US2652227A - Turbine - Google Patents

Description

p 1953 s. K. w. BOESTAD EIAL 2,652,227

TURBINE Filed Jan. 25, 1947 4 4 T i g m FIG. I

Patented Sept. 15, 1953 TURBINE Gustav Karl William Bo dor Immanuel Lindha Marble, New York,

Wis., trustees estad, Lidlngo, and Teogen, Stockholm, Sweden, assignments, to Jarvis N. Y., Leslie M. Westfield, N. J., and Percy H. Batten,

C. Merrill, Racine Application January 25, 1947, Serial No. 724,278 In Sweden November 26, 1946 7 Claims.

The present invention relates to turbines and has particular reference to elastic fluid turbines. More particularly, the invention relates to multiple stage turbines, and still more particularly it relates to such turbines in which at least the major part of the energy of the motive fluid is extracted by reaction and which are ordinarily classified as reaction turbines.

It is characteristic of turbines that a certain amount of leakage past the ends of the blades of a blade ring is unavoidable in the case of any blade ring mounted on one part of the turbine between which and another part of the turbine there is relative rotation. Thus in the case of an axial flow turbine, there is leakage past the outer circumference of the rotor blade rings and the stationary casing or stator. Likewise there is leakage between the inner circumference of the stationary or guide blade rings carried by the stator and the adjacent part of the rotor. Similarly, there is leakage past the free ends of the blade rings of a radial flow turbine of the Ljungstroms type and the disc or rotor carrying the rings of oppositely rotating blades.

The motive fluid leaking past any such blade ring flows to and through the next succeeding ring, but as will hereinafter be more fully explained, this fluid has diiferent flow characeristics than that of the main body of fluid discharged from between the blades of the ring and has a deleterious effect on the flow of fluid through the next succeeding ring, which consequently adversely affects the efliciency of that ring.

The adverse effect of leakage has long been recognized in the turbine art and many expedients have been employed to reduce the amount of such leakage. The most practical and substantially universal method of reducing such leakage is the provision of sealing strips in the form of fins or the like, notched surfaces, etc., all designed to increase the resistance to flow of the leakage fluid and usually referred to generally as labyrinth packing. Such packing has proved to be reasonably efficient, but none has yet been developed sufficiently efficient to eliminate leakage flow.

The general object of the present invention is to increase turbine enicieney by an improved construction which is effective to not only reduce ciples of the invention;

Figs. 2 to 4 inclusive are sections taken on the respectively numbered section lines of Fig. 1;

Fig. 5 is a view Fig. 5;

Fig. 7 is a fragmentary section showing part of a diiferent form of blade structure embodying the invention; and

Fig. 8 is a section taken on the line 88 of Fig. 7.

Referring now more the invention in one of its structural embodithe rotor structure of the ID and the stator struc- Two rows of stator or turbine is indicated at ture is indicated at I 2. guide blades l4 and I6 the direction of arrow32,

played for attaching the blades is not important to the present invention the details of the method of attachment have been omitted for the sake of clarity.

A ring of moving or rotor blades 22 is located between the guide blades 14 and It, the rotor blades being attached at their radially inner or root ends to a disc-like flange 24 on the rotor and at their outer ends being shown as connected by the usual shroud ring 25. As in the case of the guide blades, the specific manner of attachment of the blades 22 is immaterial to the present invention and has not been indicated.

The direction of flow of motive fluid through the blade system is assumed to be from left to right as viewed in Fig. l and as indicated by arrow 28.

Referring now to flow of the motive fluid passing through the blade system is shown, the direction of rotation of the rotor being assumed to be counterclockwise as viewed from the left-hand end of the drawing and as indicated by arrow 30.

Fluid flowing through the guide blade ring id is discharged from the outlet side of the ring in but because of the rotation of the turbine rotor in the direction of arrow 3!) the relative inlet angle of the motive fluid to the ring of rotor blades 22 is in the direction of the arrow 34, and as will be seen from the drawing the profile of the blades 22 is designed in accordance with known principles so as to provide for smooth entrance to and flow through the passages between the blades. The fluid, is discharged from the rotor blades in the direction indicated by arrow 36, but due to the relative rotation between the rotor blade ring and the next succeeding guide blade ring, the relative angle of entry of the fluid into the passages between the guide ring blades I6 is in the direction of arrow 35. This entrance angle permits smooth entry and flow of the fluid between the guide blades in accordance with known practice.

While the major portion of the fluid discharged from the ring of guide blades M flows through the succeeding rotor blade ring in the manner above described, a certain amount of this fluid leaks past the outer circumference of the rotor blade ring through the space 40 between the rotor ring and the stator structure. This leakage is reduced as far as possible by means of any suitable known form of packing which in the present instance has been indicated by labyrinth sealing fins 42 projecting from the shroud ring 26.

The nature of the shown in Fig. 3. As

flow of the leakage fluid is will be seen from this figure, fluid discharge from the guide blade ring i4 leaves this ring in the direction as indicated by arrow 32. In this case, however, the fluid leaking past the end of the ring of rotor blades 22 does not have its peripheral component of flow reversed by its flow between the rotor blades, but continues to flow across the leakage space 40 in the same sense as it enters, as indicated by arrows The result is that the leakage fluid is discharged from the leakage space to the next succeeding blade ring with a peripheral component of flow as indicated by arrow 3317, which is in the same sense as the angle of discharge from the preceding guide blade ring. In other words the peripheral component of flow is not reversed as is the case with the fluid passing through the proper channels in the rotor blade ring.

