US2392673A - Elastic fluid turbine - Google Patents

Description

Jan. 8, 1946. H. KRAFT 2,392,673

ELASTIC FLUID TURBINE Filed Aug. 2'7. 1943 2 Sheets-Sheet 1 Figl.

Inventor: Hans Kraft,

His tto rney.

Jan. 8, 1946. H KRAFT 2,392,673

ELASTIC FLUID TURBINE Filed Aug. 27, 1943 2 Sheets-Sheet 2 Inventor: Hans Kra ft,

His/Attorney.

Patented Jan. 8, 1946 ELASTIC FLUID TURBINE Hans Kraft, Schenectady, N. Y., asslgnor to General Electric Company, a corporation of New York Application August 27, 1943, Serial No. 500,232

11 Claims.

The present invention relates to elastic fluid turbines of the axial flow impulse type having nozzle and bucket passage combinations for converting thermodynamic energy of elastic fluid into mechanical energy or torque of the turbine shaft. The nozzles of these combinations are formed by stationary circumferentially spaced partitions supported on the turbine casing. and the bucket passages of said combinations are formed by circumferentially spaced, axially curved buckets secured to a disk or like support to form a bucket wheel or rotor rotatably supported by a shaft. In a pure impulse turbine all the pressure drop of the elastic fluid is effected by expansion within the nozzle passages, and no pressure drop takes place within the bucket passages. The fluid pressure at the exit of the bucket passages is the same as at the inlet. On its passage through the nozzles the fluid pressure is reduced. pressure energy of the fluid being converted into velocity energy and this velocity energy is in part converted into mechanical energy as the fluid passes through the bucket passages. A pure impulse turbine has the same uniform pressure distribution across the inlet and the exit of the bucket passages. This is important because it precludes leakage around the bucket passages with the resultant tip and root losses.

Heretofore this was the physical conception of the impulse turbine stage. bucket wheel were imagined to pass through a number of individual steam jets issuing from the nozzle openings. The buckets were intentionally made so long that at no place on its passage through the bucket was the jet interfered with by outer and inner bucket side walls. The overlap of the buckets relative to the Jet was very large. As both the art of turbine building and the science of fluid mechanics developed it became clear that a free Jet of a. fluid is not free when movin in its own surrounding atmosphere; e. g. a water jet in an "atmosphere" of air may be considered as free but a water jet in an atmosphere of water is subject to entrainment and mixing phenomena at the jet boundaries, as is a steam jet in steam. These phenomena destroy energy and thus are the cause oi losses in a turbine stage. In consequence the overlap was reduced. Now the single jets impinged on the bucket outer shroud and also were i restrained by the low pressure they created at the bucket root. This action resulted in a restraint upon the tangentially moving jets. This restraint had to be transferred to the jet fluid in the form of fluid pressure. Hence, there now existed in The buckets on the the bucket a radially variable pressure, lower at the root and higher at the tip.

Concurrently with this development the knowled e gained headway that the most efilcient design of a. turbine stage would result from a design that abandoned the conception of single jets altogether. The moving steam or gas is considered as a continuous body of fluid flowing as a unit through rows of nozzles and buckets without distinct separatin surfaces between jets. This flow whenever it moves tangentially must move on a circular path around the turbine axis. i. e., it must flow like the concentric circular flow pattern of a vortex. This kind of design is known as vortex design (sometimes called constant circulation" design). It is based on the vortex pattern for the tangential velocity components of the steam and it accepts at the same time the resulting radial pressure variations. Turbine designs based on this principle are known but they are not pure impulse turbines.

In consequence, until now it has not been possible to produce turbine designs of maximum efflciency in which the ideal condition of impulse design is accomplished. Present day turbines actually have leakage losses around the bucket passages which ordinarily are reduced by the provision of close clearances with sealing edges at the inner and outer ends of the bucket passages.

The object 0! my invention is to provide improved nozzle and bucket passage combinations whereby substantially ideal impulse operation may be attained, thus (al eliminating the need of close clearances for high efficiency and further (b) at the same time shaping the passages so as to eliminate certain losses occurring in passages not so shaped.

For a consideration of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto in connection with the accompanying drawings.

