CN111441996A

CN111441996A - Noise suppression fan

Info

Publication number: CN111441996A
Application number: CN202010265519.8A
Authority: CN
Inventors: 李晓东; 刘宇超; 陈超
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2020-04-07
Filing date: 2020-04-07
Publication date: 2020-07-24
Anticipated expiration: 2040-04-07
Also published as: CN111441996B

Abstract

The present disclosure provides a noise suppression fan, including a rotor and a stator, the rotor being adapted to disturb air and cause the air to flow in a direction of the stator; the stator comprises a plurality of static blades and a stator base, the static blades are uniformly wound on the stator base, and the rotor comprises a plurality of movable blades; the noise suppression fan also comprises a noise suppression device arranged between the rotor and the stator, the noise suppression device comprises metal wire nets with the number equal to that of the static blades, and the noise suppression device is arranged on the complete development section of the wake of the movable blade; in the complete development stage, the difference between the axial velocity of the fluid in the wake core area and the average axial velocity of the non-wake main flow is within 10 percent. The wire mesh is arranged at the complete development section of the wake of the movable blade, so that the generation of noise is effectively inhibited, and the aerodynamic performance of the fan is guaranteed.

Description

Noise suppression fan

Technical Field

The present disclosure relates to the field of cooling fans, and more particularly, to a noise-suppressed fan.

Background

A cooling fan is a commonly used heat dissipation device, which disturbs airflow by a rotating blade and delivers cooling airflow to an electronic device to achieve the purpose of controlling the temperature of an electronic product. The rotation of the cooling fan generates a large amount of noise, and particularly, the aerodynamic noise generated by the cooling fan is more serious for a high-speed, high-flow fan. The reason for this is that the trailing vortex of the fan blade of the high-speed, high-flow fan generates noise when passing through the stationary fan blade. As the airflow passes over the blades, a boundary layer is created at the blade surface, while a viscous wake is created downstream of the blade. The rotor or stator and the upstream wake are in static interference to generate discrete pure-tone noise under the passing frequency and harmonic frequency of the blade; the interaction of the leading or trailing edge of the blade with the incoming flow turbulence and the boundary layer creates turbulent broadband noise. Fan noise is therefore typically a combination of discrete tones and broadband noise.

In the prior art, the noise is generally suppressed by increasing the distance between the rotor and the stator and changing the blade profile or the blade distribution mode of the stator or the rotor. However, by increasing the distance between the rotor and the stator, the effect of reducing the interaction of the potential field between the rotating and stationary blades and the impact of the trailing track of the moving blade on the stator blade is achieved, thereby reducing the fan noise. However, this method, while effective in reducing fan noise, can result in a significant loss in the aerodynamic performance of the fan and the overall pressure ratio. Through modes such as circumferential and axial inclined stator blades and irregular stator blade spacing, the phase distribution of static interference can be changed, so that the pulsating aerodynamic force of a sound source is mutually offset, and the passing frequency noise of the blades radiated in a far field is reduced. The aerodynamic performance and pressure efficiency of the fan are also reduced by such methods. The blade design modes such as the inclined rotor blade, the sweep-type movable blade, the irregular movable blade interval and the blade design mode of installing the sawteeth on the front edge of the axial flow fan blade can obviously reduce the high-frequency broadband noise of the fan, but the suppression effect on the rotating and static interference noise is poor. The above methods all fail to ensure the aerodynamic performance of the fan and effectively suppress the noise of the fan.

Disclosure of Invention

To address the problem of cooling fan discrete tone and broadband noise combinations and to ensure aerodynamic performance of the cooling fan, the present disclosure provides

The method is realized by adopting the following scheme:

a noise suppression fan comprising a rotor and a stator, the rotor adapted to disturb air and cause the air to flow in a direction of the stator; the stator comprises a plurality of static blades and a stator base, the static blades are uniformly wound on the stator base, and the rotor comprises a plurality of movable blades; the noise suppression fan further comprises a noise suppression device arranged between the rotor and the stator, the noise suppression device comprises wire meshes with the same number as the static blades, and the noise suppression device is arranged on a complete development section of a wake of the movable blade; in the complete development stage, the difference between the axial velocity of the fluid in the wake core area and the average axial velocity of the non-wake main flow is within 10 percent.

