US1713775A - Hydraulic draft tube - Google Patents

Description

Mall, 1929. L, Q Y 1,113,775

HYDRAULIC DRAFT TUBE Filed Nov. 2a. 1922 5 Sheets-Sheet 1 May 21, 1929. L, MOODY 1,713,775

HYDRAULIC DRAFT TUBE Filed Nov. 28, 1922 5 Sheets-Sheet 2 May 21, 1%29. 1 MOODY 1,713,775

HYDRAULIC DRAFT TUBE Filed Nov. 28 1922 5 Sheets-Sheet s oawtoz May 21, 1929 F, MOQDY 1,713,775

HYDRAULIC DRAFT TUBE Filed Nov. 28, 1922 5 Sheets-Sheet 5 INVENTOR 7 Zvm%/ Patented May 21, 1929.

UNITED STATES LEWIS FERRY MOODY, 0F PHILADELPHIA, PENNSYLVANIA.

. HYDRAULIC DRAFT TUBE.

Application filed November 28, 1922. Serial No. 608,769.

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 of 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 radial-direction for discharge into the tail race.

In many modern hydraulic power plants the turbines are placed in a row with vertical shafts, the water entering the turbines on one side of the row from the penstocks or forebay and discharging at the other side into the tail race. The water leaves the runners in a downward direction at high velocity and some means should be provided which will reduce this velocity so as to correspondingly reduce the back pressure on the turbine runners and which will likewise turn the flow into a horizontal down stream direction. This means should be constructed so as 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.

For the purpose of reducing the velocity, draft tubes have been used which direct the flow from the runner radially outward 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 down-stream direction. Certain portions of the flow must be turned through substantially 180 while other portions, which leave the tube in a direction more nearly approaching the down-stream 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 reduced and 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 down-stream would be solved by the use of any suitable collector which would not cause an appreciable loss of head.

With 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 designed as to reduce further the velocity of the water and to regain this energy. The water leaving the draft tube in an Lip-stream direction may be conveniently collected from the tube by one or more spiral passages extending circumferentially around the cylindrical outlet of the tube and discharging tangentially down stream toward the tail race.

These spiral passages should be enlarged at a rate greater than is necessary to accommod-ate the cumulative flow so that the velocity of the flow therethrough will be gradually reduced.

One of the objects of the present invention is 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 and uniformly to reduce the velocity of this flow and so regain its kinetic energy. 7

Another object of my invention is to provide in addition to the spiral collector passages above described an effective means for decelerating that portion of the flow which does not enter the spiral passages.

Numerous other objects and advantages will appear from the following description taken in connection with the accompanying drawings which illustrate certain of the preferred embodiments of my invention and wherein Fig. 1 is a view showing vertical sections of a draft tube and collector taken on the line 11 of Fig. 2 looking in the direction of the arrows.

Fig. 2 is a view. showing a horizontalsection on the line 22 of Fig.1.

Fig. 3 is a View similar to Fig. 1 but showing a slightly modified construction.

Fig. 4 is a view showing a vertical section, on the line 4-4 of Fig. 5, of a still further modified form of my invention.

Fig. 5 shows a horizontal section taken on line 5--5 of Fig. 4.

Fig. 6 a vertical section on the line 6-6 of Fig. 5.

Fig. 7 which is a sectional View on line 7-7 ofFig. 8 shows a still further modification.

Fig. 8 is a horizontal sectional view on the line 8-8 of Fig. 7.

Fig. 9 shows avertical sectional" view on thelin'e' 9-9 of Fig. 8;

Fig. 10 shows a vertical section taken on the line 101O of Fig.3 looking in thedirec-,

tion of the arrows;

Fig. 11 shows in vertical section on the line 12-12 of Fig. 11.

Fig. 13 a vertical section the line'.13"13 of Fig. 12.

Fig. '14 a vertical section on the line l l la 01' Fig. 12 taken in the direction of the arrows. Fig. 15 represents a vertical section on line 15-15 of Fig. 16 and shows a modification in the form and'arrangement of the collector passage and- J V Fig; 16 'showsa section on line 1616ot Fig.15.