In the accompanying drawings Fig. 1 to 4 are explanatory views. Fig. 1 illustrates a turbine section with a nozzle and bucket combination of conventional impulse turbine design; Fig. 2 is an enlarged sectional view of several nozzles and buckets developed along line 2--2 of Fig. 1; Fig. 3 is an explanatory view of the flow principle involved in my invention: Fig. 4 is a part of Fig. 3 to an enlarged scale together with some explanatory vector diagrams: Fig. 5 is a sectional view of a turbine embodying my invention; Fig. 6 is a modification of my invention; Figs. '7 to 10 illustrate top and front of two nozzle partitions of Fig. and Figs. 11 and 12 show front and top views or a bucket according to my invention.

The conventional turbine arrangement of Fig. 1 comprises a rotor with bucket wheels Ill, each having a plurality of circumferentially spaced buckets H with an outer shroud band l2 and a disk or support It rotatably disposed within a turbine casing IS. The buckets H with the inner disk l0 and the shroud band I2 form a plurality of circumi'erentially spaced bucket passages I 4 (Fig. 2). Fluid is conducted to the bucket passages or each wheel by means of diaphragms or nozzle plates it having a plurality of circumferentially spaced nozzle partitions l1 with inner ends secured to a disk Ill and outer ends fastened to a ring l9 supported on the turbine casing IS. The partitions I! with the disk l8 and the ring I9 form circumierentially spaced nozzle passages 20, Fig. 2.

Elastic fluid, steam, gas or the like is supplied to the inlet of the nozzle passage 20 at an inlet pressure 12. We may assume that this pressure is uniform over the entire inlet area of each nozzle passage. A part 01' the pressure energy of the fluid is converted into velocity energy as the fluid passes through the nozzle, leaving the nozzle at a mean pressure pm and a mean velocity Um. In an ideal impulse turbine the pressure and the velocity of the fluid should be constant over the entire exit area of the nozzle. Actually with conventional turbine designs this is not the case. The pressure increases from the root to the tip of the exit area, whereas the velocity decreases correspondingly from the root to the tip of the exit area, the pressure at the root or the exit area having a value p: and at the tip a value pl, Fig. 1. This increase in pressure in the direction from root to tip, sometimes termed "pressure gradient, is due to the circumferential or rotational velocity of the fluid. In Fig. 2 I have indicated by a vector v the average absolute velocity of a fluid particle A in the exit area of the nozzle 20. This absolute velocity v has two components; a component vi constituting a rotational velocity (around the axis of rotation of the turbine), and a component v; constituting an axial velocity (parallel to the axis of rotation of the turbine). Thus, the particle A is rotated about the turbine axis at a speed represented by the velocity vector vi. Like any other mass constrained to rotate about a center, the particle is subject to centrifugal force tending to force it radially outward, thus requiring that the fluid build up a pressure gradient in the radial direction to constrain the particle to its circular path. This pressure gradlent from another viewpoint constitutes the centripetal force which balances the centrifugal force 01' the particle A and prevents it from moving radially outward.

The pressure gradient in the radial direction in the exit area of the nozzle is undesirable. As pointed out above, it results in an outlet pressure in at the tip of the nozzle exit which is higher than the pressure Pr at the root of the nozzle exit. If we assume that the mean exit pressure of the nozzle area is pm and that this mean pressure pm also exists over the entire exit area of the bucket, then it is clear that the higher pressure p: at the tip of the nozzle leads to leakage around the tip of the bucket from its inlet towards its outlet. Other undesirable fluid flows including leakage of fluid in the opposite direction take place around the root or the inner portion of the bucket passage, the bucket exit pressure at the root pm being greater than the bucket inlet pressure pr. This leakage usually takes place through balance holes 2| in the bucket disk. In addition, with the exit pressure pm higher than the pressure pr at the root of the bucket passage, the fluid through the bucket passage has to overcome increasing pressure which is undesirable because it leads to non-uniformity of the fluid flow and the formation of eddies in each bucket passage. Thus, the conventional nozzle or nozzle shape by its action imparts to the fluid a rotational velocity (having a certain magnitude and a certain direction) about the axis of rotation of the turbine which results in an undesirable pressure gradient in the radial direction in the exit area of the nozzle and accordingly in the clearance space between the nozzle and the bucket passage with resultant leakage losses around the bucket passage and undesirable eddies at the base of the bucket.

