Acoustic liner structure for noise reduction of centrifugal fan and centrifugal fan

Abstract

The invention relates to the technical field of noise reduction equipment for centrifugal fans, in particular to an acoustic liner structure for noise reduction of a centrifugal fan and the centrifugal fan. The acoustic liner structure for noise reduction of the centrifugal fan mainly comprises an inlet noise reduction element and an outlet noise reduction element. The inlet noise reduction element is based on an annular supporting plate, the same side of the inlet noise reduction element is sequentially, coaxially and fixedly connected with an air inlet annular perforated plate and an air inlet annular sealing plate from inside to outside, an air inlet clamping cavity is defined by the inlet noise reduction element, the air inlet annular perforated plate and the air inlet annular sealing plate, and the inner wall face of the air inlet annular perforated plate directly forms a part of an air inlet pipeline of the centrifugal fan. The core of the outlet noise reduction element is an air outlet annular perforated plate, an inner ring and an outer ring are coaxially arranged on the same side face of the air outlet annular perforated plate from inside to outside, the inner ring, the outer ring and the inner ring are clamped to form an air outlet clamping cavity, the other side face of the perforated plate serves as a component of an air outlet pipeline of the centrifugal fan, and the noise reduction structure and an airflow channel of the fan are integrally matched. The noise generated when the centrifugal fan works can be effectively reduced.

Description

Technical Field

[0001] This invention relates to the technical field of centrifugal fan noise reduction equipment, specifically to a sound liner structure and a centrifugal fan for noise reduction. Background Technology

[0002] Centrifugal fans, widely used in industrial production, building ventilation, aerospace ground support, and other fields, function primarily to transport and pressurize airflow through impeller rotation, playing an indispensable role in various fluid power systems. With the trend towards miniaturization and noise reduction in industrial equipment, noise control of centrifugal fans is receiving increasing attention from the industry.

[0003] To address the aerodynamic noise problem of centrifugal fans, the industry has developed various noise reduction technologies. Traditional methods include adding soundproof enclosures to the outside of the fan and installing external silencers on the inlet and outlet pipes. Additionally, some technologies draw on noise reduction experience from aircraft engine nacelles, applying sound-absorbing pad technology based on the Helmholtz principle to fan noise reduction. For example, an array of Helmholtz resonant cavities is installed on the outer wall of the centrifugal fan's inlet and outlet pipes. By using pre-calibrated fixed resonant frequencies, discrete noise from the number of inlet blades multiplied by the rotational frequency and the number of outlet blades multiplied by the rotational frequency is intercepted. Other methods involve attaching small Helmholtz resonant pads to the inner wall of the fan's volute, attempting to address both broadband and discrete noise reduction needs. These solutions have been tested for noise reduction retrofitting of some low-power industrial centrifugal fans.

[0004] While the application of the Helmholtz principle can reduce noise to some extent, it also has many shortcomings. The most obvious is the external or attached installation method, which not only occupies a lot of space, violating the miniaturization design requirements of the equipment, but also, because it is not integrated with the internal airflow channels of the fan, easily induces additional turbulent noise, thus failing to meet the low-noise requirements of industrial scenarios. Summary of the Invention

[0005] To address the technical problem that noise reduction is difficult to achieve while generating additional noise due to the lack of integration of the noise reduction structure with the internal airflow channel of the fan, this invention provides an acoustic liner structure for noise reduction of centrifugal fans and a centrifugal fan.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A sound-absorbing liner structure for noise reduction of centrifugal fans, comprising: The imported noise reduction element includes an annular support plate. On the same side of the support plate, an air inlet annular perforated plate and an air inlet annular closed plate are coaxially fixed from the inside to the outside. An air inlet cavity is formed by clamping the air inlet annular perforated plate, the support plate, and the air inlet annular closed plate. The inner wall surface of the installed air inlet annular perforated plate is coplanar with the inner wall surface of the centrifugal fan air inlet duct. The noise reduction element at the outlet includes an air outlet annular perforated plate. On the same side of the air outlet annular perforated plate, an inner ring and an outer ring are arranged coaxially from the inside to the outside. An air outlet cavity is formed by clamping the inner ring, the air outlet annular perforated plate, and the outer ring. The other side of the air outlet annular perforated plate after installation is coplanar with the inner wall of the centrifuge air outlet duct.

[0007] As a further improvement to the above scheme, reinforcing ribs are arranged in both the air inlet and air outlet cavities.

[0008] As a further improvement to the above scheme: each reinforcing rib is arranged evenly in sequence along the circumference of its location.

