US2390879A - Propeller fan - Google Patents

Description

m 11,1945. H F. HAGEN 2,390,879.

PROPE LLER mu Filed Sept. 21, 1940 s Sheets-Sheet 1 H. F. HAGEN PROPELLER FAN Dec. 11, 1945.

Filed Sept. '21, 1940 s Sheets-Sheet 2 kw 6Q H. F. HAGEN PROPELLER FAN Dec. 11, 1945.

s Sheets-Shet' 5 Filed Sept. 21, 1940 lnllilln Q Q 2ORDWW v ZDPPOWW 1221292243022- Havoid 17. Ha gm, 29

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Patented Dec. 11, 1945 UNITED STATES PATENT OFFICE PROPELLER FAN Harold F. Hagen. Wellesley, assignor to B. F. Sturte vant Company, Boston, Mass.

Application September 21,1940, Serial No. 351,161

rotative speeds have been desired, it has been I the practice to utilize centrifugal fans.

This invention provides a propeller fan which provides the desired high pressures and which has a performance exceeding that of centrifugal fans which it has replaced for duties requiring high pressures and involving high rotative speeds.

Pressure, speed, space and perhaps other considerations have required that relatively small diameter propeller fans with a relatively large number of blades be used. For example, seven blades may be used. Previous design data, for such fans has been at fault due to the treatment of the blades as individual air fofls performing as in a wind timnel and as a resultfailing to understand the correct, curved flow of air past the blade elements, and ass consequence failing to understand that the chords of greater length could be used with closely spaced propeller blades without interference, than has been appreciated before.

This invention provides a propeller fan with Another feature of the invention resides in the use of blade elements having cambers and chords which increase from minimum at the blade tip to maximum at the hub.

Another feature of the invention resides in providing blades having air foil sections, the chord angles of which decrease from the hub to the tip at such a rate that outer sections are out of plan view alignment with inner sections and yet which are so shaped and arranged that the contour of each outer section is contained within the enveloping contour formed by' radial line generatrices enveloping the contour of each inner blade section having a smaller radius, the contour of the inner blade section'being a directrix. This results in no outer elements of the blades falling outside of radial lines-lv extending through underlying inner elements. With such construction. the centrifugal stressesare at a improved performance in the delivery of high .80

minimum, a consideration which is important due to the high rotational speeds involved.

The purpose of a fan is to provide energy to volume of air a net increase in energy sufllcient to compensate for pressure losses. Where no initial spin is given the air entering the fan, an expression for the addition of energy to each unit volume of air may be written:

awher:

a=the angular velocity of blade. p=the mass per unit volume. Wn=the rotative velocity of the air. r=the blade radius.

In the propeller type fan under discussion, the

flow of air is substantially axial without radial divergence. Since it is desired to add equal amounts of energy to each particle of air, the expression Wm must remain constant across the section of air and at each radius. This is equivalentto saying that the product of the spin com- ,ponent of the air and the radius at which the spin is measured, is constant at each radius directly behind the fan. This product multiplied by 21r=21w7lTl8 called I and represents the circulation.- of the air stream leaving the blades and is equal to the sum of the circulations v of the individual blades.

Knowing the pressure desired Wnr can be calculated from the formula where P=pressure increase desired, and from which the value of War may be substituted in the formula for calculating the circulation at different radii.

It is also known that read With the value forthe circulation substituted in this formula; the lift coefficient determined from the selected air foil and the angle of atack. and the value of Ra determined from the vector diagrams of air flow, the proper chord for elaflcgggade element at diflerent radii may be calc initiate the flow of air and to add to each unit It may be notedthat the spin varies inversely with the blade radius, requiring for practicability a chord which increases in length from aminimum atthetiptosmaximumatthehub.

Heretoiore, in propeller fan desiginthe airioils havebeen selectedirompublisheddatasuchas given in the publications of the National Advisory Committee for Aeronautics and used without modification. Such design principles have been based upon the assumption that the flow oi the airparticlespastthebladeelementsisinstrllsht.

lines. Ihave determinedthstiiowisincurved paths of relatively sharp curvature and have "modinedtheselectcdairioilsonthisaccoimtto have camberwhichisgreaterthsnusedbeiore- Fig.3isanenlargedproflleviewoioneoithe fan .blades witha portion of the hub shown in section;

Figs. 4a, 4b, 4c, 4d, and -4e are developments of sections taken along circular section lines at different radii; By development the sections, it is meant that they appear as they would it the circular section lines referred to were straightened out to form straight; instead of curved, lines.

Fig. 5 is a vector diagram illustrating air velocities at the entrance and delivery edges 01' an airioil'blade element and the derivation of a curved center line tor the blade element;

Fig. 6 is a view'illustrating an air foil blade element formed by utilizing the curved center line derived as shown by Fig. 5 as a chord line, and

Fig. 'l is a projection drawing illustrating the relation of the profiles of different blade sections to each other and to radial lines from the shaft center extending through the profiles of sections of lesser radii.

As illustrated by Figs. 1 and 2,*the relatively large hub il has mounted thereon the seven blades II. The blades have such long chords at the hub that they overlap projected axial areas. As shown most clearly by Fig. 3, the blade ele-' ments extend substantially along radial lines in their entering portions, the increase in chord resulting from the extension of the elements having less radii, axially to the rear of the elements having greater mdli. These" features result in the desired provision or constant circulation and in the equal loading of all blade elements.

hlzig. 5 illustrates runltut velocity vectors w re Rl=the velocity at the delivery edge ot the blade element. Re=thevelocityattheentranceottheblade element, R-=the mean relative velocity. and c-l=the curved center-linens derived irom tbe velocity vectors for selecting an air toil prome.

