US2814350A - Fan blade construction - Google Patents

Description

Nov. 26, 1957 M, E. NELSON FAN BLADE CONSTRUCTION Original Filed Jan. 19. 1950 5 Sheets-Sheet 1 INVEN foe MORRIS E NELSON Afromey 1957 M. E. NELSON FAN BLADE CONSTRUCTION 5 Shegts-Sheet 2 Original Filed Jan. 19, 1950 I l/VVE/Vi'OR MORR\S E. NELSON WJM OQW Attornes Nov. 26, 1957 M. E. NELSQN 2,814,350

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2,314,350 Patented Nov. 26, 1957 Fire FAN BLADE CONSTRUCTION Divided and this application August 30, 1951, Serial N0.244,375

Claims. (Cl. 170-159) The present invention relates to fan blade airfoils and is particularly adapted to fan blades for use in the tops of cooling towers such for example as are used in oil refineries and in other industries.

More specifically, the invention pertains to fabricated, hollow, stainless steel, airfoil-type fan blades, having a gradually decreasing angle of incidence from hub or root to tip (\vasho-ut).

As is well-known in the art, it is desirable to decrease the angle of incidence of a fan blade from hub to tip as clearly disclosed in United States Patent No. 2,157,999, to compensate for the varying conditions of airflow along the span of the blade. Such construction, commonly referred to as washout has been heretofore achieved by warping or twisting the blade about its span-wise axis or by varyins the profile sections of the blade. Both of these expedients result in a blade requiring complex and expensive manufacturing. procedures.

The present invention solves this problem by providing an improved and simplified hollow blade having a substantially uniform, profile throughout its length and, at the same time, having gradually lessened angles of incidence toward the tip without the necessity of warping the blade. The advantages of such a blade, particularly in relation to cost and simplicity of production will be apparent as this description proceeds.

structurally, the novel blade takes advantage of the many benefits afforded by stainless steel construction. This fact, in connection with a novel spot welded channel construction which nearly eliminates blind rivets, has made possible a stronger and lighter blade than has heretofore been possible. The stainless steel construction has proved to be a decided improvement over the earlier cast aluminum blades which were unsatisfactory from a service standpoint, and over the mild steel blades which were considerably heavier and required more horsepower to drive.

With these and other considerations in view, it is an important object of this invention to provide a cooling tower fan blade which will be highly efficient in the face of the adverse airflow conditions present in conventional cooling towers.

Another object resides in the provision of a cooling tower fan blade that will give the highest possible air flow at low horsepower where excessive cost prohibits the use of stator vanes and a diffuser in the tower.

A: further object resides in the provision of an unwarped fan blade of substantially uniform profile having a decreasing angle of incidence towards the tip of the blade.

Another object resides in the provision of a fan blade which is easily fabricated from stainless steel at a relatively low cost.

A further object resides in the provision of a stainless steel fan blade which is ofstrong lightweight construction.

A still further object resides in the provision of a stainless. steel fan blade having a new spot welded full length channel construction which eliminates most of the blind rivets in fan blade construction.

Other objects and advantages will be apparent from the following description in conjunction with the accompanying drawings and from the appended claims.

The accompanying drawings, in which like reference numerals are used to designate similar parts throughout, illustrate a preferred embodiment for the purpose of disclosing theinvention. The drawings, however, are not to be taken in a limiting or restrictive sense since it will be apparent to those skilled in the art that various changes in the illustrated construction may be resorted to without in any way exceeding the scope of the invention.

In the drawings:

Figure 1 is a schematic diagram of a conventional cooling tower arrangement.

Figure 2 is a plan view of a preferred embodiment of the fan blade shown in the position in which it is mounted in the cooling tower.

Figure 3 is a view of the blade of Figure 2 looking from below.

Figure 4 is a detail view of the blade support, channel girder and inner structure member.

Figure 5 is a detail view of the blade of Figure-2 with the surface uppermost in Figure 2 removed to show the internal structural details of the blade.

Figure 6 is a longitudinal section of the blade taken along line 6-6 of Figure 2.

Figure 7 is a diagrammatic representation of the tip end profile superimposed on the hub end profile.

Figure 8 is a sectional view taken on line 88 of Figure 2.

Figure 9 is a hub end elevation of the blade.

Figure 10 is a fragmentary cross section of the blade taken along line 10-19 of Figure 2.

