GB2026092A

GB2026092A - Bladed rotor

Info

Publication number: GB2026092A
Application number: GB7921282A
Authority: GB
Original assignee: NEDERLANDSE APPL SCIENT RES
Current assignee: NEDERLANDSE APPL SCIENT RES
Priority date: 1978-06-30
Filing date: 1979-06-19
Publication date: 1980-01-30
Also published as: FR2438754B1; FR2438754A1; IE791224L; NL184075B; BR7904155A; DE2924613A1; IT7923986A0; GB2026092B; IN153150B; IE48768B1; CH645954A5; JPS5514997A; DK258379A; SE7905553L; IT1125412B; NL7807073A; BE876988A

Abstract

A method is provided for driving the rotor for transmitting or withdrawing kinetic energy to or from a fluid. The rotor has at least two identical, helically-extending, uniformly spaced blades 6, the radial height of which between the outer edge and the rotor core from the plane of origin towards the plane of the end of the blade remains the same, or increases or decreases gradually or in wave- shaped fashion. The blade length along the outer edge of the blade is at least equal to one and a half times the maximum blade height. The ratio between the blade height and the distance between the blades at the core is between 0.5 and 2.5. The pitch angle of the blades is between 5 DEG and 55 DEG . The relative inflow angle of fluid with respect to the outer edge of the blade lies between about 5 DEG and 10 DEG . The rotor may be used for pumping or mixing fluids, vessel propulsion, or in a wind or water motor. <IMAGE>

Description

SPECIFICATION Method of driving a rotor rotatable about a rotary axis and a rotor therefor The invention relates to a method of driving a rotor to transmit or withdraw kinetic energy to or from a fluid and rotors suitable therefor.

According to a first aspect, the invention relates to a method of driving a rotor adapted to rotate about a rotary axis for giving off kinetic energy to a fluid by using a rotor provided with at least two identical blades extending helically at a uniform distance from one another around the rotary axis of said rotor, in which the starting and terminating points of the blades are located in planes at right angles to the rotary axis of the rotor and the height of the blade measured in a radial direction between the outer or laterial edge of the blade and the core from the starting plane towards the terminal plane of the blade remains the same or increases or decreases gradually or in wave-shaped fashion, whilst the front and/or rear edges of the blades may be inclined forwardly or backwardly and the outer or lateral edges of the blades terminate in tips.

The method according to this aspect of the invention is particularly intended for many different purposes, for example the propulsion of vessels, stirring or mixing of liquids or gases with other liquids, gases or granular,solid materials, the homogenisation of coarse, coherent materials in fluids, for example, liquid manure, the aeration or gasification of liquids, the nebulation of liquids, the pumping over of liquids or mixtures of liquids with solid substances and so forth.

The usual member for practically all the purposes mentioned above has substantially the same form of a conventional ship's screw in which the blades fastened to a core or a hub have more or less streamlined profiles in cylindrical sectional planes concentric with the rotary axis of the screw. The propulsion of the fluid is then produced by a circulation produced about such a streamlined profile, since on one side the fluid flows with a higher speed from the nose to the tail than on the other side.

For various purpose of the kind set forth, worm screws have been proposed. However, in practice this did not prove to be successful because of the excessively low efficiency. In connection herewith various improvements have been proposed, for example, worms with varying pitch angles of the blades or worms having blades of more or less curved section at right angles to the rotary axis, that is to say, blades bent over forward or backward or worms having hubs of varying diameter. However, it was found that these special types of worms are also not satisfactory so that they have scarcely been employed in practice.

According to the invention an improvement can be obtained in this respect by providing a blade length measured along the outer edge of the blade at least equal to one and a half times the blade height, a ratio between blade height and relative blade distance between 0.5 and 2.5 and a pitch angle of the blades between 20' and 55 , whilst the relative inflow angle of the fluid with respect to the outer edge of the blade lies between about 5" and 10'.

In practice it has been found that, in this case, the fluid streams in the form of whirls in the direction of length of the rotary axis of the rotor between the blades to the rear, whilst a high useful output with respect to the fluid displacement is obtained.

