US2258793A - Elastic-fluid turbine - Google Patents

Description

Oct. 14, 1941. w R, NEW 2,258,793

ELAsTIc-FLUID TURBINE Filed March 19, 1940 4 SheeS-Shee'f. 2

wlNEssEs; Fr, Q 6. INVENTOR BY al, BIM

' ATTORNEY 95E/Wk 774W. WlNsToN R. New. 6. H

355 i, Flcp FGQS. I

Oct. 14, 1941. w, R, NEW 2,258,793

ELAsTIc-FLUID TURBINE Filed March 19, 1940 4 Shees-She'et Av L',

T X .33 gnu; o

BY Rf, @Aanv-1n ATroRNEY WlNsToN R. New.

Patented Oct. 14, 1941 UNITED siy T E S .531.

or to Westinghouse Electric er Manuliactg Company, East Pittsburgh, Pa., a corporation of Pennsylvania.

Application March 19, 1940, Serial No. 324,743

l1 Claims.

My invention relates to elastic-fluid turbines and it has for an object to provide apparatus of this character having blading particularly suitable for the fluid velocities to be encountered in order to secure improved performance.

I have found that turbine blades or vanes having sharp inlet edges should be used with elastic iluld entering at super-acoustic velocities and that blades or vanes having well-rounded inlet edges should be employed with elastic fluid entering at sub-acoustic velocities. A turbine blade or vane must always be capable of functioning over a range of directions of the approaching stream. If the approaching stream has a subacoustic velocity, then blades -or vanes of foil section having well-rounded inlet edges facili- 'tate orderly transport of fluid around their boundaries by propagating pressure disturbances into the approaching stream in such a way as to introduce changes in the direction and magnitude of velocity of elementary filaments before they are arrested by the solid surfaces, therebycausing the stream to accommodate itself to the blades or vanes over a wide angle of approach. A sharp inlet edge or lip produces pronounced deviation from the streamlined shape having a wellrounded inlet edge and makes a vane or blade selective in its response to various velocity directions but does not reduce its drag. Therefore, at sub-acoustic entering velocities, since a sharp inlet'edge gives no compensation for the loss of the advantage of a foil with a well-rounded inlet edge to deal with the elastic iiuid over a wide ,range of angle -of approach, blades or vanes of foil section having well-rounded inlet edges should be used.'

The possibility of affecting the velocity field upstream by means of pressure disturbances propagated from the blades or vanes disappears when the elastic fluid approaches at super-acoustic velocities. The phenomenon of compression shock ispeculiar to the super-acoustic case and it causes energy losses proportional, among other factors, to the projected areal of the leading edge of the blade or vane in the directionl of the approaching stream, and it is, therefore, desirable to minimize such projected area by providing a lip or thin leading edge in order to reduce energy losses due to compression shock.

The function .of a turbine nozzle or blade ele` ment is to derive from a change in momentum of the motive iiuid, a force which is normal to the for any. sulciently smallelement of time, the existence of a torque rests'upon continuous generation and absorption of momentum through the mechanism of continuous time change in the p vector representing velocity. Since fundamentally all turbine blades or vanes abstract energyv exists a velocity, uniquely definable in terms of conditions of state (sealer quantities) at which a pressure wave travels in the medium at those state conditions, and this velocity is the acoustic velocity. If the fluid velocity is sub-acoustic, as is usually the case with all of the blades or vanes of a conventional turbine except possibly those of the first moving row of the impulse stage, and particularly if the angle of approach to the blades or vanes varies, in consequence of variation in load or speed or both, then blades or vanes of foil section having well-rounded inlet edges should be used because the pressure disturbances set up by such inlet edges causes the element and tangential toits supporting member. With a governor valve metering the quanapproaching stream to better accommodate itself to the blades or vanes over a wide range of variation in the angle of approach of the fluid.'

