US2320733A - Screw type fluid propelling apparatus - Google Patents

Description

June 1943' J. T. MOINTYRE 2,320,733.

SCREW TYPE FLUID PRQPELLING APPARATUS Filed Nov. 4, 1938 2 SheetsSheet l (INVENTOR i ii i I 1 JT MGINTYRE BY i r June 1, 1943- J. T. M INTYRE SCREW TYPE FLUID PROPELLING APPARATUS 2 Sheets-sheaf 2 Filed NOV. 4, 1938 Patented June 1, 1943 SCREW TYPE FLUID PROPELLING APPARATUS John Taylor McIntyre, Johannesburg, Transvaal, Union of South Africa, assignor to Macard Screws, Limited, Johannesburg, Transvaal, Union ofSouth Africa Application November 4, 1938, Serial No. 238,908 In Union of South Africa January 7, 1938 '2 Claims. (01. 230-122) The invention relates to screw propeller type fans, pumps and the like, and the object of the invention is to increase the manometric efflciency of such apparatus.

This application is a continuation in part of my prior application Serial No. 195,629, filed on March 12, 1938, now abandoned. However, the subject matter of the claims of the pr s t app was part of the subject matter of the aforesaid application and was never abandoned.

In this specification, manometric efficiency means the ratio of the pressure actually obtained, to the theoretical pressure corresponding to the impeller tip speed. The term geometric pitch" is used in its ordinary sense of the axial length of one turn of the helix formed by helical extension of the chord of a section of an impeller blade or guide vane; but its use is restricted to discussion of different geometric pitches at the varying radii of a blade or vane. A helix is either righthanded or left-handed accordingly as it is generated by clockwise or by counter-clockwise rotation of its generating radius moving forward along its axis; and the term helical hand is used herein for comparing-4n this respect-different helical elements or formations, or elements or formations when considered as portions of helices. The use of the words relative curvature is restricted to the description of impeller blades to denote the ratio of the maximum ordinate between the median camber line of an aerofoil element and the chord joining thetwo ends of said median. camber line, to the length of this chord.

concavity as discussed in this specification has reference only to the relationship of the concave surface of a blade or vane to pure circumferential direction, for the purpose of specifying whether said concave surface faces, in that limited respect, in the same way as, or in the opposite way to, the sense of rotation of the impeller. Angularity of the chord of the concave surface to said circumferential direction or to the axis of the machine is absent from the meaning of the term. The concavity of the impellerblades faces in the same .vay as the sense of rotation f the impeller.

When in apparatus of the kind in question, a stream of fluid passes through the rotor, it acquires from the latter a drag velocity which, in direction, is circumferential, and, in sense, is the same as that of the rotor velocity, and the total magnitude of which is determined principally by the profile and number of the rotor blades and their rotational speed. According to the present invention, in apparatus of the kind in question,

the whole of the fluid incoming to the rotor onent produces a very substantial gain of pressure in the outgoing fluid. Accordingly in a given apparatus, the invention enables a greater pressure gain to be attained without increase of rotor blade velocity or a given pressure gain to be attained with a lower rotor blade velocity.

According therefore to the present invention a screw type fluid propelling apparatus comprises an impeller having blades of aerofoil cross-section increasing in width and in total area progressively in the direction from tip to hub with conforming relative curvature, in combination with fluid inlet means comprising a helical guidevane assembly co-axial with the impeller and arranged to impart to the whole of the fluid ingoing to theimpeller a counterswirl which, in magnitude, is substantially in excess of the impeller drag.

If the fluid outgoing from the rotor is to pass through another rotor stage, its remaining circumferential velocity may be increased to the circumferential velocity originally imparted to the fluid. If, however, the fluid is to leave the apparatus and is to leave it without rotational movement, said remaining circumferential velocity I must be counteracted, e. g., by outlet vanes tending to set up rotation in the opposite direction. This results in a decrease of energy of motion and therefore in a gain of pressure.

The invention will be further described with Figures III and IV respectively.

Figure VII is a diagram in which blade sections are shown correlated to-the radii of the blade elevation at which they occur.