In accordance with my invention I provide an improved nozzle or nozzle shape whereby the elastic fluid leaves the nozzle exit area at average velocitie and pressures which are substantially the same for radially spaced portions of the nozzle passage. Under this condition the undesirable radial pressure gradient in the clearance space between the nozzles and the buckets is eliminated, thus improving the efllciency of the turbine by the substantial elimination of previously described leakage losses at tip and root and eddies at the root. To this end the nozzle passages according to my invention are shaped so that in addition to the aforementioned circumferential velocity about the turbine axis an additional rotational velocity within the plane of the turbine axis is imparted to the elastic fluid. From another viewpoint, each particle is caused to move at a velocity which has two components; a component in (described above) around the axis of rotation, and a second component 12: located in a plane through the axis of rotation and constituting a rotational velocity about a center located radially beyond the nozzle.

In the explanatory views of Figs. 3 and 4 I have shown a ring 25 having an axis of rotation 26 corresponding to the axis of rotation of a turbine. The ring 25 constitutes a velocity ring representing the rotatlonal velocity vectors Di to which a fluid is subjected in the nozzle exit of the conventional turbine, as described above. On this velocity ring I superimpose a second so-called smoke ring or hollow toroidal-shaped velocity ring 21 concentric with and embracing the ring 25. The velocity ring 21 has a wall ring-shaped in planes through the centerline of rotation 25. The smoke ring 21 broadly constitutes a toroidal shell formed by the rotation of two approximately concentric circles or closed curves 2!], 30 about the turbine axis 26 which is located in plane with said circles. Thus, the toroidal shell has an inner toroidal surface (formed by circle 29) and an outer toroidal surface (formed by circle 30), in the present example shown concentric with the inner surface. The toroidal flow path 21 will be readily recognized as a "ring vortex" by those skilled in this art. To the particle A with the velocity component in along the ring 25 we impart now another velocity component on, which latter constitutes a velocity of rotation about the toroidal centerline 28. This centerline (28, Fig. 4) is located radially beyond the ring 25. As indicated in Fig. 4, the centrifugal force 21 due to the rotational velocity in is opposed to the centrifugal force 22 due to the rotational velocity v2, and if we make these two centrifugal forces alike by properly dimensioning the toroidal shell then the particle A with the resultant velocity o=v1+m will no longer produce a pressure gradient across the exit area of the nozzle passage. A nozzle passage according to my invention then is shaped so that it will impart a velocity v to the fluid which is the resultant of two components or and m. the component '01 representing the rotational velocity about the axis of rotation of the turbine and the component I: representing a rotational velocity within the plane of the axis of rotation.

In Fig. 4 I have illustrated the velocity components vi and 122 of two radially spaced fluid particles located in two intersecting planes of rotation, a plane of rotation 35 of the ring 25 and a plane of rotation 36 of the toroidal shell 21. The velocities in in the plane of rotation of the fluid about the turbine axis like any vortex flow velocities decrease in radial direction from the turbine center having a maximum magnitude Ulr at the root and a minimum magnitude on at the tip. The same rule applies to the velocities oz in the plane 35. They too like any smoke ring velocities decrease with increasing radii from the mean center 28 of the smoke ring 2'! having a maximum magnitude v21 at the inner surface of the toroid and a minimum magnitude v2.0 at the outer surface of the toroid. The resultant of the components on and on is v; and the resultant of the components on and v2.0 is m. The two resultants Dy and to. have different directions but equal magnitudes. Hence, a nozzle passage according to my invention is shaped to impart to the fluid velocities at and Hz at the tip and the root respectively of the passage. To this end the partitions forming said passages form different exit angles 1 at the tip and 2 at the root. Thus. in order to eliminate the radial pressure gradient in the clearance space between the nozzles and the bucket passages the nozzle partitions must have exit angles decreasing according to a certain function from the tip towards the root of, the partition. Such a nozzle partition must be warped in a prescribed manner. This warping can be readily visualized in Fig. 4. A line connecting the ends of the vectors v and U2 is inclined towards the line connecting the origins of the vectors vy and Dz. Thus, if the inlet edge of a partition according to my invention is made, for instance, radial through the turbine center, the remaining surface of the partition, in particular the outlet portion thereof, will not have any other radial lines through the turbine center. The angle wp between the vectors in and U2 determines the degree of warping of the partition,

The new average exit velocities in the nozzle outlet area of a nozzle arrangement according to my invention, as pointed out'above, are constant but have increasing exit angles from root to tip, in contrast to the aforementioned conventional nozzles in which the exit velocities decrease from root to tip but have constant exit angles.

