An acoustic design method applicable to a small hub ratio fan

Abstract

The present invention discloses an acoustic design method applicable to a fan with a small hub ratio, which relates to the field of fan acoustic design and includes: determining the diameter D of the fan; specifying the initial volume V of the expansion slot at the fan outlet; calculating to obtain the specific frequency f of the expansion slot k ; determining the maximum rotational speed N of the fan; determining the first-order blade passing frequency f2 of the fan; judging whether f k is equal to f2. If so, obtaining the designed volume of the expansion slot based on the initial volume V of the expansion slot; if not, adjusting the initial volume V of the expansion slot to the target volume V1 of the expansion slot such that f k = f2, and obtaining the designed volume of the expansion slot based on the target volume V1 of the expansion slot; completing the acoustic design of the fan based on the maximum rotational speed N of the fan, the number B of rotor blades of the fan, and the designed volume of the expansion slot; the present invention can solve the problems of insufficient low-frequency suppression, delayed high-frequency cancellation, and lack of multi-physical field coupling design of traditional noise reduction technologies for fans with small hub ratios.

Description

Technical Field

[0001] The present invention relates to the field of fan acoustic design, and particularly to an acoustic design method applicable to a fan with a small hub ratio. Background Art

[0002] If a small-hub-ratio fan is used in an aerodynamic test equipment, advantages such as small volume, light weight, and good mobility can be achieved. However, the aerodynamic noise generated during the operation of a small-hub-ratio fan (including discrete frequency noise and broadband turbulent noise) has become a key issue restricting the performance of related devices and test capabilities. If traditional noise reduction techniques are used for the noise reduction of the fan, the following limitations exist. One is that passive noise control reduces noise through blade geometry optimization (such as serrated trailing edges) or sound-absorbing materials, but the low-frequency suppression efficiency is low (<30%), and it is easy to sacrifice aerodynamic performance (the pressure loss increases by 5% - 15%). The other is that it relies on active control of reverse acoustic wave interference, but there is a high-frequency noise tracking delay (>10 ms), and the system stability problem is poor (the residual noise is amplified by 15 dB(A)), resulting in limited practicality. Summary of the Invention

[0003] The object of the present invention is to solve the problems of insufficient low-frequency suppression, high-frequency cancellation delay, and lack of multi-physical field coupling design of traditional noise reduction techniques for small-hub-ratio fans.

[0004] To achieve the above object, the present invention provides an acoustic design method applicable to a small-hub-ratio fan. The fan is installed in a fan duct, and the fan duct is connected with an expansion slot through a connection seam. The method includes:

[0005] Step 1: Determine the diameter D of the fan;

[0006] Step 2: Specify the initial volume V of the expansion slot at the fan outlet;

[0007] Step 3: Based on the diameter D of the fan and the initial volume V of the expansion slot, calculate to obtain the specific frequency f of the expansion slot k ;

[0008] Step 4: Determine the designed rotational speed N of the fan based on the diameter D of the fan;

[0009] Step 5: Based on the designed rotational speed N of the fan and the number B of rotor blades of the fan, determine the first-order blade passing frequency f2 of the fan. This frequency noise is the main noise source of the fan;

[0010] Step 6: Judge whether f k is equal to f2. If so, obtain the designed volume of the expansion slot based on the initial volume V of the expansion slot; if not, adjust the initial volume V of the expansion slot to the target volume V1 of the expansion slot so that , at this time, the present design method can effectively control the target noise, and obtain the design volume of the expansion slot based on the target volume V1 of the expansion slot;

[0011] Step Seven: Complete the acoustic design of the fan based on the diameter D of the fan, the designed rotational speed N, the number B of the rotor blades of the fan, and the designed volume of the expansion slot.

[0012] Among them, this method utilizes the condition that the noise energy of the first-order passing frequency of the fan is intensive, and realizes the efficient active absorption of the fan noise by designing the impedance of the duct wall, while effectively controlling the intensity of high-frequency harmonics. Compared with the traditional fan noise reduction means, this method does not use any sound-absorbing materials, only realizes the efficient suppression of the airflow noise by changing the characteristic impedance of the duct, cannot introduce dust pollution, and at the same time has a small duct resistance loss, that is, it can effectively improve the fan efficiency.

[0013] Preferably, the hub ratio of the fan is Xb, and Xb ≤ 0.3. The purpose of using a fan with a small hub ratio is that the length of the fan section is shorter, so as to save the volume and space of the entire fan, and it is used inside a system with requirements for space. A smaller fan volume means that the space for filling the acoustic lining is limited and the noise reduction effect is also limited. Therefore, the acoustic design of this method can be adopted to achieve a better noise reduction effect without significantly expanding the fan volume.

[0014] Preferably, the fan is an axial flow fan, which is widely used in industrial ventilation, exhaust, and providing power for aerodynamic test equipment. The expansion slot is located downstream of the fan along the airflow direction.

