Design method of low-noise roots blower

Abstract

The application provides a design method of a low-noise Roots blower, wherein the number of noise reduction backflow openings arranged on each partition is calculated according to the following formula: step (1): (fan speed * number of blades of the fan impeller * 2 times) / 60, to obtain a value 1; step (2): target frequency value (Hz) of medium-high frequency / value 1, to obtain a value 2; step (3): rounding the result of step (2), to obtain a value 3, which is the number of noise reduction backflow openings arranged on each partition, and the rounding integer of the value of this step is greater than the rounding integer. The application solves the technical problem that the gas dynamic noise is large due to the backflow impact of high-pressure gas when the Roots blower exhausts. The application can be widely applied to the noise reduction design of the Roots blower.

Description

Technical Field

[0001] This invention relates to the technical field of noise reduction for Roots blowers, and in particular to a design method for a low-noise Roots blower. Background Technology

[0002] Roots blowers are a type of positive displacement forced air conveying equipment. Due to their simple structure, convenient use and maintenance, lack of internal lubrication, almost constant exhaust volume within the operating pressure range, high volumetric efficiency, and oil-free conveying medium, they are widely used in various sectors of the national economy.

[0003] As a volumetric gas transmission device, the Roots blower has a significant drawback: the high-pressure gas backflow impact during exhaust generates considerable aerodynamic noise.

[0004] Currently, the main method for noise reduction in Roots blowers is to install silencers at the inlet and outlet to reduce aerodynamic noise. Silencers are generally divided into resistive silencers and reactive silencers. Resistive silencers mainly rely on internal sound-absorbing materials for noise reduction. These materials are effective at absorbing mid-to-high frequency noise, but have a lower absorption coefficient for low-frequency noise. Reactive silencers, on the other hand, are selective in their silencing frequency range and have a relatively narrow silencing frequency range, making them unsuitable for the multi-speed requirements of Roots blowers. Summary of the Invention

[0005] This invention addresses the technical problems of existing Roots blowers exhibiting high exhaust noise, while resistive silencers, despite their good absorption of mid-to-high frequency noise, have a low absorption coefficient for low-frequency noise, and reactive silencers have a relatively narrow silencing frequency range. The invention provides a design method for a low-noise Roots blower. This method, when designing the Roots blower casing, can improve and reduce exhaust noise through calculations, thus solving the technical problem of high aerodynamic noise generated by the backflow impact of high-pressure gas during Roots blower exhaust.

[0006] Therefore, the technical solution of the present invention is a design method for a low-noise Roots blower, wherein the number of noise-reducing return ports spaced apart on each partition is calculated according to the following formula:

[0007] Step (1): (fan speed * number of blades on the fan impeller * 2) / 60, to get the value 1;

[0008] Step (2): Calculate the target frequency value (Hz) for mid-to-high frequencies by dividing it by value 1 to obtain value 2;

[0009] Step (3): Round the result of step (2) to get the value 3. This value 3 is the number of noise reduction return ports provided on each partition. When the value of this step is rounded to an integer, it is greater than the value rounded to the nearest integer.

[0010] Preferably, the target frequency value in step (2) is higher than 500Hz.

[0011] Preferably, the low-noise Roots blower has a casing with an air inlet at the upper end and an exhaust outlet on one side of the lower end. Inside the casing is an impeller, and a grooved section on the outer surface of the impeller forms a closed cavity with the inner wall of the casing away from the air inlet and exhaust outlet. A casing noise reduction extension extends from the bottom of one side of the inner cavity toward the center of the inner cavity. The casing noise reduction extension continues to extend inward with a partition. A casing noise reduction extension also extends from the bottom of the other side of the inner cavity toward the center of the inner cavity. The casing noise reduction extension continues to extend inward with a partition. Multiple noise reduction return ports are spaced apart on the partition.

[0012] Preferably, a high-pressure gas return port is provided at the connection between the partitions on both sides.

[0013] Preferably, the noise reduction extensions and partitions provided in the inner cavities on both sides of the housing are symmetrical.

[0014] Preferably, each partition is provided with 6 noise reduction return ports at intervals, at which time the fan speed is 1450 r / min and the fan impeller has two blades.

[0015] Preferably, the width of the noise reduction return port is 10mm-12mm, the distance between two adjacent noise reduction return ports is 10mm-12mm, and the width of the return high-pressure gas release port is twice the width of the noise reduction return port.

[0016] Preferably, the opening length of the noise reduction return port along the impeller axial direction is shorter than the length of the impeller.

[0017] Preferably, the outer circumferential surface of the impeller and the inner wall surface of the noise reduction extension of the casing and the partition are provided with a gradual gap structure.