While the velocities in the exit area of my improved nozzle are constant, the components of these velocities in the axial and rotational direction vary. The axial components are the velocities m in Fig. 4 which increase from the velocity v2.0 at the root to the velocity ya at the tip while the rotational velocities U'l decrease from the velocity on at the root to the velocity on at the tip. The velocities or which are superimposed upon the velocities U1 are parallel to the turbine axis and represent the true axial exit velocity in the outlet area of the nozzle. These axial velocities are obtained by properly warping the partitions, particularly the outlet DOItiOlls thereof. In addition, it becomes necessary properl to shape the inner and outer walls of each nozzle passage. The conventional nozzle passage, as shown in Fig. i. has inner and out r cylindrical walls formed by the disk l8 and the ring l9 respectively. The nozzle passage accordin to my invention is provided with inner and outer walls conforming to the outer and inner surfaces of the toroidal shell 21. These surfaces are parts of toroidal or smoke ring surfaces. Thus. while the conventional nozzle passage is curved only in axial direction, a nozzle passage according to my invention becomes curved in axial direction as well as in a plane through the turbine axis. In actual practice only a small angular portion of the toroidal surfaces in Fig. 4 is used as indicated by an angle a. Therefore. for practical purposes it. is sufiicient in many instances to mak the inner and outer wall surfaces of the nozzle ('Ollll'nl with surfaces approaching those of the toroidal shell for the small angle u and with the spines of the cones located in the center of rotation of the turbine.

In view of the warping of the outlet portions of the partitions it is necessar in a turbine according to my invention to warp correspondingly the inlet portions of the buckets of such turbine. taking into consideration the rotational velocity of the bucket wheel at different radiall spaced points of the bucket inlet edge. As the rotational velocity of a bucket increases in radial direction, increasing velocity vectors must be added to the corresponding exit velocities of the nozzle and it can be readily seen that in view or the increase of these velocity vectors the warping of the bucket will be greater than that of the partition. If we designate the angle between the relative entrance velocities at the root and the tip of the bucket passage with we then this angle we must be greater than the aforementioned angle zap. The inner and outer walls of the bucket passages. usually formed by a bucket disk and an outer shroud band, may be cylindrical as in a conventional turbine design or these inner and outer walls ma be curved in axial direction to form a continuation of the curvature of the nozzle side walls or partitions. In the first mentioned arrangement the nozzle passages succeeding a bucket wheel have a curvature forming a continuation of that of the nozzle passages ahead of such bucket passages.

In Figs. 5 and 6 I have shown two typical designs of nozzle bucket combinations according to m invention. The turbine arrangement. of Fig, 5 comprises a casing 40, a high pressure stage including a diaphragm or nozzle plate 4i and a bucket wheel 42 and a lower pressure stage including a diaphragm l3 and a bucket wheel 45. The diaphragm I has circumlerentially spaced partitions 45 shown in detail in Fi s. 7 and 8. These partitions are warped having outlet or exit portions forming exit angles increasing from the root 46 to the tip 41. The partitions 45 together with the inner disk and an outer rim of the diaphragm form nozzles. The inner and outer walls of these nozzles defined by the corresponding surfaces 48 and 49 of the inner disk and the outer rim are curved. They form surfaces of a portion of a smoke ring or toroidal shell as described above. This curvature is also indicated in Fig. 8 although this does not necessarily imply that the end faces of the partitions have to be machined to conform to said smoke ring surfaces.

The bucket wheel 42 has circumferentially spaced buckets 50 with inlet angles, as described above, and conventional cylindrical inner and outer surfaces II and 52 respectively formed by a bucket disk and an outer shroud band.

The diaphragm 43 of the low pressure stage which during operation receives fluid from the bucket wheel 42 and conducts it to the second stage bucket wheel 44 has a plurality of circumferentially spaced partitions 53 shown in detail in Figs. 9 and 10 secured between an inner disk 54 and an outer ring 55. The partitions 53 are warped similar to the warping of the partitions 45. The inner and outer walls formed by the disk 54 and the ring 55 respectively have three distinctly curved surfaces; an inlet surface with a curvature indicated by a radius 56, an outlet surface having a curvature with a radius 51, and an intermediate surface having a curvature with a radius 58 connecting the inlet and outlet surfaces and reversing the radial fluid fiow component. The inner surfaces formed by the disk 54 are similar to the aforementioned surfaces with the radii 55, 51 and 58. With this arrangement the fluid discharged from the bucket passages of the wheel 42 is received by a passage with inner and outer surfaces forming modified continuations of the corresponding surfaces 48, 49 of the diaphragm H. The fluid is then carried through the channel in axial and radial outward direction, and by means of the intermediate surfaces the radial outward component of the fluid flow is gradually changed to a radial inward component. With this arrangement the outer radial dimensions of the turbine are kept small. The partitions 53 do not extend along the entire axial length of the passage formed between the disk 54 and the ring 55 but only through a part thereof near the outlet. Thus, an annular channel 59 is formed between the outlet face of the bucket wheel 42 and the inlet edges of the partitions 53 whose sole function is smoothly to conduct the fluid discharged from the bucket passages of the wheel 42 into the nozzle passages between the partitions 53. The bucket wheel 44 has bucket passages similar to those described above in connection with the wheel 42.