Referring to Figs. 1 and 2 reference character 20 indicates generallythe primary draft tubeand 21 the collector. The primary draft tube asshown istormed of an outer wall 22 havingja slightly tapered or conical upper portion 23 and gradually curved outward to a"horizontaldirection at its lower end. Projecting upwardly from the floor 25 of the collector passage into the flaring end of the wall 22 and concentric'therewith is a cone 26 whose concave surface is formed in relation to the outline of the flared end of the wall 22. The outer wall and cone'i lti' together form the primary draft tube which serves to direct the flow downward from the turbine run-- ner and outwardly into a horizontal plane. The cross sectional areaof this tubeas shown increases gradually so as to give a gradual decelerationto the meridian components of thefiow, and at theysame time the tube is adapted-to handle ei'i'ic-iently flow containing whirling;components about the turbine axis.

The outer wall or the tube is cut away to form the collector passage 21, the material around the outer wall of the tube'thus forminga projection 28, depending intothe collector chamber. The general contour of the bottom otthis projection is shown in Fig. 2 by the'line 29. This projection joins the side wall 30 or" the collector passage at a point 31 farthest removed from the tail water and is formed with a vertical side wall joining its bottom with the upper wall 33 of the'collector chamberat a point 32 nearest the tail water. Between these two diametrically opposite points the side wall of the projection 28'slopes inwardly a horizontal distance represented hy'the distancebetween the lines 29 and 35 in Fig. 2, thus forming a channel 36 which lies above or overhangs the flared portion of the draft tube. The outer side wall30 of the collector chamber recedes from the "projection 28st) as to provide a passage of constant- 1y increasing area which will take care of the It will be noted that the water flowing out otthe draft tube in the general down-stream direction does not pass upward into the overhanging channel36 but flows for a certain distance betwen two flatsurfaces formed by the fioor 25 and the bottom of theprojection 28. In so flowing it difiuses and isspread laterally in a general direction indicated by lines 10? and er of Fi 2. Water flowing laterally and water which flows in. anupstream direction from the draft tube will turn upwardly to till the passage 36. The lateral and upstream flows merge within passage 36 and flow in a downstream direction therein. The new in the passage 36 when reaching the downstream edge of member 28 (see Fig. 2) merges with the downstream flow disposed between the bottom and the opposed surface of projection 28. There is thus provided, in effect, a separate passage for the water leaving the draft tube in the down-stream direction and one which permits the flow to increase in area and consequently'to decrease in velocity. r

l t the rapidly moving water which is bein dischar item the draft tube in a downstream tlllebblOll which I will term the direct flow were permittedto discharge directly into tail water or other wide open space, that-is, a space which does not provide for its gradual dillusion, the kinetic energy of the flow-would be lost. Furthermore it the direct flow were permitted to mix with the slower moving water from the other portions of the draft tube eddies andcros s-currents would be created which would cause 7 a further loss of energy.

1n the form shown in Figs. 1 and 2 the upper. and lower surfaces between which the direct flow proceeds are parallel, while in Fig.3 lhave inclinedthe upper surface 43 upwardly toward'tailwater by a small angle 0: so as to give a greater reduction in velocity. The angle between the upper and lower surfaces should not exceed approximately 15 or in extreme cases 20, if an etlicient velocity conversion is to be secured.

1n the form of my invention shown in Figs. 4 to 6' Ihave maintained the outer wall of the projection 28- vertical or substantially vertical and so there is no overhanging channel 36 as shown in the prior figures. The 1 upper wall of the collector chamber is curved upwardly as is indicated at 1 1 in Fig. 6 to provide thenecessary increase in area. The lower end of the projection 28 in thesefigures has a different contour from that shown in Fig. 2 as may be readily seen. In Fig. 5 the projection extends much further down-stream and is joined at its extended end to the floor of the discharge passage by means of a'pier or partition 45. This partition is of such a form and is located at such a distance from the discharge end of the tube as not to interfere with the direct flow toward the tail water.

