EP2657531A1 - Axial fan with centripetal flow straightener having a reduced diameter hub - Google Patents

Abstract

The device has fixed vanes (7) placed opposite to mobile blades of an axial fan in a ventilation nozzle, where the mobile blades drive cooling fluid e.g. mass of air, toward an element to be cooled across a ventilation nozzle. The fixed vanes have a curved form to transform a component tangential speed of cooling fluid driven by an axial fan into radial speed of the fluid directed toward the center of the device and into an axial speed of the fluid directed toward a rotation axis of the fan. The mobile blades are fixed on a central hub (11) at proximal ends. An independent claim is also included for a generator.

Description

1. Field of the invention

The field of the invention is that of cooling systems based on fans. More specifically, the invention relates to a cooling device comprising one or more axial fans, for driving a cooling fluid (for example a mass of air) to an element whose temperature is sought to lower.

The invention finds particular, but not exclusively, applications in the field of cooling of thermal engines, for example when they are integrated in a generator.

2. Prior art and its disadvantages

Axial fans, or helical fans, are commonly used for cooling industrial plants. Their operating principle is based on the rotation of a propeller, comprising a plurality of movable blades, which makes it possible to axially drive a cooling fluid, along the axis of rotation of the propeller, towards an equipment that the it is desired to cool. Such fans operate with any type of compressible fluid, but most often with ambient air. They allow to blow fresh air to the equipment to cool.

The air flow of such an axial fan is in a ventilation nozzle, allowing the flow of fresh air to the equipment to be cooled.

Two main problems arise, however, when using such axial fans.

When the fan is in operation, its movable blades rotate and tend to act on the mass of fluid in which they rotate to drive it in turn in rotation. This rotation of the surrounding fluid decreases the relative speed of the blades relative to the fluid, which results in a decrease in the efficiency of the fan.

The patent document FR 2 784 423 proposes a solution to this first problem, in the form of an air duct for an electric fan comprising movable blades and interconnecting elements extending between an outer annular element and an inner annular element coaxial with the movable blades. Such interconnection elements deflect the flow of air towards the axial direction. Thus, the air flow is placed in the expected direction to cross the radiator, so that the penetration of air into the radiator beam is promoted.

Such an effect is also known from the use of fixed or counter-rotating blades in turbines, turbo-propellers or reactors.

A second problem encountered when using axial fans is that the centrifugal effect related to the rotation of the fan blades has the effect of increasing the flow rate, and therefore the pressure on the periphery of the fan; conversely, a zone of low pressure is generated in the center of the discharge zone.

More precisely, during the rotation of the mobile blades, an inactive cone is formed, downstream of the fan with respect to the direction of movement of the fluid, constituting a "dead" zone in which the pressure and the ventilation rate are weak or even null.

Such an inactive cone is illustrated in figure 1 , which is derived from a calculation of CFD (for "Computer Fluid Dynamic"), and illustrates the distribution of fluid velocities in the fan environment.

In the example of the figure 1 , the fan 1, when its blades rotate, sucks air, which is transmitted via a ventilation nozzle 2, to a device that is to be cooled, in this case a cooling radiator 3.

As illustrated in this figure, an inactive cone 4, whose base is located at the base of the fan blades 1, is formed downstream of the fan 1 with respect to the direction of displacement of the air flow. top may be more or less distant from the fan, depending on the characteristics and dimensions of the last. In this inactive cone 4, the speed of movement of the air is almost zero. In some cases, the air flow rate in the inactive cone 4 may even be negative, if the pressure downstream of the cooling radiator 3 is greater than that of this dead zone: a recycling phenomenon then occurs, so that hot air downstream of the radiator passes back into the dead zone of the cone 4, which causes a loss of efficiency of the system consisting of the fan 1 and the radiator 3.

As we see on the figure 2 The radiator 3 thus receives fresh air blown by the fan 1 over its entire surface with the exception of the central zone 6 in the inactive cone 4.

The entire surface of the cooling radiator 3 is therefore not optimally used for heat exchange, which leads to a loss in useful dimensions, and therefore a decrease in the efficiency of the assembly consisting of the fan 1 and the radiator 3.

To solve this problem, one solution is to move the radiator 3 (or more generally the equipment that one seeks to cool), the fan 1. Indeed, by placing the radiator sufficiently far from the fan, it manages to extract the radiator of the influence of the inactive cone 4.

However, such a solution undermines the compactness of the system and, in some contexts, leads to an unacceptable increase in the overall dimensions. This is particularly the case of generators, in which the heat engine is cooled by means of one or more cooling radiators associated with one or more axial fans, and which must meet severe constraints of space.

It should also be noted that the air duct presented in the FR 2 784 423 above does not solve this problem of appearance of a dead zone.

