US1910216A - Rotor for axial flow hydraulic machines - Google Patents

Description

May 23, 1933. J. H. w. GILL ROTOR FOR AXIAL FLOW HYDRAULIC MACHINES Fild Dec.

May 23, 1933. J w G|LL I 1,910,216

ROTOR FOR AXIAL FLOW HYDRAULIC MACHINES Filed Dec; 51, 19:50 4 Sheets-Sheet 2 W2 W/ FIG/2.

y 3,1933. J. H. w. GILL 1,910,216

' ROTOR FOR AXIAL FLOW HYDRAULIC MACHINES Filed Dec. 31, 1930 4 Sheets-Sheet 3 J. H. w. GILL 1 ,910,216v

ROTOR FOR AXIAL FLOW HYDRAULIC MACHINES May 23, 1933.

Filed Dec. 31, 1930 4 Sheets-Sheet 4 a f 6% P o a :0 n o I i o on w l3 \w Maw/at Patented May 23, 1933 UNITED STATES} PATENT OFFICE- unns'nnnnnm WAINWBIGHT GILL, or LONDON, ENGLAND FOB AXIAL FLOW HYDRAULIC MACHINES Application filed Decembcr31, 1930, Serial No. 505,890, and in Great Britain February 4, 1930. r

This invention relates to screw rotors. for construct the rotor that when applied to an hydraulic machines wherein the'general diaxial flow pump all unnecessary shock at rection of flow through the rotor is axial or inlet to the rotor is eliminated, more especialmore nearly'axial than radial, and has furly in the neighbourhood vof the boss where ther reference to the combination of such the pitch is steeper, and progressive imparta- 55 rotors with suitable casings'and with guide tion of energy to the fluid in its passage vanes or their equivalent, to constitute such through the rotor is ensured, whilst in the hydraulic machines. case of an axial flow reaction turbine the The design of such rotors has hitherto been converse efiect of progressive reception of based on the broad assumption that subenergy is attained. stantially the same speed of inflow normally In the rotor accordingto this invention obtains along all the concentric stream tubes the pitch of the blades gradually increases passing through a cross section in the anradially inwards from a chosen value at the nulus between the periphery and the boss of periphery of the rotor at such a rate that the the rotor. Frictional retardation at the outer pitch at' any radius 1' is equal to or less than 65 and inner boundaries of the annulus results,

however, in axial flow speeds which decrease Kg progressively with proximity to thes boundaries, and this effect increases witl 1 andi at th the length of the intake passage and of the K bossing or core, also with the viscosity of the fluid, and with the proportion of solid matsuspenslen therelly. where R is the peripheral radius, Kis the It 18 knewn to be deelleble 111 y exlel chosen peripheral pitch value and a is the flow mach nes to provide for a substantially ti f th b di t th i h l Inform dlstllbllt'len 0f heed the i e radius. For fluids of relatively high viscosity face, and rotors have been deslgned. to thls or fluids having a relatively large amount of end on the assumption of a correspondingly solid matter in suspension, the pitch profile ject is accomplished by departing from the lated from the accepted theoretical assumpuniformaxial flow, without consideration of curve (i y h curve f it h l tt d against the frictlonal retardation referred to hereln, di i ranged to approach nearer to or of centrifugal efiect due to the steep rise of 'th upper li it curve root pitches.

The primary object of the present inveng tion is to provide a rotor construction with which the practlcal performanqe shall be (where P is the pitch at radius 1') than for equivalent to the performance WhlCh 1s calcufluids of relatively low Viscosity. Even with fiuidsof low viscosity, however, it is seldom lated from the theoretical assumption of uniform axml flow wlth Inform head notwlth' desirable to approach close to the lower limit curve standing the modifying effect of surface retardation on flow volume, and of centrifugal tendency at the blade root pitches. This ob- KR ,1 at the inner radii in any case, and it will tions as to uniform axial fiow speed and head generally be Plefereble the Plteh to be distribution, and replacing this by an ingr ater than v p R +0.1

cidence of blade pitch which is relatively The definition of limits aboveexpressed incideme of rotor blade pitch which is calcusteeper towards the mid-annulus sections of the rotor blades.

