Low noise and high efficiency blade for axial fans and rotors and axial fan or rotor comprising said blade

Abstract

Today the low noise blades and especially the super low noise blades for large diameter axial fans which are employed in the big cooling machines and cooling plants are so costly and are requiring so many extra costs on the other related equipment, that the noise pollution abatement can increase the whole cooling apparatus cost by up to a 35%. This invention, provides a new technology to make low noise fans able to transform any common blade into a low noise or very low noise at very low cost, preserving the same high efficiency and tip speed, as opposite to all the other low noise blades at actual status of art. As the fans for the big cooling apparatus are generally their main noise source, this invention will offer the opportunity to dramatically reduce the noise pollution produced by big cooling machines and cooling plants.

Claims

1. A low noise industrial axial fan, having a diameter more than 900 mm and adjustable pitch angle and comprising a blade, for propelling air from a low air pressure space to a high air pressure space, comprising a front edge and a rear edge, the front edge being leading edge of the blade facing a direction of rotation of the fan in an operative condition, and said rear edge being a trailing edge of the blade, said blade comprising a root portion by means of which the blade is fixed to a rotor of the fan, along with a first blade portion extending from said root portion and a second blade portion extending from said first portion, wherein a portion of the leading edge as defined by said first portion and a portion of said leading edge as defined by said second portion extend along different directions and define a first obtuse angle so that a projection of the blade on a rotation plane perpendicular to an axis of rotation is V-shaped wherein the first obtuse angle extends in the direction of rotation of the fan.

2. The axial fan according to claim 1, wherein the blade, the portion of the trailing edge as defined by said first portion and a portion of said trailing edge as defined by said second portion extend along different directions and define a second obtuse angle so that a projection of the blade on a rotation plane perpendicular to the axis of rotation is V-shaped.

3. The axial fan according to claim 1, wherein the root portion is shaped so as to define a pitch adjustment axis X-X, and in that with reference to said pitch adjustment axis X-X, a vertex of the angle as defined by said portion of the leading edge as defined by said first portion and said portion of said leading edge as defined by said second portion lies on one side whilst opposite tips of said leading edge lie on another side.

4. The axial fan according to claim 3, wherein at least one of opposite tips of the leading edge is oriented towards the low air pressure space.

5. The axial fan according to claim 1, the root portion is shaped so as to define a pitch adjustment axis X-X, and in that with reference to said pitch adjustment axis X-X, a vertex of the angle as defined by said portion of the leading edge as defined by said first portion and said portion of said leading edge as defined by said second portion lies on one side along with opposite tips of said leading edge.

6. The axial fan according to claim 1, in which said first obtuse angle is comprised between 90° and 170°.

7. The axial fan according to claim 6, in which said first obtuse angle is comprised between 100° and 120°.

8. The axial fan according to claim 1, wherein at the portion of a blade where said first portion and said second portion joint, a dihedral angle of 195° between suction surfaces of the first portion and the second portion in a vertical plane.

9. The axial fan according to claim 1, wherein, in the blade, a first, inner portion is obtained starting by a rectilinear blade by rotating a part of the blade profile backwards counterclockwise, around a vertical axis passing where a pitch adjustment axis is crossing a blade root section, and a second, outer portion is obtained by rotating a part of a blade profile backwards clockwise around the vertical axis passing where the pitch adjustment axis is crossing a blade tip section.

10. The axial, fan according to claim 1, wherein the blade or an airfoil part of is a one-piece blade, made of casting aluminum or steel or plastic or any other suitable material.

11. The axial fan according to claim 1, wherein said first blade portion and said second blade portion form on said trailing edge a rounded angle.

12. The axial fan according to claim 1, wherein said first blade portion and said second blade portion have slightly curved leading edges.

13. The axial fan according to claim 1, wherein said first blade portion and said second blade portion have slightly curved trailing edges.

14. The axial fan according to claim 1, wherein said blade comprises a winglet on its tip.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, description will be given of the embodiments of the present invention as depicted in the drawings wherein, however, the present invention is not limited to the embodiments as depicted in the drawings and disclosed below.