[0009] As a further improvement to the above scheme, each reinforcing rib now has two-stage stepped connection holes for fixing.

[0010] As a further improvement to the above solution: the resonant frequency at which the outlet annular perforated plate or the inlet annular perforated plate resonates with the centrifugal fan is: f 0: ; In the formula: Perforation rate is the percentage of the perforated area on the board to the total area of ​​the board. The speed of sound is expressed in m / s. Indicates the depth of the clamping cavity, in meters (m). This indicates the effective neck length of the aperture.

[0011] As a further improvement to the above scheme: the effective neck length is: ; In the formula, For plate thickness, The aperture is indicated by a unit of meters (m).

[0012] As a further improvement to the above solution: both the exhaust annular perforated plate and the inlet annular perforated plate are made of metal plates.

[0013] A centrifugal fan includes a casing, an impeller, an inlet duct, an outlet duct, a drive motor, and an acoustic liner structure. The inlet noise reduction element in the acoustic liner structure is coaxially mounted inside the inlet duct, and the inner surface of the inlet annular perforated plate is coplanar with the inner wall surface of the inlet duct. The outlet noise reduction element in the acoustic liner structure is coaxially sleeved on the outer side of the impeller, and the surface of the outlet annular perforated plate without an outlet cavity is coplanar with the inner wall surface of the outlet duct.

[0014] As a further improvement to the above solution: an air inlet annular cavity is coaxially recessed inside the air inlet duct, and the inlet noise reduction element is installed in the air inlet annular cavity, and the air inlet clamp cavity is connected to the air inlet duct through the installation gap; an air inlet annular cavity is recessed inside the air outlet duct, and the outlet noise reduction element is installed in the air outlet annular cavity, and the air outlet clamp cavity is connected to the air outlet duct through the installation gap.

[0015] As a further improvement to the above scheme: two outlet noise reduction elements are arranged coaxially opposite each other inside the air outlet duct, and the plate surface of the air outlet annular perforated plate without air outlet clamping cavity is coplanar with the inner wall surface of the air outlet duct at its location.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention integrates the inlet and outlet noise reduction elements with the airflow channel in a structural design and installation adaptation: From a structural configuration perspective, the inlet noise reduction element adopts a ring structure, and the inner wall surface of its inlet annular perforated plate directly constitutes part of the centrifugal fan's air inlet duct and is coplanar with the inner wall surface of the air inlet duct. At the same time, the element is coaxially embedded in the pre-set inlet annular cavity of the air inlet duct, allowing the airflow to flow smoothly into the impeller along the inner wall of the air inlet duct-inlet annular perforated plate without causing airflow swirl due to protrusions or misalignments of the noise reduction structure. The outlet noise reduction element's outlet annular perforated plate has a non-cavity plate surface that is coplanar with the inner wall surface of the outlet duct and is coaxially sleeved on the outside of the impeller and embedded in the annular cavity of the outlet duct. The airflow discharged from the impeller can flow smoothly along the inner wall of the outlet duct and the perforated plate surface, avoiding the formation of turbulence by airflow impacting the edge of the noise reduction structure. Furthermore, the inlet cavity of the imported noise reduction element and the outlet cavity of the exported noise reduction element are connected to the pipeline through installation gaps without interfering with the main flow path. The entire element is stably supported by a support plate and reinforcing ribs, preventing structural displacement due to fan vibration and disruption of airflow. At the same time, the perforated plate parameters of the inlet and outlet noise reduction elements are precisely calculated using the Helmholtz resonance frequency formula, based on the discrete noise frequencies (rotation frequency × number of blades) of the fan inlet and outlet. The resonance sound absorption process only dissipates noise energy and does not obstruct the normal airflow. Compared with existing external or attached noise reduction structures, the noise reduction structure of this invention forms an integrated form where "the channel is the noise reduction surface and the noise reduction element is the channel component," fundamentally avoiding airflow disturbance and additional turbulent noise caused by the disconnect between the structure and the channel.

