US1695200A

US1695200A - Hydraulic draft tube

Info

Publication number: US1695200A
Authority: US
Inventors: Moody Lewis Ferry
Original assignee: Individual
Current assignee: Individual
Priority date: 1922-11-28
Filing date: 1926-03-26
Publication date: 1928-12-11
Anticipated expiration: 1945-12-11

Description

Dec. 11, 1928.

L. F. MOODY HYDRAULIC DRAFT TUBE 2 Sheets-Sheet 1 Original Filo ad Nov. 28. 1922 Z5 z? 7 Z-r- Z6 r? I mi? Elwvemtoz Zm zo 1010002,;

Patented Dec. 11, 1928.

PATENT OFFICE.

LEWIS FERRY IvIOODY, OF PHILADELPHIA, PENNSYLVANIA.

HYDRAULIC DRAFT TUBE.

Original application filed November 28, 1922, Serial No. 603,769. Divided and this application filed March 26, 1926, Serial No. 97,534. Renewed May 14, 1928.

This invention relates to hydraulic turbines and in particular to an improved means for receiving water from the turbine runner and delivering it to the tail race. More particularly my invention relates to means or this character wherein the water is turned or spread out from a direction along the axis of the runner into diverging; radial directions and is subsequently turned into a single direction for discharge into the tail race. This application is a division of my copending application, Serial No. 603,769, filed November 28. 1922.

In many modern hydraulic power plants the turbinesare placed in a row with vertical shafts, the water entering the turbines on one side of the row from the penstoclzs or forebay and discharging at the other side into the tail race. Tlhe water leaves the runners in a downward direction at high velocity and some means should be provided which will re duce this velocity so as to correspondingly reduce the back pressure on the turbine runners and which will likewise turn the flow into a horizontal downstream direction. means should be constructed so to perform these functions without appreciable losses of energy and should itself occupy a minimum space. The last condition is particularly desirable in order that the turbines themselves may be closely spaced and the power house dimensions made as small as possible.

F or the purpose of reducing the velocity,

draft tubes have been used which direct the flow iii in the runner radially out ard on spreading lines and discharge it horizontally in every direction. The flow may then be received by a collector which turns it into a.

common downstream direction. Certain portions of theilow must be turned through substantially 180 while other portions. which leave the tubein a direction more nearly approaching the downstream do not have to be turned through so great an angle.

If an unlimited space were available the initial velocity with which the water enters the draft tube could be reducedand its kinetic energy turned into effective head for the turbine by the use of the spreading action alone, that is, the water could be discharged outwardly in all directions at such a low velocity that but little kinetic energy would remain in it. The problem of collecting the flow and discharging it downstream would be solved by the use of any suitable collector- Thiswhich would not cause an appreciable loss of head.

VVit-h the available space limited, however. it is desirable to provide a draft tube of such dimensions that the water discharged into the collector will retain a portion of its kinetic energy and that the collector be so de signed as to reduce farther the velocity of the water and to regain this energy. The water leaving the draft tube in an upstream direction may be conveniently collected from the tube by one or more spi al passages extending; circumterentially around the cylindrical outlet of the tube and discharging tangentially downstreamtoward the tailrace. These spiral passages should be enlarged at a rate than is necessary to accommodate the cinnulative flow so that the velocity of the liow therethrough will be gradually reduced. One of the objects of the present invention to provide an improved collector of this character which is designed to receive a flow of considerable velocity from the draft tube and is adapted gradually anduniformly to re .uce the velocity of thisi'low and so regain kinetic energy. V Another object of my invention is to pro vi e in addition to the spiral collector passages above described an effective means for de elerating that portion of the flow which oes not en er the spiral passages.

l lurnerons other objects and advantages will appear from the following description ha? n in connection wi h the accompanying 0* rings which illustrate certain of the pre- -c red embodiments of my invention and wherein Fig. 1 is a sectional view on line l1 of is a horizontal sectional view on the line f2-2 of Fig. l,

l e line 3-3 of Fig. 2, Fig. at shows a vertical section taken on the line il of Fig. 2 looking in'the direction of the arrows,

Fig. 5 shows in vertical section on the line 5 5 of Fig. 6, a modification, v N Fig. 6 is a horizontal section on the line 6-6 of Fig. 5,

Fig. 7 is a vertical section on the line 7- -7 of Fig. 6, and p Fig. 8 isa vertical sectionon the line 88 of: Fig-6 taken inthe directionof the arrows.