There is therefore a need for an axial fan cooling technique to overcome these various disadvantages of the prior art. More specifically, there is a need for such a technique to improve the efficiency of the ventilation fan of an axial fan.

There is also a need for such a technique that can reduce the harmful influence of the inactive cone located downstream of an axial fan, without increasing the overall size of the cooling system.

There is also a need for such a technique which is reliable and inexpensive to implement.

There is also a need for such a technique that does not increase or reduce the sound level of the cooling system.

3. Presentation of the invention

The invention responds, in all or part of its aspects, to at least one of these needs by proposing a cooling device for a generator set comprising at least one axial fan comprising at least two rotating blades capable of driving a cooling fluid, through a ventilation nozzle, to an element to be cooled. Such a cooling device comprises at least two fixed fins arranged opposite said movable blades in said ventilation nozzle.

• d'une part, en une vitesse radiale dudit fluide dirigée vers le centre dudit dispositif de refroidissement ;
• d'autre part, en une vitesse axiale dudit fluide dirigée vers un axe de rotation dudit ventilateur.

According to the invention, such fixed fins have a curved shape capable of transforming a tangential velocity component of said cooling fluid driven by said axial fan:

• on the one hand, in a radial velocity of said fluid directed towards the center of said cooling device;
• on the other hand, at an axial speed of said fluid directed towards an axis of rotation of said fan.

Thus, the invention is based on a completely new and inventive approach to axial fan cooling. Indeed, such fixed fins disposed in the ventilation nozzle of the fan produce two combined effects: firstly, they allow a centripetal rectification of the flow of the cooling fluid, so as to remove the inactive cone and provide a flow rate of fluid through the dead zone behind the fan hub, and secondly, they make it possible to counter the rotation of the fan. coolant caused by the drive effect of the fan blades. Their presence in the ventilation nozzle, that is to say downstream of the fan relative to the direction of movement of the cooling fluid, thus increases the efficiency of the fan.

It will be noted that, by fixed fins, is meant here, and throughout the rest of this document, blades fixed in rotation, as opposed to the blades of the fan. However, it could be envisaged that such fixed vanes could be adjustable or steerable, for example to modify an angle of inclination of all or part of the vanes with respect to the direction of displacement of the fluid.

Such fins can take various forms suitable for straightening the flow of air, or more generally fluid, from the fan, from the simplest to the most complex. However, the curved shape of the fixed vanes is defined such that at any relative position of the movable vanes of the ventilator, one or more fixed vanes has a relative angle capable of transforming the tangential velocity of the fluid propelled into a radial velocity directed towards the center of the on the one hand, and transform the tangential velocity into axial velocity to straighten the flow and to promote the penetration of air into the radiator beam, on the other hand.

According to a first aspect of the invention, the mobile blades being fixed at their proximal end to a central hub, the fixed blades are connected at their proximal end to a connecting device of diameter less than or equal to the diameter of the central hub of the fan.

It is indeed necessary to provide fixing means fixed fins relative to each other and, ideally, to stiffen their assembly, subject to the flow of fluid. A device for connecting these fixed fins is therefore provided. In addition, the fan has a central hub, on which are fixed the movable blades, which is an inactive area with respect to the flow of air or fluid. In order not to aggravate the phenomenon of appearance of this inactive zone, and not to degrade the centripetal rectification effect produced by the fixed vanes, it is therefore advantageous to limit the dimensions of the connecting device so that its outside diameter remains less than or equal to the diameter of the central hub of the fan.

In a first embodiment, such a connecting device comprises a tube on which are fixed the proximal ends of the fixed wings and a reinforcing disk, located near the central hub, the diameter of the tube being substantially less than the diameter of the disc of reinforcement, and the diameter of the reinforcing disc being less than or equal to the diameter of the central hub.

In a second embodiment, such a connecting device has substantially a cone-shaped or cone-shaped curved surface, whose diameter decreases away from the central hub to the element to be cooled.

Such forms are particularly suitable for producing a piece of plastic molding, which is advantageous. In addition, such a cone-shaped cone shape with a curved surface (as illustrated in the appended figures) facilitates the reorientation of the centripetal flow towards the desired axial direction and sought for passing the cooling air through the beam, in the central area of the radiator.

According to another aspect of the invention, the fixed fins are of curved shape and have a curvature in a plane substantially perpendicular to an axis of rotation of the movable blades, called the plane of rotation.

Thus, such fixed vanes generate a centripetal effect on the cooling fluid pulsed by the mobile blades of the fan, which tends to bring cooling fluid to the central area downstream of the fan. In this way, the presence of these fixed fins prevents the creation of the inactive cone described above in connection with the prior art.

