Efficient noise reduction axial flow fan and working method thereof

Abstract

The invention discloses an efficient noise reduction axial flow fan and a working method thereof. A plurality of slits which are arranged at equal intervals are formed in the front edge of a blade, a plurality of sawteeth are arranged in the middle of the rear edge of the blade, the slits and the sawteeth penetrate through the blade, a plurality of hole sets which are arranged at equal intervals in the circumferential direction are formed in the positions, flush with the rotating circumferential face of the blade, of a fan shell, and each hole set is composed of a plurality of round holes which are arranged at equal intervals in the circumferential direction. The efficient noise reduction function can be achieved during working, incoming flow turbulence noise generated at the front edge of the blade is reduced by forming the slit in the front edge of the blade, flow loss and noise caused by blade tip clearance vortex are reduced, noise generated at the rear edge of the blade is reduced by forming the sawteeth at the rear edge of the blade, and the noise reduction effect is improved. And the hole groups are formed in the positions, aligned with the rotating circumferential surfaces of the blades, of the fan shell, so that the problems of flow loss and noise caused by blade tip clearance vortexes are further reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of fan noise reduction, and in particular relates to an axial flow fan with high efficiency noise reduction and a working method thereof. Background Art

[0002] Axial flow fans are driven fluid machines that convert mechanical energy into fluid energy. For a long time, axial flow fans have been widely used in ventilation, dust removal and cooling processes in factories, mines, tunnels, cooling towers, vehicles, ships and buildings due to their simple structure, large air volume and small size. However, noise suppression of axial flow fans has always been a difficult problem, and the aerodynamic noise generated by the rotation of fan blades is its main source. This type of noise seriously affects the surrounding environment. Long-term exposure to noise environment will cause serious harm to human health, such as hearing loss and cardiovascular disease.

[0003] The noise of axial flow fans mainly comes from various separation vortices during airflow. These vortices mainly include: the incoming turbulent noise generated when the leading edge of the blade interacts with the airflow with a certain degree of turbulence, the detached vortex noise generated by the turbulent boundary layer (turbulent boundary layer) on the blade surface falling off at the trailing edge of the blade, and the top vortex noise generated by the secondary flow from the concave surface to the convex surface at the top of the blade being carried away by the main airflow. In order to reduce the noise of axial flow fans, researchers have taken many measures, such as using silencers, using isolation covers, and modifying the blades, but the noise reduction effect varies depending on the environment. In order to obtain a more ideal noise reduction effect, the structure of the axial flow fan needs to be improved. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide an axial flow fan with high efficiency and noise reduction and a working method thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention discloses an axial flow fan with high efficiency and noise reduction, comprising a fan casing, a protective net assembly, a hub and blades. The fan casing is cylindrical, and a bracket assembly is fixed to the bottom of the fan casing; the hub is located in the fan casing, coaxially arranged with the fan casing, and driven to rotate by a motor, and the motor is controlled by a controller; a plurality of blades evenly distributed along the circumference are fixed to the hub, a plurality of slits arranged at equal intervals are opened on the leading edge of the blade, a plurality of saw teeth are opened in the middle of the trailing edge, and the slits and saw teeth all pass through the blade; a protective net assembly is fixed to the inlet of the fan casing, and a plurality of hole groups arranged at equal intervals along the circumference are opened on the fan casing at a position aligned with the rotating circumferential surface of the blade, and the hole group is composed of a plurality of circular holes arranged at equal intervals along the circumference; the circular holes pass through the fan casing.

[0007] Preferably, the bracket assembly consists of a fan bracket 1 and a fan bracket 2 which are symmetrically arranged at intervals, and the fan bracket 1 and the fan bracket 2 are both fixed to the bottom of the fan housing.

[0008] Preferably, the motor casing is fixed on a horizontally arranged motor support 1, both ends of the motor support 1 are fixed to the inner wall of the fan casing, and the upper and lower ends of the vertically arranged motor support 2 are respectively fixed to the center position of the motor support 1 and the inner wall of the fan casing.

[0009] Preferably, the protective net assembly consists of protective net one and protective net two, and both protective net one and protective net two are circular and arranged coaxially with the fan casing, the outer edge of protective net one is fixed to the inner wall of the fan casing, and protective net two is fixed on protective net one.

[0010] More preferably, the protective net 1 is composed of a plurality of vertical protective rods arranged equidistantly, and both ends of the vertical protective rods are fixed to the inner wall of the fan casing. The protective net 2 is composed of a plurality of circular protective rods arranged in concentric circles, and each circular protective rod is fixed to the cylindrical surface of each vertical protective rod at its own circumferential covering position.

[0011] Preferably, the hub is provided with a plurality of annular grooves arranged in concentric circles.

[0012] Preferably, the tips of the leading edge and the trailing edge of the blade are both rounded.

