A low-noise casing for an axial flow fan and its design method

Abstract

This invention provides a low-noise casing for an axial flow fan and its design method, comprising an outer casing and an inner casing arranged coaxially. The outer casing has a double-layer resonant structure, including an outer cylinder plate and an inner cylinder plate. The outer and inner cylinder plates are divided into multiple resonant cavities by a supporting frame, and the supporting frame has de-weighting holes. Each resonant cavity corresponding to the inner casing has multiple perforations on its inner cylinder plate, while the resonant cavity corresponding to the impeller installed at the front end of the inner casing has no perforations on its inner cylinder plate. Multiple rear guide vanes are installed between the outer and inner casings, and the rear guide vanes are single-arc blades. The fan casing of this invention uses a double-layer casing structure, without filling with sound-absorbing material, and only utilizes the resonant cavities to eliminate narrowband noise of specific frequencies, thereby achieving a significant reduction in casing radiated noise; at the same time, it provides excellent support for noise reduction in the downstream ductwork.

Description

Technical Field

[0001] This invention belongs to the field of fans, and relates to the housing of axial flow fans, specifically to a low-noise housing for axial flow fans and its design method. Background Technology

[0002] Judging from the physical characteristics of sound, all sounds with irregular variations in intensity and frequency can be defined as noise. Noise can cause hearing damage, illness, and disrupt daily life. In the workplace, noise reduces productivity. Even worse, high-intensity noise can damage buildings or facilities.

[0003] As a type of power equipment, fans are high-noise sources. Because many mobile equipment (such as locomotives, ships, and aircraft) have strict limitations on the size and weight of their loaded equipment, noise control of fans becomes even more challenging. Fans can be classified into axial flow and centrifugal types based on their structural forms. For axial flow fans, while optimizing blade profiles is one way to reduce noise, this approach has limitations when considering fan performance. However, incorporating noise insulation and absorption measures into the design of stator components such as the casing can achieve more significant noise reduction and is also easier to implement. Simultaneously, strict control over the size and weight of components is crucial for noise reduction; therefore, the invention of a lightweight, low-noise axial flow fan has become an urgent problem to be solved under these specific requirements.

[0004] Axial flow fans typically have a single-layer cylindrical casing. To meet low-noise requirements, the casing is usually made of thick sheet metal rolled and welded, or a cast casing, which offers better noise reduction. However, for lightweight mobile equipment, simply relying on thick casing walls for sound insulation is clearly insufficient.

[0005] The use of double-layer shells in low-noise fans is a common approach. Based on existing technologies, the principles can be divided into two main categories: one is to use a double-layer vacuum shell, which utilizes the principle of vacuum blocking to achieve noise reduction; the other is to use a double-layer resonant cavity with sound-absorbing materials, which utilizes limited resistance silencing combined with the main sound absorption effect to achieve noise reduction.

[0006] To achieve the specified low-noise performance requirements, axial flow fans need sufficiently thick cylindrical casings to provide sound insulation. However, given the strict limitations on dimensions and weight, achieving this sufficient thickness is impossible. While cast casings offer better noise reduction, their production cycle and mold costs are not advantageous. Furthermore, relying solely on wall thickness for noise insulation cannot achieve true noise reduction for the entire system; it only temporarily isolates noise in the fan section. The noise still exists and continues to propagate in the downstream ductwork, which is highly detrimental to overall system noise reduction.

[0007] However, the application of double-layer vacuum shells in small-batch, low-cost axial flow fans is not feasible. For double-layer resonant cavities with sound-absorbing materials, the focus is still on utilizing the sound-absorbing material to achieve noise reduction. However, non-metallic sound-absorbing materials cannot be used in special applications. Furthermore, this type of double-layer resonant cavity with sound-absorbing material requires a high porosity, typically above 25%, to achieve the desired sound absorption effect; therefore, the noise reduction resistance of this double-layer structure is very limited, and its use alone is essentially meaningless. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a low-noise casing for axial flow fans and a design method therefor, thereby solving the technical problem that existing axial flow fan casings, under the constraints of external dimensions and weight, have insufficient noise reduction performance.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] A low-noise casing for an axial flow fan includes an outer casing and an inner casing arranged coaxially. The axial length of the outer casing is greater than the axial length of the inner casing. The rear ends of the outer casing and the rear ends of the inner casing are flush. The inner casing is used to install a motor, and the front end of the inner casing is used to install an impeller driven by the motor.