If the entering velocity is super-acoustic, asfis frequently the case with the first row of moving blades of` the initial multiple-velocity-abstrac tion stage, not only would it be impossible for rounded .inlet edges of the blades to propagate pressure disturbances against the stream causing the approaching uid to better accommodate itselfto the ,blades or vanes, but, on account of shock, such edges would present excessive projected or impact area to the stream and consequently involve excessive shock losses. Therefore, with super-acoustic inlet velocity, the blades or vanes should present a minimum projected area to the approaching stream, that is, they should have thin or sharp leading edges.

The' present invention is also concerned with certain aspects of single-velocity-abstraction stages for use with substantially sub-acoustic velocities. Such stages may be either symmetrical or anti-symmetrical as regards the enthalpy change across the stationary and moving blade or vane elements. In a steam turbine stage in Y which kinetic energy is generated principally in a stationary nozzle and velocity abstraction occurs in one moving row, that is, an anti-symmetrical stage, sub-acoustic velocities are almost invariably encountered. Heretofore, turbine designers have distinguished between an impulse or Rateau stage and a reaction or Parsons stage from the point of view of geometry of blade shapes without taking into consideration that they were dealing with sub-acoustic velocities and that the only real distinction to be made was on the ground of symmetry or lack of symmetry with respect to distribution of enthalpy change over the stationary and moving blades of a stage. They did not realize that blade or vane elements encountering sub-'acoustic velocity flow should each consist of a streamlined foil with a wellrounded inlet or leading edge. ,The crescent;- type blade commonly employed in anti-symmetrical stages is a pronounced deviat-ion from the streamlined shape and it is selective in its response to various inlet velocity directions, at which all stages must operate, without compensation for loss of flexibility through decreased drag.

While impulse action in a. turbine stage involves abstraction, by the moving blades, of velocity energy already generated in the stationary blade or nozzle passages and reaction action involves transformation of heat'energy of elastic fluid into velocity energy appearing both as velocity of the moving blades and of elastic uid discharged from the latter, the usual impulse stage involves some reaction and reaction stages involve some impulse. While the transformation of velocity energy is eicient so long as the inlet edges are at an angle correct for the angle of approach of the elastic fluid and the turning angle thereof is equal to that required' by the elastic uid at the design operating conditions, departures of the angle of approach from that correct for the inlet angle result in less eilicient abstraction of-velocity energy. Also, due to flow disturbance in the moving blade passages, in consequence of such departures of the angle of approach, the reaction action would be less eiiicient. Abstraction of energy by the moving blades in both of these ways may be Iimproved, where the angle of approach of elastic fluid varies, by using blades of foil section having well-rounded inlet edges. If such blades are used, irrespective of whether the action is impulse or reaction, improved performance both of the stationary and the moving blades is secured where the velocity of approach is subacoustic. Hence, with like stationary and moving blades forming a stage, the more predominant velocity abstraction,- characte'ristic of the usual Rateau stage, may be secured by gauging so that greater enthalpy change occurs in the stationary blade passages than in the moving blade passages, and the comparatively greater reaction effect, characteristic of the ordinary re-r action or Parsons stage, may be secured bygauging of the blades so that the enthalpy changes both in the stationary and in the moving blade passages are substantially the same. Thus, for sub-acoustic velocities, the same foil section may be used both for the stationary and moving blades, thedesired distribution of enthalpy change thereover being secured by appropriate choice of orientation and pitch of the blades. Therefore, in accordance with thepresent invention, I provide a turbine having stages for elastic fluid approaching both the stationary and I moving blades thereof at sub-acoustic velocities and both the stationary and moving blades being of foil section with well-rounded inlet edges;

and, without changing the foil and shape, the distribution of enthalpy change between the stationary and moving blades of a stage is attained through variation of the pitch and orientation of the blades of the respective rows.

A further object of the invention is to provide lan' elastic-fluid turbine wherein the blades or vanes subject to super-acoustic velocity have sharp' or thin leading edges and the blades or vanes subject to sub-acoustic velocity are of foil section having well-rounded inlet or leading edges.

