US3452782A - Fluid discharge casing - Google Patents

Description

y 1969 G. w. SCHEPER, JR 3,452,782

' FLUID DISCHARGE CASING Filed July 8, 1965 FIG. I

(PRIOR ART) FIQZ INVENTOR: GEORGE W- SCHEP ERJR.

ms ATTORNEY-T;

United States Patent 3,452,782 FLUID DISCHARGE CASING George W. Scheper, Jr., Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed July 8, 1966, Ser. No. 563,812 Int. Cl. F16d 1/00, 1/12 US. Cl. 138-37 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to casings for the flow of gases or vapors. More particularly, it relates to casings for the passage of Working fluid from a large heat engine such as a gas turbine.

It is common in the gas turbine art to let out exhaust gases or compressor discharge air in a regenerative cycle at locations spaced radially as well as axially from the working members of the machine. Due to limitations of space, etc., it is not always practical to have the air discharge and the gas exhaust casings perfectly coaxial with the turbine. Thus, it is common to use an exhaust or discharge system or turning hood to conduct the fluid therein to a more remote location.

For purposes of description, the present invention will be described as it applies to a gas turbine exhaust casing, but it should be understood that the same principles and the same invention will apply as well to the compressor discharge casing. The exhaust turning hood is that conduit which receives the turbine exhaust gases and changes their direction of flow. The turning hood includes the axial turbine discharge annular diffusing passage and the duct into which the annular diffusing passage discharges. With such a turning hood, there is within a gas turbine exhaust annulus, an inherent pressure variation in the bucket exit plane and parallel planes immediately downstream of the last stage turbine buckets. That is, within the discharge annulus, there is lower gas pressure on that side of the annulus toward the direction to which the turning hood directs the gases and a higher gas pressure in that part of the annulus away from the direction of turning. This pressure differential produces a bucket vibration stimulus, one per revolution, in the turbine rotor, which could be undesirable depending on its amplitude. The present invention is useful in substantiallyreducing the amplitude of this stimulus.

Accordingly, it is an object of the present invention to provide a gas turbine compressor discharge or turbine exhaust casing with improved uniformity of fluid pressure within its annular passage.

Another object is to provide a gas turbine having compressor discharge and exhaust casings which substantially reduce the blade or bucket vibration, causing stimulus inherent in prior art casings.

Other objects, advantages and features of the present invention will become apparent from the following description of one example thereof, when taken in connection with the accommpanying drawing.

Brieflly stated, the present invention is practiced in one form by a gas turbine exhaust annulus discharging into a turning hood. At intermediate points between the inlet and the end of the exhaust diffusing annulus are circumferential slots through the outer wall thereof. The

circumferential slots each communicate with an annular manifold situated radially outside of the exhaust annulus. This provides an additional communication path between opposite sides of the exhaust annulus. The resulting boundary layer removal in the higher pressure region and added flow therein causes correspondingly decreased flow in the lower pressure region for the purpose of improved uniformity of pressure therein.

Referring now to the drawing:

FIG. 1 is a longitudinal elevation of a gas turbine exhaust system typical of the prior art.

FIG. 2 is a longitudinal elevation of a gas turbine exhaust system according to the present invention.

In FIG. 1, a turbine rotor 2 is partially shown, carrying its last stage rotor buckets 4 thereon. Rotor buckets 4 project radially into path 6 of the turbine working fluid, which path communicates with and discharges into annular diffusing exhaust passage 8. Exhaust passage 8 is coaxial with turbine rotor 2 and typically comprises a cylindrical or conical inner wall or shell 10 and a conical outer wall or shell 12. The flow area increases in the direction of flow to provide a diffusing passage which produces a substantial pressure rise, thereby recovering some of the kinetic energy leaving buckets 4.

At its outer extremity, annular exhaust passage 8 discharges into exhaust duct 14, which may extend in any direction necessitated by space requirements, thus effecting the turn from axial flow. Exhaust duct 14 is defined by duct casing 22. Inner and outer shells 10 and 12, and exhaust duct 14 comprises a turning hood. In this exhaust arrangement, typical of the prior art, there is a pressure differential within the annular exhaust passage 8 immediately downstream of the last stage rotor buckets 4 such that, in the area designated as L, the gas discharge pressure is lower than at the opposite side of the annulus in the area designated H. This is the pressure differential of the prior art to which the present invention is directed.

Referring now to FIG. 2, wherein like numbers refer to like elements in FIG. 1, the conical outer shell 120 of the annular exhaust passage is modified as compared to the shell 12 shown in FIG. 1, by providing, at spaced axial positions, annular circumferential slots or apertures 16 through the conical outer shell 120. Annular exhaust passage 80 communicates by way of slots 16 with annular manifolds 18 which surround the conical outer shell and are defined by partitions 20. Slots 16 may or may not totally surround the outer shell 120. Manifolds 18 might also be positioned radially inward of passage 80. There are as many annular manifolds 18 as there are slots 16, and manifolds 18 do not directly communicate with each other. The undescribed remainder of the structure of FIG. 2 is the same as that described in FIG. 1.