Figure VIII is a longitudinal section of part of a portion of a cased multi-stage fan.

Figure IX is a diagram in which cross-sections of a rotor blade, an inlet guide vane, and an outlet guide vane are shown collated to the radii of the blade elevation at which they occur and so as to exhibit'the geometric pitch of the blade and the variations in the inclination of the inlet and outlet guide vanes in the direction from tip to hub with respect to the axis.

With reference to Figures I, III and V, 2 indicates cross-sectional elements of inlet guide vanes; 3 cross-sectional elements or rotor blades;

illustrated example its sense is assumed to be left to right, as indicated by arrows A. The sense of the rotation of the impeller or impellers is clockwise when viewed from the left and is indicated in some of the figures by arrows B.

The function of the inlet guide vanes ,2,is to impart to the fluid entering the impeller blades a movement component which is circumferential and contrary in sense to the circumferential movement of the blades; that is, in the illustrated example, an anti-clockwise circumferential movement component. This movement component is referred to as counterswirl. The vanes may be assisted in performing this function by other means for changing fluid motion direction; but in all cases the inlet guide vanes 2 are arranged to determine the flnal direction of the fluid when it is delivered to the impeller. In order to produce the counterswirl the guide vanes 2 are helical and co-axial with the impeller and of the same helical hand as the impeller; and their concave surfaces face against'the-concave surfaces of the impeller blades. They are preferably of aerofoil crosssection in order to promote streamline flow. Moreover they usually decrease in width in the direction from tip to hub.

The proposal has been made to provide a screw impeller with inlet guide vanes which deliver the fluid to the impeller with a counterswirl of such magnitude as to counter-balance the impeller drag and so to cause the fluid to leave the impeller with pure axial movement; but in the present invention counterswirl is employed as an essential factor in pressure building, being for that purpose substantially in excess of the drag and i applied to the whole ofthe fluid ingoing to the impeller, and, utilized with an impeller which is structurally capable of producing and utilizing a counterswirl of such magnitude and so differentiated radially as to attain in practice the pressure rise latent in the counterswirl principle.

This principle may be explained withreference to Figures III and V which are respectively velocity and pressure diagrams of some arbitrarily chosen annular element of the fluid stream.

Let Va represent in magnitude and direction, the axial velocity set upfby the impeller, in the fluid flowing to it. The guide vanes 2 divert the flow into direction Vi, thus tending to add to the axial component Va a circumferential component 2,320,733 I responding to the velocity variations indicated in represented in magnitiide by Vwa and'opposite in sense to the sense of rotation of the impeller. Rotation of the impeller however tends to set up in the fluid the circumferential drag velocity represented by d, in the same sense as such rotation. The effective circumferential component of the velocity of the incoming fluid is therefore the algebraic sum of V100 and d, represented by Vwe. Pva indicates the absolute linear velocity of the impeller blade at the chosen radius; so that Pva+Vwe=Q is the effective flnid to blade circumferential velocity; and the resultant of Q and Va, viz. Vr is the velocity of inflow of the fluid. relative to the blade. Provided the blade isofl aerofoil section and the angle of attack a is mainof substantial magnitude contrary in sense to the velocity of the blades. This results in a high value of Q and so of V1; and the production by the impeller of very high fluid pressures. It is believed that the production of high pressures by the aid of counterswirl in excess of drag has not heretofore been attempted. By means of it and the other characteristics of the invention a cased screw. fan can be built up which produces pressures comparable with those of centrifugal fans, for instance with manometric efficiencies ranging from 0.3 to 0.5 and more; while having considerably greater mechanical efllciency than a centrifugal fan.

However, velocity and pressure changes of the kind indicated by the above-mentioned diagrams cannot be obtained in magnitude sufficient to build up pressures substantially greater than those produced by fans of known design, or alternatively sufficient to obtain heretofore usual pressures withsubstantially less angular impeller speed, unless the impeller blade sections at the.

various radii are made adequately powerful.