Figure 11 is a fragmentary cross section of the blade taken along line 11-11 of Figure 2.

Figure 12 is a fragmentary cross section of the blade taken along line 1212 of Figure 2.

Figure 13 is a fragmentary cross section of the blade taken along line 13-13 of'Figure 2.

Figure 14 is a fragmentary cross section of the blade taken along line 1414 of Figure 2.

Figure 15 is a fragmentary cross section similar to Figures 10'-14 showing a modification in the construction of the fan blade.

In conventional cooling tower installations, as illustrated by the schematic diagram of Figure 1, the air which is lifted by the cooling tower fan, generally indicated at 30, enters the tower through louvres 32. This air is drawn through the tower to cool water which in turn,

'acts as the cooling agent for the cooling coils submerged in a conventional opened topped tank containing the water. The Water is continuously pumped from the tank into the sprays 34 from which it is sprayed upwardly into the moving air. The tank, coils and water pump are not shown in Figure 1 since they are conventional in design and play no part of this invention.

After the upwardly moving air has mixed with, and cooled the water from sprays 34 the water is intercepted. by conventional mist eliminator 35 which serves to separate water from the air, causing it to fall back into the tank and allowing the air to be drawn out of the cooling tower by fan 34).

The improved fan 30, Figure 1, is comprised of a hub 37 secured on a shaft 38, fan blade supports or shafts 39- which are secured to hub 37 and shaft 38 and the fan blades 40 rigidly secured to the blade supports 39. Shaft 38 is turned by a conventional synchronous electric motor, not shown, and supports 39 are partially rotatable within their fastenings so that the pitch of the fan blades may be adjusted seasonally if necessary.

It must be understood that in order to lift the air, blades 40 are mounted on the fan in a position exactly inverted from the normal position of an airplane wing, that is, the low pressure side (convex surface 42 of Figure 3 of the drawings) faces down the cooling tower while the high pressure side (partly convex, partly concave surface 44 of Figure 2) faces upwardly. However, in order to avoid confusion in terminology the usual designations will be used throughout the specification so that the Figure 3 surface 42 will be referred to as the upper or low pressure surface while the Figure 2 surface 44 will be referred to as the lower or high pressure surface. In other words, for the purposes of terminology, the fan blades 40 will be referred to in the same way as any conventional airfoil even though in this particular application the airfoil is inverted from the normal position of a conventional airfoil.

The novel fan blades of this invention are provided for use in fans of 6 to 20 or more feet in diameter. As explained above, these blades are mounted in an upside down position and are adjusted to the desired blade angle as conditions of operation or installation require. It is important to note that, for any given blade setting, the angles of incidence of the novel blades, i. e., the angles which any given blade chord makes with a plane perpendicular to the axis of rotation of the fan, decrease gradually from root to tip end as will hereinafter be fully explained.

Figure 7 is a diagrammatic representation of the tip end profile, which has its leading edge at point C and its trailing edge at point B (Figures 2 and 3), superimposed on the hub end profile, which has its forward or leading edge at D (coincident with point C in Figure 7) and its trailing edge at point A, also found in Figures 2 and 3. Points E, G, H, I and J in the diagram, Figure 7, represent points spaced along the tapered trailing edge as shown in Figure 2. Since the forward or leading edge is a straight line perpendicular to the plane of Figure 7, all points on the leading edge would coincide with points D and C.

