阅读说明：本技术 一种可调背腔深度的偏流双层多孔板吸声装置 (Bias flow double-layer perforated plate sound absorption device with adjustable back cavity depth ) 是由 周昊 刘子华 于 2020-06-30 设计创作，主要内容包括：本发明公开一种可调背腔深度的偏流双层多孔板吸声装置,包括进气管段,所述进气管段的一端设有带进气孔的可移动活塞,另一端设有排气口,所述的进气管段内沿进气方向依次布置进气上游孔板和进气下游孔板,进气上游孔板和进气下游孔板阵列地布置有微孔；所述可移动活塞与进气上游孔板间为可调深度的一级空腔,进气上游孔板与进气下游孔板间为二级空腔,两级空腔形成腔内吸声结构。本发明中,偏流下的孔板相比无流下的孔板吸声性能得到明显提升；双层穿孔板的使用拓宽了吸声频带,可用于消除燃烧器内因燃烧不稳定产生的噪声,提高设备的使用寿命及安全性。(The invention discloses a bias flow double-layer porous plate sound absorption device with adjustable back cavity depth, which comprises an air inlet pipe section, wherein one end of the air inlet pipe section is provided with a movable piston with an air inlet hole, the other end of the air inlet pipe section is provided with an air outlet, an air inlet upstream pore plate and an air inlet downstream pore plate are sequentially arranged in the air inlet pipe section along the air inlet direction, and micropores are arranged in the air inlet upstream pore plate and the air inlet downstream pore plate in an array manner; the movable piston and the air inlet upstream pore plate are provided with a first-stage cavity with adjustable depth, the air inlet upstream pore plate and the air inlet downstream pore plate are provided with a second-stage cavity, and the two-stage cavities form an intracavity sound absorption structure. In the invention, compared with a non-flowing pore plate, the sound absorption performance of the pore plate under bias flow is obviously improved; the use of the double-layer perforated plate widens the sound absorption frequency band, and can be used for eliminating the noise generated by unstable combustion in the combustor and improving the service life and the safety of equipment.)

1. The utility model provides a double-deck perforated plate sound absorbing device of bias flow of adjustable back of body chamber degree of depth, includes intake pipe section (3), the one end of intake pipe section (3) is equipped with portable piston (7) of taking the air inlet hole, and the other end is equipped with gas vent (10), its characterized in that:

an air inlet upstream pore plate (1) and an air inlet downstream pore plate (2) are sequentially arranged in the air inlet pipe section (3) along the air inlet direction, and micropores are arranged in the air inlet upstream pore plate (1) and the air inlet downstream pore plate (2) in an array manner;

a first-stage cavity (5) with adjustable depth is formed between the movable piston (7) and the air inlet upstream pore plate (1), a second-stage cavity (4) is formed between the air inlet upstream pore plate (1) and the air inlet downstream pore plate (2), and an intracavity sound absorption structure is formed by the two-stage cavities.

2. The bias flow double-layer porous plate sound absorption device with adjustable back cavity depth as claimed in claim 1, wherein the micropores of the intake upstream orifice plate (1) and the intake downstream orifice plate (2) are distributed in a square matrix, the radius a of the micropores is 0.5-1mm, the center-to-center distance d of the micropores is 5-10mm, and the porosity σ is 2-5%.

3. The variable back cavity depth bias flow double layer perforated plate sound absorber of claim 2, wherein the radius of the micropores of the intake upstream perforated plate (1) is larger than the radius of the micropores of the intake downstream perforated plate (2).

4. The bias flow double-layer porous plate sound absorption device with the adjustable back cavity depth as claimed in claim 1, wherein the material of the air inlet upstream orifice plate (1) and the air inlet downstream orifice plate (2) is brass or stainless steel, and the plate thickness h is 1mm-2 mm.

5. The bias flow double-deck perforated plate sound absorber of adjustable back cavity depth as claimed in claim 1, wherein the depth of the primary cavity (5) is 0.05-0.5m, which is adjusted by the movement of the movable piston (7); the depth of the secondary cavity (4) is 0.05-0.5 m.