(2) In the drawings:

(3) FIGS. 1, 2a, 2b, 2c, 3a, 3b, 4a, 4b, 4c, 7a, 7b, show different examples of blade assemblies for axial fans according to the prior art. More in details:

(4) In FIG. 1 there is depicted a perspective view of a small diameter axial fan according to the prior art provided with a ring on its periphery;

(5) In each of FIGS. 2a, 2b, 2c there is depicted a blade according to the prior art of the kind commonly used in known large fans: in FIG. 2a there is depicted a twisted blade, in FIG. 2b there is depicted a tapered blade, in FIG. 2c there is depicted a trimmed blade;

(6) In FIG. 3a there is depicted an example of first noise level large diameter (10 meters) fan according to the prior art;

(7) In FIG. 3b there is depicted an example of second noise level large diameter (10 meters) fan according to the prior art;

(8) In FIGS. 4a, 4b and 4c there are depicted corresponding examples of blades of super low noise axial fans according to the prior art. More in details:

(9) In FIG. 4a there is depicted a blade having a leading edge both curved and swept into the space;

(10) In FIG. 4b there is depicted a blade having a leading edge swept in a plane;

(11) In FIG. 4c there is depicted a blade having a leading edge swept according to a straight line; In FIG. 5 there is depicted a top (plan) view of a blade according to a first embodiment of the present invention;

(12) In FIG. 6 there is depicted a schematic top view of a super low noise large diameter axial fan equipped with blades according to an embodiment of the present invention;

(13) In FIG. 7a there is depicted an example of a super low noise axial fan according to the prior art, having trailing and leading edge extension at outer third of the radius;

(14) In FIG. 7b there is depicted an example of super low noise axial fan according to the prior art, having trailing and leading edge extension at outer third of the radius;

(15) In FIG. 8 there is depicted a top (plane) view of a blade according to a second embodiment of the present invention wherein the blade is a tapered and twisted blade;

(16) In FIG. 8a there are compared the angles at tip leading edge and the air relative velocity of blades according to the prior art and an embodiment of the present invention, respectively;

(17) In FIG. 8b there are compared the angles at tip trailing edge and the air relative velocity of blades according to the prior art and an embodiment of the present invention, respectively;

(18) FIG. 9 schematically shows the second mode of vibration of the blade according to an embodiment of the present invention;

(19) In FIG. 10 there is depicted a blade according to the present invention, the dihedral angle being visible;

(20) In FIG. 11 there is depicted a blade according to a further embodiment of the present invention;

(21) In FIG. 12 there is depicted a blade according to a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(22) It will become apparent, in view of the following description, that the main task of the present invention is to provide a blade, in particular for large diameter super low noise industrial axial fans, this being the reason why, in the following, description will be given of a blade for super low noise large diameter industrial axial fans which can be also used with industrial fan of the type already known in the art to obtain noise reduction while preserving at least the same aerodynamic efficiency.

(23) In FIG. 5, the blade according to the embodiment of the present invention as depicted therein is identified by the reference numeral 1. The blade 1 comprises in particular a root portion 1r provided for the purpose of fixing the blade 1 to an axial rotor (not depicted in FIG. 5); in particular, the blade may be fixed to the axial fan at different orientation angles (pitch angles) with respect to the axis X-X as identified by the dashed line in FIG. 5. The rotor is supposed to be rotated, during operation of the fan, in the clockwise direction as depicted by the arrow, the axis of rotation of the fan corresponding to the axis of rotation of the rotor. With respect to FIG. 5, the axis of rotation is perpendicular to plane of the figure; the smallest pitch angle is the angle at which the projection of the blade on a plane perpendicular to the axis of rotation occupies the largest area or surface. Pitch angles of larger amounts result in the projections of the blade on the plane perpendicular to the axis of rotation (also referred to, in the following, as the “plane of rotation) occupying corresponding smaller areas or surfaces. As depicted, with the blade 1 oriented at the smallest pitch angle, in particular at zero pitch angle, the projection of the blade on the rotation plane, is such that a V shape is formed along the span of the blade (see FIG. 5). In particular, the blade 1 comprises a first, inner, portion 1a close to the rotational axis and extending from the root portion 1r, along with a second, outer, portion 1b, having approximately the same length of the first portion 1a, and extending from the first portion 1a. With respect to the axis X-X, the first portion 1a extends along a first direction (forming an angle with the axis X-X), whilst, still with respect to the axis X-X, the second portion 1b extends along a second direction other than the first direction (forming an angle with the axis X-X other than the angle formed by the first portion 1a).

(24) Moreover, with respect to the direction of rotation of the blade 1 (identified by the arrow in FIG. 5), in the blade 1 two edges can be identified, namely the leading edge 1l impinging against the air during rotation of the blade 1), and the trailing edge 1t (opposite to the leading edge 1I).