[0015] Preferably, the specific frequency f k of the expansion slot is calculated as follows:

[0016] ;

[0017] Among them, c is the speed of sound, is the ratio of the width to the depth of the joint seam.

[0018] Preferably, the calculated method of the designed rotational speed N of the fan is:

[0019] .

[0020] Preferably, the calculated method of the first-order blade passing frequency f2 of the fan is:

[0021] ;

[0022] Among them, B is the number of the rotor blades of the fan.

[0023] Preferably, the expansion slot includes an annular outer shell sleeved outside the fan duct. An annular cavity is provided inside the annular outer shell. The fan duct communicates with the annular cavity through an annular connection seam.

[0024] One or more technical solutions provided by the present invention have at least the following technical effects or advantages:

[0025] For conventional aerodynamic test equipment fans, the main methods to suppress fan noise are to reduce the fan speed and arrange acoustic linings in the fan passage. Reducing the fan speed can reduce the low-frequency and broadband noise of the fan, but it will lead to a decrease in the aerodynamic efficiency of the fan and even increase the broadband aerodynamic noise caused by the pressure pulsation on the blade surface. Arranging acoustic linings can achieve a broadband noise reduction effect within a certain frequency band, but the acoustic linings will bring additional pressure losses, resulting in an increase in the operating power of the fan. The acoustic design method for small hub ratio fans proposed by the present invention, by arranging expansion slots, reasonably matches the fan speed, the number of rotor blades, and the volume of the expansion slots, so that the expansion slots designed to adjust the acoustic impedance gradient of the wall resonate with the first-order blade passing frequency of the small hub ratio fan (the energy of the first-order blade passing frequency noise is the largest), in order to achieve the purpose of suppressing the first-order blade passing frequency noise. Thus, the amplitude of the peak discrete noise of the fan can be greatly weakened, the total sound pressure level of the fan can be reduced, and the fan has higher aerodynamic efficiency and better acoustic performance. Description of the Drawings

[0026] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the present invention, but do not limit the embodiments of the present invention;

[0027] Figure 1 It is a schematic flow chart of an acoustic design method applicable to small hub ratio fans;

[0028] Figure 2 It is a schematic side view of the installation structure of a small hub ratio fan and an expansion slot;

[0029] Figure 3 It is a schematic cross-sectional view at the expansion slot;

[0030] Wherein, 1 - fan duct, 2 - fan, 3 - expansion slot, 4 - connection seam. Detailed Embodiments

[0031] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described in detail below with reference to the drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0032] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein, and thus, the scope of the present invention is not limited by the specific embodiments disclosed below.

[0033] Embodiment 1;

[0034] Please refer to Figure 1 , Figure 1 which is a schematic flow diagram of an acoustic design method applicable to a small hub ratio fan. Please refer to Figure 2 , Figure 2 which is a side view schematic diagram of the installation structure of a small hub ratio fan and an expansion slot. Figure 3 which is a cross-sectional schematic diagram at the expansion slot. The fan 2 is installed in the fan duct 1. The fan duct 1 is connected with an expansion slot 3 through a connection seam 4. The expansion slot 3 includes an annular outer shell. The annular outer shell is sleeved outside the fan duct 1. An annular cavity is provided inside the annular outer shell. The fan duct 1 is communicated with the annular cavity through an annular connection seam 4. The connection seam 4 can be understood as a connection channel for communicating the fan duct 1 with the expansion slot 3.

[0035] The method includes:

[0036] Step 1: Determine the diameter D of the fan according to the equipment operation capacity requirements; D is determined according to the power and type selection of the fan and is an aerodynamic design parameter of the fan.

[0037] Step 2: According to the diameter D of the fan, initially give the initial volume V of the expansion slot at the fan outlet; the fan is generally used in a ventilation system. For the fan, the operation capacity requirements of the ventilation system are the pressure rise and the flow rate. After obtaining the pressure rise and the flow rate, the diameter of the fan can be determined according to the conventional fan design method in combination with the size of the equipment system where the fan is located. Since the diameter of the expansion slot is larger than the diameter of the fan, after determining the fan diameter D, the diameter of the expansion slot can be given according to a certain multiple, such as 1.1 times the fan diameter, and the height of the expansion slot can be given according to a certain multiple, such as 0.15 times the fan diameter, so as to initially calculate the initial volume V of the expansion slot.