6. The bias flow double-layer porous plate sound absorption device with the adjustable back cavity depth as claimed in claim 1, wherein the gas introduced into the air inlet pipe section (3) is air, the temperature is not more than 100 ℃, and the relative humidity is not more than 70%.

7. The back cavity depth adjustable bias flow double layer perforated plate sound absorber of claim 1, wherein the surface characteristic acoustic impedance at the intake upstream perforated plate (1) is

8. The back cavity depth adjustable bias flow double layer perforated plate sound absorber according to claim 7, wherein the surface characteristic acoustic impedance at the intake downstream perforated plate (2) is

9. The variable back cavity depth bias flow double layer perforated plate sound absorber of claim 8, wherein the overall sound absorber has an acoustic reflectance ofR and

10. The bias flow double-layer perforated plate sound absorber of claim 9, wherein the sound absorption coefficient of the double-layer perforated plate is α -1- | R purple²。

Technical Field

The invention relates to the field of noise control based on porous sound absorption, in particular to a bias flow double-layer porous plate sound absorption device with adjustable back cavity depth.

Background

The research and control of radiation noise are urgent requirements for weakening environmental noise and protecting stable operation of production equipment. The combustion noise is easily generated due to unstable combustion of the lean premixed combustion gas turbine, the aviation gas turbine and the oil-gas boiler, and the self-excited noise caused by thermoacoustic coupling can cause the vibration of a combustion system, the failure of a control system and the damage or the reduction of the service life of combustion equipment. Pressure fluctuations in the intake section of the combustor have a significant impact on self-excitation and maintenance of combustion instabilities.

The famous acoustic specialist mahara 29495in China carries out careful research on the non-flow micro-perforated plate. The perforated plate device is not afraid of high-temperature and humid environment and is durable. Compared with porous sound absorption fiber, the production process is non-toxic. However, the sound absorption performance and the sound absorption frequency band of the common single-layer perforated plate are limited, and when the structural parameters of the perforated plate, such as the pore diameter, the porosity, the plate thickness, the back cavity depth and the like, are determined, the center frequency and the sound absorption characteristic of the sound absorption device are also determined.

In order to widen the effective sound absorption band of the perforated plate, it is a mainstream practice to use composite perforated plates of a serial, parallel or serial-parallel structure, and particularly, to use a perforated plate combination of a multilayer structure. However, when the sound absorption band is widened, the sound absorption coefficient of the perforated-plate sound absorber is significantly reduced. International research in recent years has shown that the sound absorption performance of perforated plates or liners through which a glancing flow (grazing flow) or a bias flow (bias flow) passes can be much improved over that of no flow, however no research has been made on the bias flow multi-layer perforated plate muffler. In addition, the cavity depth of the prior perforated plate is usually not adjustable, so the effective working frequency band of the muffler device is often fixed, and when the noise frequency of the equipment to be subjected to sound absorption (such as a combustor) is not matched with the effective working frequency band of the muffler, the actual sound attenuation effect of the perforated plate muffler is reduced.

It was found that, in the current noise control technical literature and textbooks concerning combustion noise control, only a precedent of composite non-flow perforated plates or glancing flow multilayer liners, as disclosed in patent applications with publication numbers CN 110998187 a and CN 107420170 a, the control methods are too simple, the sound absorption capacity and the sound absorption operating frequency band are limited, and the sound absorption characteristics of the sound absorber are often fixed due to the fixed depth of the back cavity, so that the sound absorber is difficult to adapt to practical applications. At present, no bias flow double-layer porous plate sound absorption device with adjustable back cavity depth is available.

Disclosure of Invention

The technical problems to be solved by the invention are that the effective sound absorption frequency band of the existing porous plate is narrow, the sound absorption frequency band can not be adjusted according to the characteristics of incident noise sound waves, and the sound absorption performance of the non-flow porous plate sound absorber is poor.

