US2458006A

US2458006A - Bidirectional blower

Info

Publication number: US2458006A
Application number: US705370A
Authority: US
Inventors: Lee A Kilgore
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1946-10-24
Filing date: 1946-10-24
Publication date: 1949-01-04
Anticipated expiration: 1966-01-04

Description

L.. A. KILGCRE BIDIRECTIONAL BLOWER Filed 0G15. 24, 1946 Jan. 4, 1949.

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INVENTOR Lee Kilgore. BY

ATTORNEY wnNEssEs:

\ Patented Jan. v4, 1949 ammac'rxoNAL nLowEa Lee A. Kilgore, Forest Hills, Pa., alaignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania application october 24, 194s, serial No.A 105,310 1s claims. (ci. 23o-134) l My invention relates to radial-blade blowers. such as are necessary for direct-mounting on most motors, since most motors have to rotate in either direction.

Heretofore, radial-blade blowers, for the purpose stated, have generally had a maximum emy ciency of only about 13%, and they have also had a low output, as shown on curve 5, page 298 of the American Society of Mechanical Engineers Proceedings for 1924, in a paper by C. J. Fechheimer on Performance of centrifugal fans for electrical machinery. f

An object of my present invention is to greatly improve the efilclency, pressure, and volume-out'- put of bidirectional or radial-blade blowers.

A more\specifically stated object of my invention is to apply certain principles of aeronautical design, and more particularly, to apply practical criteria which I have discovered, for preventing stalling or separation of the airilow from the surfaces of the blades and the shrouds' of bidirectional blowers. f

A further object of my invention is to provide a bidirectional blower-means comprising at least 16 radially disposed blades, each having a rounded entrance-edge, at the inner periphery of the blades, and a pointed trailing-edge at the outer periphery of the blades, in combination with an annular outer shroud-means having a rounded entrance-edge.

With the foregoing and other object in view, my invention consists in the parts, elements. combinations, design-constants and systems hereinafter described and claimed, and illustrated in the accompanying drawing, wherein:

Figure 1 is a longitudinal sectional view ofthe top left quarter of a motor embodying my improved blower; and

Fig. 2 is a diagrammatic cross-sectional view of the blower, with airow-lines and velocitypressure lines as subsequently described.

My invention is applicable to any mechanism having a bidirectionally rotatable shaft. By way of example, the invention is illustrated, in Figure 1, as being applied to the construction of an external fan I for a fan-cooled motor 2. The motor is illustrated as having a cylindrical stator-frame 3, within which is supported a laminated stator-core 4 which is spaced, for the most part, from the frame 3, so as to provide a plurality of axially extending stator-vents i between the outer periphery of the stator-core I and the inside of the stator-frame l. An imperforate bracket or enclosing over S'is utilized, at each'end of the machine, having a peripheral 2 porticn 'i in a substantially air-tight relation the outerl portion of the stator-core I. The

stator-member of the machine also includes, at each end of the machine, a perforated bracket or hood l. having a peripheral portion i in a substantially air-tight relation to the end'of the frame-ring i, and having one or more ventilat ing-openings il for the ventilation of the machine. Either one of the brackets or l carries a centrally disposed bearing i2 for supporting the shaft i3 of the rotor-member il of the motor. The details of the electrical design of the motor are immaterial to my present invention.

The external blower i is disposed between the two brackets I and I at the air-inlet end of the motor, as shown. l It comprises a blade-supporting shroud-means Ii which is carried by a hub I6, mounted on the shaft il for rotation therewith. Since, in general, the' motor is bidirectional, the blower is, bidirectional, and it is so designed that it may be placed on a bidirectional motor or other machine. The blade-'supporting shroud-means may have any shape or conilguraltion, depending upon the desired airflow direction of the air, as it passes through the blower. In the particular motor illustrated, the airow conditions are such as to be satisfied by a simple radially disposed disc, for the blade-supporting rotating shroud i5.

The blower i has a plurality of radially disposed blades il, which are supported, at one end, by one side of the blade-supporting shroud il. These blades I1 are disposed in a ring, with a fluid-entrance space Il between the innerperiphery I9l of the blades and the shaft il.