Further, a distance of the wire mesh from a leading edge of the stationary blade is greater than a mesh pitch of 15 wire meshes.

Further, the perforation rate of the metal wire mesh is 50% -60%.

Further, the wire mesh is composed of wires with the diameter of 0.1mm-0.2 mm.

The noise suppression fan further comprises a movable blade casing and a static blade casing, wherein a first cavity for accommodating the rotor is formed in the movable blade casing, a second cavity for accommodating the stator is formed in the static blade casing, and the movable blade casing and the static blade casing are coaxial and are attached to each other.

Furthermore, the sum of the areas of the plurality of the metal wire meshes is 15-30% of the area of the flow passage.

Further, the stationary blade comprises a pressure surface and a suction surface, and the wire mesh is positioned on one side of the suction surface.

Further, the wire mesh is spaced from the leading edge of the stationary blade by a mesh pitch of 70 to 150 wire meshes.

The stator is disposed coaxially with the rotor, the leading edge of the stationary blade has a gap from the front end surface of the stator base, and the trailing edge of the rotor blade has a gap from the rear end surface of the rotor base.

According to the fan noise reduction device, the wire mesh is arranged on the wake of the movable blade, so that a large-scale vortex system in the wake after airflow flows through the movable blade is broken into small-scale vortices, the static interference noise generated by the interference of the viscous wake of the blade and the downstream blade is reduced, and the fan noise is reduced. Meanwhile, the airflow passes through the metal wire mesh to cause certain pressure drop, and the overhigh pressure drop is unacceptable for the fan, so the arrangement position of the metal wire mesh of the invention needs to be at the complete development section of the tail trace of the movable blade as much as possible, the speed loss in the tail trace is very small at the moment, the speed profile of the blade profile is more uniform, and the phenomenon that the metal wire mesh and the airflow form a larger speed difference after the action due to the uneven speed of the fluid in front of the mesh is avoided, so that the turbulence intensity caused by the enhancement of the shearing action is increased.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and together with the description serve to explain the principles of the disclosure.

FIG. 1 is an overall schematic view of a noise-abatement fan of the present disclosure without a casing;

FIG. 2 is a side view of FIG. 1;

FIG. 3 is a plot of a wake velocity model of a noise suppression fan;

FIG. 4 is a graph of turbulence intensity versus distance for a noise suppression fan;

FIG. 5 is a schematic view of parameters of the metal screen of FIG. 1;

FIG. 6 is a schematic diagram showing the variation of f (Re) with Re;

FIG. 7 is an overall schematic view of a noise suppression fan including a case according to the present disclosure;

FIG. 8 is a vane casing schematic view of the noise-abatement fan of FIG. 7;

FIG. 9 is a schematic view showing a mounting position of the wire-net between the rotors and the stator of FIG. 1;

fig. 10 is a schematic diagram of a microphone placement test of a noise suppression fan.

1. A rotor; 2. a noise suppression device; 21. a wire mesh; 22. a wire mesh base; 3. a stator; 31. a stationary blade; 311. a pressure surface; 312. a suction surface; 32. a stator base; 4. a movable vane casing; 5. a stationary blade casing; 51. a stationary blade casing housing; 52. a fixed part.

Detailed Description

The present disclosure will be described in further detail with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the present disclosure. It should be further noted that, for the convenience of description, only the portions relevant to the present disclosure are shown in the drawings.

It should be noted that the embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict. The present disclosure will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