[0017] 2. The perforated plate and the cavity together constitute a resonant sound-absorbing structure based on the Helmholtz principle. Its noise reduction process can be summarized as follows: each small hole on the perforated plate and the cavity (air layer) behind the plate form an independent Helmholtz resonator. The whole structure is equivalent to multiple resonators connected in parallel. When a specific frequency discrete noise (frequency equal to the rotational frequency × number of blades) generated by the centrifugal fan inlet and outlet is incident on this structure, if the sound wave frequency matches the resonant frequency of the resonator, resonance will be excited. At this time, the air column at the neck of the small hole in the perforated plate will undergo violent reciprocating vibration, and its vibration speed... When the intensity and amplitude reach their maximum values, the frictional damping between the air column and the hole wall, as well as the viscous damping of the air itself, also reach their peak values. During the vibration process, a large amount of sound energy is converted into heat energy through friction and consumed. At the same time, the expansion and contraction of the air inside the cavity will further lose sound energy due to heat conduction, thereby achieving precise reduction of aerodynamic noise at specific frequencies at the inlet and outlet of the fan. When the incident sound wave frequency deviates from the resonant frequency, the air column vibrates weakly and the sound energy loss is less. Therefore, this structure can specifically match the discrete noise frequencies at the inlet and outlet of the fan to achieve a highly efficient noise reduction effect. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the internal structure of the centrifugal fan of the present invention.

[0019] Figure 2 This is a front view of the imported noise reduction element in this invention.

[0020] Figure 3 This is a cross-sectional view of the imported noise reduction element in this invention.

[0021] Figure 4 This is a front view of the noise reduction element at the outlet in this invention.

[0022] Figure 5 This is a cross-sectional view of the noise reduction element at the outlet in this invention.

[0023] In the diagram: 10. Imported noise reduction element; 11. Support plate; 12. Inlet annular perforated plate; 13. Inlet annular closed plate; 14. Inlet cavity; 20. Outlet noise reduction element; 21. Outlet annular perforated plate; 22. Inner ring; 23. Outer ring; 24. Outlet cavity; 30. Reinforcing rib; 40. Outer shell; 50. Impeller; 60. Inlet duct; 70. Outlet duct; 80. Drive motor. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] I. Overall Construction of the Sound Liner Structure like Figures 1-5 As shown, the sound liner structure for noise reduction of centrifugal fan in this embodiment is mainly composed of two parts: inlet noise reduction element 10 and outlet noise reduction element 20. Both are designed based on the Helmholtz resonance principle and adopt a perforated plate structure made of metal to ensure structural strength and sound absorption effect. The whole structure is adapted to the limited internal installation space of centrifugal fan.

[0026] 1. Specific structure of imported noise reduction components The imported noise reduction element 10 is a coaxial ring structure. Its core components include a ring-shaped support plate 11, an air inlet ring perforated plate 12, an air inlet ring closed plate 13, and reinforcing ribs 30 in the air inlet cavity 14. All components are coaxially fixed to form an integrated structure.

[0027] The support plate 11 is made of stainless steel annular plate, and its inner diameter is the same as that of the centrifugal fan inlet duct 60. On the same side of the support plate 11, the inlet annular perforated plate 12 and the inlet annular sealing plate 13 are coaxially welded and fixed from the inside to the outside. The inner diameter of the inlet annular perforated plate 12 matches the inner diameter of the inlet duct 60, and its inner wall surface is coplanar with the inner wall surface of the inlet duct 60, directly forming part of the centrifugal fan inlet duct 60. The outer diameter of the inlet annular sealing plate 13 is the same as that of the support plate 11. The three together form a sealed inlet cavity 14, the depth of which is... h 1. It can be adjusted according to the target noise reduction frequency.

[0028] To ensure the structural stability of the air inlet cavity 14, four reinforcing ribs 30 are arranged inside the air inlet cavity 14. Each reinforcing rib 30 is evenly distributed along the circumference of the support plate 11, and the included angle between adjacent reinforcing ribs 30 is 90°. Each reinforcing rib 30 is made of stainless steel, and its two ends are welded to the outer wall of the air inlet annular perforated plate 12 and the inner wall of the air inlet annular closed plate 13, respectively, and its middle part is welded and fixed to the support plate 11.

[0029] Meanwhile, two stepped connection holes are provided in the middle of each reinforcing rib 30. The larger hole is used to accommodate the bolt head, and the smaller hole is used to insert the bolt thread, so as to achieve a stable assembly of the imported noise reduction element 10 and the fan inlet duct 60.

[0030] 2. Specific structure of the noise reduction element at the export location The noise reduction element 20 is an annular structure that is compatible with the imported noise reduction element 10. Its core components include an air outlet annular perforated plate 21, an inner ring 22, an outer ring 23, and reinforcing ribs 30 in the air outlet clamping cavity 24.

[0031] The air outlet annular perforated plate 21 is made of stainless steel. On the same side, an inner ring 22 and an outer ring 23 are coaxially welded from the inside to the outside, and the three rings enclose each other to form an air outlet clamping cavity 24. The depth of the air outlet clamping cavity 24 is... It can be adjusted according to the target noise reduction frequency. The other side of the air outlet annular perforated plate 21 is coplanar with the inner wall of the centrifugal fan outlet duct 70, directly forming part of the outlet duct 70, ensuring smooth airflow.