The blower-assembly is completed by means of an outer shroud-means, either stationary or rotating, for providing, in effect, an annularshroud 2i which is operatively associated with the outer ends of the blades I1. In the particular motor illustrated, this outer annular shroud 2i is a stationary shroud. It has an inner fluid-entrance bore or opening 21 having a diameter approximating the inner periphery il of the blades,-and if the inner periphery i! of the blades is not parallel to the shaft Il, then the shroud entrance-diameter at 22 will approximate the inner blade-diameter at the outer ends of the blades il, or the portions of the blades which come close to the annular shroud 2 I.

In accordance with my invention. I have developed designdetails for the blades il, and for the annular shroud 2i, designed to prevent stalling or separation of the airow from the surfaces of the blades or the shroud. The einer features 3 of the new fan are an airfoil blade-shape or section, and a rounded inlet edge 22 on the annular shroud, and preferred design-limitations for these elements.

The simplest form of airfoil blade-shape is a blade having flat sides, a rounded leading or entrance-edge Il, at the inner periphery Il of the blades, and a pointed trailing-edge or tail 2l. at the outer ends of the blades, as shown in Fig. 2. It will be understood, of course, that the blades I1 may have curved or bulged sides, `but since the blower is bidirectional, the blades cannot be hat on one side and bulging on the other, as in a conventional airplane wing-section. Accordingly, the preferred blade-section will generally have two approximately plane, approximately parallel, sides 26 and 2l, although I am not limited to this precise detail.

It is necessary for the entrance-edges 2l and 22 of the blades and shroud to have mean effective radii of curvature which are suiiiciently large to prevent stalling or separation. and it is necessary for the blades Il to have a blade-depth, from the entrance-edge 23 to the trailing-edge 2l, which is sufficiently large to prevent stalling. Stalling may be defined as the separation of the air-stream from the boundary-surface by more than the normal thin turbulent air-layer which is necessary to separate the moving air-stream from the relatively stationary surface. In terms of aeronautical design, stalling has been deilned as occurring when the lift-coeicient has broken away 5% from the straight-line value, when the lift is plotted against the air-speed or the angle of attack.

A test which I have devised for avoiding separation of the airiiow from the blades, is that the deceleration do/dx should not be greater than K11/x, where v is the velocity of the air-stream at distance :t beyond the point of maximum velocity over the surface. and K is a constant which is unity, within plus or minus 20%. I refer, here, to the phenomenon whereby the air which passes over the low-pressure side of the blade ilrst accelerates and then decelerates. It is in the decelerating region where stalling is likely to occur. at any point from the maximum-velocity airilowpoint, to the tip of the blade. When stalling occurs, the blade-pressure is reduced, and hence the air-pressure: and the air-volume is greatly reduced, so that the emciency is ailected very adversely. If the blade has not a suiilcient length, in the direction of airilow, stalling will be obtained.

Air-pressures and air-velocity are best studied by the plotting of airflow-lines I0, Il, and v elocity-potential lines l2, $3. The airilow-lines Il. Il may -be defined as stream-lines representing the path of the air, or more speciiically. equal tubes of now, representing equal masses of airflow through the several tubes, between adjacent airow lines. The velocity-potential lines l2, Il may be defined as air-front lines representing equal velocity-potentials of theair, defining the velocity-potentials such that the reciprocal o! the length, or distance between successive velocitypotential lines, shall represent the air-velocity. The velocity-potential lines are orthogonal, or at right angles, to the now-lines, representing airfronts or cross-sections oi' the flow.

The plotting of the flow-lines ll, Il and the velocity-potential lines I2, u is a matter requiring extreme care, and painstaking work, requiring several hours' time, by a person who has familiarized himself with such work; and even with extreme care, a 5% accuracy is a reasonably expectable accuracy. A suitable scale is chosen, at some reference-point where the airiiow is uniform, and squares are drawn, at this point, representing the airflow-lines and the velocity-potential lines. At the points where air-disturbances occur, or where boundary surfaces are to be followed, these lines must be carefully studied and plotted, using subdivisions of the squares wherever necessary, and realizing that, if the subdivisions are sufficiently small, orthogonal lines will always be obtained, and the ratio of the length to the width of any rectangle will represent the relative air-density at that point, as compared to the air-density at the reference-point where the rectangles are squares. In plotting these lines, it is important to make sure that the crossing-points of all lines are exactly at right angles to each other. and the plotted lines must be shifted and rearranged until such a result is obtained.