Referring to the specification and the drawings of fig. 1, the present disclosure provides a noise suppression fan including a rotor 1 and a stator 3. The rotor 1 of the fan includes a plurality of blades, and the stator 3 of the fan includes a plurality of vanes, and in the present disclosure, it is preferable that the number of blades is smaller than the number of vanes, and in consideration of a cooling flow rate and a flow rectification effect required by the fan, it is preferable that the rotor 1 of the fan includes 5 blades and the stator 3 of the fan includes 9 vanes. The rotor 1 is adapted to disturb the air and to cause the air to flow in the direction of the stator 3. The stator 3 further comprises a stator base 32, and the stator blades 31 are uniformly wound on the stator base 32. The stator 3 is disposed coaxially with the rotor 1, the leading edge of the stationary blade 31 is spaced from the front end surface of the stator base 32 (fig. 2), and the trailing edge of the rotor blade is spaced from the rear end surface of the rotor base. In this case, even when the rotor 1 and the stator 3 are mounted in close proximity to each other, the mounting space of the noise suppressor 2 can be made free. The noise suppression device 2 is disposed between the rotor 1 and the stator 3, and the noise suppression device 2 includes the same number of wire meshes 21 as the number of the stationary blades 31, and it is preferable that the number of the wire meshes 21 is 9 in the present disclosure. The wire mesh 21 may be connected as a unified whole by a mesh base 22 as shown in fig. 1. The wire mesh base 22 is formed in a circular ring shape, and a plurality of the wire meshes 21 are connected from the inner side of the circular ring or from the outer side of the circular ring. It is of course also possible to provide the wire meshes 21 in a spaced-apart manner, with one wire mesh base 22 being associated with each wire mesh 21, and with the stator 3 or the vane casing 5 being connected by the wire mesh base 22.

When the rotor 1 rotates, the moving blades disturb the flow of the air toward the stationary blades 31. The discrete tone noise caused by fan spin-quiet interference is a significant proportion of the total noise energy. After the airflow passes through the fan blades, a viscous wake is formed downstream of the moving blades. The larger scale vortices in the rotor blade wake carry more energy and generate more noise when interacting with the downstream stator blades 31. After the moving blade, a wire mesh 21 is arranged, the viscous wake interacts with the wire, and the large scale vortex is broken into small scale vortices. When the vortex dimensions are small enough and the local deformation ratio is large enough, the viscosity can dissipate turbulent flow energy. However, the air flow through the wire mesh 21 causes a certain pressure drop, and an excessively high pressure drop is not acceptable for the fan, so that it is necessary to reduce the turbulence intensity to the maximum extent and thus the rotational interference noise at the lowest possible pressure drop.

The wake is a free shear motion and the rotating blade wake is strongly three-dimensional. As the fluid flows through the blades, a separation zone is formed at the rear of the blades to generate wake loss. Referring to FIG. 3, the wake is characterized by a central flow velocity less than the peripheral flow velocity and a wake width that increases with flow direction. In the figure, t is the blade pitch, Uc is the mainstream region velocity, Um is the velocity deficit region minimum velocity, and U1m is the velocity maximum deficit and is the wake half width. According to the wake shown by the dotted line in fig. 3, the farther the wake is from the rotor blade, the smaller the velocity loss of the changing wake per unit length. Therefore, the arrangement position of the metal wire mesh 21 needs to be at the complete development section of the moving blade wake as far as possible, the velocity loss in the wake is small, the velocity profile of the blade profile is uniform, and the phenomenon that the metal wire mesh 21 and the air flow form a large velocity difference after acting due to the non-uniform velocity of the fluid in front of the mesh, so that the turbulence intensity is increased due to the enhancement of the shearing action is avoided. In the complete development stage, the difference between the axial velocity of the fluid in the wake core area and the average axial velocity of the non-wake main flow is within 10 percent.

Referring to fig. 4, the turbulence intensity is shown as a function of the relative axial distance before and after the air flow passes through the wire mesh 21, Ures/U represents the turbulence intensity, M is the mesh pitch of the wire mesh 21, the position where x/M is 0 on the abscissa is the axial position of the cross section where the wire mesh 21 is located in the flow channel, and a represents the initial turbulence intensity. As can be seen, the turbulence intensity decreases as the air flow approaches the area of the wire 21 due to the contraction effect and redistribution of the pressure in front of the wire; the turbulence intensity then increases sharply as the flow continues to approach the wire mesh 21, mainly due to shedding vortices of large intensity but small vortex size that are generated when the air flow passes over the wire; then, the intensity is rapidly attenuated, and after 15-25 meshes of the wire mesh 21 are arranged, the turbulence intensity is lower than the initial intensity due to the dissipation effect; the rate of decrease of the turbulence intensity with distance thereafter tends to be flat. Therefore, the distance of the wire mesh 21 from the leading edge of the stationary blade is larger than the mesh pitch of 15 wire meshes 21.