A further aspect of the invention relates to driving a rotor adapted to rotate about a rotary axis for withdrawing kinetic energy from a fluid, in which a rotor is employed which is provided with at least two identical blades extending helically about the rotary axis of the rotor at equal distances from one another on a core, in which the starting and terminating points of the blades are located in planes at right angles to the rotary axis of the rotor and the height of the blades measured in a radial direction between the outer or lateral edge of the blade and the core from the plane of the origin towards the terminal plane of the blade remains the same or increases or decreases gradually or in waveshaped fashion, whilst the front and/or rear edges of the blades may be inclined forwardly or backwardly and the outer or lateral edges of the blades terminate in tips.For driving such a rotor, for example, a windmill, in accordance with the invention, there is provided a blade length measured along the outer edge of the blade at least equal to one and half times the blade height, a ratio between blade height and relative blade distance between 0.5 and 2.5 and a pitch angle of the blades between 5" and 20 , whilst the relative inflow angle at the outer edge of the blade lies between 5" and 10 .

The invention will now be described more fully by way of example with reference to several embodiments of the invention as illustrated in the accompanying drawings, wherein: Figure 1 is a schematic developed view of part of a rotor provided with rectangular blades; Figure 2 is a side elevation of a first embodiment of a rotor in accordance with the invention; Figure 3 is a sectional view of the embodiment of Fig. 2 taken on the line Ill-Ill of Fig.

2; Figure 4 is an exploded view of a blade of the rotor shown in Figs. 2 and 3; Figure 5 shows exploded views of further embodiments of blades suitable for use on a rotor in accordance with the invention; Figure 6 illustrates a few potential embodiments of sectional areas of a rotor blade at right angles to the rotary axis of the rotor; Figure 7shows an embodiment of a rotor in accordance with the invention which is particularly suitable for the propulsion to a ship; Figure 8shows a device particularly intended for mixing liquids comprising a rotor in accordance with the invention; Figure 9 shows an arrangement particularly suitable for the homogenisation of liquids with solid substances floating therein with the use of a rotor in accordance with the invention;; Figure 10 shows a device particularly intended for mixing liquids and gases comprising a rotor in accordance with the invention; Figure 11 shows an embodiment of a rotor in accordance with the invention intended for use as a wind- or watermill; and Figure 12 shows a further embodiment of a rotor in accordance with the invention intended for use as a wind- or watermill.

The extremely simple shape of the rotor according to the invention is based on the use of comparatively very short (non-slender), sharp-edged wings as blades of a rotor wound with a constant pitch angle around a core or hub of the rotor. All sections of a blade in planes at right angles to the hub are symmetrical, which means that in these planes the blades are not inclined forward or backward and are not curved.

Fig. 1 shows schematically an exploded view of such a rotor comprising a hub or core 1 and several blades 2 arranged on said hub or core and having in the embodiment shown a rectangular shape. The hub has a diameter dand the outer edges 3 of the blades 2 are located on a diameter D.

With the construction of a rotor described above and shown schematically in Fig. 1 it appears that on the lee-side near the outer edge 3 of each blade a strong, stable whirl is produced by the fluid mass released from the pointed edge 3 of the blade and passing over the blade. This -fluid mass has a relative speed U with respect to the blade 2, which relative speed is composed of the circumferential speed coD of the edge of the blade and the axial speed V of the fluid with respect to the rotor. The fluid mass arriving obliquely at the luff-side of the blade receives from the blade at first a rearward pulse, but passes for the major part over and across the edge of the blade and winds on the lee-side in a whirl 4.

This whirl which starts near the front side of the blade, viewed in the direction of flow of the fluid, increases rearwardly in size and strength, since further fluid masses passing over are added to the fluid mass of the whirl along the whole outer edge 3. The mean speed of flow in the direction of length of this growing whirl more or less in the form of a corkscrew increases from the front to the rear ends of the blades, since the subatmospheric pressure in the core of the whirl in said direction constantly increases as a result of the centrifugal effect in the growing whirl.