According to an advantageous characteristic of the invention, such fixed vanes have a direction of curvature adapted to direct a portion of said fluid driven by said movable blades towards the axis of rotation of said fan. Such fins can be simple in shape, and therefore inexpensive. They make it possible to use the dynamic effect of the flow of air or fluid to guide part of the flow to the central zone downstream of the fan.

According to an advantageous characteristic of the invention, said fixed wings have, at their distal end, a non-zero angle with said axis of rotation. Thus, the angle formed between the string of the fins and the axis of rotation is non-zero.

Such an inclination of the distal ends of the fins makes it possible to optimize the distribution of the air pressure generated by the fan on either side of the fixed vanes, and to avoid the formation of low pressure zones behind the fixed vanes. . It also reduces the noise generated by the passage of the mobile blades of the fan facing fixed fins, which induces the creation of a pressure wave.

Advantageously, the angle formed between the string of the fin at its distal end and the axis of rotation is substantially equal to 45 °. Such an angle makes it possible to optimize the distribution of pressures upstream and downstream of the fixed fins, and thus to avoid a cavitation effect. Other values of this angle may also be adopted, depending in particular on the shape of the fixed vanes and the operating constraints imposed on the cooling device. An optimum value of this angle can be determined for example by CFD calculation or by focusing during performance tests.

Preferably, said fixed wings are twisted. Thus, they turn on their own, over their entire length, so as to increase the phenomenon of fluid flow rectification and improve the distribution of the air pressure and therefore the flow on the surface of the radiator. Note however that these fins are preferably less than a full half turn on themselves. Such twisting may be progressive and increase from the center of the fins towards their distal end.

According to another advantageous aspect of the invention, such a cooling device comprises a number N of fixed blades different from the number P of the mobile blades of the fan, in order to avoid the generation of noise by the superposition of acoustic pressure waves generated at the passage of each movable blade in front of a fixed fin.

Preferably, the number N of fixed vanes and the number P of the mobile blades of the fan are two prime numbers between them, in order to reduce as much as possible the resonance phenomenon likely to generate noise. For example, in the case of a fan with nine moving blades, there are seven fixed fins in the ventilation nozzle.

In an advantageous embodiment of the invention, such a cooling device comprises identical equidistant fixed fins, for example seven in number. The fact that the fins are identical and equidistant makes it possible to obtain a homogeneous rectification of the flow of air or fluid over the entire blower footprint.

According to another aspect of the invention, said fixed wings are connected at their distal end to a substantially annular element of diameter greater than the diameter of said axial fan, said substantially annular element having a flared shape on a portion extending upstream of said fan axial, so as to create a Venturi effect on said cooling fluid.

Such a shape contributes to the improvement of the efficiency of the fan.

According to an advantageous aspect of the invention, said element to be cooled is a cooling radiator of a thermal engine cooling system. Indeed, thermal engine cooling systems are generally equipped with one or more cooling radiators, using ambient air to cool the various fluids circulating in the radiators (cooling water of the engine block, charge air, oil , fuel, etc.). The cooling of the radiators is done by pulsed air by one or more axial fans blowing fresh air through the radiator beam. In these systems, the congestion constraint is generally a strong constraint, so that it is difficult to follow the recommendations of the fan manufacturers, who recommend placing the radiator as far as possible as far as possible from the fan (for example, according to certain specifications, at a distance of at least one and a half times the diameter of the fan), in order to extract it from the zone of influence of the inactive cone. The invention therefore applies particularly advantageously in this context.

The invention also relates to a generator comprising a heat engine and an alternator connected to said heat engine and adapted to convert into electrical energy energy received from said engine.

According to the invention, such a generator set comprises at least one cooling device as described above.

The invention also relates to a generator characterized in combination by all or some of the characteristics mentioned above or below.

