GB2110766A - Fluid flow machine particularly a turbine - Google Patents

Abstract

The machine comprises a rotor 10 formed by a pack of axially spaced annular discs 29 divided into two portions 10A, B by a central unapertured plate 30. The latter separates exhaust passages 35A, B so that working fluid supplied by peripheral nozzles 20 exhausts from the rotor at both sides. <IMAGE>

Description

SPECIFICATION A fluid flow machine, particularly a turbine The present invention relates to rotary fluid flow machines and more particularly to turbines.

In U.S. Patent No. 4,036,584 there is proposed a turbine rotor of disc construction comprising discs separated by spiral fences which eliminate both bolting and spoke-like ties to a central clamping shaft, thus eliminating regions of discontinuity caused by bolt holes which lower R.P.M. capability due to excessive centrifugal local stress concentrations.

According to the invention, there is provided a turbine including a casing, a rotor journalled for rotation in said casing, said rotor being circular and fitted within the casing with a plenum being defined around the outer rotor circumference, fluid entry means into said plenum, and nozzle means located adjacent said outer circumference, said rotor comprising a pack of spaced-apart discs that define fluid entry means in said circumference, central exhaust holes in said discs that form substantially unobstructed fluid exhaust exits at opposite sides of said rotor, said pack comprising two portions that are separated by a central solid disc that divides the flowing fluid into two oppositely flowing exhaust streams, said pack portions being connected to respective drive shafts at opposite sides of said casing.

Further according to the invention, there is provided a rotary fluid flow machine, comprising an inlet and outlet for working fluid and a rotor comprising a pack of axially-spaced annular discs having fluid inlet means at the outer circumference and fluid outlet means at the inner circumference, the pack being divided axially by a central solid disc which divides the outflowing fluid into two streams flowing axially through the center of the rotor in opposite directions.

Constant thickness discs fail at R.P.M./diameter relations much lower than those attained by conventional bladed turbine rotors in identical material specifications because a bladed rotor is tapered outwards parabolically from the hub thus providing approximately constant stress from boss to perimeter. In a preferred embodiment to be described improved results are obtained by providing hollow discs from the outside of the hub rim to disc perimeter where the hollow void is sealed by a circumferential band or hoop tying front and back faces.

This composite disc hollow construction can also be very advantageously applied to the aperture-free, center which directs the forward and aft flow of the turbine fluid because the additional structural strength thus obtained reinforces the disc packs fore and aft to which it attaches.

Embodiments of the invention will now be described, by way of example only, with refer- ence to the accompanying drawings, in which: Figure 1 is a perspective view, partly in section, of a turbine in accordance with the present invention; Figure 2 is a longitudinal section of the turbine; Figure 3 is a side elevation of the turbine taken on lines 3-3 of Fig. 1; Figure 4 is an elevation showing the turbine disc structure; Figure 5 is a section showing a modified disc; and Figure 6 is a section of two neighbouring discs with modified outer edges.

In U.S. Patent No. 4,036,584, a shaftless turbine rotor is described in which discs are separated from one another by spiral fences that guide motivating fluid towards a central exhaust opening.

The preferred embodiment of the present invention consists of a turbine in which a rotor disc is split into two portions by a central solid plate so that motivating fluid is exhausted from the center of the pack in relatively opposite directions. Each pack portion is connected to a respective shaft journalled in the turbine casing and the shafts preferably terminate adjacent the outer ends of the pack leaving central exhaust openings unobstructed. A stationary ring nozzle surrounds the rotor discs and directs motivating fluid between the discs' outer peripheries. Inner fences between the discs separate neighbouring discs and provide ties between the discs. The fences guide fluid to exhaust passageways and afford additional surfaces for motivating fluid.

In Fig. 1, the turbine 1 has at each end, a vacuum end casing support 3 with a housing portion 5 that is formed of two segments 4 and 6 and diametrically opposed fluid entries 7 at the flange joint 9 (Fig. 3). The entries 7 can be pipes tangential or normal to the casing surface. Only one end casing support 3 is shown for clarity. Also, the structural details of one end of the rotor end connections are shown in Fig. 1. The rotor assembly includes a rotor 10 with stub shafts 11 and 1 2 that are journalled to cones 14 and 1 5 of the segments 4 and 6, respectively. The cones 1 4 and 1 5 are bolted to apertured end web plates 17 and 18 and inner web plates 21 and 23 house the rotor 10 and ring nozzle 20.

As seen in Figs. 2 and 3, the nozzle 20 is bolted to plates 21 and 23 and preferably includes six segments 25 arranged around the rotor 10 which form six motivating fluid entry convergent/divergent nozzles with throats leading into the rotor. The rotor 10 is made of a pack of spaced-apart discs 29 that are divided into two portions 1 OA and 1 OB by a central solid flat plate 30. The discs 29 are cone-shaped and except for the fencing ar rangement, the same as discs 20 in Fig. 7 of U.S. patent 4,036,584. In the structure shown, flow fences 33 are preferably the only ties between the discs 29. The fences 33 ar curved flat strips located near the central hole 35 of each disc 29 and the holes 35 of the portions 1 DA and 1 OB are aligned to form fluid exhaust passageways 35A and 35B at opposite sides of plate 30.Apertured end plates 22 and 39 for portions 1 0A and 1 OB, respectively, are fixed to shafts 11 and 1 2.