[0011] The outer cylinder of the casing is a double-layer resonant structure, including an outer cylinder plate and an inner cylinder plate. The outer cylinder plate and the inner cylinder plate are divided into multiple resonant cavities by a support frame. The support frame is provided with de-weighting holes.

[0012] The inner layer plate of each resonant cavity corresponding to the inner cylinder of the casing has multiple perforations, while the inner layer plate of the resonant cavity corresponding to the impeller installed at the front end of the inner cylinder of the casing does not have perforations.

[0013] Multiple rear guide vanes are installed between the outer cylinder and the inner cylinder of the housing, and the rear guide vanes are single circular arc vanes;

[0014] The present invention also has the following technical features:

[0015] The supporting frame includes axial stiffeners and circumferential stiffeners, and both the axial stiffeners and circumferential stiffeners are provided with weight-relief holes.

[0016] The inner cylinder of the casing is also provided with perforations.

[0017] This invention also protects a design method for a low-noise casing of an axial flow fan as described above, the method comprising the following steps:

[0018] Step 1: The outer and inner cylindrical plates of the outer casing are installed on the support frame by thin plate welding, and the support frame is provided with weight-relief holes.

[0019] Step 2: The rear guide vanes are single circular arc blades, and the number of blades evenly distributed around the circumference is calculated through flow field analysis.

[0020] Step 3: Design a lightweight, low-noise casing using a double-layer thin-plate cylindrical structure.

[0021] The average sound insulation value is obtained using the calculation formula described below;

[0022] When m≤200kg / m 2 When R = 13.5logm + 14; when m > 200kg / m 2 At that time, R = 16logm + 8

[0023] In the formula:

[0024] R represents the calculated average sound insulation value, and the unit of average sound insulation is dB;

[0025] m represents the mass per unit area of ​​the cylinder, and the unit of mass per unit area of ​​the cylinder is kg / m³. 2 ;

[0026] Step four: Set the preliminary structural parameters of the low-noise axial flow fan casing for the average sound insulation value. The structural parameters include the resonant cavity length, the outer diameter of the inner cylinder plate, the inner diameter of the inner cylinder plate, the perforation diameter, the thickness of the inner cylinder plate, the perforation rate, and the perforation spacing. Given the vibration damping frequency corresponding to the structural parameters, the calculated noise reduction volume is obtained through resonant cavity noise reduction calculation. The structural parameters are repeatedly adjusted and the corresponding noise reduction volume is calculated to obtain the optimal matching relationship between the structural parameters, the vibration damping frequency, and the noise reduction volume, thus obtaining the structural parameters of the low-noise axial flow fan casing of the preliminary screening typical method.

[0027] Step 5: Manufacture a prototype of the low-noise casing for a typical axial flow fan. Through prototype testing and adjustments, find the optimal matching result.

[0028] Compared with the prior art, the present invention has the following technical effects:

[0029] (I) The outer shell of the fan casing of the present invention adopts a double-layer casing structure, without filling sound-absorbing material, and only uses the resonant cavity to eliminate narrow-band noise of a specific frequency, thereby achieving a significant reduction in casing radiated noise; at the same time, it provides excellent support for noise reduction of the downstream duct.

[0030] (II) The fan casing of this invention utilizes the principle of resonant cavity and employs a resistive resonant cavity noise reduction method. It does not use any non-metallic materials, does not increase system resistance, and greatly reduces noise in the ducts before and after the fan, thereby reducing noise propagation. At the same time, the external dimensions and weight of the fan are strictly controlled.

[0031] (III) The fan casing of the present invention reduces noise through the principle of resonant cavity, which can achieve the goal of greatly reducing noise in a limited space.

[0032] (IV) Under the limitation that the external dimensions of the ventilator must be less than 765mm×700mm×630mm and the weight must be less than 210kg, the noise of the ventilator under rated operating conditions shall not exceed 76 decibels. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the overall structure of the low-noise casing of the axial flow fan of the present invention.

[0034] Figure 2 This is a schematic diagram of the internal structure of the low-noise casing of the axial flow fan of the present invention.

[0035] Figure 3 This is a schematic diagram of the resonant cavity structure of the present invention.

[0036] Figure 4 This is a schematic diagram of the supporting rib frame of the present invention.

[0037] Figure 5 This is a schematic diagram of the distribution of the rear guide vanes.

[0038] Figure 6 This is a schematic diagram of the flow field analysis for the rear guide vanes.