4. Presentation of the figures

• la figure 1, déjà commentée en relation avec l'art antérieur, illustre la distribution des vitesses de fluide dans l'environnement d'un ventilateur axial, et plus précisément la formation d'un cône inactif en aval du ventilateur;
• la figure 2, également commentée en relation avec l'art antérieur, illustre la zone centrale d'un radiateur, disposé en aval du ventilateur axial, affectée par le cône inactif de la figure 1 ;
• la figure 3 décrit certains éléments d'un système de refroidissement de moteur thermique d'un groupe électrogène ;
• la figure 4 illustre le dispositif de la figure 3 dans lequel ont été ajoutées des ailettes fixes, conformément à l'invention ;
• la figure 5 détaille l'ensemble constitué de la buse de ventilation et des ailettes fixes de la figure 4 ;
• les figures 6A à 6I illustrent plus en détails la forme et les dimensions des ailettes fixes de la figure 5, dans un exemple particulier de réalisation de l'invention. Plus précisément :
  • ○ les figures 6A et 6B présentent les vues de face et de derrière des ailettes fixes ;
  • ○ la figure 6C illustre la vue de droite des ailettes de la figure 6A ;
  • ○ la figure 6D présente une vue en coupe A-A des ailettes de la figure 6B ;
  • ○ la figure 6E présente une vue en coupe B-B des ailettes de la figure 6B ;
  • ○ la figure 6F présente une vue en coupe D-D des ailettes de la figure 6D ;
  • ○ les figures 6G et 6H offrent deux vues en perspective des ailettes fixes, avec des détails sur le moyeu central des ailettes d'une part, et sur leur zone d'attache distale d'autre part ;
  • ○ la figure 6I offre un détail de la section des ailettes de la figure 6C.
• la figure 7 illustre la nouvelle distribution des vitesses d'air de la figure 1, après introduction d'ailettes fixes dans le dispositif de la figure 3, conformément à l'invention ;
• les figures 8A et 8B illustrent les composantes de vitesse du fluide de refroidissement au niveau des pales mobiles du ventilateur et des ailettes fixes ;
• la figure 9 présente une autre vue du dispositif de l'invention, permettant d'illustrer l'angle α formé par la corde des ailettes fixes et l'axe de rotation des pales mobiles ;
• les figures 10, 11A et 11B présentent différents exemples d'assemblage des ailettes fixes de l'invention ;
• la figure 12 présente un exemple de mode de réalisation, dans lequel les ailettes fixes présentent un angle d'inclinaison nul par rapport à l'axe de rotation des pales mobiles du ventilateur sur toute leur longueur;
• la figure 13 présente un exemple de réalisation des ailettes fixes et d'un élément annulaire auquel elles sont solidarisées ;
• les figures 14, 15 et 16 présentent un exemple de système de refroidissement selon l'invention, dans lequel un ventilateur axial est entouré par une buse de ventilation (figure 14), dans lequel des ailettes fixes sont disposées dans la buse (figure 15), et dans lequel un élément annulaire formé autour du ventilateur dans la buse présente en entrée une forme de venturi (figure 16).

Other features and advantages of the invention will appear more clearly on reading the following description, given as a simple illustrative and nonlimiting example, in relation to the drawings, among which:

• the figure 1 , already commented upon in connection with the prior art, illustrates the distribution of fluid velocities in the environment of an axial fan, and more specifically the formation of an inactive cone downstream of the fan;
• the figure 2 , also commented on in relation to the prior art, illustrates the central zone of a radiator, disposed downstream of the axial fan, affected by the inactive cone of the figure 1 ;
• the figure 3 describes certain elements of a thermal engine cooling system of a generator set;
• the figure 4 illustrates the device of the figure 3 in which fixed vanes have been added according to the invention;
• the figure 5 details the assembly consisting of the ventilation nozzle and the fixed vanes of the figure 4 ;
• the Figures 6A to 6I illustrate in more detail the form and dimensions of the fixed fins of the figure 5 in a particular embodiment of the invention. More precisely :
  • ○ the Figures 6A and 6B present front and rear views of fixed wings;
  • ○ the Figure 6C illustrates the right view of the fins of the Figure 6A ;
  • ○ the Figure 6D has a sectional view AA of the fins of the Figure 6B ;
  • ○ the figure 6E has a sectional view BB of the fins of the Figure 6B ;
  • ○ the figure 6F has a sectional view DD of the fins of the Figure 6D ;
  • ○ the Figures 6G and 6H provide two perspective views of the fixed wings, with details on the central hub of the fins on the one hand, and on their distal attachment zone on the other hand;
  • ○ the figure 6I offers a detail of the section of the fins of the Figure 6C .
• the figure 7 illustrates the new air velocity distribution of the figure 1 after introduction of fixed vanes into the device of the figure 3 according to the invention;
• the Figures 8A and 8B illustrate the velocity components of the cooling fluid at the mobile blades of the fan and fixed vanes;
• the figure 9 shows another view of the device of the invention, to illustrate the angle α formed by the fixed fin string and the axis of rotation of the movable blades;
• the figures 10 , 11A and 11B present various examples of assembly of the fixed fins of the invention;
• the figure 12 presents an exemplary embodiment, in which the fixed vanes have a zero angle of inclination by relative to the axis of rotation of the mobile blades of the fan over their entire length;
• the figure 13 shows an embodiment of the fixed vanes and an annular element to which they are secured;
• the Figures 14, 15 and 16 show an example of a cooling system according to the invention, in which an axial fan is surrounded by a ventilation nozzle ( figure 14 ), in which fixed vanes are arranged in the nozzle ( figure 15 ), and in which an annular element formed around the fan in the nozzle has at the inlet a form of venturi ( figure 16 ).

5. Description of an embodiment of the invention

We now present, in relation with the figure 3 , an embodiment of the invention, wherein the cooling device of the invention is part of a thermal engine cooling system of a generator.

It is recalled first of all that a generator is an autonomous device for producing electrical energy from a heat engine. A generator makes it possible either to mitigate a power outage of the public grid, or to power electrical appliances in areas without access to the public electricity grid.

• un bâti,
• un moteur thermique monté sur le bâti,
• un alternateur monté sur le bâti et relié au moteur thermique pour pouvoir transformer l'énergie reçue du moteur thermique en énergie électrique,
• un boîtier de commande et de raccordement relié à l'alternateur,
• au moins une entrée d'air dans le bâti pour alimenter le moteur thermique.

A generating set comprises in known manner:

• a frame,
• a heat engine mounted on the frame,
• an alternator mounted on the frame and connected to the heat engine to be able to transform the energy received from the heat engine into electrical energy,
• a control box and connection connected to the alternator,
• at least one air inlet in the frame for supplying the heat engine.

In operation, the heat engine rises in temperature, and it is It is important to provide the generator with an adequate cooling system to keep the temperature within an acceptable range to maintain proper operation. Such a cooling system also avoids the deterioration of the engine and other components of the generator, which could be caused by the rise in temperature related to the heat discharges of its components.

As explained above, such a cooling system generally comprises a radiator 3, in which circulates a fluid to be cooled (cooling water of the engine block, charge air, oil, fuel, etc.). An axial fan 1 blows fresh air through the radiator bundle 3. The air flow of this fan 1 is in a ventilation nozzle 2, which serves as a supply manifold for the radiator 3.

As illustrated in figure 8A the air is propelled tangentially and radially towards the outside, by the centrifugal effect generated by the speed of rotation of the mobile blades. The speed V of the air at the outlet of the blade therefore comprises a tangential component Vt and a radial component Vr (centrifugal effect), as illustrated in FIG. figure 8A . This radial component of the air velocity results in a much greater flow rate, as well as greater pressure, in the peripheral areas of the fan. Conversely, the flow rate and the pressure are low or even zero or even negative in the central zone of rejection (dead cone).

In order to maintain the operating temperature of the generator set within an acceptable range, both to maintain a good efficiency and to prevent deterioration of its components, it is important that the fan be as efficient as possible. According to the invention, and as illustrated on the figure 4 , therefore introduced into the ventilation nozzle 2 a set of fixed vanes 7, which form a counter-rotating system preventing the rotation of the air by the movable blades of the fan 1. By blocking the rotation of the mass of d air, thus improves the relative speed of the fan blades relative to the air, and thus the efficiency of the fan.

Moreover, the generating sets being subjected to severe space constraints (they must remain compact to satisfy the user), it is not possible to solve the problem of the appearance of an inactive cone downstream of the fan 1 by retreating the radiator 3. In accordance with one aspect of the invention, and as illustrated in the figure 4 the shape of the fixed vanes 7, formed and / or mounted in the ventilation nozzle 2 , is thus chosen so as to reduce the air flow displaced by the rotating blades of the fan 1 towards the corresponding central zone, according to FIG. prior art, to the zone of formation of the inactive cone. In doing so, we cancel the effect of this inactive cone. More precisely, according to this aspect of the invention, curved fixed fins are chosen, the curvature of which uses the dynamic effect of the pulsed air to return a part towards the center by centripetal effect.

So, and as illustrated in Figure 8B , the curved shape of the fixed vanes is defined so that at any relative position of the mobile blades of the fan, the angle of incidence of the air flow propelled at the outlet of the fan blade on a fixed vane is such that it makes it possible to transform the tangential velocity Vt of the incident air into a radial velocity Vr directed towards the center.

This component Vr of the speed comes to oppose the centrifugal speed Vr created by the rotation of the fan (see figure 8A ) and according to the shape and curvature of the fixed fins, its standard may be equal to or greater than that of the centrifugal speed Vr.

• V désigne la vitesse de l'air redressé par une ailette fixe. Sa direction est tangente à l'ailette fixe considérée ;
• Vt désigné la vitesse tengentielle de l'air en sortie de la pale mobile du ventilateur;
• V-r désigne la composante radiale dirigée vers le centre de la vitesse de l'air redressé par les ailettes fixes.

On the Figure 8B it will be noted that:

• V denotes the speed of the air straightened by a fixed fin. Its direction is tangent to the fixed wing considered;
• Vt denoted the tengential air speed at the outlet of the mobile blade of the fan;
• Vr denotes the radial component directed towards the center of the speed of the air straightened by the fixed fins.

The result of the optimization of the shape and the number of fixed blades thus allows a much more homogeneous supply of the surface of the radiator, and a pressurization of the central zone (facing the fan hub), eliminating the dead cone and providing a flow through this zone which is equivalent to that existing in the external areas.

In the most unfavorable cases, in the absence of fixed blades acting as a centripetal rectifier, the pressure is so low in the central zone between the fan and the radiator that a low back pressure downstream of the radiator is sufficient to cause a return of hot air upstream of the radiator, through this zone: such a recycling of the air greatly degrades the performance of the cooling system.

The centripetal function of the fixed fins of the invention corrects this problem and provides homogeneity of the airflow over the entire exchange surface.

In addition to this centripetal rectification effect of the air flow, the fixed fins of the invention produce a complementary effect, namely the rectification of the air flow in rotation, to make it an axially directed flow, in order to improve the efficiency. of the cooling system, placing the airflow in the expected direction to cross the radiator.

To do this, as illustrated in figure 9 the fixed wings are designed so that the angle α formed by the rope of the fixed fin and the axis of rotation of the movable blades of the fan progressively evolves by a value α = 0 ° at the proximal end fixed vanes to a non-zero value α at the distal end of the fins. For example, α = 45 ° at the distal end of the fixed fins. Note that this value can be optimized according to the geometries of fixed blades and moving blades used, for example by CFD calculation.

This angle α makes it possible to straighten the flow of air, and to transform the tangential velocity of the air at the outlet of the moving blade into axial velocity, to favor the penetration of the air into the radiator bundle.

Such a rectification of the airflow in the axial direction, combined with the centripetal rectification effect previously described, results in an improvement in the efficiency of the ventilation function.

Axial positioning of the air flow also results in a reduction of the noise generated by friction of the air against the fins and other asperities of the radiator. Without this rectifying effect, the air is driven by a rotational movement at the outlet of the fan, and this, at a speed of rotation close to that of the fan. This tangential speed acts as a "wind instrument" on the radiator beam.

It will be noted that ventilation represents a very important contribution to the overall noise of a generator type machine. The presence of a rectifier according to the invention in the ventilation nozzle of a generator makes it possible to very significantly reduce the overall noise of the group (for example a reduction of the order of 3dBA on a soundproof group of 300kVA) .

On the figure 9 the element referenced 9 corresponds to the ferrule placed around the fan and intended to improve the efficiency. This ferrule corresponds to the elements referenced 24 and 25 on the Figures 11A and 11B .

The figure 5 presents in more detail the whole, taken from the figure 4 , comprising the ventilation nozzle 2 in which was mounted the system of fixed vanes 7, according to the invention. In the particular example of the figure 5 these fins are seven in number, so that the number of movable blades of the fan 1, namely nine, and the number of fixed blades, namely seven, are two prime numbers between them, which avoids any phenomenon of resonance, and therefore to reduce the noise generated by the introduction of such fixed fins. In addition to the criterion of space, that of noise level is indeed also a strong constraint for generators. Other combinations of numbers of fixed fins on the one hand and movable blades on the other hand are of course possible.

It will be noted that on the figure 5 the arrow referenced 8 indicates the direction of rotation of the mobile blades of the fan 1 when it is in operation.

In this particular example, the fixed vanes are all identical and regularly distributed over the entire cavity of the fan 1. fins, equidistant from each other, are, in this embodiment, of particularly simple shape, since they are each in the form of a ribbon, curved in a plane parallel to the plane of rotation of the fan 1, and whose The distal end is inclined at approximately 45 ° with respect to this plane of rotation.

Thus, the presence of the fixed wings vis-à-vis the mobile blades of the fan makes it possible to counteract the rotation of the air by the driving effect of the mobile blades of the fan 1. Their curved shape makes it possible, in turn, to bring back the flow of air, by centripetal effect, towards the axis of rotation of the fan 1, in order to cancel the appearance of the inactive cone downstream of the fan. Thus, such fixed fins can maintain, in the central area downstream of the fan, a sufficient pressure to supply the central zone with fresh air and prevent hot air from returning from the center of the radiator. Finally, the inclination of approximately 45 ° at the end of the fins makes it possible to optimize the distribution of speed and air pressure on the radiator, avoiding the creation of a vacuum zone likely to form downstream of the fins. when such inclination does not exist. Such inclination of the distal end of the fixed vanes also reduces the noise that may be generated by the passage of the movable blade of the fan in front of the fixed fin, which induces a pressure wave.

The value of the angle of the distal end of the fixed vane relative to the plane of rotation must be adapted on a case by case basis, for example by calculation of CFD, in order to reduce as far as possible the appearance of zones of depression. and / or the noise generated, depending on the objectives that we set. Such an adaptation must also take into account the shape of the fixed fin.

Such fixed fins may be made of any material appropriate to the type of cooling fluid considered. In the case of ambient air, these fins may be made of metal, or, for a lower production cost, plastic. The set of fixed vanes can thus be made in the form of plastic molding, which is then reported in the ventilation nozzle. The cost of production can be further reduced by producing in a single block the assembly consisting of the ventilation nozzle and fixed fins.

The Figures 6A to 6I specify the dimensions and shapes of the fixed vanes 7 in the exemplary embodiment given here by way of illustration.

The figure 7 illustrates the distribution of air velocities in the fan environment of the figure 2 after introducing a set of fixed vanes into the ventilation nozzle. As can be noted, the fixed vanes disposed in the ventilation nozzle make it possible to supply the central zone with air, and to cancel the inactive cone of the figure 2 . In this example, the fixed fins introduced into the ventilation nozzle have a curved ribbon shape, perpendicular along its length to the plane of rotation of the mobile blades of the fan. In other words, the string of the fixed vanes form, at their distal end 31, a zero angle with the axis of rotation. (The figure 12 also illustrates such an embodiment, in which the rope fixed vanes 7 forms a zero angle with the axis of rotation referenced 33, over the entire length of these fixed vanes, ie their proximal end 30 at their distal end 31. In this configuration, it is therefore noted that certain areas 10 of low pressure (cavitation phenomenon) are formed behind the fixed fins. This defect can be corrected by tilting the distal end 31 of the fixed vanes, as mentioned above in connection with the figures 4 and 5 .

In particular, in view of the shape and the width of the cavitation zones 10, it is chosen to incline the end of the fixed wings of approximately 45 ° with respect to the axis of rotation. This angle has a degressive value, of approximately 45 ° at the distal end of the fixed wings, at 0 ° at the proximal end of these fins. Such an evolution of the inclination of the fins from the center to the periphery makes it possible, in addition to facilitating its construction, to follow the degressive shape of the cavitation zones 10.

The attenuation of these cavitation zones 10 can be accentuated by modifying the shape of the fins to give them a more complex aerodynamic profile. It can thus be envisaged that the fins have a section profile non-symmetrical, that is to say that they have a lower surface and an upper surface of different shapes.

Indeed, it will be noted that the shape, number and inclination of the fins can be optimized with respect to the example presented here, so as to optimize the efficiency of the cooling system considered. In particular, the fins may have more complex shapes of propeller blades, for example.

In the example described above, in which the fixed vanes have a relatively simple shape, the implementation of the invention has made it possible to lower the temperature of the radiator by 3 ° C., while keeping it at a distance from the radiator fan. only 10 to 15 cm.

We now describe in more detail, in relation to the figures 10 , 11A and 11B examples of assembly of the fixed wings of the rectifier of the invention.

As illustrated on the figure 9 and on Figures 11A and 11B the fan referenced 1 has a central hub 11, which is inactive with respect to the air flow. The base of the fan blades is hooked on this hub 11.

Indeed, all the axial fans physically have an inefficient zone in their center, and by construction the fan blades are fixed on a central hub. The size of these hubs varies from one manufacture to another, but their diameter represents about 20% to 40% (or even 50%) of the outer diameter of the fans.

According to the invention, it has therefore advantageously been envisaged to use this zone situated directly behind the hub of the fan to fix and stiffen the fixed vanes of the flow straightener. Thus, this surface can be used, for example, to have a binding reinforcement disc 20 for fixed fins.

The shape used in the central area of the rectifier may range from a disc 20 to a cone 21, or use a more complex shape 22 of curved surface cone. These last two forms are particularly suitable for producing a piece made of plastic molding.

Thus, the fixed vanes 7 can be fixed at their proximal end to a connecting tube 23, and the assembly can be stiffened by means of the disc of reinforcement 20 on which are also fixed fixed fins 7. In a variant, the fixed vanes 7 are fixed at their proximal end to a cone 21, 22 which serves the dual role of means of assembly and stiffening.

At their distal end, the fixed wings are assembled to an annular element 25 of diameter greater than or equal to the diameter of the fan 1. This annular element 25 has a flared portion 24, upstream of the fan, so as to create a Venturi effect on the air flow entering the fan 1.

The diameter of the disk 20 or that of the base of the cone 21, 22 equal to or smaller than that of the hub 11 of the fan 1 is preferably chosen.

The use of a central cone 21, and especially with a curved surface 22, facilitates the reorientation of the centripetal flow to the desired axial direction and sought to pass the cooling air through the beam, in the central zone of the radiator as illustrated in Figure 11B .

The optimization of the central shape of the rectifier can be carried out for each application by CFD calculation or by results of experiments (each fan diameter having the associated rectifier).

The Figures 12 and 13 show two embodiments of fixed fins 7 of the invention.

In the example of the figure 12 , the fixed vanes 7 are in the form of a ribbon, which is parallel to the axis of rotation 33 of the mobile blades of the fan, the proximal end of the fins 7 at their distal end 31. The fixed vanes 7 are elsewhere assembled together at their proximal end 30 along an edge 23, which may be in the form of a small diameter tube. At their distal end 31, the fixed vanes 7 are fixed to an annular element 25, or to the ventilation nozzle 2, by means of a tab or an attachment element 40. Such a fixing lug 40 may be formed in the fin 7 at its distal end 31. The fixing lug 40 may be connected to the annular element 25 or to the ventilation nozzle 2. Alternatively, the fixing lugs 40 may not be integrally formed with the fixed fins 7, but attached to these fins at their distal end 31. They may also be integrally formed with the annular element 25.

In the example of the figure 13 , the annular element 25 to which are connected the fixed fins 7 at their distal end 31 is substantially in the form of a cylinder whose axis of revolution corresponds to the axis of rotation of the mobile blades of the fan. The fixed vanes 7 are thus disposed inside the cylinder formed by this annular element 25. In addition, their rope inclines with respect to the axis of rotation of the fan, from a zero angle at their proximal end 30 towards an angle of about 45 ° at their distal end 31. At this distal end 31, the fixed vanes 7 are directly secured to the inner wall of the annular element 25.

The figure 14 shows an example of a cooling system 100, which comprises a ventilation nozzle 2 surrounding an axial fan 1 and a radiator 3. figure 15 illustrates the cooling system of the figure 14 , in which, in the ventilation nozzle 2, fixed vanes 7 have been added. The fixed vanes 7 can be secured to an outer annular element 25, so that the annular element 25 can be secured to the ventilation nozzle. 2 in various ways, for example by welding, by screwing, by means of rivets, by gluing, by molding, etc.

The figure 16 shows an exemplary embodiment of the cooling system 100, wherein the outer annular element 25 is also formed around the axial fan 1 and has, at the level of the air inlet, a flared form of venturi type. This shape makes it possible to improve the flow of air at the inlet of the axial fan 1 and improves the efficiency of the cooling system 100. In certain embodiments, the annular element 25 may have openings between the fixed vanes 7, way to supply air to the external areas of the radiator 3, especially when the latter has a rectangular shape. The fixed vanes 7, in turn, can generate sufficient pressure in the central zone 6 to force the cooling air towards the central zone 6.

Although the invention has been presented here in the particular context of the cooling of thermal engines of generators, it can find other advantageous applications in other technical fields, for example in the automotive field.

Claims (10)

Generator cooling device comprising at least one axial fan comprising at least two blades movable in rotation, capable of driving a cooling fluid, through a ventilation nozzle, to an element to be cooled,
said device also comprising at least two fixed wings arranged facing said mobile blades in said ventilation nozzle,
characterized in that said fixed fins have a curved shape adapted to transform a tangential velocity component of said cooling fluid driven by said axial fan: on the one hand, in a radial velocity of said fluid directed towards the center of said cooling device; on the other hand, at an axial speed of said fluid directed towards an axis of rotation of said fan. Cooling device according to claim 1, characterized in that , said movable blades being fixed at their proximal end to a central hub, said fixed wings are connected at their proximal end to a connecting device of diameter less than or equal to the diameter of said hub central. Cooling device according to claim 2, characterized in that said connecting device comprises a tube on which are fixed the proximal ends of said fixed wings and a reinforcing disk, located close to said central hub, the diameter of the tube being substantially less than diameter of said reinforcing disk, and the diameter of said reinforcing disk being less than or equal to the diameter of said central hub. Cooling device according to claim 2, characterized in that said connecting device has substantially a cone-shaped or cone-shaped curved surface, whose diameter decreases away from said central hub to said element to be cooled. Cooling device according to any one of claims 1 to 4, characterized in that said fixed fins have a curvature in a plane substantially perpendicular to an axis of rotation of said movable blades, called the plane of rotation. Cooling device according to any one of claims 1 to 5, characterized in that said fixed fins have, at their distal end, a non-zero angle with said axis of rotation. Cooling device according to claim 6, characterized in that said fixed vanes are twisted. Cooling device according to any one of claims 1 to 7, characterized in that it comprises a number N of fixed vanes and a number P of the mobile blades of the fan, N and P being two prime numbers between them. Cooling device according to any one of claims 1 to 8, characterized in that said fixed fins are connected at their distal end to a substantially annular element of diameter greater than the diameter of said axial fan, said substantially annular element having a flared shape on a portion extending upstream of said axial fan, so as to create a Venturi effect on said cooling fluid. Generating set comprising a heat engine and an alternator connected to said heat engine and capable of converting energy received from said heat engine into electrical energy,
characterized in that it comprises at least one cooling device according to any one of claims 1 to 9.

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