The rotor 10 is sealed by ring seals 41 in plates 21 and 23 to prevent fluid leakage.

The seals 41 can be graphite and spider hubs 43 and 44 in end plates 38 and 39 connect the rotor 10 to shafts 11 and 1 2 while allowing fluid exhaust from passageways 35A and 35B.

The discs 29 in Fig. 4 are similar to the conical discs of 4,036,584 except the fences 33 are relatively short streamlined strips and located near the central openings 35. The fences 33 are brazed, welded or otherwise joined to the neighboring discs 29 and to end plates 38 and 39 so that each disc braces the entire rotor pack and the center plate 30, not having any hole in the highly stressed center results in a superior load carrying capacity.

The absence of clamping holes or bolt holes enables the rotor pack to achieve higher speeds than would be possible otherwise if stress inducing bolts and holes were present.

In Fig. 5, an alternative hollow disc 1 29 is shown which is made from two plates 1 29A and 129B which plates each have one side tapered to an approximate parabolic curve similar to half a conventional turbine rotor disc. The two plates are welded or brazed at their outer perimeters to a band or hoop 1 31 and their inner perimeters to a hub ring 1 33.

The fences are omitted in this Figure.

During use, fluid such as steam or gas enters inlets 7 into the plenum 2 surrounding nozzle 20 and circulates in the plenum in the direction of rotor rotation. The fluid then enters nozzle 20 through the convergentdivergent throats in nozzle 28 formed by segments 25. The motivating fluid next enters the openings between neighbouring discs 29 of both portions 1 0A and 1 OB. The disc's outer edges can be uninterrupted or plain as shown in Fig. 4 or can be serrated as shown in Fig. 6.

In Fig. 6, the discs 229 have serrated openings 229A which are offset from the openings of neighbouring discs. This structure prevents undesirable losses due to poor fluid entry into the disc pack from the nozzle 20 and torque is increased. Fluid leakage at the rotor ends is also reduced because fluid crossflow is prevented.

Fluid in the disc pack is guided by the fences 33, which afford additional surfaces for fluid motivation, the fluid exiting through passageways 35A and 35B in opposite directions.

In my co-pending application filed of even date and entitled "A fluid flow machine, particularly a turbine'' convergent-divergent nozzles with adjustable throats are described and may be utilized herein together with the associated adjusting means. For sufficienty of disclosure, a copy of the co-pending application is included as an annex of this present application.

In the embodiments described, the split flow attained by the solid aperture-free central disc enables greater mass flow capacity without increase in either disc outside diameter or exhaust orifice diameter because effective duct passages are halved and adequate exhaust area is provided at each turbine end in place of conventional single end exhaust turbines.

A low pressure drop at the entry of the turbine is ensured via the plenum which feeds longitudinal nozzle members shaped to form convergent/divergent surfaces thus avoiding abrupt flow direction changes and delivering to the rotor a span-wise continuous flow.

When conical shaped discs are used, longitudinal straight, convergent-divergent nozzle members can be replaced with helical shaped nozzle orifices as considered in turbine side elevational view.

Efficient disc turbomachinery requires that its structure be as compact as possible without sacrifices in energy use, reliability, maintainability and longevity. With the embodiments described all these advantages are attained in greater measure than with previous designs. Turbine or pump size can be reduced by attaining higher R.P.M. while maintaining rotating material stresses well within present limitations. The fluid flow passages are improved and unnecessary pressure losses are reduced.

Claims (8)

1. A turbine including a casing, a rotor journalled for rotation in said casing, said rotor being circular and fitted within the casing with a plenum being defined around the outer rotor circumference, fluid entry means into said plenum, and nozzle means located adjacent said outer circumferences, said rotor comprising a pack of spaced-apart discs that define fluid entry means in said circumference, central exhaust holes in said discs that form substantially unobstructed fluid exhaust exits at opposite sides of said rotor, said pack comprising two portions that are separated by a central solid disc that divides the flowing fluid into two oppositely flowing exhaust streams, said pack portions being connected to respective drive shafts at opposite sides of the casing.

2. A turbine according to claim 1, wherein said nozzle means substantially spans the entire width of said disc pack.

3. A turbine according to claim 1 or 2, wherein said nozzle means comprises nozzles that are convergent/divergent in configuration and said nozzles are secured to said casing to closely surround the rotor circumference.

4. A turbine according to any one of claims 1 to 3, wherein said shafts have inner ends that terminate adjacent the outer sides of said disc pack portion, the outer end discs of said portions comprising support members with apertured hubs that are connected to said shafts.

5. A turbine according to any one of claims 1 to 4, wherein the outer edges of the discs are serrated and the serrations of adjacent discs are relatively off-set from one another.

6. A turbine according to any one of claims 1 to 5, wherein at least one of said discs is hollow and comprises two serrated plates, each circular plate having an outer tapered parabolic surface, the outer edges of said plates being interconnected by a circular band and the inner edges of said plates being interconnected by a hub ring.

7. A rotary fluid flow machine, comprising an inlet and outlet for working fluid and a rotor comprising a pack of axially-spaced annular discs having fluid inlet means at the outer circumference and fluid outlet means at the inner circumference, the pack being divided axially by a central solid disc which divides the outflowing fluid into two streams flowing axially through the center of the rotor in opposite directions.

8. A turbine substantially as hereinbefore described with reference to the accompanying drawings.