US2972468A - Full admission impulse turbine - Google Patents

Description

Feb. 21, 1961 P. u. WEBER FULL ADMISSION IMPULSE TURBINE 5 Sheets-Sheet 1 Filed Jan. 31, 1955 zzzzmm Feb. 21, 1961 WEBER 2,972,468

FULL ADMISSION IMPULSE TURBINE Filed Jan. 51, 1955 k 5 Sheets-Sheet 2 INVEN TOR;

Feb. 21, 1961 p, u WEBER 2,972,468

FULL ADMISSION IMPULSE TURBINE Filed Jan. 31, 1955 3 Sheets-Sheet 3- FULL ADMISSION IlVIPULSE TURBINE Paul Ulrich Weber, Arn-Hcrgen, Switzerland, assignor to Societe financiere dExpansion Commerciale et Industrielle SA. Sfindex, Samen, Switzerland 7 Filed Jan. 31, 1955, Ser. No. 485,253 Claims priority, application Switzerland Mar. 18, 1954 1 Claim. (Cl. 253-31) The present invention relates to full admission turbines. In all types of water turbines the racing speed n i.e. the number of revolutions in the condition of no load, is appreciably higher than the normal speed n,,.

The racing coeflicient in Francis turbines of low specific speed is approximately 1, 6, in Pelton turbines approximately 1, 8, in Francis turbines of high specific speed approximately '2, 0', and in -Kapl'an turbines (with double regulation) this coeffici'ent can rise to values of over 2, 5. Despite many efforts, no absolutely efiective means to prevent racing have been found up to now for the said turbine types which are most often used today. Since known means will become effective only after dangerously high speeds have been reached, the generator rotors must be built for the maximum possible speeds. Recently it has moreover become a standard requirement to carry out the centrifugal test at the maximum speed possible. -These parts are therefore not only very costly to build but often the limits of such executions are reached with respect to strength" and fly-wheel mass.

In full admission impulse turbines (see for instance Swiss Patents Nos. 274,595, 285,249, 287,979) the problem of limitingthe racing speed is similarly present as in the above mentioned turbine types. Since infull admission impulse turbines the normal speeds for the same flow conditions are higher however than in Francis turbines or partial admission impulse turbines (higher speeds result in lower production costs), it is extremely desirableto limit the racing speed.

An object of the presentinvention is to provide means for limiting the racing speed of full admission impulse turbines, which will act effectively and under any circumstances. A further object of the invention is the provision of means for limiting the racing speed of full admissionimpulse turbines which contrary toknown executions operate independently of any control.

A still further object of the invention is the provision of means to limit the racing speed, which act by way of destroying energy flowing to the turbine and being only efiective if the speed is at least slightly higher than the normal speed.

In order that the invention may be better understood and put into practice embodiments of the invention are hereinafter described by way of example with reference to the accompanying drawings, in which:

Fig. l is a radial section through an impeller having 65 the energy-destroylng means arranged at the vane lnlet.

Fig. 2 is a section along line I--I where the indicated flow direction corresponds to the normal speed n'=n Fig. 3 is a similar section along line I-I, where the indicated flow direction corresponds to an increased speed n n Fig. 4 is a radial section through an impeller accordtates PatentO F ing to a second embodiment showing a similar arrangement of the energy destroying means.

Fig. 5 is a view of the impeller according to Fig. 4.

Figs. 6 and 7 are sections along-lines IIII and IL-III respectively in Fig. 4.

Fig. 8 shows a radial section of an impelleraccording to a further embodiment where the energy-destroying means are arranged at the vane outlet, the limits of the flow through the impeller at normal speed it=n being indicated in dashand dot-lines in the drawing.

Fig. 9 is a radial section through the impeller according to Fig. 8,- the limits of the flow through the impeller at increased speed n n being indicated in dashand dot-lines in the drawing.

Figs. 10 and 11 are horizontal sections along lines IV and IV and V--V in Figs. 8 and 9 respectively.

Fig. 12 is a view of an impeller according to a further embodiment having energy-destroying means mounted in the form of rods.

Figs. l3, l4 and 15 show elevation plan view and section of an impeller arrangement according to another embodiment, the energy-destroying meansbeing consti tuted by guideand reversing-vanes arranged immediately behind the impeller outlet.

Fig. 16 shows the velocity diagram 'at the impeller outlet according to Figs. 13-15 at normal speed n=n Fig. 17 is 'the velocity diagram at the same point as in Fig. 16 at elevated speed n n,,.

Fig. 18 shows a radial section through an impeller having a strengthened outer crown at its lower side.

In the embodiment shown in Figs. 1 to 3 where Fig. 1 depicts a full admission impulse impeller in radial section and Figs. 2 and 3 sections through a vane of the impelleralong line I-I in Fig. 1, the impeller comprises a hub 1, vanes 2 and outer crown 3. Energy-destroying means are provided at the back side of the vane in the form of a lateral groove 4 extending over the whole of the vane entry edge 5. At normal admission of the vanes 2 (n'=n the groove 4 will not be effective, since the flow in this case will not come into contact with the back side of the vane due to the noseshaped portion 6 at the entry edge of the vane 2. If the speed of the impeller raises over a certain limit, admission of the -fiow will take place at the back side of the vane. In this case the lateral groove 4 will be efiective such that a part of the flow hitting the back side ofthe vane will be reversed in circumferential direction; Due to this effect a moment will be created which isopposed to the normal one and in addition the flow between'the vanes will be heavily disturbed. This will result in heavy losses thus appreciably reducing the maximum speed of the impeller.

