US2156921A

US2156921A - Impulse turbine

Info

Publication number: US2156921A
Application number: US90625A
Authority: US
Inventors: Moody Lewis Ferry
Original assignee: Individual
Current assignee: Individual
Priority date: 1936-07-15
Filing date: 1936-07-15
Publication date: 1939-05-02
Anticipated expiration: 1956-05-02

Description

May 2, 1 39- L. F. MOODY 2 IMPULSE TURBINE Filed July 15, 1936 2 Sheets-Sheet l L. F. MOODY IMPULSE TURBINE May 2, 1939.

2 Sheets-Sheet '2- Filed July 15, 1956 INVENTQR L. EMOOc/ ATTOR Y Patented May 2, 1939 UNITED STATES PATENT OFFlCE Application July 15,

6 Claims.

This invention relates to Pelton water wheels or tangential impulse turbines having free jets and particularly to such wheels arranged with horizontal shafts. It comprises principally a new housing or casing formation for such wheels.

I have reason to believe that in Pelton wheels of conventional design the efliciency is frequently impaired to a material degree by the form of the casing due to reflection back on the buckets and jet of water thrown oif the buckets, with consequent interference with the fiow in the jet and buckets and increased windage or resistance to the wheel rotation. I have found that although from theoretic considerations the windage due to the air resistance to rotation should be reduced by a housing which leaves limited clearance around the runner, actually the efficiency may be less when the wheel is operating in a housing of conventional design than when the housing is entirely removed. I have also found in a laboratory test that in a Pelton unit of conventional design in normal operation a considerable quantity of water flows around the inner surface of the housing in the plane of the runner, so that this flow is in a position to fall back into the runner, to interfere with the jet and to disturb the action of the jet on the buckets.

It is on object of this invention to provide a housing formation in which water which is thrown outwardly from the buckets during their rotation will be guided away from the plane or the runner so that it will not be reflected back on the buckets, nor be capable of continuing its flow around the casing where it can cause interference with the jet or fall back into the runner. Another object is to permit the provision of limited clearance between runner and housing to minimize air resistance or windage on the runner, while at the same time avoiding interference from water thrown off the buckets, or the production of spray which would increase the windage.

The housing formation includes the following elements: first, a. circular inwardly projecting deflector either inserted within the cylindrical housing wall or replacing said wall, extending around the upper portion of the housing; second, the provision of a double wall in the outermost part of the housing on each side of the runner, the outermost wall being continuous with the deflector surface but the inner wall being spaced from the deflector to leave a circumferential slot, and the double wall forming a pocket or external conduit to carry away the water 1936, Serial No. 90,625

thrown off the buckets; and third, the provision of a shield above the nozzle and jet to deflect spray or stray flow clear of the jet. These features will, however, be more clearly understood from the following drawings and description, in which:

Fig. 1 is a vertical section through a Pelton wheel housing on the plane I-l of Fig. 2, the runner being indicated conventionally with only one of its circular series of buckets being shown;

Fig. 2 is a horizontal section through the housing along the line abode of Fig. I, the runner bucket and shaft being shown intact;

Fig. 3 is a vertical section of the same housing in a plane containing the shaft axis along the line 3--3 of Fig. 1, the runner buckets and shaft being shown intact;

Fig. 4a is a fragmentary section on line 4-4 of Fig. 1, to show the nozzle shield; and

Fig. 4b is a similar view of an alternative form of shield.

In Fig. 1 the water under pressure enters through the pipe and nozzle l, under control of the needle 2, forming the power jet 3 which impinges on the buckets 4 of the type havinga central splitter to divide the water between the two halves of the bucket. The buckets, only one of which is shown, are carried by the disk 5, the buckets and disk comprising the runner; and the runner is keyed to the main shaft 6 which drives an electric generator or other driven machine. charges through the discharge passage 1 which is continued downward through the concrete substructure, not shown, and drops into the tailrace below.

Around the runner is the housing 8, which is commonly constructed of plate steel or cast iron, and is here shown as of cast iron, suitable for a unit of small or moderate size. If of plate steel the formation would be similar but with the omission of rounded corners which would be made square to accord with plate steel construction. As viewed in Fig. 1, the part of the housing above the plane of the runner axis is semicircular, and is removable. The upper semi-circular wall is a portion of a surface of revolution generated by two straight or nearly straight diverging lines 9 in V formation, thus comprising the frusta of two cones. The sides of the casings are formed of an inner plane wall ID and an outer parallel wall il. These double walls are connected by the cylindrical walls l2, forming a pocket or passage M on each side of the runner. Any water thrown off from the runner, and re- After leaving the buckets the water dis- 7 taining a circumferential velocity imparted by the runner, tends to circulate circumferentially around the runner in the plane of the runner, but its outward centrifugal force causes it to recede from the runner and the V-shaped formation of the surface 9 deflects it to either side through the circumferential gap or slot l3 left between the inner side wall 10 and the outer wall 8. It then passes into the pockets [4 and is carried clear of the runner and prevented from reentering it. Any particles of water impinging on the wall 9 will be reflected laterally and not back toward the buckets.