Theheavyd'sshedlineclisderivedbybeing drawnasasmoothcurvetangmtat lltothe vectorligandatlt paralleltoftbevectorltl.

Anairicil having isselectediromthe asoomo from the hub decreases. 'lhis feature results in greatly improved performance of the fan as indicated by increased efllciency snddecreased noise. Fig. 7 is a geometrical projection oi cylindrical I sections taken through a fan blade and shows how the contours oi th blade elements having greater radii are contained within the envelope formed by radial line generatrices enveloping the contour of any inner blade element. and illustrates how, by projection, this may be determined.

The three air toil sections shown at the center oi Fig. I are the cylindrical section ll taken at the tip, the cylindrical section it taken at a point mid-way oi the tip and hub, and the cylindrical section it taken at the hub. As shown by Fig. 7 the chord angles of the blade sections decrease as the distance of the sections from the hub increases, at such a rate that outer sections are not in plan view alignment with inner sections. It is desired that the contour of the midseotion I! be contained within the envelope formed by radial line generatrices enveloping the contour of the hub section it, and that the contour of the tip section it be contained within the radial line generatrices enveloping the contour of the mid-section I. The radial line generatrices are lines spaced axially along the center line of the Ian shaft and extending perpendicular thereto.

The radial lines il are drawn through the line It on the blade where the hub section is taken, through the line I! where the mid-section is takenandtothelinellatthe tip. Thelines II are horizontal lines of projection extending from the points of intersection oi the hub section line I! with the lines l1, through the blade asoaevo and this shows. as is also shown by the sections A-A, BB, -0, and D--D that no outer section contour has any portion-which lies outside the envelope formed by radial line generatrices enveloping the contour of any inner blade sections. The dash-dot lines drawn through sections A-A, 3-3, 0-0, and D-D are radial lines and illustrate that no outer portion of the contour of any section, taken in any plane, lies outside any radial line drawn through the contour of any inner section. This results in no elements being out of radial alignment with corresponding elements having smaller radii so that centrifugal strains are at a minimum.

The propeller may be operated at very high speeds without tendency for deformation due to centrifugal forces.

It should be understood that the contours of the outer blade sections do not naturally fall within the envelope generatrices described in the foregoing. This may only be determined by projection line drawings as described and usually it is necessary to change the physical proportions and arrangements of the selected profiles to cause them to fall within the requirements as outlined.

In the annexed claims "curved chord-lines" are defined as: The datum lines from which the ordinatesor the air foil section are measured.

While one embodiment has been described for the purpose of illustration, it should be understood that the invention is not limited to the exact arrangement disclosed as modifications thereoi may be suggested by those skilled in the art without departure from the essence of the invention.

What is claimed is:

1. In a propeller fan, an airfoil air ooacting element having as smoothly curved chord line formed tangent at the entrance edge of the element to the velocity vector Re and formed tangent at the delivery edge of the element to the vector equal to and forming the opposite vector to the vector R1 in the parallelogram of vectors including Re and R1 as adjacent sides, where Re=the relative velocity between the air and the element at the entrance edge of the element,

and

R1=the relative velocity between the air and the element atthe delivery edge of the element.

2. A propeller fan comprising a hub having a plurality of blades attached thereto, the elements of each of said blades having sections with chords, thicknesses, cambers, and chord angles, which increase from minimum at the tip to maximum at the hub, the elements of said blades havlines, the radii of curvature of said chord lines decreasing from maximum at the blade tips to minimum at the hub and being formed tangent at the entrance edges of the blade elements, to the velocity vectors Re, and being formed tangent at the delivery edges of the blade elements, to the vectors equal to, and forming the opposite vectors to vectors R1 in the parallelogram of vectors including Re and R1 as"adi'acent sides, where Re=the velocities at the entrance edges of the blade elements, and Rl=the velocities at the delivery edges of the blade element.

3. A propeller fan comprising a hub having a plurality of blades attached thereto, the elements of each of said blades having tapered air foil sections with chords, cambers and thicknesses which increase from minimum at the tip to maximum at the hub and the cambers and the chord angles or which decrease from a maximum at the hub to a minimum at the tip at such a rate that outer sections are out of plan view alignment with inner sections the contours of the blade sections being contained within the enveloping contours formed by radial line generatrices enveloping the contour of any inner blade section, said contour of said inner blade section being a dlrectrix, said elements having curved chord lines, the radii of curvature of said chordlines decreasing from maximum at the blade tip to minimum at the hub and being termed tangent at the entrance edges of the blade elements, to

the velocity vectors Re and being formed tangent at the delivery edges of the blade elements, to the vectors equal to, and forming the opposite vectorstothe vectorsRl in the parallelograml of vectors including Re and R1 as adjacent sides.

' each of said blades having sections with chords.

and thicknesses which increase from minimum at the tip to maximum at the huband chambers and the chord angles of which decrease from a maximum lit the hub to a minimum at the tip at such a rate that outer sections are out of plan view alignment with inner sections, the contours of the glade sections being contained within the enveloping contours formed by radial line generatrices enveloping the contour of any inner blade section. said contour of said inner blade section being a directrlx.

HAROLD I". BAGIN.

ing tapered air-foil sections with curved chord

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