The structure shownin Figs. 4t to 6 is less expensive to build than that shown in the previous figures and may be employed when somewhat more space is available.

The curved collector passages shown in Figs. 1 to 6 are of the double spiral type and are intended to be employed where the water is discharged from the draft tube with only small degrees of whirl, that is, such a structure is intended to be used with turbines of moderate or low specific speeds. In the form of my invention shown in the remaining figures I have provided for the collection of a whirling discharge.

In the form shown in Figs. 7 to 10 I provide a single curved collector channel which starts at a point 40 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 47 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 lower walls horizontal except that the upper wall of the outer passage is inclined upward at an angle preferably not to exceed about 15.

The passage 4-9 for discharging the direct flow is substantially rectangular in. cross seetion and is formed by the floor 25, top wall 50 which is inclined upwardly at an angle not to exceed about 20, 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.

It will be noted that the draft tubes as shown in Figs. 7 and 9 are much shorter than those shown in the previous figures and do not have theintermediate straight conical portion between the runner and the beginning of the spreading portion.

The form of my invention shown in Figs. 11 to 14 is similar to that shown in Figs. 7 to 10 except in the former the curved collector passage does not terminate in a straight 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.

The partition of Figs. 7 and 8 is omitted, there being merely a strut 56 between the upwardly extending top wall of the 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 the over-hanging passage collector shown in Fig. 1.

In Figs. 15 and 16 I have shown a modified construction and arrangement of collector for use where lateral space is limited. The collector passage here shown surrounds the outlet of the draft tube and extends downwardly therefrom and under the cone 60. The form of the inner wall of. the expanding collector passage beneath the cone is indicated by the line 61 beginning at the point 62 where this wall joins the outer wall 63and ending at 64 at the outlet While I have shown a primary draft tube which is 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. 'With theuse of 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 conduit is suiiiciently small to be sothrown 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 efficient deceleration of this yelocity of discharge from the spreading or primary draft tube may therefore materially restrict the full-load *apacity of the turbine even in cases where the primary or spreading conduit is sutlicient in itself to take care of the ordinary and normal load conditions with high eificiency. The proper formation of the collector passages therefore may have a vital effect upon the full power capacity of the turbine.

It should also be considered that by providing efficient collector passages the size of the primary portion of the draft tube may be cut down without serious loss of draft tube efficiency, but with a material reduction in the over-all dimensions of the entire draft tube, and consequently of the power-house and substructure.

lVhile I 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 shafts. I have also shown a draft tube and collector which receive water in an axial direction and dis charge it in a radial or tangential direction, that is. along a plane at substantially right angles to the axis of the draft tube. It is of course apparent that the angle between the axis and the discharge direction need not be- ;present invention as set forth Ied claims-t 7 5 exactly a right angle'as conditions of practice might make it desirableLto increase or decrease thisangle somewhat. U Z V WVh1le in the foregoing ClBSOIIPt ZLOIL I have distinguished between the primarydraft tube and the. collector, 1t willberecognized that in other forms of my invention the primary draft tub'eand collector function maybeso merged-that no one portion of the struc ure may be termed a primary draft tube and the remainder a collector. Such cases maynevertheless fall clearly within the scope of the in theappe'ncb ing into said horizontal passage and said wall havlng a port on elongated in a downstream direction to form a roof extension inthe horizontal passage, whereby said horizontal. passagecomprisesa relatively deep side passage and a relatively shallow passage, the

body portion of saiddown stream portion bcing so shaped asto ;lie entirelyinside of'a straight horizontal ;lineicontacting with any point of aside surface of saidbody portion.