In the lower part of the housing the wall l2 becomes straight and the pockets are carried downward as straight conduits, emptying into the discharge passage below the runner. On the right-hand side of Figs. 1 and 2, it will be noted that the pockets extend past the nozzle and jet on the outside of the inner side plates In, and the deflected water is thus carried clear of the nozzle and jet. The lower portions of the side plates are widened at l5 to receive the water discharged from the buckets at the point where the jet acts upon them. The sloping sides l5 deflect the discharge downward without reflecting it back on the buckets. When desired, some form of baffle, deflector or energy-destroyer (not shown) may be installed where the jet strikes the housing at the left of Fig. 1 under runaway or light-load conditions on the wheel. Without such special energy destroyer, the housing formation itself, as here shown, will provide a considerable degree of energy-destroying action, deflecting the free jet into the side pockets where it is formed into a whirling eddy and finally discharged downward.

Above the nozzle l is placed ashield [6, to catch and to deflect any stray flow or spray which has not had time to enter the side pockets and to pass off clear of the jet. The shield as here shown has a transverse entrance edge near the buckets, and is then carried downward on each side of the nozzle leaving spaces I! through which the stray flow can pass around the nozzle. In Fig. 4a the shield is of cast iron and in Fig. 419 it is slightly modified and simplified to suit plate steel construction.

For economy of construction, particularly in small units, the double side wall and side pockets may be omitted if so desired, only the deflecting V-shaped outer wall 9 being used, and the side walls l0 being spaced far enough from the buckets to permit the stray flow to drop clear of the runner. In larger installations, however, where maximum efliciency is important, it is advantageous to bring the casing walls close to the runner to reduce air resistance, using the double wall construction as shown.

It is believed that in the past efforts to improve the efliciency of Pelton wheels has centered largely on the design of the buckets and that insufficient attention has been directed to the housing. While the major portion of the flow entering the buckets is deflected outwardly and downwardly, and is directed into the discharge passage, the effects of viscosity in the fluid layers adjacent to the bucket surface and capillary forces or surface tension delay the discharge of a small but appreciable portion of the flow here termed stray flow, which is deflected from the intended path and finds its way around the upper portion of the housing. There is also probably an appreciable amount of spray formed during the action of the jet on the bucket edges, and

the air contained in the housing is likely to hold considerable amounts of water drops in suspension, increasing the runner windage during operation to a considerable degree above the windage in dry air. By forming the housing as here disclosed, means are provided for deflecting much of the stray flow and spray away from the runner and jet so that it will not cause increased windage resistance, disturbance of the jet, or, what is still more important, will not be re-entrained in the runner and interfere with the action of the jet on the buckets.

It will of course be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. In a Pelton impulse turbine having a runner with buckets of the central splitter type, a housing having a substantial portion formed as part of a surface of revolution generated by two inclined lines receding from the central plane of the runner to points beyond its sides While at the same time receding from the runner axis to form a ashaped circular surface located radially outside of the runner periphery and around a substantial portion thereof, and means for preventing water discharged along said V-shaped surface from reentering the portion of the housing in which the runner is located.

2. In an impulse turbine of the free-jet type having a runner with buckets of the central splitter type, a housing formed in part as a portion of a circular wall comprising two conical frustra, symmetrical about the central plane of the runner and having surfaces diverging from the runner to points beyond its sides and from the central plane of the runner in diagonal directions at least substantially to the runner sides, whereby said wall is located radially outside of said runner but in close proximity thereto in said central plane, and means for preventing water discharged along said circular wall from reentering the portion of the housing in which said runner is located.

3. An impulse turbine having, in combination, a runner with buckets of the central splitter type, and a housing, said housing being formed in part as a portion of a surface of revolution generated by two lines diverging diagonally from the central plane of the runner to points beyond its sides and from the runner axis; said surface of revolution being located radially outside of the runner periphery; a side wall on at least one side of said runner continuous with said surface of revolution; and a second side Wall spaced from said first side wall toward the runner, said two side Walls forming a passage between them; and a circular opening between the inner side wall and the surface of revolution through which water thrown off the runner can pass into said passage.

4. In a Pelton wheel, a jet-forming nozzle, a runner with buckets of the central splitter type, and a housing, said housing having a substantial portion of its wall formed as parts of conical frustra symmetrically disposed with respect to the central plane of the runner so that said wall diverges diagonally from the central plane of the runner to points beyond each side thereof while at the same time diverging from the runner axis; and a deflecting shield extending upwardly toward the runner from a point disposed immediately in advance of the nozzle and having an entrance edge closely adjacent to the runner buckets and a surface which extends partially around said nozzle and is adapted to guide any stray Water flow to each side of the nozzle and jet clear of contact with said jet.

5. An impulse turbine having, in combination, a runner having buckets of the central splitter type, and a housing, said housing being formed in part as a portion of a surface of revolution generated by two lines diverging diagonally from the central plane of the runner and from the runner axis; said surface of revolution being located radially outside of the runner periphery; a side wall on at least one side of said runner continuous with said surface of revolution; and a second side wall spaced from said first side wall toward the runner; said two side walls forming a passage between them; and a circular opening between the inner side wall and the surface of revolution through which water thrown off the runner can pass into said passage, said pas-- sages being continued on either side of the discharge portion of said housing and past the limits of the runner.

6. In a Pelton impulse turbine having a runner provided with buckets of the central splitter type, a housing having a circular wall formed as part of a surface of revolution generated by two inclined lines receding from the central plane of the runner while at the same time receding from the runner axis to form a V-shaped circular surface around a substantial portion of the runner periphery, and a discharge passage, said circular wall merging on one side of the runner into straight wall portions'comprising the end surfaces of the discharge passage, and said end surfaces continuing the same V- formation as characterizes the circular portion.

LEWIS FERRY MOODY.