Thus between the blades of the rotor are produced conically growing, corkscrew-shaped whirls, constantly increasing in speed which suck fluid from without along the whole length of the rotor between the rotor blades so that during the displacement of the fluid with the aid of the rotor this fluid obtains a rearward speed.

Apart from the kinetic energy imparted in the direction of the rotary axis of the rotor to the fluid mass sucked in, an excess pressure is produced on the luff side of each blade and a subatmospheric pressure on the lee-side so as to exert both a propelling force in the axial direction and a torque about the axis of the rotor.

It has been found that these effects are produced purely throughout the length of the blades and thus ensure optimum operation of the rotor only when the blade section has a certain shape and certain ratios between the blade length L and the maximum height H of the blade exist with a certain relative blade distance S sin ss, the pitch angle ss of the blade and a certain ratio between the circumferential speed wD and the relative speed V of the fluid with respect to the rotor in an axial direction of the rotor.

Therefore, in the first place, the blades have to terminate in tips at the outer circumference of the rotor in order to create a sufficiently stable whirl. Furthermore the blade length L measured along the outer circumference of the blade has to be at least one and a half times the largest height of the blade H in order to ensure the generation of an adequately strong corkscrew-shaped whirl. However, the blade height H should not differ too much from the distance between the blades S sin ss, since, with a smaller distance between the blades, the blades will adversely affect the formation of whirls between the blades, whereas with a larger distance between the blades with respect to the fluid mass present between the blades a comparatively small fluid mass will be drawn and accelerated in the corkscrew whirls.

In order to obtain an optimum effect of the rotor according to the invention the ratio between blade height H and relative blade distance S sin ss should, therefore, lie preferably between 0.5 and 2.5.

The blade length must not be too small nor too large, since otherwise each blade partly screens off the next blade viewed in the relative flow direction. This depends, of course, on the relative blade distance, the pitch angle of the blade and the relative inflow direction.

Theoretically it can be inferred that the maximum efficiency of propelling rotors, that is to say, rotors displacing fluid, increases with the pitch angle ss of the blades and will be substantially optimal with a pitch angle of about 45 . Therefore, the pitch angles of propelling rotors have to lie between about 20 and 55 , the smaller pitch angles of 20 to 35 being used with high speed rotors, for example, screws for outboard engines, whereas larger pitch angles of 30 to 55 are used for comparatively low speed rotors, for example, ship's screws.

The ratio between transverse force (pressure) and longitudinal force (friction) on a blade decreases with an increasing relative inflow angle iwith respect to the outer edge of the blade, that is to say, the pitch angle'3 of the blade decreases with the angle fe in dependence upon the speed V and the speed ccD as indicated in Fig. 1. Therefore, this inflow angle must not exceed about 5" to 10 for optimum efficiency of a rotor used for displacing a fluid.

With said optimum values of the pitch angle, the relative inflow angle and the ratio between the blade height and the space between the blades, the blade length L measured along the outer edge of the blade appears to lie between about 1.5- and 6-times the largest blade height H for rotors of the type suitable for ship's screws so as to give a sufficiently high propulsion efficiency.

When using a rotor driven by a fluid, for example, when the rotor is used in a windmill, it can be theoretically inferred that the power efficiency increases with a decreasing pitch angle p of the blades and will be substantially optimal with a pitch angle of about 10 .

Therefore, the pitch angle ss for windmills and the like will lie between 5" and 20 , the larger pitch angle of 10 to 20 being used for low speed rotors, for example, for driving pumps and the like, and the smaller pitch angles of 5" to 10 being used for high speed rotors, for example, for driving current generators.

With the aforesaid optimum values of the pitch angle, the relative inflow angle and the ratio between blade height and relative blade distance the blade length L measured along the outer edges of the blade of such fluid driven rotors has to lie between about 4- and 1 2-times the largest blade height H in order to obtain a sufficiently high power efficiency.