Referring to the figures, reference char- 3 shows a vertical sectional View on acter 20 indicates generally the primary draft tube and 21 the collector. The primary draft tube as shown is formed of an outer wall 22 having a slightly tapered or conical upper portion 23 and gradually curved outward to a horizontal direction at its lower end, the lower end of the draft tube having a barrel portion 28 depending into the collector. The outer surface of the main body portion of the barrel is cylindrical. Projecting upwardly from the floor 25 of the collector passage into the flaring end of the wall 522 and concentric therewith is a cone 26 whose concave surface is formed in relation tothe outline of the fiaredend of the wall 22. The outer wall 22 and cone 26together term the primary draft tube which serves to direct the flow downward from the turbine runner and outwardly into a horizontal plane. The cross sectional area of this tube as shown increases gradually so as to .give a gradual deceleration to the maridian components of the flow, and at the same time the tube is adapted to handle eiiicientl y flow containing whirling components about the turbine axis.

, In the form shown in Figs. 1 to 4 I provide a single curved collector channel which starts at a lateral point l at the mouth of the draft tube, is curved around the axis of the tube through an angle of approximately 180 and terminates in a straight passage 4:? having a direction downstream and substantially tangential to the draft tube. The inner and outer walls of this passage are vertical and its upper and lowerwalls horizontal except that the upper wall 50 of the outer passage is in' clined upward at an angle preferably not to exceed about The passage 49 for discharing the direct flow is substantially rectangular in crosssection and is formed by the floor 25, top wall 50 which is inclined upwardly at an angle not to exceed about side wall 51 and wall 52, the last being formed by a partition 53 which separates the passage for the direct flow from the'end of the curved passage. The top wall thereby forms an extended roof with which the primary draft tube merges to form the direct discharge passage whiehis also substantially tangent to the primary tube or passage at a point lateral of or offset from the axis of the primary tube. it is also seen that only the two passages 47 and 4-9 are providedi these having upper walls or roofs at different elevations.

The form of my invention shown in Figs. 5 to 8 is similar to that shown in Figs. 1 to 4- except in the former the curved collector passage does not terminate in astraight section but continues to curve so that the total curve exceeds 180 and also continues to flare horizontally through its entire course. This passage is quite narrow but considerably higher than those shown in previous figures. T he partition of Figs. 1 and 2 is omitted,

there being merely a strut 56 betweenithe upwardly extending top wall ofthe passage for the direct flow and the floor 25. The cone shown in this form of my invention extends upwardly through the entire draft tube to the runner and the runner shown is of the propeller type. If desired the form shown in these figures may have an over-hanging passage collector.

lVhile I have shown a primary draft tube which constructed to progressively increase in area, in certain cases it may be necessary to employ one whose principal function is to turn the water outwardly in all directions without being able to produce any substantial decrease in velocity. such tubes it would be necessary to employ a collector which will reduce the velocity of the flow from an amount which is only slightly less than its velocity at the runner.

