MXPA00009334A - Axial flow fan - Google Patents

Abstract

The axial flow fan (1;30) comprises a central hub (3;33), a plurality of blades (4;34) which have a root (5;35), and an end (6,36). According to one embodiment, the blades (4;34) are spaced at unequal angles (&thgr;¿i...., n?) which can vary in percentage (&thgr;%) from 0.5%to 10%, compared to the configuration with equal spacing angles (&thgr;=) for fans with an equal number of blades. Preferably, the blades (4;34) are delimited by a convex edge (7;37), whose projection onto the rotation planeof the fan is defined by a parabolic segment and a concave edge (8;38) whose projection onto the rotation plane of the fan is defined by a circular arc.

Description

AXIAL FLOW FAN TECHNICAL FIELD The present invention relates to an axial flow fan for moving air through a heat exchanger and is preferably for use in the cooling and heating systems of automotive vehicles. Fans of this type must meet certain requirements, among which: low noise level, high efficiency, compact dimensions and ability to obtain good pressure and supply load values.

PREVIOUS TECHNIQUE EP-0 553 598 B, in the name of the same applicant as the present one, discloses a fan with blades having equal spacing angles. The blades have constant rope length over their entire length and are limited in their edges of attack and output by two curves which, when projected on the plane of rotation of the fan path, are two circular arcs. Although fans made according to this patent achieve good results in terms of efficiency and low sound pressure, the sound distribution of the noise can be irritating to the human ear.

In fact, with the blades spaced at equal angles, there are cases of resonance with a main harmonic whose frequency is the product of the number of revolutions per second of the fan wheel multiplied by the number of blades. This resonance results in a whistling noise that can be irritating to the human ear. Even if the perception of irritation caused by a sound is mainly subjective, there are basically two reasons that influence the nuisance of noise: the degree of sound pressure, that is, the intensity of noise and how it is distributed in terms of tone. As a result, low-intensity noise can also be irritating, if the tone distribution of noise distinguishes it from background noises. To solve this problem, fans have been made with blades spaced at unequal angles. Calculating an average of the intensity values of the sound at various frequencies, with the blades spaced at unequal angles, the noise produced is almost equal to that with the blades spaced at equal angles. However, the different tone distribution of the noise allows an improvement in acoustic comfort. However, fans with blades spaced at unequal angles have several disadvantages. The first disadvantage is the fact that in many cases the efficiency of fans with blades spaced at unequal angles is less than that of fans with blades spaced at equal angles.

Another disadvantage is the fact that the fan wheel with blades spaced at unequal angles may be unbalanced.

BRIEF DESCRIPTION OF THE INVENTION The object of the present invention is to provide an improved axial fan with very low noise level. Another objective of the present invention is to provide an improved axial fan with good values of efficiency, load and supply. Still another object of the present invention is to provide an improved axial fan whose fan wheel is substantially naturally balanced. In accordance with one aspect of the present invention, an axial fan is set forth as specified in the independent claim. The dependent claims refer to the preferred and advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES The invention will now be described with reference to the accompanying drawings, which illustrate the preferred embodiments thereof, without restricting the scope of the inventive concept and in which: Figure 1 shows a front view of an embodiment disclosed in this invention; Figure 2 illustrates a front view of the geometric characteristics of a blade in some of the embodiments of the fan disclosed by the present invention; Figure 3 shows sections of a fan blade in some of the embodiments of this invention considered at regular intervals starting from the hub at the end of the blade; Figure 4 illustrates in perspective view other geometrical characteristics of a blade of some of the embodiments of the fan disclosed by this invention; Figure 5 shows an enlarged scale detail of a part of the wheel of the related conduit in some of the embodiments of this invention; Figure 6 is a front view of another embodiment of the present invention; Figure 7 shows a diagram representing, in Cartesian coordinates, the convex edge of a fan blade in any of the embodiments of the present invention; Figure 8 is a diagram showing the changes of the blade angle in different sections of a blade as a function of the fan radius in some of the embodiments of this invention; Figure 9 is a front view of another embodiment of this invention; Figure 10 shows a schematic front view defining the spacing angles of the blades in some embodiments of this invention.