In the arrangement described in Fig. 5 the passages formed between the disk and outer ring of the low pressure diaphragm 43 assume considerable axial length due to the channel 59 acting to cause radial outward flow of the fluid.

In the arrangement of Fig. 6 the axial length of the turbine is considerably reduced by shaping the inner and outer walls of the bucket wheels so that they will take over the functions of the channel 59 described in connection with Fig. 5. Thus, the arrangement of Fig. 6 shows an outer casing 60 with a first stage diaphragm 8| similar in design to the diaphragm or nozzle plate 4| of Fig. 5. The nozzles formed by the diaphragm 6| conduct elastic fluid to a first stage bucket wheel 52 which has circumferentially spaced buckets 53 similar to the buckets 50 in Fig. 1. The inner and outer walls of the bucket passages have surfaces 54 and 65 respectively which in accordance with this modification are no longer cylindrical but curved in an axial plane through the center of rotation to form continuations of toroidal or smoke ring surfaces 65 and i1 respectively of the diaphragm ii. The wheel 62 causes the fluid to flow axially and radially outward through the bucket passages, and in regard to this radial outward flow the bucket passages assume the function of the aforementioned channels 59 in Fig. 5. The fluid discharged from the bucket wheel 62 is conducted to a second stage diaphragm 68 having circumferentially spaced partitions 59 warped as described above. The nozzle passages formed between the partitions 69 have inner and outer surfaces 10 and H respectively. These surfaces are conical with the apices of the cones located in the center of rotation and said surfaces form approximations of smoke ring surfaces as described above. Fluid discharged from the low pressure diaphragm 68 is conducted to a bucket wheel 12 corresponding to the wheel 44 of Fig. 5 and having a plurality of circumferentially spaced buckets or bucket blades 13 which together with the bucket wheel disk and the outer shroud band form bucket passages. The inner and outer walls 14 and 15 are again conical, forming parts of substantially toroidal or smoke ring surfaces.

As the fluid flows through the bucket passages of a bucket wheel its velocity components due to its rotational flow about the turbine axis are removed, that is, converted into mechanical energy. The fluid then leaves the bucket passage in the axial plane only at velocities which in the arrangement of Fig. 6 increase from root to tip. This is satisfactory in the arrangement of Fig. 6 in which the inner and outer walls of the bucket passages form substantial smoke ring surfaces. In the arrangement of Fig. 5, however, such increasing axial velocities from root to tip in the exit bucket passage would be undesirable because the inner and outer walls of said passages are cylindrical and therefore it would not be possible properly to balance the pressure gradient in the bucket exit area. In order to eliminate such radial pressure gradient the fluid leaving the bucket passage must flow substantially at constant velocity. This will convert a part of the axial velocity components into mechanical energy. It is accomplished by providing the buckets in Fig. 5 with exit angle slightly decreasing from root to tip. In contrast thereto the exit angles of the buckets in Fig. 6 correspond to the inlet angles of said buckets with due consideration of the fact that the tangential velocit components have been removed.

The nozzle partitions and the bucket blades described above are warped. The term "warped" herein is used in its broad sense, meaning that the entrance or exit angles, or both, of the partitions and blades vary from root to tip. In certain instances in the arrangements shown in Figs. 7 and 9 the partitions or blades are warped and, at the same time, twisted, their outlet edges being inclined at an angle in a radial direction. This inclination of the outlet edges of the blades or partitions, however, is not an essential characteristic of their warped shape. Blades and partitions may be constructed with both inlet and outlet edges extending in a radial direction through the turbine axis. Figs. 11 and 12 show a warped bucket blade of this type comprising a dovetail base 16 for attachment to the rim of a bucket wheel disk and a blade 11 integral with the base 16. As shown in Fig. 12 the inlet and outlet edges are substantially parallel extending in a radial direction through the turbine center. The radial projection of the edge portions of the tip 18 coincide substantially with the edge portions of the root 19 of the blade. The

bucket inlet angles are determined in customary manner by simple vector diagrams. Thus, with regard to the root, a vector representing the circumferential velocity at the bucket root is added to the vector representing the fluid exit velocity at the root of the nozzle partition. As the exit angles of the nozzle partitions increase from root to tip and as the circumferential bucket velocities also increase from root to tip it follows that the bucket entrance angles increase from root to tip at a rate greater than the rate of increase of the nozzle partition exit angles.