In order to realize the purpose, the application provides a bias flow double-layer perforated plate sound absorption method and device with adjustable back cavity depth, the sound absorption coefficient of a perforated plate sound absorber is optimized, and the effective sound absorption frequency band of the perforated plate sound absorber is expanded, and the specific adopted technical scheme is as follows;

a bias flow double-layer porous plate sound absorption device with adjustable back cavity depth comprises an air inlet pipe section, wherein one end of the air inlet pipe section is provided with a movable piston with an air inlet hole, and the other end of the air inlet pipe section is provided with an air outlet;

an air inlet upstream pore plate and an air inlet downstream pore plate are sequentially arranged in the air inlet pipe section along the air inlet direction, and micropores are arranged in the air inlet upstream pore plate and the air inlet downstream pore plate in an array manner;

the movable piston and the air inlet upstream pore plate are provided with a first-stage cavity with adjustable depth, the air inlet upstream pore plate and the air inlet downstream pore plate are provided with a second-stage cavity, and the two-stage cavities form an intracavity sound absorption structure.

In the application, air enters the sound absorber through the air inlet hole in the head of the movable piston, sequentially passes through the air inlet upstream pore plate and the air inlet downstream pore plate, and finally enters the equipment to be subjected to sound absorption (such as a combustion chamber or a hearth of a combustion engine).

Preferably, the micropores of the air inlet upstream orifice plate and the air inlet downstream orifice plate are distributed in a square matrix, the pore radius a of the micropores is 0.5-1mm, the pore center distance d is 5-10mm, and the porosity sigma is 2-5%.

Further preferably, the radius of the micropores of the intake upstream orifice plate is larger than the radius of the micropores of the intake downstream orifice plate.

Preferably, the material of the air inlet upstream orifice plate and the air inlet downstream orifice plate is brass or stainless steel, and the plate thickness h is 1mm-2 mm.

Preferably, the depth of the primary cavity is 0.05-0.5m, and the depth is adjusted by the movement of the movable piston; the depth of the secondary cavity is 0.05-0.5 m.

Preferably, the gas introduced into the gas inlet pipe section is air, the temperature is not more than 100 ℃, and the relative humidity is not more than 70%.

In the present application, the intake upstream orifice plate and the intake downstreamThe rectangular array of the porous plate is fully distributed with round micropores, and the Struhal number St of each plate is obtained according to the pore diameter a and the plate thickness h of the pores of the porous plate_cω is the angular frequency of the incident sound, determined by the noise itself generated by the equipment to be sound-absorbed, and l is the effective orifice plate thickness. u. of_cFor acoustic convection velocities, the acoustic bias velocity u can be approximated in the calculation_pInstead, the average flow velocity at the orifice.

Calculating Rayleigh acoustic conductivity of the air inlet upstream orifice plate and the air inlet downstream orifice plate under bias flowK is the Rayleigh acoustic conductivity of the pore plate without flowing down, i is an imaginary number unit, C_cIs the shrinkage factor, and its value is the acoustic convection velocity u_cRatio u to jet velocity at the orifice_jThe arithmetic square root of (c) is taken to be an empirical value of 0.75 according to the Cummings recommendation.

Calculating the Helmholtz number He at the perforated plate upstream of the intake air₁＝kL₁K is the wave number of the incident sound wave, L₁Is the first level cavity depth.

In the present application, it is further preferable that the surface acoustic characteristic acoustic impedance at the intake upstream orifice plate isd₁The hole center distance of the intake upstream orifice plate, K_R1The rayleigh acoustic conductivity of the intake upstream orifice plate. The surface characteristic acoustic impedance of the perforated plate at the downstream of the air inlet is obtained by the same methodd₂Hole center distance, K, of perforated plates downstream of the inlet_R2Rayleigh acoustic conductivity, He, of perforated plates downstream of the inlet₂＝kL₂Helmholtz number, L, of perforated plates downstream of the inlet₂The depth of the secondary cavity.