Referring to fig. 5, the wire diameter, the perforation rate, and the arrangement position of the wire net 21 are selected to have an important role in reducing the influence of the narrow-band noise and the fan performance due to the rotating-static interference, the main parameters of the wire net 21 include the wire diameter d, the mesh pitch L, and the perforation rate σ, wherein the calculation formula of the perforation rate is shown in the formula (1).

Through experiments of interaction of a large number of screens with different scales and incoming flow airflow, an expression that the static pressure drop coefficient K after the incoming flow turbulence flows through the wire mesh 21 is related to the Reynolds number and the perforation rate sigma of the wire mesh 21 is obtained, and the expression is shown in formula (2).

Re_dThe expression is formula (3), wherein U is goldThe flow velocity before the wire mesh belongs to, d is the diameter of the wire mesh, and v is the air movement viscosity.

f(Re_d) Is an empirical formula, as shown in FIG. 6, f (Re)_d) Decreasing with increasing Re. As can be seen from the formula (2) and fig. 6, the larger Re is, the larger the perforation σ is, and the smaller the pressure drop coefficient is, the smaller the influence on the aerodynamic performance of the fan is. It can be seen that one of the parameters in Re increases the wire diameter d, and Re also increases. However, too high a wire diameter results in increased vortex shedding noise after the air flow passes through the wire mesh. In addition, too high a perforation ratio pair also reduces the noise reduction effect of the wire mesh. The diameter of the metal wire mesh is about 0.1mm-0.2mm, the perforation rate is about 50% -60%, the corresponding Reynolds number of the fan under the working condition is more than 40, and the static pressure loss is small.

Because the wire mesh 21 has a certain deformation rate under the impact of the high-speed incoming flow, in order to avoid the decrease of the turbulence intensity caused by the narrowing of the distance between the wire mesh 21 and the front edge of the stationary blade under the working condition, a certain reserved distance needs to be ensured. The preferred distance is a mesh spacing of 70-150 wires. Specifically, the diameter of the metal wire mesh is 0.1mm-0.2mm, the distance between the metal wire mesh 21 and the front edge of the static blade 31 is 50 mm-100 mm, and the intensity and the scale of the turbulence behind the net are ensured to be low enough under the condition that the loss of the speed of the wake of the moving blade in front of the net is ensured to be low enough.

Referring to fig. 7, the noise reduction fan further includes a blade casing 4 and a vane casing 5. A first cavity for accommodating the rotor 1 is formed in the movable blade casing 4, a second cavity for accommodating the stator 3 is formed in the stationary blade casing 5, the movable blade casing 4 and the stationary blade casing 5 are coaxially and closely attached to each other, and the first cavity and the second cavity are preferably equal in shape and size. The first casing and the second casing are perpendicular to the section plane of the casing axis, and the projection area of the cavity is the flow passage area. In order to reduce noise as much as possible and ensure the aerodynamic performance of the fan, the sum of the areas of the plurality of wire meshes 21 is 15-30% of the area of the flow passage.

Referring to fig. 8, the vane casing 5 includes a vane casing housing 51 and a fixing portion 52 provided inside the vane casing 5 for fixing the noise suppressing device 2, specifically, the fixing portion is connected to the mesh base 22, and the fixing portion 52 may be a ring or a sleeve smaller than the vane casing housing 51.

Referring to fig. 9, the wire mesh 21 is provided to limit noise generated when a wake vortex of the high flow rate fan passes through the fan stationary blades 31, so that the wire mesh 21 needs to cover the leading edges of the stationary blades 31 as much as possible, but the area of the wire mesh 21 needs to be appropriately reduced to ensure an effective flow cross section. The stationary blade 31 includes a pressure surface 311 and a suction surface 312. Based on the rotation direction of the fan, the interference effect of the tail of the movable blade and the suction surface is more obvious, and the pressure fluctuation of the suction surface close to the front edge is larger. Therefore, the wire mesh 21 is positioned on the suction surface 311 side, which can ensure noise reduction and has a large effective flow cross section.