Moreover even with these turbines wherein the discharge velocity from the spreading co duit is sufliciently small to be so thrown away when the turbine is operating at its normal capacity, it must be considered that under the usual conditions turbines are frequently called upon to operate at capacities considerably above normal and when so operating the discharge velocity from the spreading conduit rapidly increases and may represent a very material amount of velocity head in comparison with the available head on the plant. A failure to'provide for ellicient deceleration of this velocity of discharge from the spreading or prin'iary draft tube may therefore materially restrict the fullload capacity of the turbine even in cases where the primary or spreading conduit is sufiicient in itself to take care of the ordinary and normal load conditions with high e'tliciency. The proper formation of the collector passages therefore may have a vital effect upon the full powercapacity of the turbine.

it should also be considered that by proefiicient collector passages the size of "y portion of the draft tube may be without serious loss of draft tube my but with a material reduction in the over-all dimensions of the entire draft tube, and consequently of the power-house and sub-structure.

lt hile T have shown my invention as applied to turbines having vertical axes it is obvious that with slight modification of structure my invention is likewise applicable. to turbines having horizontal shaftsJ I have also shown a draft tube and collector which receive waterin an axial directionand discharge it in radial or tangential direction, that is, along a plane at substantially right angles to the axis of the drafttube. It is of course apparent that the angle between the axis and the discharge direction need not be exactly a right angle asconditions of practice With the use of might makeit desirable to increase or decrease this angle somewhat.

'Vhile in the foregoing description I have distinguished between the primary draft tube and the collector, it will be recognized that in other forms, of my invention the primary draft tube and collector function may be so merged that no one portion of the structure may be termed a primary draft tube and the remainder a collector. Such. cases may nevertheless fall clearly within the scope of the present invention as set forth in the appended claiins.

By radially spreading draft tube as employed in the claims I. mean a tube which discharges the flow radially outward in all or let of said tube being cut away to form a spiral collector passage, and said spreading wall being continued in one direction to form an inclined wall of a second passage which receives the downstream flow directly from said tube, and a partition for separating said spiral and downstream passages.

2. A turbine having a draft tube formed of an outer circular spreading wall and a central cone projecting into the space surrounded by said wall, said spreading wall at the outlet of said tube being cut away to form a spiral collector passage, and said spreading wall being continued in one direction to form one wall of a second passage which receives the downstream flow directly from said tube, and a partition disposed between said spiral and downstream passages, one of said passages being located tangential to said tube and adapted to receive therefrom a flow having tangential. component of velocity.

3. A turbine having a draft tube formed of an outer circular spreading wall and a central cone projecting into the space surrounded by said wall, said spreading wall at the outlet of said tube being cut away to form a spiral collector passage of rectangular cross section, and said spreading wall being continued in one direction to form one wall of a second passage which receives the down-. stream flow directly from the tube, and means forming a wall for both of said passages.

4:- A turbine having a draft tube formed of an outer circular spreading wall and a central cone extending through the entire space surrounded by said wall, said spreading wall at the outlet of said tube being cut away to form a spiral collector passage of a gradually increasing cross section and said wall in one direction being continued along a surface which is slightly inclined from thenormal to the axis of said tube to form one wall of a second passage which receives the downstream flow directly from said tube, and means forming anotherwall of one of said passages.

5. In a turbine a radiallyspreading draft tube and a collector adapted to receive the flow from said tube and being offset with respect to said tube, said collector being of progressively increasing area, and adaptedto produce a gradual deceleration of flow therethroughand being provided with a partition to prevent the mingling therein of streams of different velocities.

6. A turbine formed with a draft tube anda collecting chamber, the outlet of said draft tube being partly formed-by a projection ex tending from the wall of said collection cha1nher, said projection'being extended in a downstream direction and offset relative'to said tube, and a pier between the extension and opposite wall for supporting said projection.

7. .A draft tube formed by two concentric surfaces of revolution turning from a substantially axial "direction to a radially outward direction, said surfaces terminating at a greater distance from the axis in one portion of the circumference than the remaining portion and a collector surroundingsaid tube and extending in a downstream direction therefrom, said collector having a portion of its floor and roof diverging in the direction of flowand the outer one of said 1 concentric surfaces terminating within said collector passage ata point below the adja- I cent roof portion. of the collector passage.