Figs. 2 and 3 show an embodiment of a rotor in accordance with the invention for producing movement of a fluid, for example, when the rotor is employed as a ship's screw.

The rotor comprises a hub or core 5 on which a plurality of blades 6 are helically arranged.

As is shown in the exploded views of Fig. 4, the blade 6 may have more or less the shape of a rectangle triangle, the side 7 being the edge joining the core or hub 5 and the side 8 being the outer edge of the blade.

Instead of being straight, the outer edge 8 of the blade may have any wave-shaped form or the blade 6 may be rectangular as indicated respectively in Fig. 5 by the various broken lines or the solid line. It will be apparent from this Fig.5 that the blades in an exploded view may have a rectangular, triangular, arrow- or wave-shaped form. Fig. 6 shows using solid and broken lines, potential sectional areas of the blades in a plane at right angles to the rotary axis of the rotor. It is particularly important for the outer edge of the blade to terminate in a tip, the blade being thus knife-shaped, gothic shaped or the like, whereas the junction of the blade with the hub or the core of the rotor may be orthogonal or may be more or less rounded off.

As stated above, when, in operation, the rotor is caused to rotate in the direction of rotation in indicated by the arrow A, whilst the rotor is surrounded by a fluid, a whirl 4 will be produced between the consecutive blades of the rotor, the flow in this whirl being as indicated by the arrow. The inflow direction of the fluid with respect to the rotor is indicated by the arrow B. The rotor will otherwise be constructed on the basis of the aforesaid requirements. For this purpose it will in general be necessary to provide the rotor with at least two blades.

The use of the blade shapes shown, in which the height of the blade rises from zero to a given value, has inter alia the advantage that inflow losses are avoided, whilst tacking of soil contained in the fluid to the blades is prevented.

Fig. 7 shows an embodiment of a rotor having rectangular blades, which like the embodiment shown in Figs. 2 and 3 is particularly suitable as the screw of a ship or for stirring liquids.

It has been found that, when the rotor is employed as the propulsion member of a ship, a high efficiency is also obtained when the rotor rotates in the opposite sense for braking the ship.

Fig. 8 shows a rotor according to the invention arranged in a stepped housing comprising two circular section portions 9 and 1 0. A supply duct 11 communicates with the foremost portion 9 of the smaller diameter whereas a supply duct 1 2 communicates with the portion 10 of larger diameter. A desired liquid can be fed through each of the ducts 11 and 1 2. When the rotor is rotated during the feed of the liquids, these liquids will be effectively mixed owing to the whirls produced by the rotor so that a homogeneous mixture of the two liquids will be delivered in the direction of the arrow C from the outlet end of the portion 10.

Fig. 9 shows an embodiment comprising a rotor according to the invention particularly suitable for homogenisation of, for example, liquids containing solid substances. From Fig.

9 it will be seen that the rotor is arranged in an opening 14 in a partition 13, the diameter of which opening gradually decreases in the intended direction of flow indicated by the arrows D so that, near the rear side of the rotor a comparatively small gap is left between the outer circumference of the rotor which gradually increases its diameter in the direction of flow C and the inner circumference of the opening 14.

The embodiment shown in Fig. 10 is particularly intended for mixing air or gas with a liquid. From Fig. 10, it will be seen that in this embodiment the blades 6 are arranged on a hollow shaft or core 5.

The inner space 1 5 in the hollow shaft or core 5, which may be used for feeding air or gas in the direction of the arrow D, communicates at the level of the rotor with the surroundings through bores 1 6 in the blades, which bores may extend (see Fig. 10) axially and/or radially, and/or through bores 1 7 in the hub between the blades 6.

The air and/or the gas may be fed during operation through the hollow shaft under pressure or be sucked in by subatmospheric pressure generated in the shaft during operation.

The whirls produced in the liquid by the rotation of the rotor will ensure an effective mixing of gas and air.