(25) Still as depicted, the first portion 1a and the second portion 1b are oriented one with respect to the other so that an obtuse angle V (more than 90° and less than 180° is defined by the leading edge 1I, whilst an a bigger angle (more than 180°) is defined by the trailing edge 1t.

(26) Still with reference to the axis X-X which, as depicted, crosses both the blade portion 1a and the blade portion 1b, the vertex Vv of the angle V defined by the leading edge 1l is located on one side of the axis X-X, whilst the opposite tips (points B and C) of the leading edge 1l are located on the opposite side.

(27) The above disclosed feature is a unique, distinguishing feature of the blade according to the present invention and has been ideally obtained according to the following way: starting from a substantially rectilinear blade as depicted for instance in FIG. 3a, the inner part 1a is obtained by rotating (bending) the blade backwards with respect to the root portion 1r (counterclockwise with respect to FIG. 5), in particular around the vertical axis passing where the pitch adjustment axis X-X is crossing the blade root section 1r, whilst the outer part 1b is obtained by rotating (bending) the blade backwards with respect to the first portion 1a (clockwise with respect to FIG. 5), in particular around the vertical axis passing where the pitch adjustment axis X-X is crossing the blade tip section.

(28) The blade 1 has a very particular behavior with respect to noise and efficiency. Carrying out an extensive test program on a 10 feet diameter axial flow fan equipped with blades of the kind disclosed above and depicted in FIG. 5, starting first with a V angle of 170° and decreasing same to 90°, the inventor discovered that, as a result of the reduction of the angle V the fan noise also decreased. In particular, with angles between 120° and 100° it is possible to obtain a noise reduction equal or better than that of noise levels 2 and 3 of the prior art low noise fans described ahead. But, and this is extraordinary, it has been discovered that the high efficiency of common blades belonging to noise level 1 can be maintained and in some cases increased, meaning that, according to the needs and/or circumstances, the present invention can even be used just to increase the fan efficiency.

(29) A further improvement has been obtained with a blade as depicted in FIG. 10 wherein, at the joining section, the inner portion 1a and the outer portion 1b defines a dihedral angle of about 192°, meaning in particular that, in the projection of the leading edge 1l om a plane perpendicular to the rotation plane, the projections of the leading edges of the first portion 1a and the second portion 1b are oriented along different directions.

(30) Based on the above tests it has even been verified that the above disclosed design remains essentially advantageous, as compared with that of blades according to the prior art, even if the vertex Vv and/or the points B and C are shifted to positions other than those depicted in FIG. 5 as depicted, by way of example, in FIG. 11 (relating to a further embodiment of the blade 1 according to the present invention). As depicted in FIG. 11, the tip leading edge point C is forward translated with respect to the root leading edge point B.

(31) Moreover, the above disclosed geometry (design) remains effective even if the size ratio between inner and outer portions is changed.

(32) The above changes can be very helpful for the optimization of different types of blades and also because they are acting in a different way on noise and efficiency, therefore depending if noise improvement or efficiency improvement is preferred different solutions can be preferred.

(33) The main reasons why the above disclosed, indeed quite extraordinary results can be obtained with a blade according to the present invention are related to the fact that the above disclosed geometry and/or design is affecting not just one but several among the noise generating and efficiency reducing factors. Some of these factors are mentioned herewith; however, there are additional factors helping to get these results which are not mentioned because it is not yet very clear how important they are.

(34) Herewith explanation is essentially given of the main reason why the low noise levels are achieved and secondly why it was possible to preserve or improve the fan efficiency. Moreover, some more information are given as to additional advantages of the present invention such as, for instance, those related to the reduction of costs. With reference to FIGS. 6, 7a and 7b the outer portion of the blade according to the present invention (FIG. 6) will be compared in the following with that of a blade according to the prior art (FIGS. 7a and 7b) considering that, as it is well known, the outer portion of a blade is interested by over 70% of air volume, meaning that the outer portion is the most important part of the blade.

(35) The design of the blade according to the present invention can be applied to any type of common blade of the prior art and also to their combination of inner or outer part. Of course both final noise and final efficiency values are greatly conditioned by the type of blade selected to apply the invention. An optimization must follow, different case by case, depending also if low noise or better efficiency is preferred. The common, prior art blade which was selected to be modified according to the present is of the kind as depicted in FIG. 2c, which is consisting essentially of a profile with a trimmed flap on the trailing edge. However, blades as depicted in (FIG. 2b have been also briefly tested to have evidence that the invention can be really applied to any type of blades.