DETAILED DESCRIPTION OF THE INVENTION The terms used to describe the fan are defined as follows: The rope (L) is the length of a segment in a straight line subtended by the arc extending from the leading edge to the trailing edge on an aerodynamic profile of the cross section obtained by intersecting the blade with a cylinder whose axis coincides with the axis of rotation of the fan and whose radius r coincides with a point Q; The center line or the middle string line (MC) of the blade is the line joining the midpoints of the strings L to the different rays; The angle of arrow (d) measured at a given point Q of a characteristic curve of the blade, for example, represented by the curve the trailing edge of the fan blade, is the angle formed by a ray that comes from the center of the fan to the point Q involved and the tangent of the curve at the same point Q; The oblique angle or the net angular displacement (a) of a characteristic curve of the blade is the angle between the ray passing through the characteristic curve, for example, the curve representing the center line or the middle rope line of the blade , to the fan hub, and the ray that passes through the characteristic curve at the end of the blade; The angle of the spacing of the blade (?) Is the angle measured at the center of rotation between the rays passing through the corresponding points of each blade, for example, an edge at the end of the blades; The blade angle (ß) is the angle between the plane of rotation of the fan and the straight line joining the leading edge to the trailing edge of the aerofoil section of the blade section; The pitch ratio (P / D) is the ratio of the pitch of the helix, that is, the quantity by which the point Q is moved axially, that is, P = 2 - p - r - tan (ß), in where r is the length of the ray to point Q and ß is the angle of the blade at point Q and the maximum diameter of the fan; The flexure height of the profile (f) is the longest segment in a straight line perpendicular to the string L, measured from the string L to the line of flexure height of the blade; the position of the flexure height of the profile f can be expressed in relation to the rope L as a percentage of the length of the rope itself; The inclination (V) is the axial displacement of the blade from the plane of rotation to the fan, including not only the displacement of the entire profile of the plane of rotation, but also the axial component due to the flexure height of the blade, if any - also in axial direction.