A further object of the lnvention 1s so to tinuities or abrupt changes of slope or repeated undulations) which result in impracticable rotor designs, but it is to be understood that the invention only contemplates generally smooth curves (within the limits) such as will conform with the natural conditions of flow and will produce, when the rotor is operating on water under normaLdesigned' conditions, a value of pitch at the periphery of the blades which when multiplied by the number of revolutions per unit time gives a figure less than one and a half and usually less than one and a quarter times the-mean axial speed of flow (i. e. to accommodate values of slip ratio at the periphery less than 33 and usually less than 20%.) In most cases where the boss diameteris moderate the pitch at the blade tips is chosen to suit operation (with water as the working fluid) at a peripheral slip' ratio between 10% and 15%, calculated on the mean desired speed of flow.

The size of boss selected will vary to some extent in accordance with the type of machine in which the rotor is to be used as well as on the conditions of operation. For an axial flow pump or reaction turbine the boss radius may be from three-eighths to threequarters of the peripheral radius according to the area necessary to accommodate the normal desired flow with a given head and speed, whilst for reaction propellers the lower boss radius limit may be extended 'toa fifth of the peripheral radius.

In a preferred typical construction of rotor for use in an axial flowpump designed for operation on water, the pitch increases from the periphery to a mid-radius blade section approximately in accordance with the law and thence increases smoothly but more rapldly to a value approximateing to at the boss, the boss having a radius between three-eighths and one-half of the peripheral radius.

According to a further important feature whilst the pitch in the neighbourhood of the other edge will be lower and may have an approximately constant value corresponding to the chosen peripheral pitch value, the axial transition of pitch along concentric stream tubes following smooth curves. In hydraulic screw turbines and in axial flow pumps operating at slip ratios above normal values, or on viscous fluids, this axial variation of pitch is of great importance, as it provides for maximum deflection of the fluid flow within the rotor in the case of turbines, and for smooth intake to the steeper sections of the rotor in the case of pumps.

' The invention may be carried into practice in various ways depending on the type of hydraulic machine in which the rotor is used,

also on the nature of the working fluid and on the conditions of operation, but a preferred construction of rotor according to the invention and some convenient applications thereof to hydraulic machines are illustrated by Way of. example in the accompanying drawings, in which Figure 1 is a graph illustrating the pitch distribution in the blades of a rotor accordving to the invention,

Figure 2 shows acentral section through an axial flow pump designed more especially for operation on water and employing the preferred form of rotor,

Figure 3 shows a projection of half the rotor of Figure 2 on a transaxial plane,

Figure 4 is a similar half transaxial projection of the outlet guide vanes employed in the pump of Figure 2,

Figure5 illustrates one convenient application of the preferred form of rotor to an axial flow reaction turbine,

Figures 6-8 are views similar to those of Figures 2-4 for a modified form of axial flow Figures 9 and 10 are views similar to those of Figures 2 and 4: for another modified formof axial flow pump, and

Figures 11 and 12 respectively illustrate two further modifications.

The graph of Figure 1 shows a series of pitch profile curves (i. e. curves showing the relative pitch in the rotor blades plotted against distance from the axis of the rotor) for various rotors according to the invention. For purposes of comparison, the pitch profile curve for a typical uniform head rotor designed in the usual manner on the assumptionof uniform axial flow is shown at in chain line, whilst the dotted line A is the corresponding curvefor a uniform pitch rotor. The curves A, A, A A relate to rotors according to the invention, the curve A representing the preferred form, whilst the curves A A are respectively the upper and lower-limit curves, and the curve A is another limiting curve.

The preferred form of rotor', two views of a typical construction of which are shown in Figures 2 and 3, hasfrom two to six blades B (five being shown in Figures 2 and 3) carried by a cylindrical boss C, which is mounted within a cylindrical casing D on the driving shaft C In the example illustrated, the

boss Chas a radius oftw'o-fifths of the periphera I radius of the rotor blades. The edges of the blades at one end of the rotor lie on the surface of a coaxial cone, whilst edge B conforming to the line A of Figure- 1, its inlet edge B lying on a transaxial plane,

whilst the rotor employed in the turbine of Figure 5 has its edges on the surfaces of coaxial cones of opposite vertical angle.