As a result of studies by the methods hereinbefore outlined, checked with tests, I have arrived at certain practical criteria, representing designs which satisiy, or approach reasonably closely to, the best blower-operation in accordance with my invention.

The depth of each blade I1, at substantially all airilow-lines 30, should be more than approximately nineteen-twentieths of the mean pitch of the blades, that is, the pitch at the mean diameter of the blades at that airow-line. This is believed to be the best design, or the design which is safest, from the standpoint of the designengineer who is confronted with the problem of designing a good blower. Fair results may possibly be obtained, however, in which the bladedepth is approximately four-fifths of the mean pitch, or any depth greater than this limit. The pitch may be either the circular pitch or the chord-pitch. the two being substantially identical. for within the accuracy-tolerances of the design, in laying out any lblower-design in accordance with my invention. In Fig. 2, the mean pitch is shown at Dori-Ds) 2N The lformula stating that the blade-depth B should be greater than a certain constant, K, times the average pitch may be written.

which is another way of Saying that the minimum blade-number N is dependent upon the ratio B/Dl oi' the blade-depth to the inner diameter of whether the blades are close in towards the shaft,

the blades, which depends upon My invention has been successfully applied. inv

various designs having 16. 18, and 24 blades, respectively, and, in fact, there is no theoretical limitas to the maximum number of blades, up

to the point where the blade-number is raised so high that there is practically no room for air to flow between them. As blades cost money, no designer would choose a blade-number which would be so unreasonably high. Within practical limits. therefore, the blade-number can be considerably larger than in the blowers which I have already tested. I consider that my invention is mainly applicable, in general. only to blowers having 16 blades, or more.

The thickness T of each blade I1, or if the blade does not have uniform thickness, the thickness T of each blade at a point near its entrance-edge Il, should be more than approximately onetwelfth of the pitch near the entrance-edges of the blades, which may be represented by the Ditch '(Di-i-T) This determines the average effective radius of curvature at the rounded entrance-edge Il. The ngure Just given represents the preferred bladethickness T, and the ratio I2 may be decreased to such values as 8.4 and 6.5. or even smaller values, -without approaching a value which will unduly throttle the air, or become vimpractical mechanically. This preferred lower limit of blade-thickness, which is` expressed asA onetwelfth of the pitch near the entrance-edge, could be reduced to one-sixteenth of the pitch near the entrance-edge. with av fair approximation to my preferred design-conditions. in some cases. 1

The mean eective radius of curvature of the rounded entrance-edge 22 of the annular shroud 2| should be greater than approximately onetwelfth of the effective width of the blower, that is, the axial distance, or the air-front distance. between the two shrouds 2l and I5 at the inner periphery il of the blades I1. This minimum radius of curvature of the shroud .entrance-edge 21 is needed, in order to prevent separation as a result of the air-velocity of the air which enters the entrance-space Il underneath the blower. While the ratio, one-twelfth, represents the preferred minimum mean effective curvature-radius for the annular shroud 2|, this ratio could be reduced to one-sixteenth, with a fair approximation to the preferred design-constants of my blower.

There is one lother design-feature which is on the preferred list of my design-requirements, al-` though it is not obligatory, and small departures from it seem to be largely immaterial. This requirement is the requirement that substantially all parts of the entranceand trailing-edges of the blades shall approximate a right-angular relation to the airilow-lines ll at the respective points. This approximation need not, by any means, be accurate; as a small angle of difierence between the entranceor trailing-edge and the corresponding velocity-potential line Il, at that point, will be largely immaterial. It is theoretically desirable. however, for the entranceand exit-edges of the ian-blades l1 to approximately conform to the air-fronts at these points. so that the parallel tubes of airflow, through the blower, will all be operated upon'at the same time. by the blades. This approximation is to be taken with a wide margin of tolerance. however.