[0032] Four reinforcing ribs 30 are also arranged inside the air outlet cavity 24. Each reinforcing rib 30 is evenly distributed along the circumference of the air outlet annular perforated plate 21, with an included angle of 90° between adjacent reinforcing ribs 30. Their two ends are welded to the outer wall of the inner ring 22 and the inner wall of the outer ring 23, respectively, and their middle parts are welded to the air outlet annular perforated plate 21. Each reinforcing rib 30 also has two stepped connection holes with the same specifications as the connection holes of the imported noise reduction element 10, for subsequent assembly with the air outlet duct 70.

[0033] II. Parameter Design of Perforated Plates Both the inlet annular perforated plate 12 and the outlet annular perforated plate 21 are metal perforated plates, and their perforation parameters are based on the target resonant frequency. The resonant frequency is determined by calculation using the resonant frequency formula to achieve precise noise reduction of discrete noise at specific frequencies at the inlet and outlet of the centrifugal fan.

[0034] The formula for calculating the resonant frequency of a perforated plate is as follows: ; The effective neck length is: ; In this embodiment, the speed of sound is set. c =340m / s.

[0035] The specific parameters are designed as follows: The inlet annular perforated plate 12 has the known inlet noise frequency of 900Hz, i.e., the target resonant frequency of 900Hz; the inlet clamping cavity 14 has a depth of... =0.025m, thickness of the air inlet annular perforated plate 12 =0.002m, its aperture was determined by calculation. =0.0015m, effective neck length 0.0034m.

[0036] The perforation rate can be calculated by substituting into the formula. To achieve 2.45%, through holes with a diameter of 1.5 mm are evenly opened on the air inlet annular perforated plate 12 to ensure that the perforated area accounts for 2.45% of the total plate area.

[0037] The outlet perforated plate has 21 parameters; the centrifugal fan outlet noise frequency is 1800Hz, which is the target resonant frequency of 1800Hz; and the outlet clamping chamber has a depth of 24. =0.007m, thickness of the outlet annular perforated plate 21 =0.002m, its aperture was determined by calculation. =0.0015m, effective neck length 0.0033m.

[0038] Substituting into the formula, we can obtain the perforation rate. To achieve 2.52%, through holes with a diameter of 1.5 mm are evenly opened on the air outlet annular perforated plate 21 to ensure that the perforated area accounts for 2.52% of the total plate area.

[0039] III. Overall Assembly of Centrifugal Fan with Acoustic Liner Structure like Figure 1 As shown, the centrifugal fan in this embodiment includes a housing 40, an impeller 50, an air inlet duct 60, an air outlet duct 70, a drive motor 80, and the aforementioned acoustic lining structure.

[0040] An air inlet annular cavity is coaxially recessed on the inner wall of the air inlet duct 60. The size of the air inlet annular cavity matches the outer diameter of the inlet noise reduction element 10. The inlet noise reduction element 10 is coaxially placed into the air inlet annular cavity. The inlet noise reduction element 10 is fixed in the cavity by bolts through the two stepped connecting holes on the reinforcing rib 30. After assembly, the air inlet clamping cavity 14 is connected to the inside of the air inlet duct 60 through the installation gap, without affecting the airflow. At the same time, the inner plate surface of the air inlet annular perforated plate 12 is coplanar with the inner wall surface of the air inlet duct 60.

[0041] First, two annular recesses are recessed into the inner wall of the outlet duct 70, with the two recesses arranged opposite each other. Two outlet noise reduction elements 20 are coaxially installed in the two annular recesses, with each outlet noise reduction element 20 coaxially sleeved on the outside of the impeller 50 and fixed by bolts passing through the connecting holes on the reinforcing rib 30. After assembly, the surfaces of the annular perforated plates 21 of the two outlet noise reduction elements 20, without the outlet clamping cavities 24, are coplanar with the inner wall of the outlet duct 70 at their respective locations, and the outlet clamping cavities 24 are connected to the outlet duct 70 through an installation gap.

[0042] The drive motor 80 is fixed on the fan base, and its output shaft is connected to the central shaft of the impeller 50 to provide power for the rotation of the impeller 50. The outer casing 40 covers the outside of the impeller 50, the air inlet pipe 60 and the air outlet pipe 70 to form a sealed fan cavity, ensuring the overall aerodynamic performance of the fan.