In face projection on a transaxial plane (see Figure 3) the edges B B of the blades do not overlap and are convex with reference to straight lines joining the roots and tips of the blades, the degree of convexity and distribution of bladearea being governed by the incidence of blade pitch at the different radii taken in conjunction with the degree of substantially straight line taper in the pro- 0 file view of the blades. The total face projected area of the blades lies between, say, and ofthe total projected area of the annulus between the boss and the periphery, depending upon the loading allowed for per unit of blade area and the amount of guidance required by the fluid.

The pitch distribution in the blades of the rotor can best be described with reference to the graph of Figure 1. In this graph the abscissae are radial distances from the axis of the. rotor, the graph extending from the surface of the boss to the periphery of the rotor whilst the peripheral radius is taken as the unit. The ordinates represent the pitch at the. various radii, the peripheral pitch value being taken as the unit. As above mentioned the curve A represents the upper limit pitch profile curve and follows the law whilst the curve A represents the lower limit curve defined by'the law where a=0.4 in the example chosen. Whilst 'ythedmention comprises within its scope all 6; curve A and in the majority of instances the pitch profile curve will lie above the curve A, which conforms to the law i. in the example illustrated The preferredv rotor conforms to the curve A This curve extends from the peripheral pitch value, which is chosen to suit operation at a normal peripheral slip ratio of, say, 12.5% calculated on the mean axial flow speed, and increases from this value to a midblade radius (at seven-tenths of the peripheral radius) in accordance approximately with the law R 0.75, P K

curves within the scope of the invention) is less hollow than the curve A for the known uniform head rotors designed on the assumption of uniform axialflow, and by accelerating the flow through the. middle portion of the annulus it enables the desired compensationto be obtained for the'eflect of surface retardation, and allows for the different centrifugal tendencies at the different radii. In

the case of working fluids of higher viscosity increased by an amount dependent on the viscosity of the fluid, whilst the ratio of the pitch at the. boss to the peripheral pitch remains at 2.5 for the same boss diameter ratio.

' In addition to the radial variation of pitch above described, the rotor blades may also have an axial pitch variation. In one convenient arrangement (incorporated in the rotor of Figures 2' and 3) the blades have the same peripheral pitch value at the discharge edge B and at the inlet. edge" B and the pitch along the discharge edge B conforms to the curve A, whilst along the inlet edge B the pitch is uniform at all radii (conforming tothe straight line A) or increases only slightly inwards, the pitch varying continuously and smoothly. along each stream tube from its inlet edge value to its discharge edge value.

The manner in which the rotor is employed in an axial flow hydraulic machine will depend on the type of machine and on the con ditions in which the machine is to operate. In the case of an axial flow pump it will usually be preferable to mount the rotor within a cylindrical casing between coaxially-arranged inlet and outlet guide vanes, although in certain instances, for exampe when the direction of discharge is to be at right angles to the axis of the rotor within a confined space, the coaxial outlet guide vanes may be situated in expanded sections of the casing, whilst in extreme cases these guide vanes may be replaced by a whirl chamber of expanding trumpet shape-with a central core or of a scroll or voluteform, or by adjustable guide vanes of the balanced wickettype, the last mentioned alternatives also being especially suitable for the reverse application to an axial flow reaction turbine. In other instances for other hydraulic machines as well as for pumps, for example when the head is high and the revolution speed moderate, a second oppositely-rotating coaxial rotor may replace the outlet guide vanes. Typical instances of such hydraulic machines are illustrated in Figures 2-12 of the accompanying drawings.

Thus in the axial flow pump shown in Figures 24, the rotor as above described operates between adjacent fixed coaxial guide vanes in a cylindrical casing D. The inlet guide vanes E are. preferably from two to six in number and may be arranged radially or tangentially or may be curved in plan view. These vanes are normally designed to maintain an axial direction of inflow to the rotor, although they may be curved towards or against the direction of rotation of the rotor to accommodate or to impose special conditions of inflow.

