US1749528A - Blading for reaction turbines - Google Patents

Description

March 4, 1930. J.. DE FREUDENREICH ET AL 1,749,523

BLADING FOR REACTION TURBINES Filed May 15, 1926 Fig.4.

Fig.2.

Patented Mar. 4, 1930 UNITED STATES.

PATENT OFFICE JE AN nu FREUDENREICH, OF IBADEN, AND KARL FREY, 0F ENNETBADEN, SWITZER- LAND, ASSIGNORS TO AKTIENGESELLSCHAFT BROWN BOVERI & CIE., 0F BADEN,

SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZERLAND.

BLADING non REACTION 'runnmns Application filed May 13,1926, Serial No.

This invention relates to the construction of turbines actuated by expansion fluid, as ex-' amplified by steam turbines. It pertains particularly to steam turbines of the reaction type, and has to do with the construction or arrangement of theblading for both or either the stator or rotor;

. The general object of the invention is the provision of a blading arrangement for reaction turbines which will increase the power efliciency of the engine.

Another object is the provision of a blading arrangement which will, in many instances, permita reduction in the size of the machines.

Another objectis the provision of a construction which will reduce cost, by decreasing the number ofblades in a stage.

Other and further objects will be pointed out or indicated hereinafter, or will be obvious to one skilled in the art upon an understanding of the invention.

In the drawing forming a part of this specification we illustrate two designs embodying the present improvements, but the same are presented for the purpose of illustration only, and are not to be construed to impose limitations on the claims short of thetrue and most comprehensive scope of the invention in the art.

In the drawing,

Fig. 1 is a diagrammatic illustration of a portion of a stage of blading demonstrative ot the invention, showing three blades each of adjacent stator and rotor rings, the blades being shown in section taken concentrically I with the turbine axis.

Fig. 2 is a graph illustrating the relationship of parts of the blade profile. I

Fig. 3 is a section diagram of blading of the conventional Parsons design.

. tures illustrated in Figs. 3 and 4.

Fig. 4 is a diagram of a blading profile demonstrative of the invention in a. design differing from that of Fig. 1. v

Fig. 5 is a graph illustrating the relationship of certain parts of the respective struc- Heretofore in thedesigning oi reaction turbines, so far as we have been able to ascertam,rap1d changes 1n the cross section and r The movin blades are desi 108,728, and in Switzerland May 27, 1925.

direction of the flow of steam through the blading have been regarded as disadvantageous, and consequently have been avoided, the designs having been arranged to give the steam passages or channels between the blades a form of gradually contracting contour free from abrupt change of direction. Moreover, it has been considered of importance to have the narrower portion of the passage at the profile have shown, contrary to the beliefs eretofore held, that the design and arrange-- ment of blading which provides a steam passage Which is comparatively wide in the portion adjacent the entrance side, and changes direction quite sharply, giving an acute'exit angle and having the narrow exit portion of the ath comparatively short, gives sub stantially increased power efficiency, as well as various constructional advantages.

The nature of the invention may be ascertained by reference to the drawing, wherein Fig. 1 illustrates a profile and arrangement of our improved blading, as applied to an axial-flow steam turbine. In this figure the upper row of blades, designated 10, repre sents-a section of blading on a wheel or rotor of a reaction turbine, while the row designated 11 represents a section of 'a portion of the adjacent row offixed blading. It is wellv to observe at this point that our new blading construction is equally ada ted for both moving and stationa stages 0 reaction turbines, and that it can e employed to best advantage when utilized in both in conjunction. ated 12 and the secondary b ades 13. It wil be observed that their form and arrangement are suchthat the steam passage or channel between the blades exit side. This contracted exit portion of the passage, which we will designatethe velocity portion, is comparatively short in respect to both the total length of the passage and the exit portion of the previous standard design, which is illustrated in Fig. 3. Thus the passage may be roughly apportioned as a pressure portion, which is relatively wide, an exit portion which is narrow and quite short,

' and an intermediate contracting portion in which the direction of flow changes rapidly. In the illustrated example the pressure por-' tion may be regarded as the zone X, the intermediate portion as the zone Y and the velocity portion as the zone Z. As a result ofthese particulars of the design, the change in direction of the flow passage is relatively abrupt as compared with the previous design, resulting in the turning of the steam path to an acute exit angle in considerably shorter length. In the illustration given, the exit angle 1s approximately 18, which is suggested as re resenting an average between the limits of t e most efiective arrangements,

exit angles varying between 16 and 20 hav- 1ng been found productive of the best effects. We have ascertained also that the rate of contraction in the width of the steam passage from the pressure portion to the velocity portion may be determined and laid out in accordance with a fairly accurate rule, of which the following method is an illustration.

- to the blade profiles, as shown in Fig. 1.

Let the line a in Fig. 2 represent the development of the median steam path a.w between the blades, and the cross sections 0, 1, 2, 3 .7,- set np on the line a represent the radii of the correspondingly numbered circles inscribed in the steam passage tangent With a properly chosen profile the line (Z generated along the ends of the radii 0 should incline toward the line a at an angle of something over 15 throughout that portion representative of the intermediate zone Y. The end portions of the line d will deviate from the intermediate portion, the part Z representing the comparatively straight restricted velocity portion of the steam passage, while the part f represents the portions where the blades are rounded ed at entry in the example shown. It will beobserved in the example given that the portion Z represents only between one fourth to one fifth of the length of the entire path wa. An effective design may also generate a line corresponding to the line d but curved, thechord of the intermediate portion being inclined at an angle of more than 15 to the line a. In order that the condition for a rapid change of the passage width may be fulfilled, said curved line in the intermediate portion should be convex upwardly. If concave, it is a sign that the transition will be gradual. The dotted curved in Fig. 2 is illustrative of one form.

