US1673554A

US1673554A - Blading for reaction turbines

Info

Publication number: US1673554A
Application number: US206491A
Authority: US
Inventors: Freudenreich Jean De; Frey Karl
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1925-05-27
Filing date: 1927-07-18
Publication date: 1928-06-12
Anticipated expiration: 1945-06-12
Also published as: GB272837A; FR32194E; US1749528A; BE334235A; DE522464C; CH122943A; FR616250A; CH115781A; GB252702A

Description

June 12, 1928. 1,673,554

J. DE FREUDENREICH ET AL BLADING FOR REACTION TURBINES Filed July 18, 1927 C 05 I ob yam M W.

Patented June 12, 1928.

UNITED STATES 1,673,554 PATENT OFFICE.

JEAN DE FREUDENREICH, OF BADEN, AND KARL FREY', OF ENNET BADEN, SWITZER- LAND, ASSIGNORS TO AKTIEN'GESELLSCHAFT BROWN BOVERI & CIE., OF IBA'D'EN, I SWITZERLAND, A JOINT-STOCK COMPANY 01? SWITZERLAND.

BLADING FOR REACTION TURBINES.

Application filed July 18, 1927, Serial No. 206,491, and in Germany June 21, 1826.

This invention relates to steam turbines, and pertains particularly to the construction of blading for turbines of the reaction type. The subject matter of the present applica- 5 tion constitutes an improvement on that claimed in our co-pending application Serial No. 108,728 filed May 13, 1926, and the present application is a continuation in part of that.

The general objectof the present invention is the provision of an improved reaction blading which will increase the eificiency of the turbine in the utilization of the energy of the actuating elastic fluid.

Another object is the provision of a form of reaction blading which will be substantial in construction and which will lend itself to economy in production.

Other and further objects will be indim cated or pointed out hereinafter, or will appear to one skilled in the art upon an understanding of the invention or its employment in practice.

In the drawing forming a part of this specification, we illustrate one design of blading which is in conformity with our invention, but it is to be understood that the same is presented for purpose of illustration only and is not to be accorded any interpretation having the eifect of limiting the claims short of th true and most comprehensive scope of the invention in the art.

In the drawing,

Fig. 1 is a diagram illustrating two adjacent blades in cross section normal to their longitudinal axes, and a procedure for analyzing or arriving at the design of their face contours;

Fig. 2 is a diagram illustrating a prom cedure for the analyzing or designing of the blade contours;

Fig. 3 is a diagram illustrating associated groups of stationary and rotor blades in cross section and in a plane development;

and

Fig. 4 is a detail illustrating in cross section a modification of a blade form at the exit side.

The construction of blading for reaction turbines as described in our previous application above referred to marked a rather distinct divergence from the general trend of reaction blading design up to that time. The features which perhaps distinguish the conportion of the steam passage in which the steam flow is at a materially increased velocity over the velocity at entrance, and a quite sharp or sudden rise of velocity between the entrance side and the exit throat, as distinguished from the more gradual velocity increase characteristic of previous conventional designs. The present invention contains a further development in the same general direction and is concerned with obtaining a further increase in efliciency. The immediate effects which the present inventlon is aimed to obtain, and from which result certain improvements in efiiciency, include a more sudden increase in the steam veloc ty, the delay of the radical increase in velocity until a point is reached toward the exit side, and a further shortening of the steam path through which the steam travels at the increased velocity.

In the previous application we disclosed a procedure for analyzing and defining the blade contours, and we will use the same procedure for indicating the characterizing features of the present invention. In Figs. 1 and 3 the reference numerals 10 designate cross sections of blades for a reaction turbine, the group designated S in Fig. 3 bein intended to represent a portion of a stage 0 stationary blades, and the group designated R a portion of the adjacent ring of rotor blades. The blades, it will be observed, are identical in cross section, with concave front and convex rear sides associated to aiford intervening steam passages. Since it is the form of these steam passages which determines the action of the steam therein and on the blading, we will devote the present description principally to the form of the steam passage, it being understood, of course, that .in so doing we are at the same time describing the face contours and relative disposal of the blades. As a procedure for demonstrating characteristics of the blading arrangement illustrated in Fig. 1, which is representative of the invention, a number of circles C C G9, etc., are inscribed within the steam passage tangent to the surface lines of the blade profiles. The

curve A--A following the centers of these circles represents, therefore, the mean of the steam path between the blades. Now, developing this mean steam path as a straight line A'A as in Fig. 2, the circles C, 0-, G etc., are set up on said line with center spacing as in Fi 1, and the enveloping lines BB and D developed, these illustrating, in their relationship, the relationship of the confines of the steam passage. One of the characterizing features of the present invention is, that when developed in this fash ion, the envelope is concave with respect to the mean steam path in the portion at the entrance side, and convex with respect to the mean steam path in the portion adjacent the exit side, with a sharp convergence toward the mean steam path, such convergence of the envelope toward the mean steam path being substantially greater in an intermediate part than at the ends. In Fig. 2, it will be observed, these convex and concave portions of the line BB meet at the point of inflection b, and the concave and convex portions of the envelope line DD meet at the point of inflection (I. As a guide for determining a construction which will attain the results which characterize the present invention, it may be stated that with the envelope developed as above described, the tangents i and 2 at the points of inflection d and I) should make an angle of more than 16 with the developed line A' of the mean steam ath; and the inclination of the envelope wit respect to the developed line A'A' of the mean steam path should exceed 16 over a sufliciently large portion of its length, said portion being that which delimits the part of the steam path in which the radical acceleration of the steam velocity takes place. As a manner for arriving at an approximation of this critical portion of the steam passage confines, the radius of the inscribed circle 0* at the points of inflection b and d, is set out on the envelope lines at each side of said points to establish the