Thus, with my invention I have accomplished an improved turbine and nozzle bucket passage combination of the axial flow impulse type. In such a turbine the radial pressure gradient in the nozzle exit area is partly or entirely compensated and the fluid velocities in such area are the result of fluid flow velocity components along a torus or smoke ring and components in a ring about the center of turbine rotation. The tangential or angular velocities of. the fluid in such ring decrease with increasing radii. This type of flow is generally known as vortex flow. The tangential or angular velocities in the torus or toroidal shell decrease likewise with increasing radii from the center line of the torus, thus inducing the kind of flow present in a smoke ring. Now, instead of superimposing the velocities of a vortex with those of a smoke ring, the same conception may be visualized by taking a body of fluid forming a smoke ring or a vector thereof concentric with the turbine shaft and rotating it about the shaft at certain angular velocities decreasing with increasing radii from the turbine center and corresponding to the velocities of a vortex, in other words, by rotating a smoke ring flow at vortex velocities.

Generally, as explained above, it is desirable to eliminate radial pressure gradients. There are certain instances, however, where such elimination may not be possible nor desirable. In such cases pure impulse operation may still be attained by a design in accordance with my invention. All that is necessary in such instances is to make sure that the radial pressure gradient at the outlet of the bucket passages is the same as the radial pressure gradients at the inlet thereof, with equal pressures existing or being maintained across the roots and the tips, respectively.

It is clear that no leakage across the tips of the buckets can take place as long as the pressures on both sides of the tips are the same. The same applies to conditions at the roots of the buckets or bucket passages. Thus, a pure impulse turbine, according to my invention, in its broader aspects has nozzle and bucket passage shapes whereby smoke ring velocities are imparted to the vortex velocities of the operating medium, resulting in one case in the complete elimination of radial pressure gradients at the outlets of the respective passages, and resulting in the othercase in radial pressure gradients which are alike for both the entrance and exit areas of the bucket passages.

Having described the method of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

i. In an elastic fluid turbine of the axial flow impulse type, nozzle bucket passage combinations comprising circumferentially spaced nozzles each being formed by a pair of partitions and inner and outer walls, each partition being warped to form exit angles increasing from root to tip of the partition, said walls having axially curved surfaces forrning parts of a toroidal shell, the warp of the partitions and the axial curvature of the walls being dimensioned to cause elastic fluid flowing through the nozzle to leave such nozzle at exit velocities which are constant for radially spaced parts of the nozzle exit area to eliminate radial pressure gradients in the nozzle exit area, and circumferentially spaced bucket passages with inlet areas axially spaced from the nozzle exit areas, each bucket passage being formed by a pair of bucket blades and inner and outer walls, said blades being warped to form inlet angles increasing from root to tip at a rate greater than that of the nozzle partition exit angles. and the cross-sectional area of flow through each bucket passage being substantially constant from the inlet to the outlet of such passage.

2. In an elastic fluid turbine of the axial flow impulse type, nozzle bucket passage combination according to claim 1 in which the inner and outer walls of the bucket passages have substantially cylindrical surfaces.

3. In an elastic fluid turbine of the axial flow impulse type, nozzle bucket passage combination according to claim 1 in which the inner and outer walls of the bucket passages are axially curved having toroidal surfaces forming smooth continuations of the corresponding surfaces of the nozzles.

4. In an elastic fluid turbine of the axial flow impulse type, nozzle bucket passage combinatlons comprising circumferentially spaced nozzles each being forrmed by a pair 01' partitions and inner and outer walls, each partition being warped to form exit angles increasing from root to tip of the partition, said walls having axially curved surfaces forming parts of a toroidal shell, the warp of the partitions and the axial curvature of the walls being dimensioned to cause elastic fluid flowing through the nozzle to leave such nozzle at exit velocities which are constant for radially spaced parts of the nozzle exit area to eliminate radial pressure gradients in the exit area, and circumferentially spaced bucket passages with inlet areas axially spaced from the nozzle exit areas, each bucket passage being formed by a pair of bucket blades and inner and outer walls, said blades being warped to form inlet angles increasing from root to tip at a rate greater than that of the partition exit angles, the cross-sectional area of flow through each bucket passage being substantially constant from the inlet to the outlet of such passage, and other circumferentially spaced nozzles for receiving fluid from said bucket passages, said other nozzles having warped partitions and inner and outer walls with surfaces which near the outlet of the bucket passages form substantial continuations of the corresponding surfaces of the first mentioned nozzles.