With reference to the accompanying drawings, the fan 1 rotates about an axis 2 and comprises a central hub 3 which mounts a plurality of curved blades 4 in the plane of rotation XY of the fan 1. The blades 4 have a root 5, a end 6 and are delimited by a convex edge 7 and a concave edge 8. Since satisfactory results have been obtained in terms of efficiency, noise level and load, rotating the fan made in accordance with the present invention either in one direction is in the other, each of the convex edge 7 and the concave edge 8 may be either the leading edge or the trailing edge of the blade. In other words, the fan 1 can rotate in such a way that the air to be moved is first with the convex edge 7 and then with the concave edge 8 or, vice versa, firstly with the concave edge 8 and then with the edge convex 7. Obviously, the aerodynamic profile of the blade section must be oriented according to the operation mode of the fan 1, that is, according to whether the air to be moved meets the convex edge 7 or the concave edge 8 first. At the end 6 of the blades 4, a reinforcing ring 9 can be provided. The ring 9 reinforces the set of blades 4 avoiding, for example, that the angle β of the blade 4 varies in the area at the end of the blade due to the aerodynamic loads. further, the ring 9, in combination with the conduit 10, limits the swirling of the air around the fan and reduces the vortices at the end 6 of the blades 4, creating these vortices, as is known, with different pressure on the two sides of the blade 4. For this purpose, the ring 9 has a thick lip portion 11, which fits into the correspondence seat 12 made in the conduit 10. The distance (a), very small in the axial direction, between the lip 11 and the Seat 12 together with the labyrinth conformation of the part between the two elements, reduces the swirl of air at the end of the fan blades. In addition, the special adjustment between the outer ring 9 and the conduit 10 allows the two parts to come into contact with each other, while at the same time reducing the axial movements of the fan. In general, the ring 9 has the shape of a nozzle, that is, its inlet section is larger than the section through which the air passes at the end of the blades 4. The larger suction surface maintains the flow of air. air at constant speed compensating the resistance to flow. However, as shown in Figure 6, the fan according to the present invention need not be equipped with the outer reinforcing ring and the related conduit. The blade 4, projected on the plane of rotation XY of the fan 1, has the geometric characteristics described below. The angle of the center (B), assuming as the center the geometric center of the fan that coincides with the axis of rotation 2 of the fan, corresponding to the width of the blade 4 in the root 5, is calculated using a relation that takes into account the gap that should exist between the two adjacent blades 4. Indeed, since fans of this kind are preferably made of plastic using injection molding, the blades on the die should not overlap, otherwise the die used to make the fan It has to be very complex and as a result production costs inevitably rise. In addition, it must be remembered that, especially in the case of automotive applications, the fans do not work continuously because much of the time that the motor is running, the heat exchangers to which the fans are connected are cooled by the flow of air. air created by the movement of the vehicle itself. Therefore, the air must be allowed to flow through easily, even when the fan is not spinning. This is achieved by leaving a relatively wide gap between the fan blades. In other words, the fan blades should not form a screen that prevents the cooling effect of the air flow created by the movement of the vehicle. The ratio used to calculate the angle (B) in degrees is: B = (360 ° C / No. of blades) - K; Km = 3 (diameter of the cube, height of the profile of the blade in the cube). The angle (K) is a factor that takes into account the minimum distance that must exist between the two adjacent blades to avoid overlapping during molding and is a function of the diameter of the cube: the larger the diameter of the cube, the smaller the be (K) The value of the angle (K) can also be influenced by the height of the profile of the blade in the hub.

The following description, given by way of example only and without restricting the scope of the inventive concept, refers to a mode of a fan made in accordance with the present invention. As shown in the accompanying drawings, the fan has seven blades, a hub with a diameter of 140 mm and an outside diameter, corresponding to the diameter of the outer ring 9, of 385 mm. The angle (B), corresponding to the width of a blade in the cube, which is calculated using these values, is 44 °. The geometrical configuration of the fan 1 will now be described: the blade 4 is first defined as a projection on the plane of rotation XY of the fan 1 and the projection of the blade 4 on the XY plane is then transferred to the space. With reference to the detail shown in Figure 2, the geometric construction of the blade 4 consists of drawing the bisector 13 of the angle (B) which is delimited both by the ray 17 on the left and beam 16 on the right. A ray 14 is then drawn rotated in the counterclockwise direction by an angle A = 3/11 B in relation to the bisector 13, and a ray 15, also rotated in the opposite direction of the clock hands by an angle (A), but in relation to the ray 16. The rays 14, 15 are thus rotated simultaneously by an angle A = 3/11 B, that is, A = 12 °. The intersections of rays 17 and 16 with cube 3 and intersections of rays 14 and 15 with outer ring 9 of the fan (or with a circle equal in diameter to outer ring 9) determine four points (M, N, S , T) which are in the XY plane, which defines the projection of the blade 4 of the fan 1. The projection after the convex edge 7 is also defined in the cube, by a first card 21 inclined at an angle C = 3/4 A, that is, C = 9 °, in relation to ray 17 passing through point (M) in cube 3. As can be seen in figure 2, the angle (C) is measured in the direction of the hands of the clock in relation to the ray 17 and therefore the first tangent 21 is forward of the beam 17 when the convex edge 7 is the first to meet the air flow, or behind the beam 17 when the convex edge 7 is the last one that meets the air flow, that is, when the edge 8 is the first one that meets the air flow. In the outer ring 9, the convex edge 7 is also defined by a second tangent 22 which is inclined at an angle (W) equal to 6 times the angle (A), ie 72 °, in relation to the ray 14 which passes through the point (N) in the outer ring 9. As shown in Figure 2, the angle (W) is measured in the counterclockwise direction in relation to ray 14 and therefore the second tangent 22 is forward when the convex edge 7 is the first one to meet the air flow or behind the beam 14 when the convex edge 7 is the last to meet the air flow, ie, with the edge 8 is the First to meet the air flow. In practice, the projection of the convex edge 7 is tangent to the first tangent 21 and the second tangent 22 and is characterized by a curve with a single convex portion, with no inflection points. The curve that defines the projection convex edge 7 is a parabola of the type: y = a x2 + b x + c. In the illustrated mode, the parabola is defined by the following equation: y = 0.013 x2 - 2J x + 95J .. This equation determines the curve illustrated in the Cartesian diagram, shown in Figure 7, as a function of the related x and y variables of the XY plane. Looking at figure 2 again, the end points of the parabola are defined by the tangents 21 and 22 at the incised points (M) and (N) and the maximum convexity zone is closest to cube 3. Experiments have shown that the convex edge 7, with its parabolic projection, on the plane of rotation XY of the fan, provides efficiency and excellent noise characteristics. As regards the projection of the concave edge 8 of the blade 4 on the XY plane, any second degree curve arranged in such a way as to define a concavity can be used. For example, the projection of the concave edge 8 can be defined by a parabola similar to that of the convex edge 7 and disposed in substantially the same way. In a preferred embodiment, the curve defining the projection of the concave edge 8 on the XY plane is a circular arc whose radius (Rcu) is equal to the radius (R) of the cube and, in the practical application described herein, the value of this radio is 70 mm.