[0039] Figure 7 The diagram shows the radiated noise characteristics of the casing for method one.

[0040] Figure 8 The diagram shows the radiated noise characteristics of the casing for method one.

[0041] Figure 9 The diagram shows the radiated noise characteristics of the casing pipe inlet and outlet for Method 1. The upper layer of the diagram represents the pipe inlet, and the lower layer represents the pipe outlet.

[0042] Figure 10 The diagram shows the radiated noise characteristics of the casing pipe inlet and outlet for Method 2. The upper layer of the diagram represents the pipe inlet, and the lower layer represents the pipe outlet.

[0043] The meanings of the labels in the diagram are as follows: 1-outer casing cylinder, 2-inner casing cylinder, 3-motor, 4-impeller, 5-perforation, 6-rear guide vane;

[0044] 101-Outer cylindrical plate, 102-Inner cylindrical plate, 103-Supporting rib, 104-Resonance cavity, 105-De-weighting hole;

[0045] 10301 - Axial stiffener, 10302 - Circumferential stiffener.

[0046] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0047] Traditional fan casings, limited by their dimensions and weight, cannot achieve the objectives of this invention. It should be noted that this invention is not limited to a single embodiment; by adjusting the matching of the main parameters mentioned in this invention, the objectives can also be achieved. In the development of specific engineering projects, considering factors such as machining accuracy and production costs, appropriately adjusting the area and size of the perforations can serve as alternative solutions.

[0048] The technical requirements to be achieved by this invention are: under the constraints that the external dimensions of the ventilator must be less than 765mm×700mm×630mm and the weight must be less than 210kg, the noise of the ventilator under rated operating conditions must not exceed 76 decibels.

[0049] It should be noted that, unless otherwise specified, all components and materials in this invention are those known in the art.

[0050] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0051] Example 1:

[0052] This embodiment provides a low-noise casing for an axial flow fan, such as... Figures 1 to 5 As shown, it includes an outer casing 1 and an inner casing 2 arranged coaxially. The axial length of the outer casing 1 is greater than the axial length of the inner casing 2. The rear ends of the outer casing 1 and the rear ends of the inner casing 2 are flush. The inner casing 2 is used to install a motor 3. The front end of the inner casing 2 inside the outer casing 1 is used to install an impeller 4 driven by the motor 3.

[0053] The outer cylinder 1 of the casing is a double-layer resonant structure, including an outer cylinder plate 101 and an inner cylinder plate 102. The outer cylinder plate 101 and the inner cylinder plate 102 are divided into multiple resonant cavities 104 by a support frame 103. The support frame 103 is provided with a weight-relief hole 105.

[0054] Multiple perforations 5 are provided on the inner layer plate 102 of each resonant cavity 104 corresponding to the inner cylinder 2 of the casing, and no perforations are provided on the inner layer plate 102 of the resonant cavity 104 corresponding to the impeller 4 installed at the front end of the inner cylinder 2 of the casing.

[0055] Multiple rear guide vanes 6 are installed between the outer casing 1 and the inner casing 2. The rear guide vanes 6 adopt single circular arc blades; while optimizing the flow field, they also provide support.

[0056] As a preferred embodiment, the support frame 103 includes an axial stiffener 10301 and a circumferential stiffener 10302, both of which are provided with weight-reducing holes 105. This perfectly solves the weight reduction problem while ensuring sufficient support strength.

[0057] As a preferred embodiment, the inner cylinder 2 of the housing is also provided with perforations for better noise reduction.

[0058] Example 2:

[0059] This embodiment provides a design method for a low-noise casing of an axial flow fan as in Embodiment 1. The method includes the following steps:

[0060] Step one: The outer and inner cylindrical plates of the outer casing are installed on the support frame using thin-plate welding. The support frame has weight-relief holes. Figure 4 As shown.

[0061] Step two: The rear guide vanes adopt a single circular arc design, and the number of circumferentially distributed vanes is calculated through flow field analysis. The single circular arc design of the rear guide vanes optimizes the flow field while also providing support. The single circular arc guide vanes are easy to manufacture, and the thin plate shape helps reduce weight. The number of circumferentially distributed vanes is calculated through flow field analysis. The distribution diagram of the rear guide vanes and the flow field analysis diagram are shown below. Figure 5 and Figure 6 As shown.

[0062] In this embodiment, the number of rear guide vanes is 17.