The sound reflection coefficient of the whole sound absorption device isR andthe modulus and phase of the acoustic reflection coefficient. The sound absorption coefficient of the bias flow double-layer porous plate is alpha-1- | R | air distribution²。

In the application, the sound absorption characteristic curve of the bias flow double-layer perforated plate sound absorption device with the adjustable back cavity depth can be obtained according to the calculation formula of the bias flow double-layer perforated plate. And selecting proper depths of the air inlet upstream pore plate, the air inlet downstream pore plate and the primary cavity according to the prediction result and the actual radiation noise frequency generated by actual equipment to be subjected to sound absorption (such as a combustion chamber). The following perforated plate aperture radii are preferred: 0.5mm, 1 mm. The pore plate is preferably made of brass and is drilled, milled or drilled by laser. The following perforated plate porosities are preferred: 2 to 5 percent. The plate thickness of the perforated plate is 1-2 mm. The following depths of the secondary cavities are preferred: 0.05-0.50m, and the sound absorption coefficient of the sound absorber to the target frequency (namely the incident sound frequency generated by the equipment to be silenced) is maximized according to the calculation and optimization of the depth of the primary cavity.

Measure bias current double-deck perforated plate sound absorbing device's sound absorption characteristic through the acoustic impedance pipe, include: the test method comprises a frequency sweep test for measuring the change rule of the acoustic reflection coefficient along with the incident acoustic frequency, a sound intensity changing test for measuring the change rule of the acoustic reflection coefficient along with the incident acoustic intensity, a cavity depth changing test for measuring the change rule of the acoustic reflection coefficient along with the depth of a primary cavity, and an air volume changing test for measuring the change rule of the acoustic reflection coefficient along with the deflection speed.

The structural parameters of the actual pore plate are further optimized through experiments, the more suitable aperture and pore space are selected, and the sound absorption effect of the sound absorber is improved. And the depth of the primary cavity is changed by adjusting the stroke of the piston, so that the effective sound absorption frequency band of the sound absorption device is changed.

In the above arrangement, the air entering the sound absorber should be kept dry with a relative humidity of no more than 70%. The temperature must not be too high (not exceeding 100 ℃) in order to avoid that the piston cannot advance or retreat due to thermal expansion. Meanwhile, oil is needed to lubricate and seal the gap between the piston and the inner wall of the pipe periodically.

In the above-described devices, the orifice plate porosity σ cannot exceed 10%, otherwise the inter-orifice interaction needs to be considered. The thickness of the orifice plate should not exceed 5mm because the calculation is based on thin plates. The actual noise control effect must be determined experimentally because the computational model is based on linear acoustic theory and non-linear acoustic effects need to be considered if the sound pressure level of the incident sound exceeds 130 dB.

The sound absorption principle of the bias flow perforated plate is that incident sound energy is converted into turbulent kinetic energy in a vortex shedding mode when incoming flow passes through a small hole, or heat energy is converted in a mode that the incoming flow rubs with a hole wall, and therefore the purpose of sound elimination is achieved. Compared with the traditional porous sound absorption materials such as metal foam and glass fiber, the porous plate sound absorption structure is not limited by materials and is easy to process and manufacture. Compared with the traditional non-flow perforated plate, the non-flow perforated plate has better sound absorption effect, and the sound absorption frequency band of the multi-layer plate is wider than that of a single-layer plate. The bias flow double-layer perforated plate is arranged at the air inlet section of the combustor, so that the radiation noise caused by unstable combustion can be effectively eliminated, and the safe operation of equipment is ensured.

The invention has the beneficial effects that:

the bias current is utilized to improve the sound absorption effect (namely, the sound absorption coefficient is improved) of the double-layer porous plate, the double-layer plate is utilized to solve the problem that the effective sound absorption frequency band of the single-layer plate is narrow, and the piston of the adjustable back cavity is utilized to adjust the sound absorption frequency band of the sound absorber according to the actual conditions;

the bias flow double-layer porous plate sound absorption device with the adjustable back cavity depth can be installed at a gas collection chamber of a combustor, the pressure fluctuation of a gas inlet section is fully inhibited by adjusting the upstream acoustic boundary condition, and the noise transmission is cut off, so that the purposes of stabilizing combustion and improving the operation safety of equipment are achieved.