A further object of the invention is to provide turbine blading including an initial multiple-velocity-abstraction impulse stage wherein the rst row of moving blades thereof have sharp or thin leading edges and the second row of moving blades are of foil section and have Well-rounded inlet or leading edges.

A further object of the invention is to provide a turbine having single-velocity-abstractian impulse stages for sub-acoustic velocity elastic fluid and wherein both the stationary and moving blades of each stage are of foil section and have well-rounded inlet or leading edges, the distribution of enthalpy change over the stationary and moving blades of each stage being secured by variation of the pitch and orientation of the blades in the row without any changes in the foilshape.

These vand other objects are effected by my invention as will be apparent from the following description and claims taken inconnection with the accompanying drawings forming a part of this application, in which:

Fig. 1 is a diagrammatic view showing a multiple-velocity-abstraction stage-having the iirst row of moving blades thereof suitable for superacoustic velocities and the last row of moving bladesl thereof modified for elastic fluid entering at sub-acoustic velocity;

Fig. 2 is a view similar to Fig. l but showing modification of the nozzles and the iirst row of moving blades as Well as of the intermediate reversing blades;

Fig. 3 is a side elevational view of a turbine sectioned to show stages thereof;

Fig. 4 is a detail sectional view 'of stages of the turbine shown in Fig. 3; Figs. 5 'and 6 are sectional views showing partial-peripheral-admission and full-peripheral admission diaphragms of the' turbine shown in Fig. 3:

Fig. 7 is a sectional view showing a multiplevelocity-abstraction stage followed by stages of the type wherein the distribution of enthalpy change over the stationary and moving blades is uniform; x

Figs. 8 and 9 are detail views of 4blade elements suitable for receiving elastic iluid at sub-acoustic Velocity;

Figs. 10, 11 and 12 are diagrammatic views explanatory of principles involved.

The multiple-velocity-abstraction stage, at I0, has the customary nozzle group or groups including vane elements I4 defining nozzle passages I5, a first row of moving blades I6, an intermediate row of stationary reversing blades I1, and a second row of moving blades I8.

As elastic fluid issues from the nozzle passages l5 at super-acoustic velocity, the rst row of moving blades I6 have sharp leading or inlet edges I9 in order to minimize the projected area presented to the approaching stream so as to reduce energy losses due to compression shocks.

If elastic uid approaches the intermediate reversing blades I1 at super-acoustic velocity, then these blades should also have thin or sharp leading edges. Due to abstraction of velocity energy from the elastic uid by the first row of moving blades I6 and to inherent losses both in the blades I6 and I'I, the elastic fluid usually-approaches the bladesy I8 of the second row at a sub-acoustic velocity and the blades should, for that reason, be of foil section and have Wellrounded inlet or leading edges.

Impulse blades of the sharp-edge type should have a total geometrical turning angle equal to that required of the fluid at design operation conditions. On the other hand, with sub-acoustic velocities of approach of elastic iluid, this is Y immaterial for blades of foil section and having well-rounded inlet edges.

Preferably, as shown in Fig. 2, the iirst moving row of impulse blades ISa, in addition to presenting sharp inlet edges I9, have concave faces 20 and polygonal convex faces 2| defining Prandtl-Meyer streamline ow passages 22 for elastic iiuid entering at super-sonic velocity, as disclosed and claimed in the application of Stewart Way, Serial No. 335,465, led May 16, 1940, and assigned to the Westinghouse Electric & Manufacturing Company. Each convex face 2i includes a pluralityr of fiat portions 23 joined by corner portions 24, the corner portions function to induce turning of the stream in each passage under the conditions provided by the concave face. As pointed out in said application, the advantage for this type of passage is to minimize shock loss. l

Fig. 2 also shows vane elements Ia. dening nozzle passages Ia of high expansion ratio, the vane/elements being constructed and arranged to provide for pressure-velocity conversion and the turning of the jet in each passage with expansion to a super-acoustic velocity with minimum energy losses. Each of the vanes has a corner 25 to produce the new around a corner effect in each -passage in turning the jet in the latter. The vane elements have Well-rounded inlet edges 26, thin'exit edges 21 and the corners 25. From the inlet edges, the foils have substantially fiat ,surfaces 28y and 29 which converge inwardly to the throat sections defined by the corners and the opposed fiat surfaces 29. Beyond the throat approach. As changes in load or turbine speed or both cause the angle of approach to vary, the

capacity of the rounded inlet edges to bring.

about the automatic accommodation of Athe stream to suit the blade profiles with minimum energy losses is important. This will be clear from a consideration of Figs. and 11.