As shown in Figure 2, the projection of the concave edge 8 is delimited by points (S) and (T) and is a circular arc whose radius is equal to the radius of the cube. The projection of the concave edge 8 is thus completely defined in geometric terms. Figure 3 shows eleven profiles 18 representing eleven sections of blade 4 made at regular intervals from left to right, from cube 3 to outer edge 6 of blade 4. Profiles 18 have some characteristics in common, but all are geometrically different in order of being able to adapt to the aerodynamic conditions which are substantially a function of the position of the profiles and the radial direction. The characteristics common to all blade profiles are particularly suitable for achieving high efficiency and load and low noise. The first profiles on the left are more arched and have a greater angle of cross (ß) because, being closer to the cube, its linear speed is lower than that of the outer profiles. The profiles 18 have a face 18a comprising an initial segment in a straight line. This straight line segment is designed to allow airflow to flow smoothly, preventing the blade from "whipping" the air that would interrupt the smooth air flow and thus increase noise and reduce efficiency. In Figure 3, this segment in a straight line is marked as (t) and its length is 14% to 17% of the length of the rope (L). The rest of the face 18a is substantially constructed of circular arcs. Passing from the profiles near the hub towards those at the end of the blade, the circular arcs constituting the face 18a become increasingly larger in radius, that is, the flexure height of the profile (f) of the blade 4 decreases. with respect to the rope (L), the profile flexure height (f) is located at a point, marked with (1f) in figure 3, between 35% and 47% of the total length of the rope (L ). This length should be measured from the edge of the profile that meets the air first. The back part 18b of the blade is defined by a curve, in such a way that the maximum thickness (Gmax) of the profile is located in an area between 15% and 25% of the total length of the blade rope and preferably at 20 % of the length of the rope (L). In this case too, this length should be measured from the edge of the profile that meets the air first. Moving from the profiles closest to the cube where the maximum thickness (Gmax) has its highest value, the thickness of profile 18 decreases in constant proportion towards the profiles at the end of the blade where it is reduced by approximately a quarter of its value . The maximum thickness (Gmax) decreases according to the substantially linear variation as a function of the radius of the fan. The profiles 18 of the sections of the blade 4 in the outermost portion of the fan 1 have the minimum thickness value (Gmax) because their aerodynamic characteristics must make them suitable for high speeds. In this way, the profile for the linear speed of the blade section is optimized, obviously increasing this speed with the increase in the fan radius.