[0013] The present invention provides a working method of an axial flow fan with high efficiency and noise reduction, which is specifically as follows:

[0014] The controller controls the motor to drive the hub to drive each blade to rotate, sucking the gas from the inlet of the fan housing and discharging it from the outlet; during the rotation of each blade, the incoming turbulence at both ends of each slit interacts with each other to generate two sound sources, and fh / u=(2n-1) / 2 is designed, where n is a positive integer, f is the sound source frequency, u is the speed of sound, and the wavelength difference between the two sound sources during propagation is h. Then the phase difference 2πfh / u of the two sound sources is an odd multiple of π, so that the two sound sources interfere and destroy each other in phase and cancel each other out, thereby reducing the incoming turbulence noise generated at the leading edge of the blade; in addition, the tip gap vortex formed in the gap between the blade tip and the fan housing is weakened when interacting with the slit during flow, thereby reducing the flow loss and noise caused by the tip gap vortex; At the same time, the serrations on the trailing edge of the blade reduce the convection velocity of the turbulent eddy along the serration edge and weaken the sound scattering, thereby reducing the noise generated by the turbulent boundary layer at the trailing edge of the blade. The serrated trailing edge of the blade splits the large-scale vortex into small-scale vortices by strengthening turbulent mixing, thereby improving the spanwise distribution of the vortex, reducing the spanwise dimension of the wake vortex, making the wake vortex distribution more uniform, and further reducing the noise at the trailing edge of the blade. In addition, during the rotation of each blade, since a hole group is provided on the fan casing at a position aligned with the rotating circumferential surface of each blade, a pressure difference is generated in the gap between the blade tip and the fan casing at the trailing edge of each blade. The pressure difference destroys the secondary flow formed in the gap between the blade tip and the fan casing at the trailing edge of the blade, thereby further reducing the flow loss and noise caused by the tip gap vortex.

[0015] The present invention has the following beneficial effects:

[0016] The present invention can achieve a highly efficient noise reduction function when working. Specifically, the present invention provides a slit on the leading edge of the blade, and the two sound sources of the incoming flow turbulence at both ends of the slit interfere with each other in phase, cancel each other out, and reduce the incoming flow turbulence noise at the leading edge of the blade. In addition, the tip gap vortex interacts with the slit during flow and is weakened; further, the present invention provides serrations on the trailing edge of the blade, so that the convection velocity of the turbulent vortex along the serration edge is reduced, thereby achieving the effect of reducing sound scattering and reducing the noise at the trailing edge of the blade; in addition, the present invention provides a hole group at a position aligned with the rotating circumferential surface of each blade on the fan housing, and uses the pressure difference in the gap between the blade tip at the trailing edge of the blade and the fan housing as a driving force, destroying the secondary flow formed in the gap between the blade tip at the trailing edge of the blade and the fan housing, further reducing the flow loss and noise problems caused by the tip gap vortex, while improving the aeroacoustic performance of the fan, it will not reduce the aerodynamic performance of the fan. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The overall structure of the present invention is three-dimensional Figure 1 ;

[0018] Figure 2 The overall structure of the present invention is three-dimensional Figure 2 ;

[0019] Figure 3 It is a schematic diagram of the structure of the hub and blades in the present invention;

[0020] Figure 4 It is a schematic diagram of a part of the structure at the leading edge of the blade in the present invention;

[0021] Figure 5 It is a schematic diagram of a part of the structure at the trailing edge of the blade in the present invention;

[0022] Figure 6 It is a side view of the overall structure of the present invention;

[0023] Figure 7 for Figure 6 Enlarged view of part A. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the accompanying drawings.

[0025] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, the present invention is an axial flow fan with high efficiency and noise reduction, comprising a fan casing 1, a protective net assembly, a hub 9 and blades 10; the fan casing 1 is cylindrical, and a bracket assembly is provided at the bottom of the fan casing 1, the bracket assembly is composed of a fan bracket 1 4 and a fan bracket 2 5 which are symmetrically and spaced apart, the fan bracket 1 4 and the fan bracket 2 5 are both fixed to the bottom of the fan casing 1, and the symmetrical arrangement of the fan bracket 1 4 and the fan bracket 2 5 ensures the uniformity of the force on the bracket assembly, thereby ensuring the smooth operation of the fan; the hub 9 is located in the fan casing 1, is coaxially arranged with the fan casing 1, and is driven to rotate by a motor 6, and the motor 6 is controlled by a controller, and a plurality of blades 10 uniformly distributed in the circumferential direction are fixed on the hub 9; a plurality of slits arranged equally apart are provided at the leading edge of the blade 10, and a plurality of slits arranged equally apart are provided at the trailing edge A plurality of serrations are provided in the middle, and the slits and serrations pass through the blade 10; serrations are provided in the middle of the trailing edge of the blade 10, and no serrations are provided near the tip and the root of the blade. This design allows the effective working area of ​​the blade to remain relatively large, thereby ensuring the performance of the fan while reducing noise; a protective net assembly is provided at the inlet of the fan casing 1, and the protective net assembly consists of a protective net 1 2 and a protective net 2 3, and both the protective net 1 2 and the protective net 2 3 are circular and are arranged coaxially with the fan casing 1, the outer edge of the protective net 1 2 is fixed to the inner wall of the fan casing 1, and the protective net 2 3 is fixed to the protective net 1 2; a plurality of hole groups arranged equidistantly along the circumferential direction are provided on the fan casing 1 at a position aligned with the rotating circumferential surface of the blade, and the hole group consists of a plurality of circular holes arranged equidistantly along the circumferential direction; the circular holes pass through the fan casing.