Drawings

FIG. 1 is a schematic view of a bias flow double perforated plate sound absorber with adjustable back cavity depth;

FIG. 2 is a schematic diagram of measuring the sound absorption coefficient of a perforated plate using a bias flow acoustic impedance tube;

FIG. 3 is a schematic diagram of a perforated plate sample of a biased flow double layer perforated plate sound absorber;

FIG. 4 is a comparison of the theoretical value of the acoustic reflection coefficient of the acoustic absorber and the actual measurement result; wherein A represents the acoustic reflectance patternThe quantity | R | varies with the frequency of the incident sound, and B represents the phase of the acoustic reflection coefficient

As a function of incident acoustic frequency;

in the figure: 1-an intake upstream orifice plate; 2-an air intake downstream orifice plate; 3-an air inlet pipe section; 4-a secondary cavity; 5-primary cavity; 6-air inlet pipe of piston head; 7-a movable piston with air inlet holes; 8-a dynamic pressure sensor; 9-impedance tube; 10-an exhaust port; 11-a loudspeaker.

Detailed Description

In the following description, numerous 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 present invention is not limited to the specific embodiments disclosed below.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

Referring to fig. 1 and 2, the drift double-layer porous plate sound absorption device in the embodiment includes an air inlet pipe section 3, wherein one end of the air inlet pipe section 3 is provided with a movable piston 7 with an air inlet hole, and the other end is provided with an air outlet 10. An air inlet upstream pore plate 1 and an air inlet downstream pore plate 2 are sequentially arranged in the air inlet pipe section 3 along the air inlet direction, and micropores are arranged in the air inlet upstream pore plate 1 and the air inlet downstream pore plate 2 in an array mode. A first-stage cavity 5 with adjustable depth is formed between the movable piston 7 and the air inlet upstream pore plate 1, a second-stage cavity 4 is formed between the air inlet upstream pore plate 1 and the air inlet downstream pore plate 2, and an intracavity sound absorption structure is formed by the two-stage cavities. Air enters the sound absorber through an air inlet hole at the head of the movable piston 7, sequentially passes through the air inlet upstream orifice plate 1 and the air inlet downstream orifice plate 2, and finally enters equipment to be subjected to sound absorption (such as a combustion chamber or a hearth of a combustion engine).

In this embodiment, the cross sections of the air intake upstream perforated plate 1, the air intake downstream perforated plate 2 and the air intake pipe section 3 are circular, wherein one perforated plate has a structure as shown in fig. 3, micropores are distributed in a square matrix, the hole radius a of the micropores is 0.5-1mm, the hole center distance d is 5-10mm, and the porosity σ is 2-5%

The movable piston 7 is made of stainless steel material with piston rings embedded inside the piston groove and lubricating oil is used to fill the air gap between the movable piston 7 and the inner wall of the intake pipe section 3. The depth of the primary cavity 5 is generally 0.05-0.5m, and the depth of the secondary cavity 4 is generally 0.05-0.5 m. The depth of the secondary cavity 4 can not be adjusted after the sound absorption device is assembled, the depth of the primary cavity 5 can be adjusted by twisting a claw screw of a movable piston 7 at the end part, the piston moves forwards or backwards along the airflow direction, and the depth of the primary cavity is correspondingly reduced or increased, so that the purpose of adjusting the sound absorption frequency range is achieved.

The present embodiment is directed to a combination of two perforated plates with different apertures and the same porosity, and the law of change of acoustic reflection coefficient with incident acoustic frequency at the optimal bias flow rate is determined, and a specific implementation of the present application is described.

The incident acoustic frequency is assumed to be 160 Hz. The configured double perforated plates comprise plate thickness air inlet upstream perforated plates and air inlet downstream perforated plates, the plate thickness h is 1.00mm, the porosity sigma is 3.14%, and the optimal bias flow rate u of the corresponding double plates_pIt was 6.92 m/s. The radius a of the small holes of the air inlet upstream orifice plate is 1.00mm, and the hole spacing d is 9.40 mm; the radius a of the small holes of the air inlet downstream orifice plate is 0.50mm, and the hole distance d is 4.70 mm. The depth of the primary cavity is 0.150mm, and the depth of the secondary cavity is 0.357 mm.