5. In an elastic fluid turbine of the axial flow impulse type, nozzle bucket passage combinations comprising clrcumferentially spaced nozzles each being formed by a pair of partitions and inner and outer walls, each partition being warped to form exit angles increasing from root to tip of the partition, said walls having axially curved surfaces forming parts of a toroidal shell, the warp of the partitions and the axial curvature of the walls being dimensioned to cause elastic fluid flowing through the nozzle to leave such nozzle at exit velocities which are constant for radially spaced parts of the nozzle exit area to eliminate radial pressure gradients in the exit area.

6. A diaphragm for conducting fluid from a bucket wheel to a succeeding bucket wheel of an elastic fluid turbine 01 the axial flow impulse type, said diaphragm comprising a row of circumferentially spaced warped partitions with exit angles increasing in radial direction, and inner and outer walls curved in axial direction with the inlet and outlet portions of the walls convexshaped and the intermediate portions of the walls concave-shaped when viewed from the turbine axis '7. In an elastic fluid turbine of the axial flow impulse type, a plurality of circumferentially spaced nozzles for conducting elastic fluid to a bucket wheel, said nozzles having circumferentially spaced warped partitions and inner and outer walls curved in axial direction and having surfaces forming parts of a toroidal shell in which smoke ring fluid flow guided by said shell is subjected to centrifugal forces about the mean centerline of the shell, which forces counteract and substantially balance the centrifugal forces to which such fluid is subjected due to its vortex flow about the turbine axis whereby radial pressure gradients in the nozzle exit are eliminated.

8. In an elastic fluid turbine of the axial flow impulse type, a plurality of circumferentially spaced nozzles for conducting elastic fluid to a bucket wheel, said nozzles having circumferentially spaced warped partitions with exit angles increasing in radial direction and curved inner and outer walls forming parts of a substantially toroidal shell dimensioned to produce relative velocities in the nozzle exit area which are constant in magnitude for radially spaced points in said area and have axial components equal to the smoke ring velocities in said toroidal shell.

9. In an elastic fluid turbine oi the axial flow impulse type according to claim 8, a plurality of circumferentially spaced bucket passages for receiving fluid from the nozzles, said passages being formed between circumferentially spaced bucket blades and inner and outer substantially cylindrical walls, the bucket blades having warped inlet edge portions forming inlet angles greater than the corresponding exit angles of the partitions, and said bucket blades having warped outlet edge portions forming exit angles decreasing from root to tip whereby fluid entering a bucket passage at axial velocities increasing from root to tip is discharged from such passage at axial velocities substantially constant from root to tip.

10. In an elastic fluid turbine of the axial flow impulse type, nozzle means forming a plurality of nozzle passages and a bucket wheel having a plurality of circumierentially spaced buckets forming bucket passages for receiving elastic fluid from the nozzle passages, the nozzle passages having axially curved inner and outer walls forming parts of a toroidal shell shaped to produce a flow of an operating medium supplied to the turbine which flow at all points constitutes the resultant of a vortex flow component and a smoke ring flow component to produce velocities and corresponding pressures in the nozzle exit area which pressures match the pressure distribution in the bucket exit area and thereby effect equal radial pressure gradients in the bucket entrance and exit areas.

11. In an elastic fluid turbine the combination of nozzle means including a plurality of circumierentially spaced partitions forming nozzle passages having axially curved inner and outer walls forming parts of a toroidal shell, and a bucket wheel with a plurality of circumierentially spaced bucket blades defining bucket passages having inner and outer Surfaces forming substantially smooth continuations of said toroidal nozzle surfaces, the partitions and the buckets having entrance and exit angles, at least one of said angles varying from root to tip with regard to the partitions and the buckets at a rate so selected that an operating medium entering the nozzle passages at a certain pressure and temperature produces a flow path having velocities which constitute the resultants of vortex and smoke ring components to produce like radial pressure gradients in the bucket passage entrance and exit areas.