[0018] Preferably, the gradient gap is largest at the very end of the partition, and is set to 5mm-8mm.

[0019] The beneficial effect of the present invention is that, since a noise reduction extension is provided at the bottom of the inner cavity on one side of the housing and extends towards the center of the inner cavity of the housing, and a partition is provided further inward on the noise reduction extension, and multiple noise reduction return ports are provided on the partition, the impact frequency of the high-pressure gas return is changed, and the center frequency of its aerodynamic noise is changed. This center frequency enters the frequency range of mid-to-high frequency noise, and the noise reduction effect of the resistive silencer is greatly improved.

[0020] The appropriate number of noise reduction return ports can be calculated based on the motor speed and the number of blades on the Roots blower impeller, thereby changing the center frequency value of the aerodynamic noise and making it fall into the frequency range of mid-to-high frequency noise, thus improving the noise reduction effect of the resistive silencer and reducing the noise during the operation of the Roots blower.

[0021] Furthermore, because the design of the high-pressure return gas release port is larger than that of the noise reduction return port, when the high-pressure return gas flows back into the original closed cavity, the pressure inside the original closed cavity reaches equilibrium and then begins to rise again, the high-pressure return gas release port can quickly release the pressure inside the original closed cavity. As the high-pressure gas is discharged, the noise of the Roots blower is reduced while ensuring the operating efficiency of the Roots blower. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of one embodiment of the present invention;

[0023] Figure 2 This is a cross-sectional schematic diagram of an embodiment of the present invention;

[0024] Figure 3 yes Figure 1 Enlarged view at point Z;

[0025] Figure 4 This is a top view of the noise reduction return port section;

[0026] Figure 5 This is a schematic diagram of the structural layout of the noise reduction reflux port and the reflux high-pressure gas release port;

[0027] Figure 6 It is a schematic diagram of the gradual gap structure between the outer circumferential surface of the impeller and the inner wall surface of the noise reduction extension and partition of the casing.

[0028] Explanation of symbols in the diagram:

[0029] 1. Housing; 2. Exhaust port; 3. High-pressure gas; 4. Return high-pressure gas; 5. Impeller; 6. Enclosed cavity; 7. Partition; 8. Noise-reducing return port; 9. Noise-reducing extension of housing; 10. Air inlet; 11. Return high-pressure gas release port; 12. Original enclosed cavity; 13. Trajectory line of the outer working surface of the impeller; 14. Gradual gap. Detailed Implementation

[0030] We know that the aerodynamic noise of a Roots blower is generated by the backflow impact of high-pressure gas 3 at the blower's exhaust port 2. This backflow of high-pressure gas 3 is not continuous; rather, each time the enclosed cavity 6 formed by the impeller 5 and the casing 1 connects to the exhaust port 2, the high-pressure gas 3 flows back to the original, lower-pressure enclosed cavity 12. As the impeller 5 rotates continuously, the high-pressure gas 3 repeatedly backflows and impacts the exhaust port 2. The impact frequency of this backflow constitutes the center frequency of the aerodynamic noise of the gas at the exhaust port 2.

[0031] like Figure 1-6 This is an embodiment of the design method for a low-noise Roots blower according to the present invention. Figure 2 As can be seen, the noise-reducing housing of the Roots blower is provided with a housing 1. The upper end of the housing 1 is provided with an air inlet 10, and the lower end of the housing 1 is provided with an exhaust port 2. Inside the housing 1, there is a set of impellers 5. The grooved section on the outer surface of the impeller 5 forms a closed cavity 6 with the inner wall of the housing 1 away from the air inlet 10 and the exhaust port 2. A housing noise-reducing extension 9 is provided at the bottom of the inner cavity on one side of the housing 1 and extends towards the center of the inner cavity of the housing 1. The housing noise-reducing extension 9 continues to extend inward and is provided with a partition 7. A housing noise-reducing extension 9 is also provided at the bottom of the inner cavity on the other side of the housing 1 and extends towards the center of the inner cavity of the housing 1. The housing noise-reducing extension 9 continues to extend inward and is provided with a partition 7. Multiple noise-reducing return ports 8 are provided at intervals on the partition 7.

[0032] Figure 5 As can be seen, the high-pressure gas release port 11 is provided at the connection of the partitions 7 on both sides.

[0033] In this embodiment, the noise reduction extension 9 and the partition 7 provided on both sides of the inner cavity of the housing 1 are symmetrical. This symmetrical structure can more smoothly improve the center frequency when the high-pressure gas 4 returns, thereby improving the center frequency of the aerodynamic noise when the Roots blower is working, and achieving the purpose of smoothly controlling the center frequency.