[0063] Step 3: Design a lightweight, low-noise casing using a double-layer thin-plate cylindrical structure.

[0064] The average sound insulation value is obtained using the following formula;

[0065] When m≤200kg / m 2 When R = 13.5logm + 14; when m > 200kg / m 2 At that time, R = 16logm + 8

[0066] In the formula:

[0067] R represents the calculated average sound insulation value, and the unit of average sound insulation is dB;

[0068] m represents the mass per unit area of ​​the cylinder, and the unit of mass per unit area of ​​the cylinder is kg / m³. 2 ;

[0069] Step 4: Set the initial structural parameters for the low-noise axial flow fan casing, including the resonant cavity length, inner layer plate outer diameter, inner layer plate inner diameter, perforation diameter, inner layer plate thickness, perforation rate, and perforation spacing. Given the vibration damping frequency corresponding to the structural parameters, calculate the calculated noise reduction through resonant cavity noise reduction calculation. Repeatedly adjust the structural parameters and calculate the corresponding noise reduction to obtain the optimal matching relationship between structural parameters, vibration damping frequency, and noise reduction, thus obtaining the structural parameters for the initially screened typical low-noise axial flow fan casing.

[0070] For example, after comparing multiple design options, four typical preliminary screening methods, as shown in Method 1 to Method 4, were found.

[0071] Method 1: Conventional double-layer cylinder, i.e., without perforations;

[0072] Method 2: Double-layer cylinder, with perforations in the inner layer (single aperture, same spacing);

[0073] Method 3: Double-layer cylinder, with perforations in the inner layer (different hole diameters and spacings);

[0074] Method 4: Double-layer cylinder, with perforated inner layer (single hole diameter, different spacing).

[0075] The results of the resonant cavity noise reduction calculations for the above four different typical methods of preliminary screening using lightweight and low-noise housings are compared in Table 1.

[0076] Table 1. Results of resonant cavity noise reduction calculations for four typical preliminary screening methods.

[0077]

[0078] As shown in Table 1, targeted noise reduction at specific calculated frequency spikes yields significant results. To achieve optimal noise reduction, perforation can be used in the inner layer of the double-layer casing for noise reduction, with single-frequency noise reduction reaching approximately 14-17 dB. Perforation can also be applied to the inner cylinder of the casing, similarly reducing noise spikes at specific frequencies.

[0079] Step 5: Manufacture a prototype of the low-noise casing for a typical axial flow fan. Through prototype testing and adjustments, find the optimal matching result.

[0080] Four different manufacturing methods were used to process the lightweight, low-noise housing. Noise testing was conducted on the prototype assembled from the produced parts, and the 1 / 3 octave band noise characteristics were obtained as follows:

[0081] For example, specific test values ​​for the radiated noise from the fan casing. Figure 7 , Figure 8 As shown in Tables 2 and 3.

[0082] Table 2 Comparison of Resonant Cavity Noise Test Results for Four Typical Preliminary Screening Methods

[0083]

[0084] Depend on Figure 7 , Figure 8 As shown in Table 2, the comparison of the noise reduction effects of the four methods for lightweight, low-noise housings reveals the significant impact of matching the perforation size, plate thickness, and perforation rate (hole spacing) on ​​noise reduction within the effective axial length. The noise reduction results from these different matching relationships perfectly match the expected trends in the calculated results. Therefore, this invention selected method four as the final prototype design scheme. This also demonstrates that this design method can be applied in lightweight, low-noise design and has achieved the expected results.

[0085] Comparison of noise test values ​​for the inlet and outlet pipes of the fan under different conditions in Method 1 and Method 2. Figure 9 , Figure 10 As shown in Table 3.

[0086] Table 3. Comparison of test results of the impact of two typical resonant cavities on pipeline noise.

[0087]

[0088] From such Figure 9 , Figure 10 As can be seen from the noise data of the pipeline inlet and outlet tests shown in Table 3, the noise reduction effect of the lightweight, low-noise casing is good when fed back to the pipeline inlet; the effect is even greater when it is applied to the pipeline outlet. Therefore, it can be concluded that the lightweight, low-noise casing has a huge noise reduction effect on the entire system.

[0089] The prototype using this design method achieved the following technical specifications: the fan's dimensions were 765mm × 600mm × 610mm, and its weight was 207 kg, fully meeting the limitations of dimensions less than 765mm × 700mm × 630mm and weight less than 210 kg. After testing the physical prototype, the fan's noise level under rated operating conditions was 75.82 decibels, meeting the design requirement of not exceeding 76 decibels (see noise data in Method 4). The widespread application of this lightweight, low-noise axial flow fan will have significant energy-saving, cost-reducing, and environmental protection demonstration effects.