Still referring to Figure 7, the line 45 indicates the chord line of the root end profile while 52 indicates the chord line of the tip end profile. The low pressure surface of the blade is represented by line 42 and the high pressure surface by line 44. Upper surface 42 is an unwarped arcuate surface of uniform camber along the entire span comprising a portion of the surface which is generated by a line normal to the plane of the root or hub end profile moving along the low pressure camber line AT D of the profile. The lower surface 44, is a reverse curved surface comprising a convex portion adjacent the leading edge of the blade which blends into an intermediate, substantially planar, inclined portion 47 between points X and Y (Figure 7) which in turn merges into a concave transition portion 48 at approximately 50% of the root chord length. The concave transition portion 48 of high pressure surface 44 merges with the low pressure surface 42 along line of tangency T which is parallel to the leading edge and indicated in the drawing (see Figures 2 and 3) by the broken line extending from point T at the root end of the blade to point T at the tip end. Thus the upper and lower surfaces form a hollow forward or leading blade portion which comprises roughly two-thirds of the average chord length, and therefore is large enough to enable the insertion of a blade support 39 with only a very small hump 49, and a thin solid trailing portion extending from the line of tangency T to the trailing edge 50. The profile sections of the hollow leading portion of the blade are identical throughout the span. The complete profile section, i. e., including both the hollow leading and the solid trailing portion, is similarlyuniform along the entire span except that the length of the solid portion decreases from root to tip. Thus, in Figure 7, the trailing portion at the root end extends from point T to A and at the tip end from T to B. This produces a tapered trailing edge passing through points A, E, G, H, I, J and B. Since upper surface 42 is of uniform curvature from one end to the other and is not twisted or warped, this taper along trailing edge 50 results in decreasing chord lines from hub to tip. These chords are angularly displaced from hub to tip as may be best seen from Figure 7 in connection with Figures 2 and 3 wherein the angular displacement between the hub chord 45 connecting points A and D and the tip chord 52 connecting point B and C is clearly shown. Since, by definition, the angle of incidence of the blade is the angle measured between the plane of rotation and the chord line it will be understood that a gradually decreasing blade angle of incidence from the hub to the tip end of the blade is obtained.

Thus the angle of incidence of the blade varies from the hub to the tip without altering the shape of the profile sections or warping the blade. The importance of this feature becomes more apparent when the ease of production afforded thereby is taken into account. For example, as shown in the drawings, particularly Figures 8, 10-15, the blade is formed of sheet metal upper and lower surfaces 42 and 44, welded and riveted to each other and to various internal structural elements.

In production, the upper and lower sheet metal surfaces may be stamped from flat sheets. The die patterns for forming these surfaces can be produced by cutting a single template for each side, setting the template between parallel bars and creating the surface by pulling this template over the wet plaster in a direction normal to its plane. Such simplicity of manufacture of a washed out fan blade surface is impossible for warped blades or blades having dissimilar profiles.

The improved fan blade is preferably a fabricated structure to utilize to the fullest extent the many advantages aiforded by stainless steel. Our preferred construction is light in weight requiring relatively less driving horsepower, is easily fabricated from stainless steel, and requires very little servicing. The blade support 39 on which the blade is mounted is secured to the fan shaft 38 by means of the collar 54, Figures 2, 3 and 9, which is bolted to a suitable casting, indicated diagrammatically at 37 in Figure 11, fixed on the end of shaft 38. Support 39 extends into the blade for a distance of approximately one-third the total length of the blade as is most clearly illustrated in Figures 4 and 5.

In assembling the blade the inner structure member 55 is spot welded at its flanges 56 to the channel sides 57 of the channel girder 58, Figures 4 and 10-13, inclusive. The channel 59 of channel girder 58, Figures 5 and 10-13, is formed at its hub end so that the channel bottom is rounded to conform to the periphery of blade support 39, and this round bottomed portion extends for a distance equal to the length of the structure member 55 which is the distance support 39 extends into the blade. Beyond the round bottomed portion of channel 58 into which support 39 must extend, the channel bottom is flattened out as shown at 60, Figures 4, 5 and 14, so that lower surface 44 which is adjacent to the channel bottom, Figures 2 and 14, is bumped only where it abuts the rounded portion of the channel, Figures 10-13.

The blade support 39 is inserted into the rounded opening formed for it by structure member 55 and channel girder 58 for a distance equal to the length of the member 55 and riveted in place by blind rivets 62, Figure 4. Following this step, support 39, member 55 and channel girder 58 are secured to upper surface 42 by spot welding the flanges 63 of channel girder 58 to the under side of upper surface 42, as is best illustrated in Figure 5. Flanges 63 are curved in a manner to closely conform with the curvature of surface 42. In addition to spot welding upper surface 42 to the flanges 63 of channel girder 58 the surface 42 is also riveted by blind rivets 64 to member 55 and blade support 39, Figures 3 and 10-13.