HANS KRAFT.

Certificate of Correction Patent N 0. 2,392,673.

January 8, i946.

HANS KRAFT It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 3, first column, line 74, strike out y,, and insert instead 1: )age 5, second column, line 39, claim 4, for forrmed" read formed; and that the said otters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oifice.

Signed and sealed this 21st day of May, A. D. 1946.

[SEAL] LESLIE FRAZER,

First Assistant Commissioner of Patents.

ture of the walls being dimensioned to cause elastic fluid flowing through the nozzle to leave such nozzle at exit velocities which are constant for radially spaced parts of the nozzle exit area to eliminate radial pressure gradients in the exit area.

6. A diaphragm for conducting fluid from a bucket wheel to a succeeding bucket wheel of an elastic fluid turbine 01 the axial flow impulse type, said diaphragm comprising a row of circumferentially spaced warped partitions with exit angles increasing in radial direction, and inner and outer walls curved in axial direction with the inlet and outlet portions of the walls convexshaped and the intermediate portions of the walls concave-shaped when viewed from the turbine axis '7. In an elastic fluid turbine of the axial flow impulse type, a plurality of circumferentially spaced nozzles for conducting elastic fluid to a bucket wheel, said nozzles having circumferentially spaced warped partitions and inner and outer walls curved in axial direction and having surfaces forming parts of a toroidal shell in which smoke ring fluid flow guided by said shell is subjected to centrifugal forces about the mean centerline of the shell, which forces counteract and substantially balance the centrifugal forces to which such fluid is subjected due to its vortex flow about the turbine axis whereby radial pressure gradients in the nozzle exit are eliminated.

8. In an elastic fluid turbine of the axial flow impulse type, a plurality of circumferentially spaced nozzles for conducting elastic fluid to a bucket wheel, said nozzles having circumferentially spaced warped partitions with exit angles increasing in radial direction and curved inner and outer walls forming parts of a substantially toroidal shell dimensioned to produce relative velocities in the nozzle exit area which are constant in magnitude for radially spaced points in said area and have axial components equal to the smoke ring velocities in said toroidal shell.

9. In an elastic fluid turbine oi the axial flow impulse type according to claim 8, a plurality of circumferentially spaced bucket passages for receiving fluid from the nozzles, said passages being formed between circumferentially spaced bucket blades and inner and outer substantially cylindrical walls, the bucket blades having warped inlet edge portions forming inlet angles greater than the corresponding exit angles of the partitions, and said bucket blades having warped outlet edge portions forming exit angles decreasing from root to tip whereby fluid entering a bucket passage at axial velocities increasing from root to tip is discharged from such passage at axial velocities substantially constant from root to tip.

10. In an elastic fluid turbine of the axial flow impulse type, nozzle means forming a plurality of nozzle passages and a bucket wheel having a plurality of circumierentially spaced buckets forming bucket passages for receiving elastic fluid from the nozzle passages, the nozzle passages having axially curved inner and outer walls forming parts of a toroidal shell shaped to produce a flow of an operating medium supplied to the turbine which flow at all points constitutes the resultant of a vortex flow component and a smoke ring flow component to produce velocities and corresponding pressures in the nozzle exit area which pressures match the pressure distribution in the bucket exit area and thereby effect equal radial pressure gradients in the bucket entrance and exit areas.

11. In an elastic fluid turbine the combination of nozzle means including a plurality of circumierentially spaced partitions forming nozzle passages having axially curved inner and outer walls forming parts of a toroidal shell, and a bucket wheel with a plurality of circumierentially spaced bucket blades defining bucket passages having inner and outer Surfaces forming substantially smooth continuations of said toroidal nozzle surfaces, the partitions and the buckets having entrance and exit angles, at least one of said angles varying from root to tip with regard to the partitions and the buckets at a rate so selected that an operating medium entering the nozzle passages at a certain pressure and temperature produces a flow path having velocities which constitute the resultants of vortex and smoke ring components to produce like radial pressure gradients in the bucket passage entrance and exit areas.

HANS KRAFT.

Certificate of Correction Patent N 0. 2,392,673.

January 8, i946.

HANS KRAFT It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 3, first column, line 74, strike out y,, and insert instead 1: )age 5, second column, line 39, claim 4, for forrmed" read formed; and that the said otters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oifice.

Signed and sealed this 21st day of May, A. D. 1946.

[SEAL] LESLIE FRAZER,

First Assistant Commissioner of Patents.

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