[0090] Application example:

[0091] The invention has been tested with a prototype, and its performance has met the design goals, proving that the invention is feasible.

[0092] [Comparison of Key Technical Parameters]

[0093] name unit Target value Measured value flow <![CDATA[m 3 / h]]> 8000 8000 wind pressure Pa 2000 2150 noise dB(A) ≯76 75.8 External dimensions mm 765mm×700mm×630mm 765mm×600mm×610mm weight kg ≤210 207 power kW 7.5 7.5

[0094] Using the design method of this invention, a prototype assembled from different components was designed. Prototype testing verified that the noise level met design requirements. The test results fully demonstrate the effectiveness of this design method. The lightweight, low-noise axial flow fan designed using this method and technology can accomplish weight-limiting and noise-reduction tasks that traditional axial flow fans cannot meet. Especially in mobile equipment with strict size and weight limitations, it can improve the design level of low-noise fans.

Claims

1. A design method for a low-noise housing of an axial flow fan, wherein the low-noise housing of the axial flow fan includes an outer housing cylinder (1) and an inner housing cylinder (2) arranged coaxially, the axial length of the outer housing cylinder (1) is greater than the axial length of the inner housing cylinder (2), the rear end of the outer housing cylinder (1) and the rear end of the inner housing cylinder (2) are flush, the inner housing cylinder (2) is used to install a motor (3), and the front end of the inner housing cylinder (2) inside the outer housing cylinder (1) is used to install an impeller (4) driven by the motor (3), characterized in that: The outer casing (1) is a double-layer resonant structure, including an outer cylindrical plate (101) and an inner cylindrical plate (102). The outer cylindrical plate (101) and the inner cylindrical plate (102) are divided into multiple resonant cavities (104) by a supporting rib frame (103). Multiple perforations (5) are provided on the inner layer plate (102) of each resonant cavity (104) corresponding to the inner cylinder (2) of the casing. No perforations are provided on the inner layer plate (102) of the resonant cavity (104) corresponding to the impeller (4) installed at the front end of the inner cylinder (2) of the casing. Perforations (5) are also provided on the inner cylinder (2) of the casing. Multiple rear guide vanes (6) are installed between the outer casing (1) and the inner casing (2), and the rear guide vanes (6) are single circular arc vanes; The supporting frame (103) includes an axial stiffener (10301) and a circumferential stiffener (10302), and both the axial stiffener (10301) and the circumferential stiffener (10302) are provided with weight-relief holes (105). The method includes the following steps: Step 1: The outer and inner cylindrical plates of the outer casing are installed on the support frame by thin plate welding, and the support frame is provided with weight-relief holes. Step 2: The rear guide vanes are single circular arc blades, and the number of blades evenly distributed around the circumference is calculated through flow field analysis. Step 3: Design a lightweight, low-noise casing using a double-layer thin-plate cylindrical structure. The average sound insulation value is obtained using the calculation formula described below; When m≤200kg / m 2 When R = 13.5logm + 14; when m > 200 kg / m 2 At that time, R = 16logm + 8 In the formula: R represents the calculated average sound insulation value, and the unit of average sound insulation is dB; m represents the mass per unit area of ​​the cylinder, and the unit of mass per unit area of ​​the cylinder is kg / m³. 2 ; Step four: Set the preliminary structural parameters of the low-noise axial flow fan casing for the average sound insulation value. The structural parameters include the resonant cavity length, the outer diameter of the inner cylinder plate, the inner diameter of the inner cylinder plate, the perforation diameter, the thickness of the inner cylinder plate, the perforation rate, and the perforation spacing. Given the vibration damping frequency corresponding to the structural parameters, the calculated noise reduction volume is obtained through resonant cavity noise reduction calculation. The structural parameters are repeatedly adjusted and the corresponding noise reduction volume is calculated to obtain the optimal matching relationship between the structural parameters, the vibration damping frequency, and the noise reduction volume, thus obtaining the structural parameters of the low-noise axial flow fan casing of the preliminary screening typical method. Step 5: Manufacture a prototype of the low-noise casing for a typical axial flow fan. Through prototype testing and adjustments, find the optimal matching result.

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