The rope length (L) of the profiles (18) also varies as a function of the radius. The rope length (L) reaches its maximum value in the middle part of the blade 4 and decreases towards the end 6 of said blade to reduce the aerodynamic load in the outermost portion of the fan blade and also to facilitate the passage of air when the fan is not operating, as indicated above. The blade angle (ß) also varies as a function of the fan radius. Mainly, the angle of the blade (ß) decreases according to an almost linear law. The law of variation of the angle of the blade (ß) can be chosen according to the aerodynamic load required in the outermost portion of the blade of the fan. In a preferred embodiment, the variation of the blade angle (ß) as a function of the fan radius (r) follows a cubic law defined by the equation (ß) = - 7 • 10"6 • + r3 + 0.0037 • r3 - 0J602 r + 67.64 The variation law of (ß) as a function of the radius of the fan (r) is shown in the diagram shown in figure 8. Figure 4 shows how the projection of the blade 4 is transferred in the XY plane in space The blade 4 has an inclination V relative to the plane of rotation of fan 1.

Figure 4 shows the segments joining the points (M \ N ') and (S, T, #) of a blade (4). These points (M \ N ', S' T ') are obtained when starting from the points (M, N, S, T) that are located in the XY plane and delineate perpendicular segments (M, M '), (N, N'), (S, S *), (T, T ') that determine by thus an inclination (V) or, in other words, a displacement of the blade 4 in the axial direction. Further, in the preferred embodiment, each blade 4 has a shape defined by the arcs 19 and 20 in FIG. 4. These arcs 19 and 20 are circular arcs whose curvature is calculated as a function of the length of the straight line segments ( M \ N ') and (S \ T'). As shown in Figure 4, arcs 19 and 20 are offset from the corresponding straight line segments (M \ N ') and (S \ T ') by the lengths (h1) and (h2) respectively. These lengths (h1) and (h2) are measured on the perpendicular to the plane of rotation XY of the fan 1 and are calculated as a percentage of the length of the segments (M \ N ') and (S \ T') of themselves . The dashed lines in Figure 4 are the curves-parabolic segment and circular arc with respect to the convex edge and the concave edge 8. The inclination V of the vane 4, both with respect to its component of axial displacement and with respect to its curvature, it makes it possible to correct the deflections of the blade due to the aerodynamic load and to balance the aerodynamic moments in the blade in such a way that a uniform axial air flow is obtained distributed over the entire front surface of the fan.

All the characteristic values of the fan blade, according to the modality described, are summarized in the following table, where r is the radius of the generic fan and the following geometric variables that refer to the value of the corresponding radius: L indicates the rope length; f indicates the flexure height of the profile t indicates the initial segment in a straight line of the cross section; If indicates the position of the flexure height of the profile with respect to the rope L; ß indicates the profile angle of the cross section in sixtieth degrees; x and y indicate the Cartesian coordinates in the XY plane of the parabolic edge of the vane.

Experiments comparing conventional fans with those built according to the modalities using separate blades at an equal angle? Show that there is a decrease in sound power of approximately 25% to 30%, measured in dB (A) with an improvement in acoustic comfort. 8 In addition, under the same air supply conditions, fans built according to the modalities with blades separated at an equal angle?, Have developed gradient values up to 50% higher than those compared with conventional fans of this type. In fans constructed according to the modalities, with blades separated at an equal angle?, Which pass from a later configuration of the blades to a previous configuration thereof, there are no considerable changes in the sound level. Moreover, under certain operating conditions of the fan, particularly in the high elevation scale, the previous configuration of the blades provides 20-25% more than the later configuration of the blades. Figures 9 and 10 show another embodiment of a fan 30 comprising a wheel 31 with blades 34 spaced at unequal angles?. The modality with the blades of unequal angles? It also improves the acoustic comfort. The different fan sound distribution according to this mode, makes it even more pleasing to the human ear. With reference to figures 9 and 10, the wheel 31 has seven vanes 34 placed at the following angles, expressed in sixtieth degrees: 01 = 55.381; 92 = 47.129; T3 = 50,727; 94 = 55,225; 95 = 50,527; 96 = 48,729; 97 = 52.282 If the wheel 31 has the blades 34 spaced at equal angles or as the ventilators modeled in Figures 1 and 6, the separation angle would be? == 36077 = 51.429 °.