The foregoing discussion has had more particular reference to blowers in which the airvelocity does not exceed the velocity of sound. which is the usually understood design-limit of blowers, at the present day.

The practical effect of my invention will be appreciated by comparison with the best previously known form of radial-blade blowers, which. for a long time, have had a performance which has remained substantially stationary at the gures shown in the above-mentioned Rechheimer paper. As compared with a previous maximum eillciency of about 13%, my new fan .has a 40% eillciency, or better. It develops about twice the air-pressure, and itA delivers about 40% more volume, than the generally used. previously known, form of radial-blade blower. My new radial-blade fan or blower is even better than the inclined-blade fans and the curved-blade fans which are shown in the Fechheimer paper, and which were good for operation in only one direction of rotation.

While I have described my invention in a single illustrative form of embodiment, and while I have explained its principles in accordance with my best present understanding, I wish it to be understood that my invention is of fairly general application. I desire, therefore. that the appended claims shall be accorded the broadest construction consistent with their languue.

I claim as my invention:

1. A bidirectional blower-means, comprising the combination, with a bidirectionally rotatable shaft, of a blade-supporting shroud-means for providing, in effect. a running shroud carried by the shaft; blades, supported, at one end, by one side of said blade-supporting shroud-means, with a duidentrance space between the inner periphery of the blades and the shaft; and an outer shroudmeans for providing, in effect, an annular shroud operatively associated with the outer ends of the blades, said annular shroud having an inner peripheral fluid-entrance diameter approximating the innerl periphery of the blades at the outer ends of the blades; each blade having two approximately plane, approximately parallel, sides; each blade also having a rounded entrance-edge at the inner periphery of the blades, and a pointed trailing-edge at the outer periphery of the blades, substantially all parts of the entrahc'eand trailing-edges of the blades approximating a rightangular relation to the airflow-ligas at the respective points. l

2. The invention as defined in plalm l. characterized by such a number of blades, and such a depth of blade between the inner and outerpe-.'

ripheries of the blades, that the depth of each blade, at substantially all iluid-ilow lines, is more than approximately four-fifths of the pitch at the mean diameter of the blades at that uidow line.

3. The invention as defined in claim l. characterized by the thickness of each blade at a point near its entrance-edge being more than ap-l proximately one-sixteenth of the pitch near the entrance-edges of theblades.

4. The invention as defined in claim l. charfacterized by such a number of blades, and such a depth of blade between the inner and outer at least sixteen radially disposed 7 peripheries of the blades, that the depth of each blade, at substantially all fluid-flow lines, is more than approximately four-fifths ot the pitch at the mean diameter of the blades at that fluidilow line, and the thickness of each blade at a point near its entrance-edge being more than approximately one-sixteenth of the pitch near the entrance-edges of the blades.

5. The invention as defined in claim 1, characterized by the annular shroud having al rounded entrance-edge.-

6. The invention as defined in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripheries of the blades, that the depth of each blade, at substantially all fluid-flow lines, is more than approximately four-fifths of the pitch at the mean diameter oi' the blades at that fluidflow line, and the annular shroud having a rounded entrance-edge.

7. The invention as defined in claim 1, characterized by the thickness of each blade at a point near its entrance-edge being more than approximately one-sixteenth of the pitch near the entrance-edges of the blades, and the annular shroud having a rounded entrance-edge.

8. The invention as defined in claim 1, characterized by such a number of bladesVand such a depth of blade between the inner and outer peripheries'of the blades, that the depth of each blade, at substantially all fluid-flow lines, is more than approximately four-fifths of the pitch at the mean diameter of the blades at that fluidow line, the thickness of each blade at a point near its entrance-edge being more than approximately one-sixteenth of the pitch near the entrance-edges of the blades, and the annular shroud having a rounded entrance-edge.

9. The invention as defined in claim l, characterized by the annular shroud having a rounded entrance-edge having a mean effective radius of curvature greater than approximately one-sixteenth of the effective width of the blower, between the two shrouds at the inner periphery of the blades.