points

7 and 7 and 8 and 8 as the approximate limits of the accelerating zone. The general inclination of this critical ortion of the envelope line to the straight line development of the mean steam path is determined by the angle of the straight line joining the limit points, such as88' or 7-7, with respect to the line A This angle, represented by the angle 8 A A must be of at least 16. By giving the blades a form such as to provide a steam passage as above described, the desired acceleration of the steam, first slowly, and then rapidly increasing, is obtained, and the steam passage may be regarded as comprising three zones, namely, a pressure zone X at the entrance side, in which the acceleration is slow, an accelerating zone Y, in which the contraction of the passage is rapid and the acceleration correspondingly rapid, and finally an exit zone Z which gives direction to the leaving steam. In order that loss may be minimlzed, the contraction of the passage should be as near the exit end as possible, and the exit zone as short as possible. The late and sudden increase in velocity is accompanied by a slmilarly late utilization of the available heat drop for the sta e, and therefore the increase in volume,whic is proportional to the heat drop, also occurs late. The increase 1n velocity consequent on increase in volume, accordin ly, takes place in conjunction with the ve ocity increase due to the contraction of the passage.

Although it is an advantage to have a distmct point of inflection of the concave and convex portions of the envelo e curve, considerations of desi n may lea to their joinmg in substantial y straight line portions converging on' the developed mean steam path at an angle of at least 16. Obviously, the inlet and outlet margins of the blade must conform to structural requirements. These portions should not be made longer than is absolutely necessary, although it may be convenient to slightly extend the exit sides owing to the divergent form of the jet, or to thin them somewhat, as illustrated in Fig. 4, to decrease interruption of the jet as it leaves the blades. The actual mean steam path between the blades must conform primarily to the direction of the jet approaching the entry side. The ratio of peripheral speed to steam speed is usually chosen with the purpose of obtaining entry of steam in the axial direction. Since the blades must have a certain thickness, however, and the inlet edges must be made thin to prevent loss due to shock, it is impossible in practice to provide for true axial entry along both sides of the blade. Under the circumstances, it has been found to be most advantageous if the inlet angle m at the back of the blade is greater than 90 while the inlet an 1e 11. on

.the hollow side of the blade is less t an 90.

One feature of the present invention which contributes important constructional advantages is the increase in pitch which it accommodates, as compared with that customary in reaction blading, without sacrificing proper guiding of the leavin jet. For guidance in proper design, it may e stated that the itch 12 should be at least of the axial wi th 10 of the blades.

What we claim is:

1. Blading for reaction turbines comprising radial blades associated to define a curved intervening steam passage the boundary walls of which are so shaped and related that when developed in relation to a straight line representing the mean steam path of the passage, they converge on such line in concave relationship thereto in portions on the entrance side and in convex relationship thereto in portions on the exit side.

2. Blading for reaction turbines comprising radial blades associated to define a curved intervening steam passage, the profile surfaces of said blades forming the walls of said passage and being so shaped and related that it developed as the envelope of a series of circles corresponding to circles inscribed in the steam passage and arranged on a straight line of centers, said envelope will converge on the line of centers in concave relationship thereto on the inlet side and in convex relationship thereto on the exit side.

3. Blading for reaction turbines comprising radial blades, alike in size and shape,

arranged to define a curved intervening steam passage, the profile surfaces of said blades hearing such relationship to the mean steam path of said steam passage, that if developed as the envelope of a series of circles inscribed in the steam passage and set up on a straight line of centers, said envelope will converge on said straight line in a concave relationship on the inlet side and in convex relationship on the exit side.

4:. Blading for reaction turbines as specitied in claim 2, wherein the tangent of the point of inflection of said concave and convex portions of the envelope is at an angle of more than 16 with the line of centers.

5. Blading for reaction turbines as specified in claim 2, wherein a straight line passing through the point of inflection of the concave and convex portions of the envelope and passing also through the points in the envelope at opposite sides of the point of inflection and within the radius therefrom of IV the inscribed circle at the point of inflection, is at an angle of more than 16 with respect to the line of centers.

6. Blading for reaction turbines as speci' fied in claim 2, wherein the pitch of the blades is at least seven tenths of the axial width of the blades.

7. Blading for reaction turbines as s ecified in claim 2, wherein the entry ang e of the concave side of the blades is less than 90 and that of the rear side of the blades is more than 90.

8. Blading for reaction turbines as speci fied in claim 2, wherein said bla'ding is arranged in alternate rows on both the stator and rotor of the turbine.

9. Blading for reaction turbines as specified in claim 2, wherein said blading is car ried by the rotor of the turbine.

In testimony whereof We have hereunto subscribed our names this 24th day of June A. D. 1927 at Zurich, Switzerland.

JEAN 1m FREUDENREIOH. KARL FREY.