2; A draft tube for hydraulic turbines, comprising vertical and horizontal passages, said vertical passage having a wall projecting'into saidhorizontal passage and said wall having a portionelongated in a down stream direction to form a roof extension in the horizontal passage,-whereby sa d horizontal passage comprises a relatively deep side passage and a, relatively shallow passage, the body portion of said down stream portion being so shaped'as to lie entirely inside of a straight horizontal line contactingwithany point of a sidesurface of. said body portion, the upstreamwall of said horizontal passagebeing substantially tangent to one point of theontletiof said vertical passage. I

3, A draft tube for. hydraulic turbines, comprising substantially vertical and horizontal passages, said vertical pass geihaving a wall projecting into said horizontal,pas

sageand said wall having a portion cion-' gatedin a down stream direction toform a froof extension in the horizontal passage 7 whereby there are formed relatively deep side "passages and .a'trelatively shallow central passage, the body portion of said down stream extension bemg so shaped as to he entirely inside of a straight horizontal line 'contact- 7 ing with any point of the sidesurfaces of said body portion. 7 I

A draft tube for hydraulic-turbines,

shaped,

' at. A draft tube for hydraulic turbines,

comprising substantially vertical and hor1- zontal passages, said vertical-passage having a wall projecting into said horizontalpassage to provide an outlet for the vertical passage, said projecting wall being elongated in a down stream directionto form an offset e roof, whereby said horizontalqpassage includes passages having upper surfaces (118* posed at different elevations, the body portion of saidprojected'wall and its elongated portion being so shaped, as to heentirely 1nside of a 'aight horizontal line contacting vwith any point of a side surface of said body portion. p Y.

5. A draft tube for hydraulic turbines, comprising substantially vertically and horizontally extending walls forming substantially vertical. and horizontal passages, said verti cal wall projecting intosaid horizontal-pas. sage and extending up and down-stream, the

- n of said projection down-stream being reater than that Lip-stream, and th ebody r portion of said projecting Wall and itsdown stream proje'ction'being so shaped asto lie entirely inside of a straight horizontal line contactin with any point of the side surfaces of saidbody portions j. l

i 6. A draft tube for hydraulic turbines, comprising substantially vertically and horizontally extendin g Walls forming substantially, vertical and horizontal passages, said vertical wall projecting into said horizontal passageand extending up and down-stream, the dnnension. of said pro ection down-stream being greaterthan that up-stream and the body portion of said projecting wall and its downstream projections being so shaped as to lie entirely inside of a straight horizontal line contacting with any pointof the side surfacesof said body portion, and the floor of said horizontal passage. and the under surface of said downstream extension being relatively diverged. l a r a a 7. A draft tube 'for hydraulic turbines comprising a horizontal passageprovided with a roof' and floors, and a vertical passage projecting into said horizontal passage and having a flared end the forward part of which is continued forwardly to form a longitudinal roof extension disposed atalower elevation than that of said'other roof, and said floor and roof extension being relatively diverged and thebody portioniof said projecting wall and its downstream projection being so shaped as to lie entirely inside of a straight horizontal line contacting with any point of the side surfaces of said body portion. is v 8.7 A draft tube for -,a hydraulic turbine, comprising a horizontal passage and a vertical passage having a wall projecting into said horizontal passage, the rip-stream side of said well being. of generally elliptical formation while its down-stream side-iris 'wedge 9. A draft tube for a hydraulic turbine, comprising a horizontal passage and a vertical passage having a wall projecting into said' wall being of generally elliptical formation while its down-stream side is wedge shaped, and means forming a projection extending laterally from said wall.

11. In a turbine, a draft tube having a radially spreading vertical passage provided with an outlet, and a collector passage having a spiral side wall beginning adjacent the outlet of said vertical passage and having a portion occupying space lying nearer to the axis of said vertical passage than the outlet thereof, a direct discharge portion forming a downstream continuation of the vertical passage outlet and adapted to decelerate the flow between upper and lower surfaces, and a lateral projection extending substantially the length of said direct discharge portion.

12. In a turbine, a draft tube having a radially spreading vertical passage provided with an. outlet and a collector having a spiral side wall beginning adjacent the outlet of said vertical passage and having a portion occupying space above the outlet of vertical passage tube and nearer to the axis thereof than said outlet is, a direct discharge portion forming a down-stream continuation of the vertical passage outlet and adapted to de celerate the flow between upper and lower surfaces, and a lateral projection extending the full length of said discharge portion.