Two perforated plates were mounted in the impedance tube shown in fig. 2 for acoustic testing, with a bias flow double perforated plate sound absorber with adjustable back cavity on the left side and a horn driven by a power amplifier (YAMAHA P5000S) on the right side. The impedance tube is 1015mm long, and the first acoustic cut-off frequency is 1490 Hz. The air inlet upstream pore plate, the air inlet downstream pore plate and the horn are respectively arranged on the position where x is 0mm and L is₂357mm and L₅1372 mm. Air enters the resistance tube through an air inlet hole at the head of the piston and is finally discharged from an air outlet. The amplitude and frequency of the excitation sound of the horn are adjusted by digital signal generators (GWINSTEKAFG-2105). M₁、M₂For inserting dynamic pressure transmissionsA sensor (CYG type 1406) to measure the sound pressure at a specific location of the impedance tube. The sound pressure signal is sent to Labview operated at the PC end through a multi-channel digital acquisition card (NI, USB6210) for data preprocessing and storage. The sampling time was 5s and the sampling frequency was 20 kHz.

The acoustic reflection coefficient of the bias flow double-layer perforated plate is measured by using a double-microphone transfer function method and a sensor interchange technology. Double microphone transfer function method even through M₁、M₂The acoustic transfer functions of the two pressure measuring points are obtained by the dynamic pressure time sequence data, and the acoustic transfer functions can be obtained by referring to national standard documents: GB T18696.2-2002. The transducer interchange technique is to measure the acoustic transfer function, then to interchange the microphone position and measure again, finally to take the arithmetic square root value of the product of the two test results as the final acoustic transfer function value H₁₂. The average sound velocity c can be obtained by measuring the intake air temperature and taking the gas constant into consideration₀Then, according to fig. 2, the acoustic characteristic impedance of the bias flow double-layer porous plate is calculated according to the following formula:

where ζ is the characteristic acoustic impedance measured, H₁₂Is the acoustic transfer function, ω is the acoustic angular frequency, c₀Is the average speed of sound, L₃For a microphone M₁Distance to upstream perforated plate, L₄For a microphone M₂Distance to upstream perforated plate, L₂The spacing between two perforated plates. i is an imaginary unit.

Obtaining the acoustic characteristic impedance of the actually measured bias flow double-layer porous plate, and obtaining an acoustic reflection coefficient according to the following formula:

the sound absorption coefficient can be further obtained according to the actually measured sound reflection coefficient:

α＝1-|R|²

FIG. 4 is a comparison of the theoretical value of the acoustic reflection coefficient of the acoustic absorber and the actual measurement result; wherein A represents the variation of the acoustic reflection coefficient modulus | R | with the incident acoustic frequencyB diagram shows acoustic reflection coefficient phaseAs a function of the incident acoustic frequency. The modulus of the acoustic reflection coefficient is firstly reduced and then increased along with the increase of the frequency, and a main peak and a secondary absorption peak exist near 150-160Hz and 315-325Hz respectively. The acoustic reflection coefficient reaches the minimum value near the main peak 150-160Hz, and the modulus of the acoustic reflection coefficient is smaller than 0.1, which means that the acoustic absorption coefficient is larger than 0.99, namely 99% of incident acoustic energy is effectively absorbed by the bias flow double-layer porous plate sound absorption device with adjustable back cavity depth.

Meanwhile, as can be seen from fig. 4, the calculation results of the modulus and the phase of the acoustic reflection coefficient are well matched with the measured values, and the sound absorption frequency band is wide, the incident sound of 250-450Hz can still be effectively absorbed, and the acoustic reflection coefficient does not exceed 0.5, i.e. 75% of the sound energy is effectively absorbed even if the depth of the primary cavity is not adjusted by the piston.

In order to make the practical practicability of the bias flow double-layer perforated plate sound absorption device with adjustable back cavity depth stronger, the main frequency of the equipment to be muffled can be diagnosed in advance by sound or pressure measuring equipment, and the optimal first-stage cavity depth and second-stage cavity depth can be determined by a calculation program. When the sound absorption device is actually installed, the depth of the primary cavity can be changed by adjusting the stroke of the piston, and the sound absorption effect on the target frequency is further optimized.

The above description is only exemplary of the preferred embodiments of the present invention, and is not intended to limit the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.