When the support 39, member 55, channel girder 58 and upper surface 42 have been rigidly assembled as shown in Figure 5 the lower surface 44'is spot welded and riveted to the assembly to complete the blade. As best illustrated in Figure 2 the edges of lower surface 44 and upper surface 42 are spot welded together except at the opening for blade support 39 and at a drainage hole 65. The trailing portions of these surfaces are also welded together as shown at 66 in Figures 2 and 3 to form the thin solid trailing portion of the blade. Lower surface 44 is further secured to the channel girder 58 and blade support 39 by blind rivets 67 and to the channel girder only with blind rivets 68. Transverse of the length of the blade, ribs, beads or embossments 69 are formed in lower surface 44 in order to add structural strength to the blade. It will be seen from the foregoing description that the principally welded stainless steel construction described has reduced to a minimum the number of blind rivets necessary in the fabrication of the blade.

A modified blade construction is shown in Figure 15, Sheet 1, in which the separate channel girder and inner structure member are eliminated and the channel 70 is formed as a part of lower surface 44. The upper edges of the channel walls are formed with shoulders 72 into which is fitted a cover piece 74 which is spot welded to shoulders 72 as shown. Cover plate 74 is also secured firmly to blade support 39 by means of rivets 75, while upper surface plate 42, the bottom of channel 70 and support 39 are riveted together by rivets 76.

It will be understood from the foregoing description that this invention provides an eflicient solution to the long standing problems connected with the operation of a conventional cooling tower. By means of a novel design and construction light weight fan blades are provided which may be fabricated into large diameter fans without excessive weight support or power requirements. The fabricated steel construction, adapted to the difiicult forming requirements of stainless steel, provides a lighter corrosion resistant blade which may be driven with low horsepower and requires minimum field service and replacement. Thus, not only is the fan efliciency increased but the efiiciency of the cooling tower as a whole raised by this novel fan blade.

The present application is a division of application Serial No. 139,374, filed on January 19, 1950, for Fan Blades, and now United States Patent No. 2,682,925.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

l. A fan blade assembly comprising a pair of aerodynamically cambered surfaces joined together to enclose a space and to form a double cambered airfoil shaped fan blade; an internal support structure for said blade comprised solely of an open side channel member disposed in the space formed between said pair of surfaces and secured to one of said surfaces with its open side disposed toward said one surface and a support member extending spanwise into the blade and positioned by said channel member; fastening means jointly securing said support and channel members to the other of said surfaces; additional fastening means securing said support member to said one surface; and chordal reinforcing means comprising only a plurality of spaced, substantially parallel reinforcing ribs formed integrally on one of said surfaces and extending substantially chordwise of said fan blade.

2, The fan blade assembly defined in claim 1 wherein said reinforcingribs are channel-shaped embossments in said one surface and are spaced apart spanwise of the blade along the entire span of said blade.

3. The fan blade assembly defined in claim 1 wherein said surfaces are respectively cambered high and low pressure airfoil surfaces and said reinforcing ribs are beads formed on the high pressure surface.

4. A fan blade assembly comprising a pair of unitary aerodynamically cambered surfaces secured together at their respective edges so as to form an airfoil-shaped fan blade, said surfaces being of such configuration individually and with respect to each other that said fan blade has a hollow leading portion of uniform profile section along the entire span thereof and a thin, substantially solid trailing portion of progressively decreasing chordal length toward its tip formed by merger of corresponding portions of said surfaces and comprising a substantial minor portion of the average chord length of the blade; an internal support structure comprised solely of an elongated channel member disposed spanwise within said hollow leading portion of the blade; a support member extending spanwise into the blade and positioned by said channel member; fastening means jointly securing said support and'channel members to one of said surfaces and additional fastening means securing said support member to the other of said surfaces.

5. A fan blade assembly comprising a pair of unitary, aerodynamically cambered, sheet metal surfaces secured together at their respective edges to form an airfoil-shaped fan blade, said surfaces being of such configuration individually and with respect to each other that said fan blade has a hollow leading portion of uniform profile section along the entire span. of the blade and a thin, substantially solid trailing portion formed by merger of corresponding portions of said surfaces and constituting a substantial minor portion of the average chord length of the blade; an elongated channel member disposed spanwise within said blade, said channel member having divergently extending sidewalls terminating in flanges conforming to the camber of and fastened to one of said surfaces; 2. blade support member positioned in the bottom of said channel member; fastening means jointly se curing said support member and the bottom of said channel member to the other of said surfaces; an inner structure member secured to the side walls of said channel member above said support member with respect to the channel bottom so as to positively position said support member in the channel member; additional fastening means jointly securing said inner structure member and said support member to said one surface between said flanges; and a plurality of reinforcing beads formed on said other surface and spaced in parallel relation along the entire span of said fan blade and intermediate said first mentioned fastening means.