(36) The reason why the type c blade has been preferred for the test program, was that there were several options as to the dimensions of the V angle and the locations of the points Vv, B and C relative positions to be tested and it was requiring a large number of different blades. This type of blade appeared ideal to be manufactured in a very fast and simple way. In fact, this blade can be made out of extruded or pultruded profile and to make a different executions it is only matter of cutting and drilling and joining in a different way. Actually this is a preferred embodiment for its simplicity. Other embodiments foresee to add on this blade prior art systems which are particularly effective on the invented design like winglets on tip or saw teeth on the trailing edge.

(37) A further preferred embodiment foresees an adequate attachment to the hub, which has been identified as a rectangular shape attachment because laser, plasma, oxy cutting systems could be used to cut any type of shape in a metal sheet and then the optimized position of the blade with respect to the fan radius can be obtained at low cost.

(38) A second mode vibration attachment as sketched in the FIG. 9 would be ideal for this type of blade, not only because it is lowering the loads but also because if the bade is not too long this attachment could enter the blade for an extension that it would give the possibility to reach the outer profile part so that it could be directly fixed on it. However fixing the two blade parts together is very simple in this case and numerous solutions could be used.

(39) Within the meaning of the present invention, the blade 1 can be provided both by joining together the inner portion 1a and the outer portion 1b (prepared in advance) or even by forming the blade 1, comprising inner portion 1a and outer portion 1b as a single one piece blade, casting aluminum, steel or plastic to get the shapes according the invention, for small and medium size blades. For large blades instead it could be used any of the fiberglass construction systems actually used for the common large blades.

(40) Of course, this construction system could be also used for the small blades.

(41) A combination of different embodiments for inner and outer part of blade could also could be a good solution.

(42) The extraordinary results achieved by means of the blade according to the present invention can be fully understood when noise and aerodynamic efficiency are considered.

(43) In the following, as anticipated, the blade according to the present invention (FIG. 6) will be compared with blades according to the prior art (FIGS. 7a and 7b).

(44) As to the noise level, the following has to be considered.

(45) The forward sweep angle that the leading edge is forming at the tip with the air relative velocity direction as indicated by the arrows (see also FIG. 8a), is comparable to that of the low noise fan of FIG. 6 and much larger than that of FIGS. 7a and 7b, taking the maximum advantage derived by the noise attenuation related to the forward swept leading edge blade technique;

(46) The forward sweep angle that the trailing edge is forming at the tip with the air relative velocity direction (FIG. 8b) is smaller than that of any of the low noise fan shown in FIGS. 7a and 7b, taking the maximum advantage derived by the noise attenuation related to the forward swept trailing edge blade technique.

(47) The leading edge extension is wider than that of FIGS. 7a and 7b, in a range from 1.05 to 1.46 times, desirably, though not necessarily, 1.2 times. Therefore larger than the prior art will be the noise benefit.

(48) The trailing edge extension is much larger than prior art by a unique very large amount, in a range from 1.1 to 3 times, desirably, though not necessarily, 1.5 times. Therefore much larger will be the related noise benefit. Additionally the relevant extension of the trailing edge allows to utilize in a much more efficient way the several well-known techniques to reduce the sound emission to be applied on the trailing edge, for example a serrated system.

(49) The average tip clearance on the tip will be greatly smaller because the chord is smaller and the noise originated by the tip vortices will be reduced.

(50) The relatively small size of tip chord is allowing to still apply as a standard the tip winglets which, as it is well known, can further reduce the noise. The tip winglet cannot be applied on large chord blades because at high pitch angle has a negative effect.

(51) With reference to the aerodynamic efficiency, the following has to be considered. The described geometry or design is realized stacking in blade span direction wing profile having very high aerodynamic efficiency.

(52) The blade span is increased maintaining the same chord width, allowing to increase the ratio length/width and consequently, as well known from whom is skilled in the aerodynamics, the blade efficiency.

(53) The blade can be not only twisted but also tapered from root to tip the get the best efficiency as a common fan of noise level 1. At the contrary the fan blades according to the prior art are tapered from tip to root decreasing the blade efficiency.

(54) Furthermore, the blade airfoil sections are disposed in the optimal direction with respect to the incident air stream, optimizing the air circulation around the section itself, particularly on the outer part of the bade where the most part of the flow passes through.

(55) The winglet at the tip will also improve the efficiency, allowing less backflow to pass. With reference to the manufacturing costs, the following should be considered.

(56) The reduced chord width distribution all along the radial span makes the fan blade lighter than the known solutions, consequently the bending and axial loads at the radial sections are reduced, particularly at the root.