13. In a turbine, a draft tube having a radially spreading vertical passage provided with an outlet and a collector adapted to receive water from said vertical passage at a considerable velocity and to cause said water to be continuously decelerated, said collector occupying space above and within the radial limits of the outlet of said vertical passage, and having a spiral side wall beginning adjacent the out-let of said vertical passage, a direct discharge portion forming a downstream continuation of the vertical passage outlet adapted to decelerate the flow between upper and lower surfaces.

14. In a turbine, a draft tube having a radially spreading vertical passage provided with an outlet and a collector adapted to receive water from said vertical passage at a considerable velocity and to cause said water to be continuously decelerated, said col lector occupying space above and within the radial limits of the outlet-of said draft tube vertical passage, and having a' spiral side wall beginning adjacent the outlet of said vertical passage, a direct discharge portion forming a down-stream continuation of the vertical passage outlet and adapted to decelcrate the flow between upper and lower surfaces, and a lateral projection extending the full length of said discharge portion.

15. A draft tube having means for discharging water radially in substantially all directions, means for conducting the water discharged in one direction between fiow surfaces which diverge by an angle not exceed ing 20, and means for collecting the water discharged in other directions and conducting it through a channel of increasing area whereby it is turned into the said one direction and its velocity diminished.

16. The combination in a draft tube comprising a radially spreading vertical passage provided with an outlet and a collector formed of two spiral. passages which are arranged to receive water discharged from said vertical passage in substantially all directions except a general down-stream direction, said vertical passage having a wall projecting into said collector to form the outlet of said vertical passage, and said wall,

having a continuation in a down stream direction to form a roof of a passage to receive and conduct, toward the tail race, water discharged in a downstream direction from said vertical passage, said continuation having a port-ion extended radially with respect to the main body portion thereof and the outer edge of one portion having a curvature different from that of the outer surface of the other portion, and all of said passages gradually increasing inarea at such rates that the velocity head of the flow entering said passage is efficiently converted into pressure head.

17. A draft tube for hydraulic turbines, comprising walls forming substantially vertical and horizontal passages, the wall of said vertical passage projecting into said horizontal passage and being turned so as to extend up and downstream, the dimension of said downstream project-ion being greater than that upstream and the body portion of said projecting wall and its downstream projection being so shaped as to lie entirely inside of a straight horizontal line contacting with any point of the side surfaces of said body portion, while the side surfaces of said downstream projection have vertical portions of material depth.

18. A draft tube for hydraulic turbines, comprising walls forming substantially vertical and horizontal passages, the, wall of said vertical passage projecting into said horizontal passage and being turned so as to extend up and downstream, the dimension of said downstream projection being greater than that upstream and the body portion of: said projecting Wall and its downstream pro-' jection being so shaped as to lie'entirely in-' side of a straight horizontal line contacting With any point of the side surfaces of said body portion, whereby said horizontal passage has twolateralpassages which are dis-- posed entirely above the ffloor of said horizontal passage. .7 q

19. A draft tube for hydraulic turbines,

comprising Walls forming substantially vertical and horizontal passages, the Wall of said vertical passage projecting into said horizontalpassage and being turned so-as to extend up and downstream thedimension of said downstream projection being greater than that upstream and the bodyportion of said projecting all and its downstream pro:

jectionbei'ng so shaped as tolie entirely inside of a straight horizontal line contacting with any point of the side surfaces of said.

body portion, whereby said-horizontal passage has two lateral passages of greater depth than the passage beneath the said. downstream projection and said lateral passages being disposed substantially entirely above the flow of said passage beneath the downstream pro ection.

LEWIS FEa YMeon CERTIFICATE OF CORRECTION.

Patent No. 1,713, 775. Granted May 21, 1929, to

LEWIS FERRY MOODY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 6, line 27, claim 19, for the word "flow" read "floor"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of July, A. D. 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents.

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