[0043] IV. Noise Reduction Effect Verification In this embodiment, the centrifugal fan underwent noise testing after the acoustic liner structure was installed. Without the acoustic liner structure, the noise level at the fan inlet (900Hz band) was 85dB, and the noise level at the outlet (1800Hz band) was 88dB. After the acoustic liner structure was installed, the noise level at the inlet (900Hz band) dropped to 62dB, and the noise level at the outlet (1800Hz band) dropped to 65dB. This effectively reduced the discrete noise at specific frequencies at the inlet and outlet, and the overall structure did not occupy any additional external space for the fan, meeting the design requirements for miniaturization and integration of the fan.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A sound-absorbing liner structure for noise reduction of centrifugal fans, characterized in that, include: The imported noise reduction element (10) includes an annular support plate (11). On the same side of the support plate (11), an air inlet annular perforated plate (12) and an air inlet annular closed plate (13) are coaxially fixed from the inside to the outside. An air inlet cavity (14) is formed by clamping the air inlet annular perforated plate (12), the support plate (11) and the air inlet annular closed plate (13). The inner wall surface of the air inlet annular perforated plate (12) is coplanar with the inner wall surface of the centrifugal fan air inlet duct (60). The outlet noise reduction element (20) includes an outlet annular perforated plate (21). An inner ring (22) and an outer ring (23) are arranged coaxially from the inside to the outside on the same side of the outlet annular perforated plate (21). An outlet clamping cavity (24) is formed between the inner ring (22), the outlet annular perforated plate (21) and the outer ring (23). The other side of the outlet annular perforated plate (21) is coplanar with the inner wall of the centrifuge outlet duct (70).

2. The acoustic liner structure for noise reduction of a centrifugal fan according to claim 1, characterized in that, Reinforcing ribs (30) are arranged in both the air inlet clamp (14) and the air outlet clamp (24).

3. The acoustic liner structure for noise reduction of a centrifugal fan according to claim 2, characterized in that, Each reinforcing rib (30) is arranged evenly along the circumference of its location.

4. The acoustic liner structure for noise reduction of a centrifugal fan according to claim 3, characterized in that, Each reinforcing rib (30) has a two-stage stepped connection hole for fixing.

5. A sound liner structure for noise reduction of a centrifugal fan according to any one of claims 1-4, characterized in that, The resonant frequency at which the outlet annular perforated plate (21) or the inlet annular perforated plate (12) resonates with the centrifugal fan is: f 0: In the formula: Perforation rate is the percentage of the perforated area on the board to the total area of ​​the board. The speed of sound is expressed in m / s. Indicates the depth of the clamping cavity, in meters (m). This indicates the effective neck length of the aperture.

6. The acoustic liner structure for noise reduction of a centrifugal fan according to claim 5, characterized in that, The effective neck length is: In the formula, For plate thickness, The aperture is indicated by a unit of meters (m).

7. The acoustic liner structure for noise reduction of a centrifugal fan according to claim 6, characterized in that, Both the exhaust annular perforated plate (21) and the inlet annular perforated plate (12) are metal plates.

8. A centrifugal fan, characterized in that, The device includes a housing (40), an impeller (50), an inlet duct (60), an outlet duct (70), a drive motor (80), and a sound liner structure for noise reduction of a centrifugal fan as described in any one of claims 1-7; the inlet noise reduction element (10) in the sound liner structure is coaxially installed inside the inlet duct (60), and the inner plate surface of the inlet annular perforated plate (12) is coplanar with the inner wall surface of the inlet duct (60); the outlet noise reduction element (20) in the sound liner structure is coaxially sleeved on the outer side of the impeller (50), and the plate surface of the outlet annular perforated plate (21) without outlet cavity (24) is coplanar with the inner wall surface of the outlet duct (70).

9. A centrifugal fan according to claim 8, characterized in that, An air inlet annular cavity is coaxially recessed inside the air inlet duct (60), and the inlet noise reduction element (10) is installed in the air inlet annular cavity. The air inlet clamping cavity (14) is connected to the air inlet duct (60) through the installation gap. An air outlet annular cavity is recessed inside the air outlet duct (70), and the outlet noise reduction element (20) is installed in the air outlet annular cavity. The air outlet clamping cavity (24) is connected to the air outlet duct (70) through the installation gap.

10. A centrifugal fan according to claim 9, characterized in that, Two outlet noise reduction elements (20) are arranged coaxially opposite each other in the air outlet duct (70), and the surface of the air outlet annular perforated plate (21) without air outlet cavity (24) is coplanar with the inner wall surface of the air outlet duct (70) at its location.

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