-In Figs. 4 to .7 a similar'embodiment is shown and parts corresponding to those in Figs. 1 to 3 are given the same reference numerals. At normal speed 11,, of the impeller the flow through the latter will be substantially between the lines terminating at 7 and 8 in Fig. 4. If the speed is increased to n=n for instance, the flow in the impeller will be displaced outwards, outlet now taking place between 9 and 10. The water flow will therefore abut against vane portions which are not contacted at the normal speed n =n Those vane portions of the impeller which are only in contact with the flow at elevated speeds n n are formed such that they will produce a braking effect by disturbing the flow. A lateral groove 11 is arranged at the back side of the vane corresponding to the groove shown in the previously described embodiment. In its outer portion this groove 11 is wider in cross section and in addition there is provided an outwardly projecting rim portion 12 serving to revise the flow such that a moment will Patented Feb. 21, 1961 be produced which is opposed to the normal moment. Further a whirling effect will be created which will disturb the normal flow between the blades.

In the embodiment shown in Figs. 8 to 11 the energydestroying means according to the invention are arranged at the outlet edge of the impeller vane. The range of the water outlet .at the vane is at normal operation (11:74 between points 13 and 14 (Fig. 3). When the speed increases (n n this range will be outwardly displaced and will be situated at n=n between points 15 and 16 (Fig. 9). Between points 14 and 16 the outer extremity of the vane has a forwardly directed portion, which is not in contact with the flow at normal speed (Fig. 10). At elevated speed the flow is reversed at this portion creating thus a braking moment. Since the outlet cross-section in the range of points 14 to 16 is too small for the water quantity, the flow along the vanes is also disturbed from this side and the speed is reduced due to the high loss in the flow.

In the embodiment according to Fig. 12 the impeller and its vanes are of similar form as in the previously described embodiment and reference is made to Figs. 8 and 9, the outlet edge at the vane being contacted by the flow at normal speed again between 13 and 14 and at the speed n=n between 15 and 16. In the range between points 1.4 and 16 i.e. the portion of the vane edge, which is only contacted at elevated speed n n energy-destroying means in the form of rods 17 are provided having angular or circular cross-section as shown in Fig. 12. These rods 117 permit the water to flow out but create deceleration and a whirling effect in the waterflow, thereby increasing the losses in the impeller and reducing the racing speed. At normal speed the rods 17 have no disturbing effect, since they rotate in air and will not come into contact with the working medium.

In Figs. 13 to 17 an embodiment is shown where the energy-destroying means according to the invention are arranged immediately behind the impeller in the form of guide or reversing vanes.

Figs. 13 and 14. These vanes are radially directed such that at normal operational speed n=n the direction of the vane corresponds to v (see velocity diagram Fig. 16). Therefore the water passes the vanes 19 in shockless flow so that the impeller flow is not influenced. If the speed is increased, the circumferential velocity increases from 1: to n Since the vane angles and water quantities remain constant, therefore also W2 will remain constant as to direction and size. velocity v will change to v The flow will impinge in an inclined direction against the outlet vanes 19 (Fig. 17) and the water will be reversed in circumferential direction. Since the vanes are not positioned parallel with respect to the impeller axis but are inclined to such an extent, that the flow will not only be reversed in circumferential but also in axial direction upwards as shown Below the outlet side of the impeller 13 guide vanes 19 are arranged as shown in The absolute outlet I in Fig. 15. The casing 20 which is contacted by the reversed flow directs the water inwards and it will fall back onto the impeller. The flow circulates as indicated by the dashand dot-line 21. The reverse water flow will disturb the normal flow between the impeller vanes and thereby effect a reduction of the racing speed. At a speed which is lower than normal" the water Will be downwardly directed and no appreciable disturbance is created.

In the embodiment shown in Fig. 18 the impeller 22 has arranged at its lower side an exterior crown 23 having increased thickness, whichrnay be provided with ob-' structions. Thiscrown 23 rotates in the annular channel 24, which is empty at normal speed. At normal speed n=n the outlet edge of the vane is contacted by the flow between points 25 and 26 and only spray water will enter the annular channel 24 and leave it immediately again through openings 27 in the channel structure. If the speed increases, the flow in the impeller will be outwardly displaced and the outlet edge of the vane will be contacted between 28 and 29 at n=n There part of the water flow will enter the annular channel 24, the opening 27 of which will not be sufficient to let off all the water. The crown-of the impeller will therefore rotate in water instead of air, which will multiply the impeller friction. The speed of the impeller will thereby be reduced and limited at a safe level.

I claim:

- A full admission impulse turbine having two dilferent types of flow of the turbine-operating medium, namely, a regular flow at normal speeds of the turbine and a different flow at maximum speeds of the turbine, having a turbine wheel comprising vanes having front surfaces receiving and guiding said regular flow and back surfaces receiving and guiding said different fiow, and grooves formed upon said back surfaces, said grooves being located outside of said regular flow and being engaged solely by said different flow to disturb it and thereby reduce the speed of the turbine wheel.

References Cited in the file of this patent UNITED STATES PATENTS 1,008,550 Lowenstein Nov. 14, 1911 1,097,752 Fisher May 26, 1914 1,156,549 Perry Oct. 12, 1915 1,544,253 Marsland June 30, 1925 1,864,803 Clark June 28, 1932 2,284,295 Moody May 26, 1942 2,382,108 Seewer Aug. 14, 1945 2,407,454 Seewer Sept. 10, 1946 FOREIGN PATENTS 163,079, .Australia June 11, 1953 178,314 Switzerland July 15, 1935 963,540 France Jan. 4, 1950

Images