In Figrl, the stream approaches in the direction a relatively to the blades b of streamlined section and having Well-rounded inlet edges c.v

region d in such a manner as to cause the streamlines to accommodate themselves to the blade section.' This action induced by the well-rounded inlet edges results in a now condition similar to a sharp edge or lip extending from the forward side ofthe blade in the direction of approach of the stream. If the direction of approach changes from a of Fig. 10 to a' of Fig. 11, the bladey sections in these views being identical in all respects, it will be obvious that a sharp edge or lip correct for the direction a would be is, the sharp edge or lip, for good efliciency, is

critical to the angle of approach. On the other hand, the streamlined section with a well-rounded inlet edge operates with good efficiency over a wide range of variation in the angle of approach.

The diierence in efliciency of the sharp edge blade as compared with the foil section with a well-rounded inlet edge is shown in Fig. 12, where the curve e is the efficiency curve for a sharp-edged blade and the curve f is that for a streamlined section with a well-rounded inlet edge. The top or peak portion of the curve ,f

is much flatter than e showing that good effi-f ciency is had over a wide velocity ratio range, and, as the direction of approach changes with changes invelocity ratio, good emciency is maintained with variation of the angleof approach over a wide range. Hence, in Fig. 11, even though the direction of approach a is substantially different from a in Fig. 10, the action is the same, that is, the well-rounded inlet edge sets up a disturbance which is propagated backwardly into the stream and causes the latter to accommodate itself to the blade section. f

The gauging, or ratio of opening o to the pitch s (all Fig. 9), of the stationary vane elements may be equal to or less than that of the cooperating moving vaneA elements. If the ratios are equal, then the stage is symmetrical with respect i to the distribution pf enthalpy change over the As the velocity of approach is sub-acoustic, the

well-rounded inlet edges c propagate disturbancesbackwardly into the stream in the general stationary and moving vane elements. On the other hand, if the ratio for the stationary vane elements of a stage is smaller than that for the moving vane elements thereof, then the stage is anti-symmetrical with respect to distribution of enthalpy change over the vane elements, that is, the proportion of kinetic energy generated in the nozzle passages of the stationaryvane elements becomes larger, as said ratio for the 'stationary vane elements is made smaller.

If the elastic fluid approaches the intermediate stationary or reversing blades ofthe initial multiple-veiocity-abstraction stage at sub-sonic .velocity, then such blades, as shown at I'I'a in Figs. 2 and 7, should be of foil'section having well-rounded inlet edges. Blades of foil section with well-rounded in Vlet edges should not be used with velocities of an initial multiple-velocity-abstraction stage, at

IIJ, followed by single-velocity-abstraction stages, at II and I2. Each single-velocity-abstraction stage, at il, comprises a diaphragm 32 having arcuate groups or vane elements 33 providing nozzle passages 3E for delivering elastic fluid to the moving bladel or vane elements 35 carried by the disk 36, the diaphragm and the disk such root portions fastened in-a groove, the desired orientation and pitch of the blade portions 38 will be had.

For the same blade width, the dimensions of the streamlined or foil section may vary substantially; however, in all cases, the inlet edge should be well-rounded, that is, its radius of curvature should be substantial in relation to the maximum section thickness. As shown, the thickness, or diametral dimension, of the inlet edge at the point where the concave face surface joins the convex inlet edge surface, the point of reverse curvature, is equal to at least the major portion ofthe maximum thickness ol the section, or, stated another way, the radius of the inlet edge should not' be greater than half the maximum thickness of the section and not less than onequarter thereof.