[0034] We will illustrate the application method of this invention with an example. Taking a Roots blower under a specific operating condition as an example, we calculate the center frequency of its aerodynamic noise. Assuming the blower speed is 1450 r / min and the blower impeller 5 has two blades, the high-pressure gas 3 recirculates 4 times per revolution of the blower. Therefore, the center frequency of the aerodynamic noise is f = 1450 * 4 / 60 = 96 Hz. This is clearly within the low-frequency noise range. Sound-absorbing materials have a low absorption coefficient for low-frequency noise but a high absorption coefficient for mid-to-high-frequency noise. Therefore, the noise reduction effect of the resistive silencer at the exhaust port of the Roots blower is not ideal.

[0035] By adding a partition 7 at the exhaust port 2 of the casing 1, when the sealed cavity 6 is connected to the exhaust port 2, the backflow of high-pressure gas 3 is not a one-time event, but rather as the sealed cavity 6 comes into contact with the opening on the exhaust port 2 of the casing 1 in sequence, the backflow of high-pressure gas 4 also impacts the gas in the sealed cavity 6 in a backflow manner. This artificially increases the number of backflow impacts, and the number of backflow impacts directly determines the center frequency of the exhaust port noise.

[0036] For the example above, we installed six noise-reducing return ports 8 at intervals on each partition 7. This reduces the center frequency F of the original exhaust noise to six times the center frequency f of the example above, which is 576Hz. This frequency falls within the mid-to-high frequency range of noise, significantly improving the noise reduction effect of the resistance silencer and effectively reducing the noise at the Roots blower exhaust port. In the noise spectrum, frequencies below 350Hz are considered low frequency, 350Hz-1000Hz are considered mid frequency, and frequencies above 1000Hz are considered high frequency. 600Hz falls roughly in the middle of the mid-frequency range. Therefore, the improved noise reduction effect of the resistance silencer effectively reduces the noise at the Roots blower exhaust port.

[0037] In this embodiment, six noise reduction return ports 8 are provided at intervals on each partition 7, which can well meet the requirements of a fan speed of 1450 r / min. The fan impeller 5 is used for a two-bladed Roots blower.

[0038] Experimental verification shows that in this embodiment, the width of the noise reduction return port 8 is 10mm-12mm, the distance between two adjacent noise reduction return ports 8 is 10mm-12mm, and the width of the return high-pressure gas release port 11 is twice the width of the noise reduction return port 8. This design is optimized and can achieve excellent noise reduction effect.

[0039] In this implementation, the opening length of the noise reduction return port 8 along the axial direction of the impeller 5 is shorter than the length of the impeller 5, generally 4mm-5mm shorter on one side and about 10mm shorter overall, to ensure that the high-pressure gas 3 works smoothly and that the return high-pressure gas 4 can smoothly return and be discharged according to the set fluid operation channel.

[0040] In this embodiment, a noise reduction extension 9 is provided on the bottom of one side of the inner cavity of the housing 1, extending towards the center of the inner cavity of the housing 1. The noise reduction extension 9 extends further inward to provide a partition 7, and multiple noise reduction return ports 8 are provided on the partition 7 at intervals. This changes the impact frequency of the high-pressure gas return and the center frequency of its aerodynamic noise. This center frequency enters the frequency range of mid-to-high frequency noise, and the noise reduction effect of the resistive silencer is greatly improved.

[0041] In this implementation, because the design of the high-pressure return gas release port 11 is larger than that of the noise reduction return port 8, when the high-pressure return gas 4 flows back into the original closed cavity 12, the pressure inside the original closed cavity 12 reaches equilibrium and begins to rise again, the high-pressure return gas release port 11 can quickly release the pressure inside the original closed cavity 12. As the high-pressure gas 3 is discharged, the noise of the Roots blower is reduced while ensuring the operating efficiency of the Roots blower.

[0042] In this implementation example, the appropriate number of noise reduction return ports 8 can be calculated based on the motor speed and the number of blades of the Roots blower impeller 5, thereby changing the center frequency value of the aerodynamic noise so that the frequency value falls into the frequency range of mid-to-high frequency noise, thereby improving the noise reduction effect of the resistive silencer and reducing the noise when the Roots blower is running.

[0043] Therefore, under specific Roots blower parameters, calculations are required to determine the number of noise reduction return ports 8, thereby achieving a noise reduction structural design.

[0044] The calculation method is given below:

[0045] Step (1): (fan speed * number of fan impeller blades * 2) / 60, to get the value 1; that is, the ratio of the value obtained by multiplying the fan speed * number of fan impeller blades * 2 to 60, to get the value 1.

[0046] Step (2): Calculate the target frequency value (Hz) of the mid-to-high frequency range / value 1 to obtain value 2; that is, the ratio of the target frequency value (in Hz) of the mid-to-high frequency range to value 1 to obtain the value of value 2.