The outlet guide vanes F are preferably from four to eight in number (six as shown) and have their inlet edges F so curved as to receive the fluid approximately in its absolute direction of discharge from the rotor, making a small angle with a transaxial plane near the boss and a larger angle therewith near the periphery. The function of these vanes is to recover head or pressure energy from the whirl imparted to the fluid by the rotor. The degree of curvature of these vanes is governed bythe law 8 tan y (1-8) tan ,8,where,B and 7 represent the angles made with a surface normal to the stream tube at any radius, by the outlet edge 'of the rotor blade and by the inlet edge of the outlet guide vane respectively, whilst s is the slip ratio at that radius. The discharge edges F of the outlet guide vanes are designed to promote an approximately axial direction of outflow and the vanes themselves may be arranged tangentially (as shown) or radially or curved in plan view. The cross-sections of these vanes are preferablyof such stream-lined form and thickness that the sector-shaped spaces between the vanes follow, in the direction of flow, approximately the chan es of cross-sectional area proper to expan ing passages for the maximum recovery of head.

The spacing between the rotor and the adjacent edges of the guide vanes will normally be made small, but for the purpose of dealing with solid matter in suspension or for meetin considerable variations in pumping'duty, th1s spacing may be varied, a radially out- Wards increase in this spacing being desirable in many cases even when solid matter is not present.

The shape and size of the bosses situated in the spaces occupied axially by the guide vanes are arranged to suit those of the rotor boss C, andin some instances it may be desirable to depart from a cylindrical shape for the rotor boss, in which case the body representing the combined rotor and guide vane bosses E C, F as a whole may be of streamlined or tapered or bulbous or other suitable shape. The casing D will have such shape in relation to that of the bosses as may be necessary to regulate the area for axial flow.

The arrangement'above described, as also the modified forms of axial flow pump to be described later, is operable in reverse as an axial flow reaction turbine. It will however usually be preferable to employ a volute chamber or balanced wicket guide vanes for controlling the turbine inflow, and one such convenient application of the invention to an axial flow turbine is illustrated in Figure 5. In this arrangement the rotor G, which is constructed in the manner above described, rotates within a vertical casing H of generally cylindrical shape. The inflow to the top of the casing H takes place through an inclined annular passage H and is controlled by guide vanes J of the balanced wicket type, these vanes being simultaneously adjustable by suitable means such for instance as the rotatable slotted crown J In this construction the rotor G is adjustable in an axial direction (as indicated by the dotted lines) in order to accommodate varying conditions of operation.

In some instances, both for pumps and for turbines, it may be convenient so to design the rotor that it may readily be interchanged with other rotors according to the invention, such rotors having approximately the same axial length but, having difl'erent nominal pitch values and correspondingly different numbers of blades. Again, it is sometimes necessary to provide for inspection and cleaning of the working parts of a pump, without dismantling the casing, and in order that this may be readily efl'ected, the outlet and inlet guide vanes between which the rotor operates ma casing instead of to the casing itself, whe eby the whole pump can be lifted bodily out of the casing, and the inlet guide vanes may be be fixed to a removable liner within the I so arranged that the rotor can be passed axially between these vanes, if desired. 7

In other instances changes in the normal working conditions can be accommodated by rotation of the rotor blades about their radial axes. A convenient practical arrangement of this kind is illustrated in Figures 6-8. In this arrangement each of the rotor .blades K ismade with a trunnion extension K which is tightly gripped in the boss, which is transversely cut into two halves L, L for the purpose, the two halves of the boss being held together by means of bolts L engaging in grooves K in the trunnions in order to hold the blades radially in position against centrifugal action. i

Whilst it is true that such rotational adjustment of the rotor blades will throw them somewhat out of pitch, and thereby slightly lower the, efliciency of the pump, the law governing the itch distribution in the rotor according to t e invention is such that the loss in efiiciency by rotation of the blades through, say, 7 on either side of the normal position will be very small, and the disadvantage of such a reduction in efliciency is amply made up for by the advantage of the adaptability of the pump to varying working conditions. An alternative method of mounting the blades is to provide a slotted flange on the root of the blade, by which it i can be bolted on to the boss, the slots in the flange being of such a length as to allow the desired 7 adjustment on either side of the normal blade position.