'I'he term enthalp y" as used herein, has the sense of a thermodynamic conception o1' derived quantity. It has the signicance of heat drop in the Molliere diagram. See page 47, chapter 3, of Notes on Thermodynamics, third edition, Dr. John A. Goii', published by John S. Swift Company, Inc., St. Louis, 1939.

While I havel shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as aref specically set forth in the appended claims.

What I claim is:

1. In an elastic-huid turbine, a plurality of stages, each including stationary and moving rows of blades, the initial stage including means for converting heat energy of elastic uid into velocity energy such that elastic iluid is supplied to blades thereof at super-acoustic velocity, the first row of blades of the initial stage receiving elastic fluid at 'super-acoustic velocity having sharp inlet edges, and the remaining blades each being of foil section and having well-rounded inlet edges so that those bladeswhich encounter a sub-acoustic inlet velocity can accommodate a accommodate themselves to the blade over a wide range of variation in the angle of approach of the elastic iluid; and said other stages including stationary and moving blades each of foil section and having an inlet edge suiiiciently wellrounded to cause streamlines of elastic iluid approaching at sub-acoustic velocity to accommodate themselves to the blade over a-wide range of variation in the angle of approach of the elasticfluid.

V4. In an elastic fluid turbine, a multiple-velocity-abstraction stage including a iirst row of moving blades having sharp inlet edges, a second row of moving bladesrof foil section and having inlet edges sufficiently well-rounded to cause the streamlines of elastic fluid approaching at sub-acoustic velocity to accommodate themselves to the blades over a wide range of variawide range of variation in the angle of approach of the elastic iiuid.

2. In an elastic-fluid turbine, alternately-arranged stationary and moving rows of blades,

A nozzles for supplying elastic fluid at super-acoustic velocity to the rst row of moving blades, the blades receiving elastic' uid at super-acoustic velocity having sharp inlet edges and the remaining blades receiving elastic uid at s ubacoustic velocities each being of foil section with an inlet edge sufliciently well-rounded to cause the streamlines of elastic iiuid approaching at sub-acoustic velocity to accommodate themselves to the blade over a wide range of variation in the angleof approach.

3. In an elastic uid turbine, a plurality of stages for progressively abstracting energy from elastic iiuid and comprising an initial stage and a plurality of other stages; said initial stage in- /cluding rst and second rows of moving blades.

f a row of stationary reversing blades arranged between the rst and second rows oi.' moving blades, and nozzles for supplying elastic iiuid at superacoustic velocity to the rst row of moving blades, the blades of said first moving row having sharp inlet edges and those of said second moving row each being of foil section and having -an inlet edge sum'ciently well-'roundedv to cause the streamlines of approaching elastic fluid to tion in the angle of approach of elastic iluld, intervening reversing blades, and nozzles for supplying elastic iiuid at super-acoustic velocity tc the first row of moving blades.

5. In an elastic-fluid turbine, a multiple-velocity-abstraction stage including a first row of moving blades having sharp inlet edges, a second row of moving blades, stationary reversing blades between the first and second rows of moving blades. said stationary reversing blades and said second row of moving blades each `being of foil section with an inlet' edge sufciently well-rounded to cause streamlines of elastic fluid approaching at sub-acoustic velocity to accommodate themselves to the blade over a wide range of Variation in the angle of approach of elastic uid, and nozzles for supplying elastic iiuid at super-acoustic velocity to the first row of moving blades.

6. In an elastic-fluid turbine, a stage for abstracting energy from elastic fluid delivered thereto at sub-acoustic velocity, said stage comprising a row of stationary vanes delivering elastic uid tov a row of moving vanes, said stationary and 'moving vanes each being of streamlined foil section and having an inlet edge sumciently wellrounded to cause streamlines of elastic uid approaching at sub-acoustic velocity to accommodate themselves to the vane over a wide Arange of variation in the angle of approach of elastic fluid and the ratio of opening to pitch for the stationary vanes being smaller than that for the moving vanes in order to provide for greater' enthalpy change in the former than in the latter.