8. The combination with a draft tube, of a sage for receiving the directdownstream flow from the draft tube. I 9. The combination with a draft tube, of a collector having a passage provided with a spiral Wall starting at a lateral point of the draft tube, and means forming a second pas sage for receiving the direct downstream flow from the draft tube, said direct downstream passage extending inwardly from said lateral point to a point intermediate said lateral point and the spiral wall.

10. The combination with a draft tube, of a collector having a passage provided with a spiral wall extending in an upstream direction from a lateral point of the draft tube and curving into. a downstream direction, and means forming a passage for directly discharging the downstream flow from the draft tube, the depth of said spiral wall being greater than that of the direct discharge passage.

11. The combination with a draft tube, of a collector having a passage provided with a spiral wall extending in an upstream direction from a lateral point of the draftitube and curving into downst-reanr direction, and means forming a passage for directly C115;

charging the downstream flow from the draft tube, the depth of said spiral wall being greater than that of the direct discharge passage, and said direct: discharge passage; having-a verticallyrinclinedsurface in the down 12. The combinationwith adrafttube, of.

a collector having a passage provided with a spiral wall extendingin an upstream direction from apoint laterally otthe draft tube:

andrthen curving into a downstream direction, thereby permitting upstream flow from the draft I tube to be turned in .a a downstream direction, means torminga passage extending inadownstremn direction: for: receiving the direct downstream discharge i'rom the draft tube, and acone disposed in S2t1l1-'(l121ft.tllb.

for directing fluid flowto thedirectdischarge passage and to said passage having said spiral wall.

13.- The combination:with adratt tube having a flaring-inner wall and a projecting-bar.-

rel portion, a collector passage surrounding said barrel, an outer'portion of the main body of said barrel beingcylindrical, and another portion of the draft tubemerging with an extended root of said collector passagein a downstream direction, said passage which surrounds saidbarrel having a spiral 1 wall.

15. The combination with a drafttube, of a collector passage for receiving the discharge from said tube, comprising means forming a passage substantially tangent to said draft tube and being-offset with respect-to the central downstream H-XISOf the collector passage,

and'means forming a second passage surroundingone s1de ofthe draft tube, one of said passages having a roof disposed at'an elevation difl'ercnt irom the roof of: ch-exotherpassage.

16. 'lhe-combi-nation with a a draft. tube, of a collec-torp assage torreceiving tlie discharge troinsaiditube, comprising means forming a passage substantially tangent to 1 said draft;

tube at alateral pointthe-reol, means tor1ning a second passage surrounding one s1de oitthe dratttub'e, one of said passages having a roof disposed at an elevation :difl'ferentii rom.

the root of the otherpassage, and apier disposed'at the juncture of sa-idlroots forrsupporting the same from the floor of saidpassages. v

17. The COHlblntltlOIl*Wltllit draft tube, of a collector passage constituting only two.

downstream passages,-one otiwhich has a roof.

disposedat an elevation different from the root oflthe other passage.

18. The combinationwitha dratt'tube, of

a collector passage having only apairot' downstream passages whose combined Width is ofiset withrespect to the draft tube axis, and the roofs of" the respective passages being at different elevationsr 19. A turbine having a draft tube formed.

of an outer circular spreading wall and a central cone pro ect1ng into: th eespace sur rounded by said a wall, said spreading wall:

at the. outletot said tube being cutaway to form a spiral collector passage, and said spreading wall being continued in 011G.Cli1'GC.- tion to form an inclined horizontally extending wall of-a second passage which receives the downstream flow directly from said tube.

and a partition spaced downstream from said cone 'l'o-r separating said splral and down stream passages.

20. In a turbine a radially spreadingclraitt' tube and a collector adapted te receive the flow from said tube and being offset with re-v spect to said tube, said collector being of progressively increasing area, and adapted to produce a gradual deceleration of flow thereth'rough and being provided with apartitio n to prevent the mingling therein of streams of different velocities;

IiEl VIS FERRY MOODY.