10. The invention as defined in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripheries of the blades, that the depth of each blade, at substantially all fluid-flow lines, is more than approximately four-fifths of the pitch at the mean diameter of the blades at that fluidtlow line, and the annular shroud having a rounded entrance-edge having a mean eil'ective radius of curvature greater-than approximately one-sixteenth of the eiective width of the blower, between the two shrouds at the inner periphery of the blades.

11. The invention as defined in claim 1, characterized by the thickness of each blade at a point near its entrance-edge being more than approximately one-sixteenth of the pitch near the entrance-edges of the blades, and the annular shroud having a rounded entrance-edge having a mean ei'ective radius of curvature greater than approximately one-sixteenth of the eilectlve width of the blower, between the two shrouds at the inner periphery of the blades.

12. The invention as dened in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripherles of the blades, that the depth oi' each blade. at substantially al1 iluid-flow lines, is more than approximately four-fifths o! the pitch at the mean diameter oi' the blades at that duid-dow line, the thickness of each blade at a point near its entrance-edge being more than approximately one-sixteenth of the pitch near the entranceedges of the blades, and the annular shroud having a rounded entrance-edge having a mean effective radius of curvature greater than approximately one-sixteenth of the effective width of the blower, between the two shrouds at the inner periphery of the blades.

13. The invention as dened in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripheres of the blades, that the depth of each blade, at substantially all fluid-flow lines, is more than approximately nneteen-twentieths of the pitch at the mean diameter of the blades at that fluid-flow line.

14. The invention as defined in claim 1, characterized Aby the thickness of each blade at a point near its entrance-edge being more than approximately one-twelfth of the pitch near the entrance-edges of the blades.

15. The invention as defined in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripheries of the blades, that the depth of each blade, at substantially all fluid-flow lines, is more than approximately nineteen-twentieths o! the pitch at the mean diameter of the blades at that fluid-now line, and the thickness of each blade at a point near its entrance-edge being more than approximately one-twelfth of the pitch near the entrance-edges of the blades.

16. The invention as defined in claim 1, characterized by the annular shroud having a rounded entrance-edge having a mean effective radius o1' curvature greater than approximately onetwelfth of the effective width of the blower, between' the two shrouds at the inner periphery of the blades.

17. The invention as defined in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripheries of the blades, that the depth of each blade, at substantially all iiuid-fiow lines, is more than approximately nineteen-twentieths of the pitch at the mean diameter of the blades at that fluid-now line, and the annular shroud having a rounded entrance-edge having a mean effective radius of curvature greater than approximately one-twelfth of the eilective width of the blower. between the two shrouds at the inner periphery of the blades.

18. The'invention as defined in claim 1, characterized by the'thickness of each blade at a point near its entrance-edge being more than approximately one-twelfth of the pitch near the entrance-edges of the blades, and the annular shroud having a rounded entrance-edge having a mean effective radius of curvature greater than approximately one-twelfth of the effective width of the blower, between the two shrouds at the inner periphery of the blades.

19. The -invention as defined in claim 1, characterized by such a number of blades, and such a depth of blade between the inner and outer peripheries of the blades, that the depth of each blade, at substantially all iluid-iiow lines, is more than approximately nlneteen-twentieths of the pitch at the mean diameter of the blades at that fluid-flow line, the thickness of each blade at a point near its entrance-edge being more than approximately one-twelfth of the pitch near the entrance-edges ot the blades, and the annular :memos 0 v l0 shroud having` a. rounded entrena-edge hsvinl J n. mean enective radius o! :rester than 'A STAM PATENTS approximately one-twelfthot'thefeectlve widthl Number..- NW10 Date of the blower, betweenthe two sirouds 'at the 772.989 -Williems Oct. 25, 1904 inner periphery of the blades.y lf v 5 938.624' Basler July 20, 1909 un: Af.' mom'. 983.187 Heald- Jan. 31, 1911 f 1.183.075 Kiefer May 16, 1916 REFERENCES CITED 2,347,817 McMillan July 1, 1941 The following references are of record in the 2385366 aleman June 2 1942 111e of this patent: