Patent Publication Number: US-11391282-B2

Title: Axial ventilator having noise reducing fan wheel blades

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Application No. 10 2019 105 190.8, filed Feb. 28, 2019. The disclosure of the above application is incorporated herein by reference. 
     FIELD 
     The disclosure relates to an axial ventilator having a housing and a fan wheel arranged in the housing to generate an axial airflow through the housing. 
     BACKGROUND 
     In axial ventilators, with ring-shaped housings enclosing the fan wheel, head gap turbulence arises at the head gap between the fan wheel blades and the housing inner wall. This results in practice, in significant noise development. There are already multiple approaches for the noise reduction in the prior art. However, these are not suitable for every use. For example, the diameter of the axial ventilator can be enlarged. However, this is counterproductive with respect to its efficiency and wind load behavior. Alternatively, there is the option of influencing the inflow or outflow, however, additional components usually add an increased structural space requirement that is necessary for this purpose. 
     SUMMARY 
     The disclosure is based on the object of improving the noise behavior of an axial ventilator. 
     This object is achieved by an axial ventilator with a housing and a fan wheel arranged in the housing to generate an axial air flow through the housing. The fan wheel comprises multiple fan wheel blades. The blades extend radially outward from a hub up to the respective blade tip. The blades extend spaced apart over a head gap from an inner wall of the housing. The fan wheel blades comprise boreholes along the respective blade tip. 
     According to the disclosure, an axial ventilator, with a housing and a fan wheel arranged in the housing, for generating an axial airflow through the housing is proposed. The fan wheel comprises multiple fan wheel blades that extend from a hub radially outward up to the respective blade tip. The blades extend spaced apart, via a head gap, to an inner wall of the housing. The blade tip is the extension of the fan wheel blades along the inner wall of the housing. This encloses the fan wheel as a housing ring. The fan wheel blades comprise boreholes along the respective blade tip. 
     In operation, the boreholes along the respective blade tip interact directly with the head gap turbulence and reduce the noise emission of the fan wheel. In particular, the shape and propagation of the flow turbulence along the blade tips of the fan wheel blades is favorably influenced. In axial ventilators that differ exclusively by way of the fan wheel blades, with and without boreholes provided along the blade tip, it was possible to achieve reductions of the noise development by greater than 20% in measurements. 
     The boreholes have particularly advantageous effects in axial ventilators where the fan wheel blades have a very flat angle of attack in relation to the axial plane extending perpendicularly to the flow direction. The angle is in particular in the range of 5-25°, preferably 10-20°. 
     One refinement of the axial ventilator includes the boreholes formed on both axial sides of the fan wheel blades. In one preferred embodiment, the boreholes are formed as through boreholes through the fan wheel blades. 
     Preferably, a plurality of boreholes per fan wheel blade are provided along the respective blade tip. The number of the boreholes is at least two, but in particular at least three, preferably at least five, more preferably at least seven. The boreholes extend in this case along a line parallel to the blade tip. The arrangement is thus established via the profile of the blade tip along the head gap in relation to the inner wall of the housing. 
     An embodiment of the boreholes having a circular cross section has proven to be particularly advantageous. The size of the boreholes is defined via its diameter. In one advantageous embodiment of the axial ventilator, the boreholes have a maximum diameter DBmax, that corresponds to 0.7-1.5%, preferably 1% of a maximum fan wheel diameter of the fan wheel. 
     A special arrangement of the boreholes in relation to one another also promotes the noise reduction. An embodiment variant is favorable where the boreholes have a distance A, that corresponds to twice the maximum diameter DBmax of the boreholes, along the respective blade tip in relation to one another. The distance A is measured in each case at the center point of the respective borehole. In relation to the maximum fan wheel diameter D of the fan wheel, the distance A of the boreholes in relation to one another along the respective blade tip is advantageous if it corresponds to 2% of the maximum fan wheel diameter D. 
     Furthermore, it is advantageous that the boreholes are spaced apart somewhat radially inward from the respective blade tip of the respective fan wheel blade. Accordingly, they are nonetheless adjoining. Thus, the radial outer blade tip of the respective fan wheel blade extends continuously and uninterruptedly. One advantageous embodiment with respect to the noise generation includes the boreholes with a maximum diameter DBmax and are spaced apart from the respective blade tip over a radial length LS, so that the following applies: DBmax≤LS≤2.5×DBmax. Particularly preferably, LS=1.5×DBmax. In other words, the boreholes are preferably offset radially inward from the blade tip by 1.5 times the borehole diameter. Measurement is also always performed here in the center point of the boreholes. 
     In relation to the maximum fan wheel diameter D of the fan wheel, the length LS, over which the boreholes are spaced apart from the respective blade tip, preferably corresponds to 1.5% of the maximum fan wheel diameter D of the fan wheel. 
     Preferably, all boreholes of the fan wheel are each formed identically with respect to shape and size. 
     In one advantageous embodiment variant of the axial ventilator, the boreholes are arranged over an extension along the blade tip of the respective fan wheel blade that corresponds to 10-40% of the maximum extension of the blade tip along the head gap. This means that there is a predominant section along the blade tip where no boreholes are provided, but a minimum quantity and a minimum extension are not to be undershot. Furthermore, it is advantageous to arrange the boreholes in a region of the blade tip that adjoins the respective blade front edge and/or respective blade rear edge. If the fan wheel blades extend radially indented in the transition region from the blade tip to the blade front edge or respective blade rear edge and a head gap to the housing no longer exists in this section, boreholes can nonetheless also be provided in this section along the blade tip. 
     In one advantageous embodiment variant, the axial ventilator moreover provides that each of the fan wheel blades comprises a middle section. The middle section is free of boreholes along the blade tip and adjoining a radial center line of the fan wheel blades on both sides. The boreholes are thus provided in a region of the front edge and/or rear edge of the fan wheel blades. The middle section preferably defines 20-90%, more preferably 40-80% of the maximum extension of the respective fan wheel blade in the circumferential direction. 
     In one refinement of the axial ventilator, the boreholes are additionally provided along a front edge and/or a rear edge of the fan wheel blades. The distances in relation to one another or in relation to the front edge and/or a rear edge preferably correspond in this case to those of the boreholes along the blade tip or in relation to the blade tip. 
     Furthermore, an embodiment is favorable where, in the axial ventilator, the respective number of the boreholes along the front edge and/or the rear edge of the fan wheel blades is additionally less than or equal to the number of boreholes along the blade tip. This means that the number of the boreholes on the front edge and on the rear edge is always not greater in each case than the number of the boreholes on the blade tip. 
     In one embodiment, the axial ventilator includes the fan wheel designed as reversible. Its flow direction generated in operation is dependent on its rotational direction. The boreholes are then preferably provided both on the front edge and also the rear edge and on both axial sides of the respective fan wheel blades. 
    
    
     
       DRAWINGS 
       Other advantageous refinements of the disclosure are characterized in the dependent claims and/or are described in greater detail hereafter together with the description of the preferred embodiment of the disclosure on the basis of the figures. In the figures: 
         FIG. 1  is a top plan view of a first embodiment of an axial ventilator. 
         FIG. 2  is an enlarged detail view of the axial ventilator from  FIG. 1 . 
         FIG. 3  is a perspective front view of the axial ventilator from  FIG. 1 . 
         FIG. 4  is a perspective rear view of the axial ventilator from  FIG. 1 . 
         FIG. 5  is a top plan view of a second embodiment of an axial ventilator. 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment variant of the axial ventilator  1  is shown in  FIGS. 1-4 . It has a ring-shaped closed housing  2  and a reversibly designed fan wheel  3 . The fan wheel  3  generates the axial airflow. The air flow direction is dependent on the rotational direction of the fan wheel  3 . The fan wheel  3  includes hub  5  with multiple ventilation openings  25  arranged in a circular shape. The drive motor is accommodated in the hub  5 . The motor is electrically supplied via the terminals  14 . 
     On the rear side, the drive motor is held by the holder  20 . The holder  20  is connected to the housing  2  via webs  11  arranged distributed in the circumferential direction. The webs  11  extend linearly but are inclined in relation to a radial plane. 
     The fan wheel blades  4  extend radially outward from the hub  5  up to the respective blade tip  8 . The blade tip  8  forms the blade edge adjacent the inner wall of the housing  2 . The head gap  12  is provided between the blade tips  8  and the inner wall of the housing  2 , so that the fan wheel  3  can rotate in relation to the housing  2 . The fan wheel blades  4  are each formed identically. Each blade tip  8  has a radially indented section  9  on both sides viewed in the circumferential direction. Here, the blade edge still does face radially outward but is spaced apart from the inner wall of the housing  2 . Adjoining this, the blade edge merges into the front edge  17  and rear edge  18 . The blade tips  8  each face in the circumferential direction, but are each formed indented in the circumferential direction in relation to the radial outermost section of the fan wheel blades  4 . 
     Along the respective center axis, viewed in the circumferential direction, an axial step  24  is formed on each of the fan wheel blades  4 . The step  24  enlarges viewed radially inward and runs out toward the blade tip  8 . Thus, a continuous profile of the fan wheel blade  4  is provided in the region of the blade tip  8 . 
     A plurality of boreholes  7 , with circular cross section, are provided on each of the fan wheel blades  4  along the respective blade tip  8 . The boreholes  7  are formed at the respective identical position on both axial sides. Thus, they have the respective identical center axis. It is preferably provided that the boreholes  7  are formed as through boreholes. 
     In the embodiment according to  FIGS. 1-4 , eight boreholes  7  are provided on both end sections facing toward the front edge  17  and toward the rear edge  18  along the blade tip  8 . Thus, a total of 16 boreholes  7  per fan wheel blade  4 . Per the region having boreholes  7 , respectively, six boreholes  7  are located along the blade tip  8  along the head gap  12  and, respectively, two boreholes  7  are located in the indented region  9 . 
     In the embodiment according to  FIG. 5 , only seven boreholes  7  are provided in each case on the respective end sections along the blade tip  8 . Thus, a total of 14 boreholes  7  per fan wheel blade  4 . In relation to the embodiment according to  FIGS. 1-4 , in the embodiment according to  FIG. 5 , the boreholes  7  are displaced further outward viewed in the circumferential direction. Thus, four of the seven boreholes  7  are located, respectively, along the blade tip  8  along the head gap  12  and, respectively, three boreholes  7  are located in the indented section  9 . Otherwise, the embodiments according to  FIGS. 1-4  and  FIG. 5  are identical. 
     Although it is not shown in the two embodiments, corresponding boreholes  7  can also be provided in the region of the front edge  17  or the rear edge  18  and also both on the front edge  17  and also the rear edge  18  of the respective fan wheel blades  4 . The number of the boreholes, respectively, along the front edge  17  or the rear edge  18  is established as less than that of the radial outer edge. 
     Each of the fan wheel blades  4  comprises a middle section  15 , which is free of boreholes  7 , along the blade tip  8 . The middle section  15  adjoins a radial center line of the fan wheel blades  4  on both sides. The middle section  15  without boreholes  7  defines, in both embodiments according to  FIGS. 1 and 5 , the comparatively larger region. Thus, over a greater extension of the respective fan wheel blade  4 , no boreholes  7  are provided. The boreholes  7  are essentially located in the circumferential edge sections. 
     In both embodiments of  FIGS. 1 and 5 , the fan wheel blades  4  have a very small angle of attack of less than 25° in relation to the axial plane extending through the housing  2 . This can be seen well in  FIG. 3 . In the case of such small angles of attack, the boreholes  7  are particularly effective. 
     The size, shape, and arrangement of the boreholes  7  significantly influences the noise-reducing effect. Advantageous dimensions are recorded in  FIG. 5 , which are also identically applicable to the exemplary embodiment of  FIGS. 1-4 . The boreholes  7  have a maximum diameter Dbmax. It corresponds to 1% of the maximum fan wheel diameter D of the fan wheel  4 , measured in each case in the center point of the boreholes  7 . 
     The distance A of the boreholes  7  in relation to one another along the respective blade tip  8  corresponds to twice the maximum diameter DBmax and 2% of the maximum fan wheel diameter D of the fan wheel  4 . The boreholes  7  are spaced apart from the blade tip  8  over the length LS. This makes up 1.5% of the fan wheel diameter D and 1.5 times the maximum diameter DBmax. 
     The radial outer blade tip  8  of the respective fan wheel blade  4  extends continuously and uninterruptedly. According to the embodiment in  FIG. 5 , the distribution of the boreholes  7  along the blade tip  8  is performed over a length which corresponds to 10% of the blade tip length L, along which the head gap  12  is formed. In the embodiment according to  FIGS. 1-4 , it is 20%. 
     In both embodiments according to  FIGS. 1-4 and 5 , all boreholes  7  are each formed identically. Alternatively, however, it can also be provided that the boreholes  7  differ in relation to one another in shape and size. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.