In order to evaluate the noise reduction effect and the flow loss of the present disclosure, experimental comparisons were made for a reference fan and a fan using the inter-rotating-and-stationary wire net 21. The fan measures flow in the backpressure-flow pipeline through a pitot tube, and the working condition of the fan is controlled through a throttle valve at the rear part of the pipeline. The fan sound field is measured in a fully muffled room. The distance between the fan outlet and the microphone is 2m, the total number of the measuring points is 5, the distance between every two adjacent measuring points is 30 degrees, and the schematic diagram of the measuring points is shown in the attached figure 10.

The wire mesh 21 occupies a small flow channel space between the rotor and the stator, and is only 20% of the total flow channel area, the adopted wire mesh 21 is preferably a supercritical screen, and the static pressure loss is low. The flow of the fan in the pipeline is measured through the pitot tube, and compared with an original fan, the flow of the fan after the wire mesh 21 between the rotor and the stator is adopted, the flow loss is about 2-3%. The total sound power level is reduced by 1.5-2 dBA. For the test point No. 1, namely the microphone facing the outlet of the fan, the frequency spectrums of the fan after the reference fan and the wire mesh 21 between the rotors and the stators are all greatly reduced in amplitude at the frequency of 3, 4 and 5 orders. It can be known that the technical scheme of the present disclosure can control the flow loss to be small and achieve the technical effect of order frequency noise reduction.

In the description herein, reference to the description of the terms "one embodiment/mode," "some embodiments/modes," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/mode or example is included in at least one embodiment/mode or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to be the same embodiment/mode or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/aspects or examples and features of the various embodiments/aspects or examples described in this specification can be combined and combined by one skilled in the art without conflicting therewith.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

It will be understood by those skilled in the art that the foregoing embodiments are merely for clarity of illustration of the disclosure and are not intended to limit the scope of the disclosure. Other variations or modifications may occur to those skilled in the art, based on the foregoing disclosure, and are still within the scope of the present disclosure.

Claims

1. A noise suppression fan comprising a rotor and a stator, the rotor adapted to disturb air and cause the air to flow in a direction of the stator; the stator comprises a plurality of static blades and a stator base, the static blades are uniformly wound on the stator base, and the rotor comprises a plurality of movable blades; the method is characterized in that: the noise suppression device comprises wire meshes with the number equal to that of the static blades, and is arranged on a complete development section of a wake of the movable blade; in the full development section, the difference between the axial flow velocity of the wake central fluid and the axial flow velocity of the wake main fluid is within 10%.

2. A noise suppressing fan as defined in claim 1, wherein: the distance between the wire mesh and the leading edge of the stationary blade is greater than the mesh pitch of 15 wire meshes.

3. A noise suppressing fan as defined in claim 1, wherein: the perforation rate of the metal wire mesh is 50% -60%.

4. A noise suppressing fan as defined in claim 3, wherein: the metal wire mesh is composed of metal wires with the diameter of 0.1mm-0.2 mm.

5. A noise suppressing fan as defined in claim 4, wherein: the distance between the metal wire mesh and the front edge of the stationary blade is 50-100 mm.

6. A noise suppressing fan as defined in claim 3, wherein: the wire mesh is spaced from the leading edge of the stationary blade by a mesh spacing of 70-150 wire meshes.

7. A noise suppressing fan as defined in any one of claims 1-6, wherein: the noise suppression fan further comprises a movable blade casing and a fixed blade casing, a first cavity for accommodating the rotor is formed in the movable blade casing, a second cavity for accommodating the stator is formed in the fixed blade casing, and the movable blade casing and the fixed blade casing are coaxial and are attached to each other.

8. A noise suppressing fan as defined in claim 7, wherein: the sum of the areas of the plurality of the metal wire meshes is 15-30% of the area of the flow passage.

9. A noise suppressing fan as defined in any one of claims 1-6, wherein: the stator blade comprises a pressure surface and a suction surface, and the metal wire mesh is positioned on one side of the suction surface.

10. A noise suppressing fan as defined in any one of claims 1-6, wherein: the stator and the rotor are coaxially arranged, a gap is formed between the front edge of the static blade and the front end face of the stator base, and a gap is formed between the rear edge of the moving blade and the rear end face of the rotor base.