6. A fan blade comprising an internal support structure composed solely of a channel member extending the full length of the blade and having sidewalls terminating in flanges conforming to the camber of one surface of the covering, a support member extending into said channel member from the hub end for a minor portion of the length of the blade and a structural member coextensive in length with and attached to said extending portion of said support member and secured at its lateral edges to said channel sidewalls; and an outer covering comprising a blade side fastened to said support member and said channel flanges and a second blade side fastened to the base of said channel member, said blade sides extending substantially beyond said channel flanges and being joined together along their spanwise edges on opposite sides of said support structure, one of said blade sides having a plurality of substantially parallel, rib-like formations extending substantially the entire chord width of the fan blade to provide the only chordal reinforcement of said blade.

7. In a fan blade having an internal support structure composed solely of a channel member extending the full length of the blade, a support member extending into the channel member for a distance equal to approximately one-third the span length of the blade and positioned by said channel member: an airfoil surface comprising a sheet-like member having a convex surface of uniform camber comprising one side of the blade riveted to the support member and a sheet-like member having a reverse curved surface comprising the other side of the blade riveted to said channel and support members and substantially continuously joined to said convex surface on each side of said channel and support members, said reverse curved surface merging with said convex surface at a point whose distance from the leading edge is between 50 and 80% of the average chord length of the blade.

8. In a fan blade, a pair of unitary cambered surfaces joined together at their edges, and supported in spaced relation from their joined leading edges to a line parallel to the leading edge to form a hollow leading portion, by an internal support structure comprised solely of a support member having a portion extending into the blade, an inner structure member riveted to the portion of the support member extending into the blade, a channel girder extending the full length of the blade and welded to said inner structure member and to one of said cambered surfaces and having as their sole chordal reinforcement, reinforcing ribs embossed on one of said surfaces at spaced intervals along the entire span of the fan blade.

9. A fan blade comprising a pair of cambered surfaces of different curvatures joined together at their edges; an internal support structure consisting [solely] of an elongate support member having a peripheral surface with opposite portions, one of said portions being disposed adjacent one of the cambered surfaces and the opposite portion disposed adjacent the other of said cambered surfaces, an inner structure member shaped to abut one of said portions of the peripheral surface of the support member and riveted thereto and a channel girder shaped to abut the said opposite portion of the peripheral surface of said support member and welded to said inner structure member so as to hold the support member therebetween, said channel girder being Welded to one of said surfaces and riveted to the other surface; and sole chordal reinforcing means comprising a plurality of substantially 0 parallel, spaced reinforcing ribs formed integrally on one of said surfaces.

10. A fan blade having a substantially hollow leading portion of substantially uniform profile section throughout its spanwise length comprised solely of a channel member with a midportion and two flange portions positioned in said hollow portion, a blade support member positioned in said channel, a convex surface comprising one side of said blade secured to the two flanges of said channel and to said support member, and a concave-convex surface comprising at least a major portion of the other side of said blade secured to the midportion of said channel and to said support member, said two blade surfaces being fastened together at their leading edges to form said hollow portion and chordal reinforcing means comprising a plurality of substantially parallel, spanwise spaced, reinforcing ribs formed integrally on one of said surfaces and extending substantially the entire chord length of the blades.

References Cited in the file of this patent UNITED STATES PATENTS 1,044,064 Lorenzen Nov. 12, 1912 1,313,599 Ingells Aug. 19, 1919 1,751,957 Towle Mar. 25, 1930 2,157,999 Charavay May 9, 1939 2,342,421 Moore Feb. 22, 1944 2,362,301 Pecker Nov. 7, 1944 2,364,635 Hasler Dec. 12, 1944 2,415,380 Weber Feb. 4, 1947 2,450,440 Mills Oct. 5, 1948 2,460,351 Hoffman Feb. 1, 1949 2,483,134 Gitz et al Sept. 27, 1949 2,524,870 Adamtchik Oct. 10, 1950 2,574,980 Meyers Nov. 13, 1951 2,589,193 Mayne Mar. 11, 1952 2,682,925 Wosika July 6, 1954 FOREIGN PATENTS 361,799 Great Britain Sept. 28, 1931 OTHER REFERENCES Elements of Practical Aerodynamics, by B. Jones, 3rd edition, pp. '35 and 36.

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