Accordingly, the impeller blades are made throughout their length of a form known per se. viz., of aerofoil section, by which is meant a section defined by back and front surfaces so differently cambered that the sectionis curved in the direction of the blade width and so also as to make the section of substantial thickness relatively to its chord length and with its leading edge thicker than its trailing edge; such section progressively increasing, in the direction from tip to hub, in its structural thrust-producing factors, viz., its blade section width, total area, and preferably also the ratio of thickness to chord length,

and the relative curvature at all sections being in conformity with the varying values of said factors.

Such increase is shown in Figure VII where C,

. D, E represent the cross-section of the blade at three different radii viz. the tip radius 10, an intermediate radius rd and the hub radius re respectively. It will be seen that the chords of the aerofoil sections, indicated at the different radii by cc, cd, ce, increase in length progressively from section C to section E and that the ratio of thickness t to chord length, that is, the relative thickness of the aerofoil section, also progressively increases so that the whole blade section area increases in the same direction. The relative curvature of the thus varying sections is adjusted in the manner well known in aerofoil designing, to ensure that the factors mentioned co-operate to give the required lift or thrust combined with the v optimum drag/lift ratios for the various sections of the blade. In practice the relative curvature remains constant, or, as is shown, increases in the its helical hand-or more particularly the helical handof thetangent 'I (Figure 111) to the median line at the receiving ends of its vanes-As the same as that of the chords of the impellerblades and of the inlet vane assembly 2. Secondly its concavity faces with the concavity of the impeller blades. A further characteristic of the assembly 4 is that the said tangent I makes a substantial angle, b Figure III, with the rotor axis so as to receive without shock th residual counterswirl from the impeller.

.-Figure V shows graphically the static pressure variations of the fluid duringdts passage through the apparatus. I The pressure drops during fluid through the guide vanes 2, where the circumferential velocity is imparted to it. This drop of pressure is followedby a very considerable gain of pressure during its passage through the rotor, and by a further increase of pressure during the passage of-the fluid through the vanes 4, where its'remaining circumferential velocity is counteracted.

Figures III and V refer to conditions at th'eone stream element selected. Since the, rotor blade ing to the radial position of the blade element at the passage of the V velocity and the 'dragwary in magnitude'accordwhichthey occur, and the pitch angle of the'blade is usually also difierent at different radii, thecircumferential velocity component Vwa and the angle 7 (gamma) may also be varied correspondingly at diflerent radii.- For instance assuming a rotor design with constant geometric pitch from tip to root of blade and constant angle of attack.

then the angle 7 (gamma) would decrease from tip to root ofthe inlet guide vane with corresponding rotation of the outlet guide vane, if present, toward parallelism with the axis in-ordeiitomaintain the same proportionate increase 'in' manometric emciency over the whole working area.

Double-stage apparatus (FigureII) comprises inlet vanes 2, primary rotor blades 3, interstage" vanes 5, secondary rotorblade's 6 and outlet vanes 4.

The inlet vane elements 2, primary rotor blade elements 3 and outlet vane elements 4 correspond to the inlet vaneelements 2, rotor blade elements 3 and outlet vane elements 4 of Figure I.

As illustrated in Figure IV the fluid entering i V the rotor 3 has imparted to it by the inlet vanes 2 a velocity Vi composed of the axial velocity component Va and the circumferential velocity-comonent Vwa. During the passage of the fluid through the rotor 3 the circumferential velocity 1 of the rotor-blade.

velocity component Va and the-circumferential velocity component Vwe. The interstage vane assembly 5 (Figure II) is of the same helical hand as the inlet assembly 2 and as the impeller blades: and its component vanes have concave surfaces facing opposite1y to the concavity of the impeller blades, and said vanes have the feature in common with the outlet vanes 4 that their tangents I (Figure IV) make a substantial angle b with the rotor axis. They thus receive fluid with aboslute velocity Ve and deliver-itwith an absolute velocity which, in most cases, is similar in direction and: magnitude to Vt. During its passage through thesecondrotorjthe drag d decreases itscircumferential ;veloci'ty component Vwa tovwe; thus the fluid leaves; the second rotor with an absolute Velocity-V8 compifising the cirnlfi-VWSO that the fluid leaves thevane's 4 Substantlally without circumferential velocity.