The inlet guide vanes M are fixed between a boss M and the cylindrical casing M and are arranged in a manner generally similar' and of flow velocity head from the rotor to tational adjustment of the rotor blades. To this end each of the outlet guide vanes N is supported on a short shaft N extending through the wall of the casing M and is gripped in position by means of a nut N on the end of the shaft N In other respects the outlet guide vanes N are arranged generally in the same manner as the outlet guide vanes in the construction of Figures 2-4.

Instead of mounting the outlet guide vanes rotatably in the casing, a generally similar result can be obtained by providing these vanes with adjustable inlet edges, Such an arrangement is shown in Figures 9 and 10,

wherein each outlet guide vane is formed in two parts 0, 0 the upper part 0 being fixed in the casing whilst the lower part 0 is provided with a circular flange O fittinginto a hole in the casing. This arrangement not only allows slight rotational adjustment of the inlet part O of the vane, but also permits ready removal of this part of the vane and substitution of a differently curved alternative inlet edge for the vane.

Figure 9 also serves to show a modified arrangement for the inlet guide vanes (equally applicable to the constructions of axial flow pump shown in the other figures), especially intended for instances in which the pump is operating on liquids with solid matter in suspension. In this arrangement each inlet vane is made up of a series of tongues P bolted to narrow plates P extending radially inward from the casing and joined together at the axis, the upper edges of the tongues lying adjacent to the inlet edges ofthe rotor blades.

In the example illustrated four such tongued inlet vanes are employed, and the arrangement is such that, in addition to performing their normal function of guiding the liquid properlyto the rotor, these guide vanes cooperate with the rotor! Q to effect disintegration of any solid matter present in the the discharge orifice. With this arrangement it is sometimes desirable to have adjustable inlet guide vanes to accommodate changes in the normal working conditions, and to'this end the inlet guide vanes T are each supported on a short shaft T extending through the wall of the casing R, the arrangement being generally analogous to the rotatable outlet guide vane arrangement of Figures 6-8.

Figure 12 shows an arrangement in which the outlet guide vanes are replaced by a second rotor, and whilst this arrangement will be described with. reference to its use'as an axial flow pump, it will be appreciated that it can readily be employed as a power transmitter or for other purposes. In this arrangement the two rotors U, V are mounted left-handed. The rotor U at the inlet side is constructed in the manner above described, but the second rotor V (whose function in a pump is similar to that of outlet guide vanes) has a pitch distribution in its blades suited to the proper conversion of the discharge whirl from the rotor U into pressure head.

The inlet guide vanes in this instance are replaced by a stream-lined fin W supporting 10 the shaft U and a similar supporting fin W may be provided for the shaft v Axial-flow pumps having rotors according to this invention may also be constructed as multi-stage series pumps, with two or more rotors on the same shaft, separated by fixed guide vanes, which (when the series stages are close together) may be designed to serve as outlet guide vanes for one rotor and as inlet guide vanes for the next rotor in the series.

The rotor may also be used either alone or in combination with guide vanes or additional rotors in other, axial flow hydraulic machines such for example as propellers, mixers or power converters.

It will be appreciated that the particular arrangements above referred to may be modified to suit requirements within the scope of the invention; for example, the profile and face projections of the rotor blades may follow various forms and area ratios and the rotors may be of open or of shrouded type, whilst cylindrical sections of the rotor blades may follow stream-lined or other suitable form.