The table below shows the values of the unequal angles? ,,., N, 9 = and the absolute and percentdeviations of the values of the unequal angles? ,, ... n compared to the corresponding value of the angle equal? = for fans with seven blades: Precisely, the second column shows the values of the angles 9 n according to the present modality; the third column shows the values of the angles 9 = when all the angles are equal; the fourth column shows the algebraic difference or algebraic deviation between the values of the angles of the second and third column; the fifth column shows the value of the deviation of the fourth column expressed as a percentof the angles in the third column? =. The table shows that the percentand algebraic deviation in the angles are relatively smaller compared to the configuration of separate blades at equal angles. According to the present embodiment, the values of percentdeviation of the blade separation angles should be between 0.5% and 10%. Therefore, even if an improvement in the sound characteristics is achieved, the efficiency of the wheel with the blades spaced at equal angles is substantially the same. As can be seen in greater detail below, if the percentdeviation values are maintained within these limits, wheels that are substantially balanced with any number of blades n greater than three, and therefore different from the wheel, can be constructed. 31 that has seven blades as shown in the example. Even the modalities performed with a number of blades 34 different from seven and with those limitations in relation to angular separation achieve good results in terms of efficiency and sound level. The sound produced by the fans built with the angles 9 ... .... that were mentioned above, has almost the same intensity but is less annoying to the human ear. A good result was obtained referring to the comfort in terms of noise in the configuration with the blades forward and with the configuration with the blades backwards. Preferably, the aforementioned configuration of the blades 34 can be used, in combination with the blades 4 with a parabolic edge 7 of other previously mentioned modes. Also in this case, the unevenness, supply and efficiency values are substantially invariable.

Another advantof this configuration is that the center of gravity is always located on the axis of rotation 32 of the fan 30. In analytical terms, considering a reference system whose origin is on the axis of rotation, apply the following equation:? ¡= X = 0; yg =? m '' y = 0.? m where Xg and Yg are the Cartesian coordinates of the center of gravity of the fan wheel 30 and m¡ x¡ and ¡are the mass and the Cartesian coordinates of the center of gravity of each blade 34, respectively. In the example, shown in figures 9 and 10 of a wheel 31 with blades n of equal mass m, the formula is as follows: With this configuration, it is possible to achieve a blade 31 that is already substantially balanced without the need to intervene in the mass of the blades 34, or any given intervention is reduced to a minimum compared to that which is needed to balance the wheel of the type that It has separate blades at unequal angles. Therefore, there are more advant in terms of its simple and economic construction.

Claims (6)

