure in said chamber above the pressure of the coolim air adjacent the suriace oi the wheel.

t. A gas turbine for aircraft comprising a bucket wheel having a. web with a rim; and a ring oi buckets secured to the web, means including a bearing for rotatably supporting the bucket wheel, a nozzle box located on one side of the wheel retellally spaced from the bearing and having a ring of nozzles for conducting gases to the ring. of buckets, means for circulating cooling air through the space formed between the bearing and the nozzle box along the inlet side of the web, and

. fluid sealing means between the nozzle box and the'rim to preclude such cooling air from entering the clearance space between the ring of nozzles and the ring of buckets, said sealing means including a, ring having an edge sealed to the nozzle box and another edge closely spaced with the rim, said ring and adjacent wall portions of the nozzle box and the rim forming an annular sealing channel, and means to induce the flow of gases from the nozzle box to the channel to set up a gas pressure therein higher than the pres sure of the cooling air near the web, said last named meansincluding a plurality of nozzles having a root diameter smaller than the adjacent root diameter 01' the ring or buckets.

Jossrn s. ALI'DRD.