[0026] Wherein, assuming that the width of the slit is w, the depth is h, and the spacing between adjacent slits is d, a better noise reduction effect can be achieved when d / w=5. In addition, the tooth height s and tooth width λ of the sawtooth can be adjusted to achieve a more ideal noise reduction effect; in this embodiment, the width w of the slit is 2mm, the depth h is 20mm, the spacing d between adjacent slits is 10mm, the total length of the sawtooth section formed by all the sawtooths at the trailing edge of the blade 10 is 60mm, and the distances from the tip and root of the trailing edge of the blade are 61mm and 68mm respectively, the tooth height s of the sawtooth is 6mm, and the tooth width λ is 6mm; the diameter D of the circular hole is 3mm.

[0027] As a preferred embodiment, the shell of the motor 6 is fixed on a horizontally arranged motor support 7, both ends of the motor support 7 are fixed to the inner wall of the fan casing 1, and the upper and lower ends of the vertically arranged motor support 2 8 are respectively fixed to the center position of the motor support 7 and the inner wall of the fan casing 1. The motor support 1 7 and the motor support 2 8 are conducive to the smooth operation of the motor 6, reduce jitter, and reduce the noise generated when the motor 6 is working.

[0028] As a preferred embodiment, the protective net 1 2 is composed of a plurality of vertical protective rods arranged equidistantly, and both ends of the vertical protective rods are fixed to the inner wall of the fan casing 1. The protective net 2 3 is composed of a plurality of circular protective rods arranged in concentric circles, and each circular protective rod is fixed to the cylindrical surface of each vertical protective rod at its own circumferential covering position.

[0029] As a preferred embodiment, the wheel hub 9 is provided with a plurality of annular grooves arranged in concentric circles to reduce the weight of the wheel hub 9 .

[0030] As a preferred embodiment, the tips of the leading and trailing edges of the blades are both chamfered by 2 mm. The rounded corners can guide the airflow more smoothly and make the airflow flow more smoothly on the blade surface.

[0031] The present invention provides a working method of an axial flow fan with high efficiency and noise reduction, which is specifically as follows:

[0032] The controller controls the motor 6 to drive the hub 9 to drive the blades 10 to rotate, so that the gas is sucked in from the inlet of the fan housing 1 and discharged from the outlet; during the rotation of each blade 10, the turbulent flow at both ends of each slit interacts with each other to generate two sound sources, such as Figure 4As shown, since the slit depth is h, the wavelength difference between the two sound sources during propagation is h, and h is designed to make fh / u=(2n-1) / 2, where n is a positive integer, f is the sound source frequency, and u is the speed of sound. The phase difference 2πfh / u between the two sound sources is an odd multiple of π, which causes the two sound sources to interfere and destroy each other in phase and cancel each other out, thereby reducing the incoming turbulent noise generated at the leading edge of the blade; in addition, the tip gap vortex formed in the gap between the blade tip and the fan casing interacts with the slit during flow and is weakened, thereby reducing the flow loss and noise caused by the tip gap vortex. Although the slits at the leading edge of the blade reduce the incoming turbulent noise generated by the interaction of turbulent flows, the turbulent boundary layer is increased, which increases the broadband noise generated by the vortex convection (scattering) through the trailing edge of the blade. The serrations on the trailing edge of the blade of the present invention reduce the convection speed of the turbulent vortex along the serrations, thereby weakening the sound scattering and reducing the noise generated by the turbulent boundary layer at the trailing edge of the blade. In addition, the serrated trailing edge of the blade splits the large-scale vortex into small-scale vortices by strengthening turbulent mixing, thereby improving the spanwise distribution of the vortex, reducing the spanwise dimension of the wake vortex, making the wake vortex distribution more uniform, and further reducing the noise at the trailing edge of the blade. In addition, during the rotation of each blade 10, since a hole group is opened at a position on the fan housing 1 that is aligned with the rotating circumferential surface of each blade, a pressure difference is generated in the gap between the blade tip at the trailing edge of each blade and the fan housing. The pressure difference destroys the secondary flow formed in the gap between the blade tip at the trailing edge of the blade and the fan housing, further reducing the flow loss and noise caused by the tip gap vortex, thereby improving the aeroacoustic performance of the fan without reducing the aerodynamic performance of the fan.