[0038] Step 3: Based on the diameter D of the fan and the initial volume V of the expansion slot, calculate and obtain the specific frequency f of the expansion slot k ; The calculation method of the specific frequency f of the expansion slot k is as follows:

[0039] ;

[0040] wherein, c is the speed of sound, and the value of c can be 340 m / s, is the ratio of the width to the depth of the connection seam, and the value range of

[0041] Step Four: Determine the designed rotational speed N of the fan based on the diameter D of the fan; The calculation method for the designed rotational speed N of the fan is as follows:

[0042] ;

[0043] Step Five: Determine the first blade passing frequency f2 of the fan based on the designed rotational speed N of the fan and the number B of rotor blades of the fan; The calculation method for the first blade passing frequency f2 of the fan is as follows:

[0044] ;

[0045] Wherein, B is the number of rotor blades of the fan, and the value range of B is 2 - 8;

[0046] Step Six: Determine whether f k is equal to f2. If so, obtain the designed volume of the expansion slot based on the initial volume V of the expansion slot; If not, adjust the initial volume V of the expansion slot to the target volume V1 of the expansion slot so that f k = f2, and obtain the designed volume of the expansion slot based on the target volume V1 of the expansion slot;

[0047] Step Seven: Complete the acoustic design of the fan based on the designed rotational speed N of the fan, the number B of rotor blades of the fan, and the designed volume of the expansion slot.

[0048] Wherein, in the embodiment of the present invention, the hub ratio of the fan is Xb, and Xb ≤ 0.3. The hub ratio of a conventional fan is in the range of 0.4 - 0.7, and a hub ratio less than 0.3 refers to a small hub ratio.

[0049] Wherein, in the embodiment of the present invention, the fan is an axial flow fan, and the expansion slot is located downstream of the fan along the air flow direction.

[0050] The following is a detailed example of the present invention:

[0051] Step One: According to the device design status, determine the diameter D of the small hub ratio fan = 2.2 m;

[0052] Step Two: According to the diameter D = 2.2 m of the small hub ratio fan, initially specify the expansion slot volume V at the outlet of the device, and let V = 0.1 m 3 ;

[0053] Step Three: Calculate the specific frequency f of the expansion slot k , Take the value of 0.4, the value of c is 340 m / s, f k = 192 Hz;

[0054] Step Four: Determine the designed rotational speed of the small hub ratio fan, N = 2483 rpm;

[0055] Step Five: Determine the first-order blade passing frequency f2 of the low hub ratio fan. Assume the number of rotor blades of the low hub ratio fan B = 4, and f2 = 165.5 Hz;

[0056] Step Six: Compare f k and f2. If f k is greater than f2, then adjust the expansion slot volume V, and inversely calculate that when V1 = 0.134 m 3 , f k = f2 = 165.5 Hz;

[0057] Step Seven: Obtain the designed rotational speed N = 2483 rpm of the low hub ratio fan, the number of rotor blades of the fan B = 4, and the target volume V1 = 0.134 m 3 of the outlet expansion slot, and complete the design of the above key parameters.

[0058] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0059] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. An acoustic design method applicable to a small hub ratio fan, characterized in that, The fan is installed inside a fan duct, and the fan duct is connected with an expansion slot through a connecting seam. The method includes: Step 1: Determine the diameter D of the fan; Step 2: Specify the initial volume V of the expansion slot at the fan outlet; Step 3: Based on the diameter D of the fan and the initial volume V of the expansion slot, calculate to obtain the specific frequency f of the expansion slot k ; Step 4: Determine the designed rotational speed N of the fan based on the diameter D of the fan; Step 5: Determine the first-order blade passing frequency f2 of the fan based on the designed rotational speed N of the fan and the number B of rotor blades of the fan; Step 6: Determine whether f k is equal to f2. If so, obtain the designed volume of the expansion slot based on the initial volume V of the expansion slot; if not, adjust the initial volume V of the expansion slot to the target volume V1 of the expansion slot so that f k = f2, and obtain the designed volume of the expansion slot based on the target volume V1 of the expansion slot; Step 7: Complete the acoustic design of the fan based on the designed rotational speed N of the fan, the number B of rotor blades of the fan, and the designed volume of the expansion slot.

2. The acoustic design method for a small hub ratio fan according to claim 1, characterized in that, The hub ratio of the fan is Xb, where Xb ≤ 0.

3.

3. The acoustic design method for a small hub ratio fan according to claim 1, wherein The fan is an axial-flow fan, and the expansion slot is located downstream of the fan in the air flow direction.

4. The acoustic design method for a fan with a small hub ratio according to claim 1, wherein The specific frequency f of the expansion slot k is calculated as follows: ； where c is the speed of sound, is the ratio of the width to the depth of the joint seam.

5. The acoustic design method for a small hub ratio fan according to claim 1, characterized in that, The calculation method of the designed rotational speed N of the fan is: 。 6. The acoustic design method for a small hub ratio fan according to claim 1, characterized in that, The calculation method of the first-order blade passing frequency f2 of the fan is: ； where B is the number of rotor blades of the fan.

7. An acoustic design method for a fan with a small hub ratio according to claim 1, characterized in that The expansion slot includes an annular outer shell that is sleeved outside the fan duct. An annular cavity is provided inside the annular outer shell, and the fan duct communicates with the annular cavity through an annular connecting seam.

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