(57) The reduced chord width, particularly at the outer part of the blade, contributes to reduce the inertial torsional moment at the root section.

(58) The higher efficiency of the blade means lower drag force at the same lift, with a consequent reduction of shear loads at the radial sections, particularly at the root.

(59) The load reduction all along the blade radial span and particularly at the root section allows to design reduced sections to resist to them with a significant reduction in material cost.

(60) In the following, with reference to FIG. 12, a further embodiment of a blade according to the present invention will be described.

(61) In FIG. 12, the blade according to the embodiment of the present invention as depicted therein is still identified by the reference numeral 1. The blade 1 still comprises a root portion 1r provided for the purpose of fixing the blade 1 to an axial rotor (not depicted in FIG. 12); again, the blade may be fixed to the axial fan at different orientation angles (pitch angles) with respect to the axis X-X as identified by the dashed line in FIG. 12. The rotor is supposed to be rotated, during operation of the fan, in the clockwise direction as depicted by the arrow, the axis of rotation of the fan corresponding to the axis of rotation of the rotor. With respect to FIG. 12, the axis of rotation is perpendicular to plane of the figure; the smallest pitch angle is the angle at which the projection of the blade on a plane perpendicular to the axis of rotation occupies the largest area or surface. Pitch angles of larger amounts result in the projections of the blade on the plane perpendicular to the axis of rotation (also referred to, in the following, as the “plane of rotation) occupying corresponding smaller areas or surfaces. As depicted, with the blade 1 oriented at the smallest pitch angle, in particular at zero pitch angle, the projection of the blade on the rotation plane, is such that a V shape is formed along the span of the blade (see FIG. 12). In particular, the blade 1 comprises a first, inner, portion 1a close to the rotational axis (to the root portion 1r) and extending from the root portion 1r, along with a second, outer, portion 1b, and extending from the first portion 1a. With respect to the axis X-X, the first portion 1a extends along a first direction substantially parallel to the axis X-X, whilst, still with respect to the axis X-X, the second portion 1b extends along a second direction other than the first direction (forming an angle with the axis X-X).

(62) Moreover, with respect to the direction of rotation of the blade 1 (identified by the arrow in FIG. 12), in the blade 1 two edges can still be identified, namely the leading edge 1l impinging against the air during rotation of the blade 1), and the trailing edge 1t (opposite to the leading edge 1I).

(63) Still as depicted, the first portion 1a and the second portion 1b are oriented one with respect to the other so that an obtuse angle V (more than 90° and less than 180°) is still defined by the leading edge 1I, whilst a bigger angle (more than 180°) is defined by the trailing edge 1t.

(64) Aa apparent, the main difference between the embodiment of FIG. 5 and the embodiment of FIG. 12 relates to the fact that, in the embodiment of FIG. 12, with reference to the axis X-X which, as depicted, crosses both the blade portion 1a and the blade portion 1b, the vertex Vv of the angle V defined by the leading edge 1l and the opposite tips (points B and C) of the leading edge 1l are located on the same side with respect to the axis X-X.

(65) Moreover, a further difference with respect to the embodiment of FIG. 5 may relate to the length of the bade portions 1a and 1b which, in the embodiment of FIG. 12, have different lengths.

(66) However, even in the embodiment of FIG. 12 the blade portions 1a and 1b may have substantially the same length. In the same way, as anticipated, the blade portions in the embodiment of FIG. 5 may have different lengths.

(67) It has therefore been demonstrated, by means of the above description of the embodiments of the present invention depicted in the drawings that the present invention allows to overcome the drawbacks affecting the solutions according to the prior art.

(68) Although the present invention has been clarified by means of the above description of the embodiment thereof as depicted in the drawings, the present invention is not limited to the embodiments as disclosed above and depicted in the drawings.

(69) As an example, within the meaning of the present invention, the blade can be manufactured according to different methods among those known in the art, for instance extruding and/or pressing and/or forging one or both of the two blade portions and joining them by welding, screwing, gluing or the like.

(70) Moreover, one or both of the blade portions may be hollow or not.

(71) Finally, it is pointed out that even if the blade according to the present invention (to each embodiment thereof) has been disclosed as being particularly adapted to the used in combination with large diameter axial fans, the possible applications of the blade according to the present invention are not limited to large diameter axial fans but comprise fans of any size and/or diameter.

(72) Moreover, the blade according to the present invention may be used in combination with fans provided for purposes other than cooling such as in fans of helicopters and/or airplanes or the like.

(73) The scope of the present invention is rather defined by the appended claims.