[0047] Step (3): Round the result of step (2) to get the value 3. This value 3 is the number of noise reduction return ports provided on each partition. When the value in this step is rounded to an integer, it is greater than the integer value. For example, if the obtained value is 6.2, then take the integer value as 7. If the obtained value is 5.8, then take the integer value as 6.

[0048] In step (2), the target frequency value is generally taken to be higher than 500Hz. This way, the adjusted noise frequency will enter the desired mid-to-high frequency noise range, achieving the effect of sound absorption and noise reduction. The target mid-to-high frequency value can be determined according to the performance characteristics of the selected silencer. For example, values ​​such as 550Hz, 600Hz, 800Hz, 1000Hz, etc. can be selected during calculation. As long as the target noise reduction value is achieved according to the calculation and experimental test, the design can be finalized.

[0049] Figure 6As can be seen in the figure, the outer circumferential surface of the impeller 5 and the inner wall surface of the casing noise reduction extension 9 and the partition 7 are designed with a gradual gap structure. The trajectory line 13 of the outer working surface of the impeller can be seen in the figure. A gradual gap 14 is provided between the trajectory line 13 and the inner wall surface of the casing noise reduction extension 9 and the partition 7. The gradual gap 14 is the largest at the very end of the partition 7, which is generally set between 5mm and 8mm. The gradual gap 14 is the smallest near the inner surface of the casing noise reduction extension 9. That is to say, when the impeller 5 just rotates to the inner surface of the casing noise reduction extension 9, the gradual gap 14 is the smallest, and the gap is the largest when it is far away from the very end of the partition 7. This gradual gap 14 setting can eliminate the micro-airflow vibration generated by the cooperation between the impeller 5 and the casing noise reduction extension 9 and the partition 7 during operation. It can also eliminate the micro-airflow vibration generated when the high-pressure gas 4 returns quickly to the original closed cavity 12 and is released to the exhaust port 2. It is also beneficial to reduce the additional vibration noise generated when the Roots blower is running.

[0050] This embodiment modifies the noise spectrum characteristics of the Roots blower by simply adding some design elements to the structure of the Roots blower housing 1, thereby achieving better noise reduction for the Roots blower. The method is simple, the structure is simple, and the manufacturing cost is low, making it a suitable noise reduction method with extremely high promotional value.

[0051] However, the above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made in accordance with the scope of protection of the present invention should still fall within the scope of the claims of the present invention.

Claims

1. A design method for a low-noise Roots blower, characterized in that: The number of noise reduction return ports installed on each partition is calculated according to the following formula: Step (1): (fan speed * number of fan impeller blades * 2) / 60, to get the value 1; Step (2): Calculate the target frequency value (Hz) for mid-to-high frequencies by dividing it by value 1 to obtain value 2; Step (3): Round the result of step (2) to get the value 3. This value 3 is the number of noise reduction return ports provided on each partition. When the value of this step is rounded to an integer, it is greater than the value rounded to the nearest integer. The low-noise Roots blower includes a casing with an air inlet at the upper end and an exhaust outlet on one side of the lower end. An impeller is located inside the casing, and a grooved section on the outer surface of the impeller forms a closed cavity with the inner wall of the casing away from the air inlet and exhaust outlet. A noise-reducing extension extends from the bottom of one side of the inner cavity towards the center of the inner cavity, and a partition extends further inward from the noise-reducing extension. A noise-reducing extension also extends from the bottom of the other side of the inner cavity towards the center of the inner cavity, and a partition extends further inward from the noise-reducing extension. Multiple noise-reducing return ports are spaced apart on the partition. A high-pressure gas return port is provided at the connection point between the partitions on both sides; Each partition is equipped with 6 noise reduction return ports at intervals. At this time, the fan speed is 1450 r / min, and the fan impeller has two blades. The width of the noise reduction return port is 10mm-12mm, the distance between two adjacent noise reduction return ports is 10mm-12mm, and the width of the return high-pressure gas release port is twice the width of the noise reduction return port. The outer circumferential surface of the impeller and the inner wall surface of the noise reduction extension of the casing and the partition are provided with a gradual gap structure; the gradual gap is the largest at the very end of the partition, and is set to 5mm-8mm.

2. The design method for a low-noise Roots blower according to claim 1, characterized in that: The target frequency value in step (2) is higher than 500Hz.

3. The design method for a low-noise Roots blower according to claim 1, characterized in that: The noise reduction extensions and partitions on both sides of the inner cavity of the housing are symmetrical.

4. The design method of a low-noise Roots blower according to claim 1, characterized in that: The opening length of the noise reduction return port along the impeller axial direction is shorter than the length of the impeller.

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