The pressure (see Figure VI) 'decrea'ses during" 3 the passage of the fluid through vanes 22 is considerably increased in'the first rotor 3: is somewhat decreased in the interstage vanes 5: is again considerably increased in the second rotor 63 and an additional gain inipressure is attained by the 5 action of the outletivanes I.

In Figure VIII the rotors 3 and} are carried by tire driving shaft 8 mounted in, bearings ;9 and;

positioned axially within the casinglll; 1The lat- I v ter also encloses the inlet guide vanes 2, the m terstage guidevanefljiid theio'utlet guide vanes 4, if present: and'is substantially'cylindrical about said parts in order to keepthe flOW-f fl 'ee from.

radial component.

In Figure IX, 0, D and sections of the rotor blade at three different radii, in the same manner as they are illustrated in Figure VII; F, G and H represent three aerofoil cross-sections of -an inlet guide vane at thesame radii. It will be seen that the inclinationo'f the V aerofoil section chords of said inlet guide-van aeo; the axis decreases from tip'to root, thejchordimj j clination of the tip' section- F beingthe greatest" and thechord inclinationy'of the rootse ion being the smallest. r, K. and! represent-"cert spending aerofoll'cross sections ofan outietguide vane, audit-will be seen from'the'iffiigure that the inclination of the aerofoilj sectionf-chordstof'the axis decreases correspondingly with thlefdecrease' of chord inclination of said inlet 'guide vane sec-' tions. The decrease of-chordiinclizi'ation of: the inlet guide vanesis, such that the-angle of attack.

4 is substantially constant along-the 'whole-length It is preferred remake the render baa ameter-tohubdiametersuch: entry of air into the rotor;

- The present invention is concerned ,with tn e provision-of ex'eess counterswlrl inscrew propeller I I I I type machines, irrespective of the kind'of'pitch oi the impeller blades. "This inventionis'thus, to a certain extent, generic to the invention of my copendingapplication, Serial No'. 231,428, now matured '1nto..Patent o- ,224,519. which deals with such apparatus-in which-counterswirl is produced component Vwa is decreased by the drag d to Vwe;

and the fluid thus leaves the rotor-with the smaller absolute velocity Ve composed of the axial in which p er: b des are of. decreasing Pitchtowards the hub,

I claim:

1. A multi-stage screw type fluid propelling aprenrsent-me-cross- Y section increasing in width and total area progressively in the direction from tip to hub with fluid inlet means comprising helical inlet guide vanes coaxial with the impeller, the concavity of which vanes faces in the circumferential direction opposite from that of the impeller blades to impart to the whole ofthe fluid ingoing to the impeller a counterswirl substantially in excess of the impeller drag to increase the difference between the velocity of the rotor and that of the incoming fluid; to consequently increase the pressure at fluid discharged by the rotor; the guide vanes being of the same helical hand as that of the impeller blades, and the tangents to the median lines of the interstage vanes, at their receiving ends, making a. substantial angle with the axis.

2. A'cased screw type fluid propelling apparatus, comprising an impeller having blades of aerofoil cross-section increasing in width and total area progressively in the direction from tip to hub, in combination with fluid inlet means comprising helical inlet guide vanes coaxial with the impeller, the concavity of which vanes faces, in the circumferential directionopposite from that of the impeller blades, to impartto the whole of the fluid ingoin to the impeller a counterswirl substantially in excess of the impeller drag 'to increase the difference between the velocity of the rotor and that of the incoming fluid, to consequently increase the pressure of fluid discharged by the rotor; and comprising a helical final outlet guide vane assembly coaxial with the rotor, the helical hand of said assembly being the same as that of the impeller blades, and the tangents to the median lines of the vane sections of said assembly at the receiving end making a substantial angle with the axis to convert the remaining excess counterswirl into an axial component and a consequent increase in pressure.

JOHN TAYLOR McINTYRE.

Images