What I claim as my invention and desire to secure by Letters Patent is 1. A rotor for an axial flow hydraulic machine comprising a boss, and blades carried thereby, the pitch of the blades gradually increasing radially inwards from a chosen value at the periphery of the rotor at such a rate that the pitch at radius 1' is considerably less than but is greater than I except in the neighborhood of the boss where the pitch increases rapidly towards a value approximating to e5 creasing radially inwards from a chosen value at the periphery of the rotor at such a rate that the pitch at radius r is considerably less than but is greater than except in the neighborhood of the boss where the pitch increases rapidly towards a value approximating to where R is the, peripheral radius, K is the chosen peripheral pitch value and a is the ratio of the radius of the boss to the peripheral radius, whilst in the inner half of the rotor the pitch increases more rapidly so that at the boss it has a value approximating to 4. A rotor for an axial flow hydraulic machine comprising a boss, and blades carried thereby, the pitch of the blades at one edge of the rotor gradually increasing radially inwards from a chosen value at the periph ery of the rotor at an increasing rate such that the pitch at radius 1' is equal to or less than T and greater than where R is the peripheral radius, K is the chosen peripheral pitch value and a is the ratio of the radius of the boss to the peripheral radius, the pitch and the rate of radial increase of pitch both decreasing gradually in an axial direction towards the other edge of the rotor.

5. A rotor for an axial flow hydraulic ma chine, comprising a boss, and blades carried thereby, the pitch of the blades gradually increasing both radially inwards from the periphery of the rotor to the boss and axially from one edge of the rotor to the other in such a manner that in the neighbourhood of one edge of the'rotor the pitch increases radially inwards from a chosen valueK at the periphery at an increasing rate such that at any radius r the pitchlies between radii.

and greater than A rotor for an axial flow hydraulic machine, comprising a boss, and blades carried thereby, the pitch of the blades at the periph-' cry of the rotor being chosen to suit operation (with water as the working fluid) at a periph-' eral slip ratio of between and the pitch of the blades gradually increasing radially inwards from this peripheral value at such a rate that the pitch at radius 1- is considerably less than 1 but is greater than except in the neighborhood of the boss where the pitch increases rapidly towards a value approximating to 5 2 1'v Where R is the peripheral radius and K is the chosen peripheral pitch value, whilst a which lies between one-fifth and three-quarters is the ratio of the radius of the boss to the peripheral radius.

7 A rotor for an axial flowhydraulic machine'comprising a boss, and blades so mounted on the boss that each blade can be rotat- I ably adjusted about a radial axis through a small angle on either side of a normal posichosen peripheral pitch value and a is the ratio of the radius of the boss to the peripheral radius.

8. The combination with the features set forth in claim 1, of a casing surrounding therotor, ide vanes mounted coaxially with and ad acentto the rotor on both sides thereof within the casing, and means whereby each of the guide vanes on one side of the rotor can be rotatably adjusted about its longitudinal axis.

9. The combination with the features set forth in claim 7, of a casing surrounding the -rotor, guide vanes mounted coaxially with and adjacent to the rotor on both sides thereof within the casing, and means whereby each of the guide vanes on one side of the rotor can be rotatably adjusted about its longitudinal axls.

10. The combination with the features set forth in claim 1, of a casirgg surrounding the rotor, and guide vanes mounted coaxially with and adjacent to the rotor on both sides thereof within the casing, each of the guide vanes on one side of the rotor being divided longitudinally into two parts, of which the part nearer to the rotor is so mounted as to be readily removable and replaceable by a similarr but differently curved part.

ll. The combination with the features set forth in claim 1, of a casing surrounding the rotor a suitably shape-d whirl chamber constituting an extension of the casing on one side of the rotor, and guide vanes mounted coaxially with and adjacent to the rotor with in the casing on the other side thereof, each of such guide vanes being rotatable about its longitudinal axis.

12. The combination with the features set forth in claim 4, of a casing surrounding the rotor, a suitably shaped whirl chamber constituting an extension of the casing on one side of the rotor, and guide vanes mounted coaxially with and adjacent to the rotor within the casing on the other side thereof, each of such guide vanes being rotatable about its longitudinal axis.

In testimony whereof I have signed name to this specification.

JAMES HERBERT WAINWRIGHT GILL.

tion, the pitch of the blades when in their nor- .mal position gradually increasing radially inwards from a chosen value at the periphery of the rotor at an increasing rate such that the pitch at radius r is equal to or less than where R is the peripheral radius, K is the

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