As will be apparent from inspection of Fig. 3,

Fig. 2, the normal path of account by the use of 1 between the guide the direction of entry of this leakage steam to the ring of guide blades [6 is such that if the fluid impinged blades having the normal blade profile designed to receive fluid discharged from the preceding blade ring with the proper relative inlet angle indicated by arrow 38, the leakage steam would impinge on the back rather than the front faces of the blades. With prior forms of construction this is what occurs and the impingement of the leakage steam upon the blades with an entrance angle materially different from the normal entrance angle creates eddy currents and like disturbances which impair the efiiciency of the system. This loss, due to interference with or modification of the normal flow by leakage fluid at the leakage end zone of the blades is a definitely established factor in turbine performance and is ordinarily taken into empirically established formulae when calculating the efficiency of a turbine design.

In accordance with the present invention this loss, occasioned by entry of leakage fluid to a turbine ring with an angle of entrance other than the normal angle, is reduced if not entirely eliminated and the flow of leakage fluid utilized, by providing special channels at the end zone of the blade ring where leakage fluid from a preceding blade ring enters, which zone may for convenience be referred to as the leakage end zone. In the present embodiment, these channels are provided in the guide blade rings by removing the leading edge portions of the guide blades at the ends where they are attached to the stator structure to provide channels 44 and 46 which are relatively narrow longitudinally of the blades and which as will be seen more clearly from Fig. 3 provide for smooth guidance into and flow through the passage between the guide blades of leakage fluid entering the blade ring with an entrance angle entirely different from that with which the main body of fluid is discharged from the blades of the preceding blade ring.

Considering the nature of the leakage flow past the inner shrouds of the stator rings as illustrated in Fig. 4, it will be apparent that the leakage fluid flowing through space 4.8 between the shroud l8 and the rotor it will pass the ring of guide blades M with a direction of flow as indicated by arrow 36, which represents the direction of discharge from the blades of the preceding row of moving rotor blades. Since this leakage fluid does not have the sense of its peripheral component of flow reversed by passage blades 14, its direction of discharge to the ring of rotor blades 22 will also be with substantially the same peripheral component, and as will be apparent from Fig. 4, if no provision were made for taking care of this fluid, it would impinge on the backs of the blades 22.

since the moving rotor blades are subject to tension, particularly at the root ends, due to centrifugal force to which the stator blades are not subjected, it may in some instances be undesirable to weaken the rotor blades by diminishing the sectional area to provide the desired channels for leakage fluid, and in the embodiment illustrated this is avoided while essentially accomplishing the desired object through the provision of special channels 50 formed in the rotor flange 24 to which the blades are secured. As will be evident from the figure, such channels serve to smoothly receive and guide the leakage fluid which in its course of flow reaches these channels before it reaches the inner periphery expedient or both combined may be used at the leakage end zone of both stator and rotor blades.

The same principles apply to a radial flow turbine, a part of a blade "system of which is shown by way of example in Fig. 5.

In this figure, one of the turbine rotors is indicated at 56 and is shown as carrying blade rings 58 and 60 by means of the usual supporting rings 62 and 64, respectively.

The counter-rotating rotor disc is indicated at 66 and carries blade ring 68 by means of the supporting ring 19. Direction of fluid flow is indicated by arrow 12, fluid past the diiferent rings is indicated by age end zone of each of the blade rings.

Since the difference in flow between the main body of fluid and the leakage fluid is governed by the same principles The embodiments previously described illustrate constructions in which blade stock of uniform profile may be employed, which from a manufacturing standpoint is frequently advantageous because of minimum cost.

providing the special end zone channels for leak age fluid through the medium of blades of special contour having profiles at the leakage end zone shaped to a diiferent profile 84 These two profiles are at the leakage joined by suitand 88. As

6 ences in relative inlet angle or (portions of the main body of fluid entering the blade system at different radii, and that for "that and other reasons blades have been employed which have different profile contours at different radii. In-

What is claimed is: 1. A multiple stage turbine comprising two relatively rotatable carrying members, a first positioned to discharge fluid at an outlet angle having a peripheral component opposite to said magnitude as the outlet angles of the blades of the next preceding blade ring of the same series.

2. A blade system as defined in claim 1 in which the means providing said channels comprises blade end portions of different profile than that of the portions of. the blades traversing said main passage.

3. A blade system as defined in claim 2 in which the profiles of said end portions of the blades are formed with leading edges recessed with respect to the leading edges of the major portions of the blades traversing said main passage.

4. A blade system as defined in claim 1 in which said carrying members are grooved to form said channels.

5. A blade system as defined in claim 1 in which said channels are formed in part by grooves in said carrying members and in part by end portions of said blades of different profile than that of the major portions of the blades traversing said main passage.

6. A blade system as defined in claim 1 in which said carrier members consist of a stator and a rotor carrying rings providing an axial flow main passage and in which said channels are provided at the radially inner ends of the rotor blades and at the radially outer ends of the stator blades.

7. A blade system as defined in claim 1 in which said blade carrying members consist of two oppositely rotatable rotors carrying axially extending blades providing a radial flow main passage and in which said channels are provided in successive blade rings at alternating axially opposite sides of said passage.

GUSTAV KARL WIILIAM BOESTAD.

TEODOR IMMANUEL LINDHAGEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,141,473 Metten June 1, 1915 1,740,372 Rosenlocher Dec. 17, 1929 2,291,828 New Aug. 4, 1942 2,355,413 Bloomberg Aug. 8, 1944 2,402,418 Kroon June 18, 1946

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