The novelty of this type of blade profile,

and the manner in which it differs from the usual standard reaction blading (Parsons), may be demonstrated by a comparison with a similar analysis of the steam passage of the" latter. In Fig. 3 is shown a diagram of standard Parsons blading, and in Fig. 5 a diagrammatic analysis of the same obtained by the method described above. It will be observed that in this diagram the line 03, corresponding to the line d of Fig. 2', is concave upwardly in the intermediate portion and makes an angle of less than15 to the line a; The narrowest section Z comprises a considerably greater proportion of the line d, demonstrating that the length of the contracted exit portion of the steam channel is considerably greater than is the case with profiles arranged according to the present invention.

While one advantage accruing from the present invention lies in the fact that it allows of a very small exit angle and a corresponding increase in the peripheral component of the steam force on the moving blades, with reduced frictional losses, improved power factor efficiencies may be obtained by use of the invention in suitably designed blading in which the exit angle is greater than 20. In Fig. 4 is shown an example of such an arrangement, the profile being shaped in accordance with the method described above, and illustrated by the line d in Fig. 5. As demonstrated by the analysis, this design presents a profile'frpm which the line (1'' is generated to extend through the greater proportion of its length at an angle of more than 15 to the line a".

In the operation of the turbine, it is believed, the steam entering a ring of rotary bladin exerts amomentary initial impulse on the ilades, following which the remaining kinetic energy of the steam becomes converted into pressure which builds up in the pressure portion of the passage. T e pressure, in turn, is transformed into kinetic en ergy again in the velocity portion, exerting its reaction against the blades. drop incident to the development of the exit velocity is very rapid, so that the reaction effect is very pronounced, and the friction losses low, even with a small exit angle.

While one-of thegreat advantages of the invention as demonstrated by practical use, is the increased power eflicienc obtained, which in various instances has. een found to be as high as 6%, other important and use- The heat ful results follow from the employment of the principles cha. \cterizing the invention. For example, it wn' be observed that with the same circumferential pitch of thenew blading as emplgyed in the old, the width of the blades may be materially reduced. Likewise, thewidth of the stages may be substantially reduced. Furthermore, there may also be a reduction in the number of blades required onv a given diameter. These various factors result in an important decrease in the portions connecting through trance side and a relativellyl cost of manufacture, and it is believed, contribute somewhat to the strength and stability of the mounting of the blades. As an example of a further development of the con-- struction disclosed, reference is made to our copending application Serial No. 206,491, filed July 18, 1927.

What we claim is 1. Reaction turbine blading comprising blades extending radially and defining intervening steam passages,the blades having a profile and arrangement giving said passages a relatively wide pressure portion at the enshort and ree exit side, said an intermediate portion of rapidly contracting width s'tricted velocity portion at t wherein the blade profile converges on the mean steam path of the passage at a rate elxceeding that of-the sides of an angle of 2. Reaction turbine bladin as specified in claim 1, wherein the intermediate portion of the steam passa e changes the direction of steam flow rapitfi 3. Reaction turliine blading as specified in claim 1, wherein the pressure portion of the steam assage is longer, on the axial line of the tur ine, than is the velocity portion.

4. Reaction turbine blading as specified in claim 1, wherein the length of the velocit portion is not over one fourth of the length of the total median steam path. I,

5. Reaction turbine blading as specified in glaim '1, wherein the exit angle is less than 6. In a reaction turbine, the combination with a rotary member, of reaction blades mounted thereon in ali nment circumferentially, said blades space to rovide intervening steam passa es, the bla e profile defining sa1d passages witli a relatively wide pressure portion on the inlet side and a relatively narrow and short velocity portion on the exit Tide, said passage changing direction abrupty portion and its median line progressing throughout its length from. inlet to outlet in the direction counter to that of the blades movement.

7 Reaction turbine bladin blades extending radially an tervening steam passages, the blades having a profile and arrangement such that the encomprising from the pressure portlon to the veloclty' velope of a series of circles inscribed in the passa e, when they are set up on a straight line 0 centers, converges for the greater part of its length on said line of centers at an angle in excess of 15.

8. In a fluid turbine, complementary blades spaced with respect to each other to provide a fluid passage; the profile of adjacent faces of said blades being such as to provide said passage at the entrance side thereof with a relatlvely wide pressure portion, to provide said passage at the exit side thereof with a contracted veloclty portion relatively short as compared with the length of said passage, and to provide said passage intermediate said portions with a contracting portion angularly disposed at all points with respect to said pressure portion m a direction counter to that of the blade movement to provide at such intermediatecom .tractin portion for relatively rapid change portion and the exit e rapidly contracting steam passages, each passage having a wide pressure portion at the entry side, a short velocity portion at the exit side and a rapidly contracting accelerating portion between the pressure and velocity portions, the 'mean steam path in the pressure and acceleratlng portions bending continuously toward the exit side in the circumferential direction of the row.

In testimony whereof we have hereunto subscribed our names at Zurich, Switzerland,

on the 27th day of. March, A. D. 1926.

- 7 JEAN ma FREUDENREIOH.

KARL FREY.

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