7. In an elastic-Huid turbine, a plurality of' stages including a plurality of single-velocityabstraction stages, each single-velocity-abstraction stage comprising a stationary row of vane elements and a moving row of vane elements, both the stationary and the moving vane elements being of streamlined foil section and having an inlet edge. suillciently well-rounded t0 cause streamlines of elastic fluid approaching at sub-acoustic velocity to accommodate themselves to the vane element over a wide range of.

variationin the angle of approach of elastic fluid and the ratio of opening to pitch for the station- -ary vane elements being smaller than that for the moving vane elements in orderi-provide for greater enthalpy change in thea'ormeir `than in -the latter. V e f 8. In an elastic-fluid turbine, a plurality of stages including a multiplicity of single-velocity- Aabstraction stages, thel single-velocity-abstraction stages including partial-peripheral admission and full-peripheral admission stages each comprising stationary and moving vanes, each of said vanes being of streamlined foil section and having an inlet edge sufciently well-roundedtoI cause streamlines of elasticl iluid approaching at sub-acoustic velocity to accommodate themselves to the vane over a wide range of variation in the angle of approach of elastic uid and the ratio of opening to pitch for the stationary vanes being smaller than that for the moving vanes in order to provide for greater enthalpy change in the former than in the latter.

9. In an elastic-fluid turbine, a plurality of stages inclu/ding a plurality of single-velocity-abstraction stages, each single-velocity-abstraction stage comprising a casing diaphragm, a rotor disk, stationary vane elements carried by the dlaphragm and providing nozzle passages, moving vane elements carried by the disk and providing passages for elastic fluid delivered by the nozzle passages, both thelstationary and the moving vane elements being of streamlined foil section with an inlet edge suiciently well-rounded to cause streamlines of approaching elastic fluid to accommodate themselves to the vane elements over a wide range of variation in thevangle of approach of elastic fluid and the ratio of opening to pitch for the stationary vane elements being smaller than that for the moving vane elements in order to provide for greater enthalpy change in the former than in the latter.

l0. In an elastic-fluid turbine, an initial multiple-velocity-abstraction stage followed by a plurality of single-velocity-abstraction stages;

each single-velocity-abstraction stage comprising a casing diaphragm, a rotor disk, stationary vane elements carried by the diaphragm and providing nozzle passages, and a moving row of vane elements carried by the disk and providing passages for elastic iluid delivered by the nozzle passages, both the stationary` and the moving vane elements each being of streamlined foil section and having an inlet edge sulciently wellrounded to cause streamlines of elastic :duid approaching at sub-sonic velocity to accommodate themselves to the vane element over a Wide range of variation in the angle of approach of elastic uid and the ratio of opening to pitch for the stationary vane elements being smaller than that for the moving vane elements in order to provide for greater enthalpy change in the former than in the latter.

11. In an elastic-iiuid turbine, an initial multiple-velocty-abstraction stage followed by a plurality of single-velocity-abstraction stages the multiple-velocity-abstraction stage comprising iirst and second rows of moving vane elements, an intervening row of reversing vane elements and nozzles for delivering elastic fluid at super-acoustic velocity to the ilrst row of moving vane elements; each single-velocity-abstraction stage comprising stationary vane elements providing nozzle passages, a row of moving .vane elements providing passages for elastic fluid delivered by the nozzle passages; the rst row of moving vane elements of the multple-velocity-abstraction stage having sharp inlet edges and the second row of moving vane elements thereof and both the stationary and moving vane elements of each of the single-velocity-abstractionistages each being of streamlined foil section and having an inlet edge suiciently well-rounded to cause streamlines of elastic iluid approaching at sub-acoustic velocity to accommodate themselves to the vane element over a wide range of variation in the angle of approach of elastic fluid and the ratio of opening to pitch for the stationary vane elements of the single-velocity-abstraction stages being smaller than that for the moving vane elements thereof in order to provide for greater enthalpy change in the former than in the latter.

WINSTON RANDOLPH NEW.

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