The rotor may be disposed directly in a liquid-containing trough or the like, but, if desired, the rotor may be surrounded by a venturi tube 18, which is also arranged in the space containing the liquid. The rear side of the rotor, viewed in the direction of displacement of the liquid, is located at the level of the smallest sectional area of the venturi tube as is shown in Fig. 10. As a further alternative, the rotor is not directly arranged in a liquid containing space, but instead the liquid is fed through a conduit 1 9 to a housing 20 surrounding the hub and joining one end of the venturi tube 1 6 as indicated by broken lines in Fig. 10.

Fig. 11 illustrates an embodiment of the invention for use as a wind- or watermill. In this embodiment the blades 6 are fastened to a hub 5 arranged between a streamlined head 21 located in front of the hub 5 and a flowout body 22 located behind the hub and supported by a supporting member 23. In this embodiment of a wind- or watermill the largest height of a blade 6 is preferably about one seventh of the outer diameter of the hub 5.

Around such a hub with a streamlined inflow head a drastically increased speed is produced in a layer thickness of about 1 /7th of the hub diameter, in which the kinetic energy of the incoming stream is concentrated so that energy can be withdrawn with high efficiency.

The fluid will flow in as indicated by the arrows in Fig. 11 and be circulated by the streamlined head 21 in the direction of the outer circumference of the hub 5. The incoming fluid will thus drive the hub with the blades fastened thereto so that again the flow effect described above is obtained. The hub may be coupled, for example, to an electric motor or the like for supplying energy.

The blades of a wind- or watermill of gradually increasing height as shown in Fig. 11 may be replaced by blades having a rectangular shape in exploded view as indicated in Fig.

1 2.

As a matter of course, the disposition of the rotor has to be such that the fluid can flow in to an ample extent in a radial direction in order to produce the intended whirl.

Claims

1. A method of driving a rotor rotatable about a rotary axis for transmitting or withdrawing kinetic energy to or from a fluid, comprising using a rotor which is provided with at least two identical blades extending helically about the rotary axis of the rotor and spaced apart by a uniform distance on a core, the points of origin and termination of the blades being located in planes at right angles to the rotary axis of the rotor, whilst the height of the blade measured in a radial direction between the outer or lateral edge of the blade and the core from the plane of origin towards the plane of the end of the blade remains the same or increases or decreases gradually or in wave-shaped fashion, the front and/or rear edges of the blades optionally being inclined forwardly or backwardly and the outer or lateral edges of the blades terminating in tips, and wherein, with a blade length measured along the outer edge of the blade which is at least equal to one and a half times the blade height, a ratio between the blade height and the distance between the blades of between 0.5 and 2.5 and a pitch angle of the blades of between 5" and 55 are obtained and wherein the relative inflow with respect to the outer edge of the blade lies between about 5" and 10 .

2. A method of driving a rotor rotatable about a rotary axis for transmitting kinetic energy to a fluid comprising using a rotor which is provided with at least two identical blades extending helically about the rotary axis of the rotor and spaced apart by a uniform distance on a core, the points of origin and termination of the blades being located in planes at right angles to the rotary axis of the rotor, whilst the height of the blade measured in a radial direction between the outer or lateral edge of the blade and the core from the plane of origin towards the plane of the end of the blades remains the same or increases or decreases gradually or in waveshaped fashion, the front and/or rear edges of the blades optionally being inclined forwardly or backwardly and the outer or lateral edges of the blades terminating in tips, and wherein, with a blade length measured along the outer edge of the blade which is at least equal to one and a half times the blade height, a ratio between the blade height and the distance between the blades of between 0.5 and 2.5 and a pitch angle of the blades of between 20 and 55 are obtained and wherein the relative inflow angle of the fluid with respect to the outer edge of the blades lies between about 5" and 10 .