NOVELTY OF THE INVENTION CLAIMS

1. - An axial flow fan (1; 30) that rotates in a plane (XY) and that comprises a central hub (3; 33), a plurality (n) greater than three of the blades (4; 34), each blade has a root (5; 35) and one end (6; 36) the blades (4; 34) are also delimited by a first edge (7; 37) and a second edge (8; 38), and consist of sections with aerodynamic profiles (18) with a blade angle (ß) that gradually and steadily decreases from the root (5; 35) to the end (6; 36) of the blade (4; 34) the blade angle (ß) is defined as the current angle between the plane of rotation (XY) and a straight line joining the leading edge towards the trailing edge of the aerodynamic profile (18) of each blade section, the blades (4; 34) are separated in angles unequal (9¡ .... n). also characterized because these unequal separation angles (? ¡.... n) can vary in percentage (9%) by values between 1.5% and 8.5% compared with the configuration of equal separation angles (? _) for fans with the same number (n) of blades, that is: 1.5% < 9% 8.5% where?% = "" "'- - = 100, such that the fan (30) is substantially naturally balanced, in which the projection of the convex edge (7) on the plane (XY) is defined by a parabolic segment and in which the projection of the concave edge (8) on the plane (XY) is defined by a geometric curve Second grade.

2. The fan according to claim 1, further characterized in that it comprises seven blades (34) and in which the unequal separation angles (9 ... n) of the blades (34) have the following values, expressed in degrees: 91 = 55,381, 92 = 47,129; 93 = 50,727; 94 = 55,225.95 = 50,527; 96 = 48,729; 97 = 52.282.

3. The fan according to any of the preceding claims, further characterized in that the projection of the concave edge (8) on the plane (XY) is defined by a parabolic segment.

4. The fan according to claim 1, further characterized in that the projection of the concave edge (8) on the plane (XY) is defined by a circular arc.

5. The fan according to any of the preceding claims, further characterized in that the aerodynamic profiles (18) have a face (18a) comprising at least one straight line segment (t).

6. The fan according to claim 5, further characterized in that the aerodynamic profiles (18) have a face (18a) comprising a segment, after the initial segment (t), which is substantially made by circular arcs. 1. The fan according to claim 5 or 6, further characterized in that the aerodynamic profiles (18) have a cord length (L) and a backrest (18b) defined by a convex curve which, in combination with the face (18a) determines a maximum thickness value (Gmax) of the profile in an area between 15% and 25% of the total length of the rope (L) that is measured from the edge that first makes contact with the air. 8. The fan according to any of the preceding claims, further characterized in that each blade (4) projected on the plane (XY) is delimited by four points (M, N, S, T), distributed in the plane (XY) ) and defined as a function of an angle (ß) in relation to the width of a single blade (4) subtended at the center of the fan; and further characterized because the four points (M, N, S, T), are determined by the following characteristics: The points (M) and (S) are located in the cube (3) or the root (5) of the blade (4) and are defined by the rays (16, 17) that emanate from the center of the fan and form the angle (ß); the point (N) is located at the end 6 of the blade (4) and is displaced counterclockwise by an angle (A) = 3/11 (ß) relative to the bisector (13) of the angle (ß) ); the point (T) is located at the end (6) of the blade (4) and is displaced counterclockwise by an angle (A) = 3/11 (ß) with respect to the ray emanating from the center of the fan and what happens through point (S). 9. The fan according to claim 8, further characterized in that the projection of the convex edge (7) on the plane (XY) at point (M) has a first tangent (21) inclined by an angle C equal to three quarters of A with respect to a passing ray 17 through the point (M); and further characterized in that the projection of the convex edge 7 on the XY plane at the point N has a second tangent inclined by an angle W equal to six times A with respect to the ray 14 passing through the point N; the first and second tangents (21, 22) are forward of the corresponding rays 17, 14 when the direction of rotation of the fan 1 is such that the convex edge (7) is the first to contact the air flow and the first and second tangents (21, 22) are positioned in such a way as to define a curve in the XY plane having a simple convex portion without inflection points. 10. The fan according to any of the preceding claims from 4 to 9, further characterized in that the circular arc formed by the projection of the concave edge (8) on the plane (XY) has a radius (Rcu) equal to radius R of the cube (3). 11. The fan according to any of the preceding claims, further characterized in that the blades (4) are formed of sections whose aerodynamic profiles (18) have a blade angle (ß) that decreases gradually and steadily from the root (5). ) towards the end (6) of the blade (4) in accordance with the cubic law of variation as a function of the radius.