Claims

1. An axial flow fan with high efficiency and noise reduction, comprising a fan casing, a protective net assembly, a hub and blades, the fan casing is cylindrical, and a bracket assembly is fixed to the bottom of the fan casing, the hub is located in the fan casing, coaxially arranged with the fan casing, and driven to rotate by a motor, and the motor is controlled by a controller, a plurality of blades uniformly distributed along the circumferential direction are fixed on the hub, and a protective net assembly is fixed to the inlet of the fan casing, characterized in that: The leading edge of the blade is provided with a plurality of equidistantly arranged slits, the middle portion of the trailing edge is provided with a plurality of serrations, and both the slits and serrations penetrate the blade; the fan housing is provided with a plurality of equidistantly arranged hole groups at a position aligned with the rotating circumferential surface of the blade, the hole groups are composed of a plurality of equidistantly arranged circular holes; the circular holes penetrate the fan housing.

2. The axial flow fan with high efficiency and noise reduction according to claim 1, characterized in that: The support assembly consists of a fan support 1 and a fan support 2 which are symmetrically arranged at a distance, and the fan support 1 and the fan support 2 are both fixed to the bottom of the fan housing.

3. The axial flow fan with high efficiency and noise reduction according to claim 1, characterized in that: The motor housing is fixed on a horizontally arranged motor support 1, both ends of which are fixed to the inner wall of the fan housing, and the upper and lower ends of the vertically arranged motor support 2 are respectively fixed to the center position of the motor support 1 and the inner wall of the fan housing.

4. The axial flow fan with high efficiency and noise reduction according to claim 1, characterized in that: The protective net assembly consists of a protective net one and a protective net two, and both protective net one and protective net two are circular and arranged coaxially with the fan housing. The outer edge of protective net one is fixed to the inner wall of the fan housing, and protective net two is fixed on protective net one.

5. The axial flow fan with high efficiency and noise reduction according to claim 4, characterized in that: The protective net 1 is composed of multiple vertical protective rods arranged at equal intervals, and both ends of the vertical protective rods are fixed to the inner wall of the fan casing. The protective net 2 is composed of multiple circular protective rods arranged in concentric circles, and each circular protective rod is fixed to the cylindrical surface of each vertical protective rod at its own circumferential covering position.

6. The axial flow fan with high efficiency and noise reduction according to claim 1, characterized in that: The wheel hub is provided with a plurality of annular grooves arranged in concentric circles.

7. The axial flow fan with high efficiency and noise reduction according to claim 1, characterized in that: The blade tips of the leading edge and the trailing edge of the blade are both rounded.

8. A method for operating an axial flow fan with high efficiency and noise reduction according to any one of claims 1 to 7, characterized in that: The details are as follows: The controller controls the motor to drive the hub to drive each blade to rotate, sucking the gas from the inlet of the fan housing and discharging it from the outlet; during the rotation of each blade, the incoming turbulence at both ends of each slit interacts with each other to generate two sound sources, and fh / u=(2n-1) / 2 is designed, where n is a positive integer, f is the sound source frequency, u is the speed of sound, and the wavelength difference between the two sound sources during propagation is h. Then the phase difference 2πfh / u of the two sound sources is an odd multiple of π, so that the two sound sources interfere and destroy each other in phase and cancel each other out, thereby reducing the incoming turbulence noise generated at the leading edge of the blade; in addition, the tip gap vortex formed in the gap between the blade tip and the fan housing is weakened when interacting with the slit during flow, thereby reducing the flow loss and noise caused by the tip gap vortex; At the same time, the serrations on the trailing edge of the blade reduce the convection velocity of the turbulent eddy along the serration edge and weaken the sound scattering, thereby reducing the noise generated by the turbulent boundary layer at the trailing edge of the blade. The serrated trailing edge of the blade splits the large-scale vortex into small-scale vortices by strengthening turbulent mixing, thereby improving the spanwise distribution of the vortex, reducing the spanwise dimension of the wake vortex, making the wake vortex distribution more uniform, and further reducing the noise at the trailing edge of the blade. In addition, during the rotation of each blade, since a hole group is provided on the fan casing at a position aligned with the rotating circumferential surface of each blade, a pressure difference is generated in the gap between the blade tip and the fan casing at the trailing edge of each blade. The pressure difference destroys the secondary flow formed in the gap between the blade tip and the fan casing at the trailing edge of the blade, thereby further reducing the flow loss and noise caused by the tip gap vortex.

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