3. A method of driving a rotor rotatable about a rotary axis for withdrawing kinetic energy from a fluid comprising using a rotor provided with at least two identical, uniformly spaced blades extending helically around the rotary axis of the rotor and arranged on a core, the points of origin and termination of the blades being located in planes at right angles to the rotary axis of the rotor, whilst the height of the blade measured in a radial direction between the outer or lateral edge of the blade and the core from the plane or origin towards the plane of termination of the blade remains the same or increases or decreases gradually or in wave-shaped fashion, the front and/or rear edges of the blades optionally being inclined forwardly or backwardly and the outer or lateral edges of the blades terminating in tips and wherein, with a blade length measured along the outer edge of the blade which is at least equal to one and a half times the blade height a ratio between the blade height and the distance between the blades of between 0.5 and 2.5 and a pitch angle of the blades of between 5" and 20 are obtained and wherein the relative inflow angle with respect to the outer edge of the blade lies between about 5" and 10 .

4. A rotor, particularly intended for use in the method claimed in claim 2, comprising at least two identical, uniformly spaced blades extending helically about the rotary axis of the rotor and arranged on a core, in which the points of origin and termination of the blades are located in planes at right angles to the rotary axis of the rotor, whilst the height of the blade measured in a radial direction between the outer or lateral edge of the blade and the core from the plane of origin towards the plane of termination of the blade remains the same or increases or decreases gradually or in wave-shaped fashion, the front and/or rear edges of the blades optionally being inclined forwardly or backwardly, and the outer or lateral edges of the blades terminate in tips, wherein the blade length measured along the outer edge of the blade is at least equal to one and a half times the blade height, the ratio between blade height and blade distance between two neighbouring blades lies between 0.5 and 2.5 and the pitch angles of the blades lies between 20 and 55'.

5. A rotor as claimed in claim 4, wherein the pitch angle lies between 20 and 35o.

6. A rotor as claimed in claim 4, wherein the pitch angle lies between 30 and 55o.

7. A rotor as claimed in any one of the preceding claims 4 to 6, wherein the blade length measured along the outer edge is about 1.5- to 6-times the blade height.

8. A rotor as claimed in any one of the preceding claims 4 to 7, wherein the hub of the rotor is hollow and the interior of the hub communicates with the outer circumference of the rotor.

9. A rotor as claimed in claim 8, wherein the blades have substantially axially extending passages establishing communication between the interior of the hub and the outer circumference of the rotor.

10. A rotor as claimed in claim 8 or 9, wherein the blades have substantially radially extending passages for a communication between the interior of the hub and the outer circumference of the rotor.

11. A rotor as claimed in any one of claims 8 to 10, wherein the hub has passages between the blades for a communication between the interior of the hub and the outer circumference of the rotor.

1 2. A rotor, particularly intended for use in the method claimed in claim 3, comprising at least two identical, uniformly spaced blades extending helically around the rotary axis of the rotor and arranged on a core, in which the points of origin and termination of the blades are located in planes at right angles to the rotary axis of the rotor, whilst the blade height measured in a radial direction between the outer or lateral edge of the blade and the core from the plane of origin towards the plane of termination of the blade remains the same or increases gradually or in wave-shaped fashion, the front and/or rear edges of the blades optionally being inclined forwardly or backwardly, and the outer or lateral edges of the blades terminate in tips wherein the blade length measured along the outer edge of the blade is at least equal to one and a half times the blade height, the ratio between the blade height and the distance between the blades lies between 0.5 and 2.5 and the pitch angle of the blades lies between 5" and 20 .

1 3. A rotor as claimed in claim 12, wherein the pitch angle lies between 10 and 20 .

14. A rotor as claimed in claim 12, wherein the pitch angle is lying between 5" and 10 .

1 5. A rotor as claimed in any one of the preceding claims 1 2 to 14, wherein the blade length measured along the outer edge is about 1 . 5- to 1 2-times the blade height.

1 6. A rotor as claimed in any one of the preceding claims 1 2 to 15, wherein the maximum height of a blade is about 1 /7th the diameter of the hub of the rotor.

1 7. A method of driving a rotor according to claim 1, substantially as described herein.

1 8. A rotor according to claim 4, substantially as described herein.

19. A rotor according to claim 12, sub stantially as described herein.

20. A rotor for transmitting or withdrawing kinetic energy to or from a fluid, substantially as shown in the accompanying drawings and described herein with reference thereto.