The operation of the present invention will best be understood by reference again to FIG. 1 as a starting point. In steady state operation of the turbine represented in FIG. 1, there will be a lower gas pressure in the area designated L than that in the area designated H within annular exhaust passage 8, this being the unmodified exhaust passage of the prior art. This pressure differential persists as an inherent pressure variation during operation of the turbine, and is inherent in all types of turning hoods due to the change in direction of fluid flow. Now, imposing this condition as a reference point on the exhaust system shown in FIG. 2, the operation is as follows:

Higher pressure discharge gas from that part of the exhaust annulus 80 in the region designated H, flows through slots 16 into annular manifolds 18. The gas flows inside the manifolds 18 around to the other side of the manifolds near the low pressure region L The flow leaves manifolds 18, reentering annular duct 80 due to the lower pressure therein. This flow, through slots 16 and annular manifolds 18, is of course a small proportion of the total gas flow, the bulk of it continuing straight through annular exhaust duct 80 and turning into exhaust duct 14. The slots 16 and manifolds 18 create a secondary flow from the high pressure region to the low pressure region, thereby improving the diffuser action in the high pressure region due to removal or suction of the low momentum fluid of the boundary layer. In addition, due to the fact that there is entry of gas flow from mani folds 18 through slots 16 in the low pressure, L region, thus interfering with direct exhaust flow in that region and diminishing the diffuser action there, the direct exhaust flow in the low pressure region is slightly reduced. Thus, with exhaust flow in the H high pressure region slightly increased and exhaust flow in the L low pressure region slightly decreased, the tendency to equalization of flow is also a tendency toward equalization of pressure. In practice, it has been found that the pressure variation, or differential between H and L regions, resulting from the use of the present invention is on the order of A to /2' of the pressure variation between the H and L regions of an unmodified exhaust system, as in FIG. 1. To that extent, then, the undesirable effect of the bucket vibration stimulus, occuring at a fundamental frequency of once per revolution, is decreased or modified by a factor of A to /2 It will be apparent that the above-described invention has necessarily been described in one environment, that being in an exhaust turning hood. The present invention is equally applicable to other environments such as, for example, compressor discharge turning hoods, where the same pressure differential phenomenon occurs. Furthermore, the number of slots 16 and annular manifolds 18 is variable according to the size of the machine, the configuration of the hood, etc.

It may occur to others of ordinary skill in the art to make modifications of the present invention which will lie within the concept and scope thereof. Accordingly, it is intended that the invention be not. limited by the details by which it has been described but that it encompass all within the purview of the following claims.

What is claimed is:

1. A fluid turning hood comprising:

an inner shell and an outer shell substantially defining an open-ended annular diffusing flow passage therebetween,

a casing defining a duct in communication with said annular passage at one end thereof,

said duct angularly disposed relative to said annular passage, and

conduit means external to said annular passage providing communication between diametrically opposed portion thereof.

2. A fluid turning hood according to claim 1 in which 4 said conduit means comprises an annular manifold disposed circumferentially around said outer shell, said outer shell defining an aperture effecting communication between said manifold and said annular passage, said aperture being the sole opening of said manifold.

3. A fluid turning hood according to claim 2 further including a plurality of said annular manifolds and said apertures, said manifolds in separate and sole communication through said apertures with said annular flow passage.

4. A fluid turning hood according to claim 2 in which said aperture is continuous, extending circumferentially between said annular passage and said manifold.

5. An annular passage adapted to be disposed in communication at one of its ends with an annular workingfluid path of a turbomachine,

said annular passage surrounded by a manifold,

a circumferential aperture in the outer wall of said annular passage effecting communication between said passage and said manifold,

said annular passage communicating at its other end with a duct defining a flow passage disposed at an angle relative to the axis of said annular passage.

6. A turning hood for fluids in which annular fluid flow made to change its direction sustains a pressure differential in corresponding locations around the annulus, fluid pressure within the first side portion of the annulus toward the turn being generally lower than fluid pressure within the second side portion of the annulus away from the direction of turn, comprising:

an inner shell and an open-ended outer shell substantially defining said annulus therebetween,

an annular manifold disposed circumferentially relative to said annulus, and

means between said manifold and said annulus to effect communication between said manifold and said annulus on at least the first and second side portions thereof.

References Cited UNITED STATES PATENTS 2,666,453 1/ 1954 Davidson 13837 2,781,057 2/ 1957 Fletcher 138-39 2,948,148 8/ 1960 Anfreville.

FOREIGN PATENTS 94,591 1/ 1963 Denmark.

SAMUEL ROTHBERG, Primary Examiner.

US. Cl. X.R. 253-39

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