A passive noise reduction device and method based on rigid geometric contour constraining gas phase aggregation region

Abstract

The present application belongs to the technical field of passive acoustic control, and particularly relates to a passive noise reduction device and method based on rigid geometric profile constraint of gas phase aggregation area. The device comprises a first rigid member and a second rigid member, and a matching micro gap with a width of 0.02 mm to 0.2 mm is formed between the two. Under the action of an incident sound field, a transient negative pressure area is formed in the micro gap, and a micro-scale gas phase aggregation area is spontaneously generated; the generation, compression and collapse of the gas phase aggregation area are constrained by the rigid geometric profile, sound energy is converted into heat energy, wideband noise reduction and pulsating sound pressure suppression are achieved. The device is a full-rigid integrated structure, and does not require porous materials, damping films and electric control systems, is resistant to high temperature and oil stains, is not blocked, and is suitable for industrial mass production.

Description

Technical Field

[0001] This invention belongs to the field of passive acoustic control technology, specifically relating to a passive noise reduction device and method based on rigid geometric contour constraints on gas phase accumulation regions. Background Technology

[0002] In equipment such as fluid pipelines, pump and valve assemblies, ventilation and air conditioning systems, automotive thermal management circuits, industrial rotating machinery, and household range hoods, fluid disturbances, boundary layer separation, and structural vibrations can easily induce mid-to-high frequency broadband noise and periodic howling, adversely affecting equipment operation smoothness, user experience, and structural durability. Currently, commonly used passive acoustic control methods in engineering mainly include porous sound-absorbing materials, viscoelastic damping patches, resonant cavity structures, and a small number of active noise cancellation systems.

[0003] Porous materials dissipate sound energy through air friction and fiber vibration within their internal pores, offering lower cost. However, they suffer from poor resistance to high temperatures and oil stains, are prone to dust accumulation, powdering, aging, and collapse, and have short lifespans under harsh conditions, posing a risk of contamination. This is particularly true in range hoods, where sound-absorbing cotton is highly susceptible to oil contamination and failure. Viscoelastic damping structures dissipate vibrational energy through material deformation, but they are highly temperature-sensitive, softening at high temperatures and becoming brittle at low temperatures. Prolonged use can lead to delamination and failure, making them unsuitable for oily or high-pressure environments. Resonant acoustic structures are effective only within a narrow frequency range; their noise reduction capability drops sharply beyond the resonant frequency, and their micropores are prone to clogging, resulting in high processing and maintenance costs. While active noise cancellation systems can achieve good low-frequency noise reduction, they rely on power supplies and complex electronic control units, leading to low reliability and making stable application difficult in high-vibration, unpowered, high-temperature, and oily industrial, automotive, and kitchen appliance environments.

[0004] It should be noted that existing acoustic control technologies generally rely on material constitutive properties or resonant structures, all of which regard cavitation as harmful and aim to suppress it. No technical solution has yet emerged that uses the dynamics of micro-gap gas-phase accumulation regions as the core acoustic damping mechanism and achieves active constraint through rigid geometry. For a long time, the field has regarded cavitation as harmful and suppression as the conventional approach, without considering the dynamic behavior of micro-gap gas-phase accumulation regions as the core control mechanism for acoustic damping. Therefore, this invention breaks through conventional industry biases, transforming the dynamic evolution effect of micro-scale gas-phase accumulation regions into a beneficial acoustic energy dissipation mechanism. In principle, it avoids the inherent defects of traditional solutions, such as easy aging, easy clogging, narrow bandwidth, and poor environmental adaptability, providing a novel passive control path. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a device and method for achieving passive, wideband, adaptive acoustic damping and noise suppression with a purely rigid structure, which addresses the technical defects of existing noise reduction solutions such as poor environmental adaptability, easy attenuation, narrow bandwidth, and inability to work stably for a long time under extreme conditions.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A passive noise reduction device based on a rigid geometric contour constraining a gas-phase accumulation region includes a first rigid component and a second rigid component, which fit together and define a fitting micro-gap with a width of 0.02 mm to 0.2 mm between them. At least one rigid component has a rigid geometric contour formed on its mating surface. The rigid geometric contour is at least one of a step, groove, ridge, or curved surface undulation, used to spatially constrain the morphology and evolution of the micro-scale gas-phase accumulation region. Under the action of an incident sound field, a local transient negative pressure zone can be formed within the fitting micro-gap, thereby generating a micro-scale gas-phase accumulation region. This micro-scale gas-phase accumulation region refers to a gas-rich area formed by ambient air being drawn into the micro-gap. Through the periodic compression, expansion, and collapse process of the micro-scale gas-phase accumulation region under the alternating pressure of the incident sound field, sound energy is converted into heat energy, achieving acoustic damping and noise suppression.

[0008] A passive noise reduction method based on a rigid geometric profile constraining a gas phase accumulation region includes: setting a fitting micro-gap between rigid components and setting a rigid geometric profile; placing the fitting micro-gap in a sound field to form a microscale gas phase accumulation region under the excitation of the incident sound field; converting sound energy into heat energy through the periodic compression, expansion, and collapse process of the microscale gas phase accumulation region under the alternating pressure of the incident sound field; and controlling the pressure change law and dissipation intensity of the gas phase accumulation region through the rigid geometric profile to achieve passive broadband acoustic damping and noise reduction.

[0009] The beneficial effects of this invention lie in transforming the dynamic effects of microscale gas-phase accumulation regions into acoustic energy dissipation mechanisms. By constraining the evolution of gas-phase accumulation regions through rigid geometric contours, it avoids the inherent defects of traditional solutions that rely on material constitutive properties. Employing a fully rigid, integrated structure, it eliminates the need for porous materials, damping films, and electronic control systems. It is high-temperature resistant, oil-resistant, non-clogging, and reliable under all operating conditions. Based on the same core structure, various acoustic damping functions can be achieved by selecting different rigid geometric contours, demonstrating strong versatility. All structures can be integrally molded using injection molding, die casting, or precision machining processes, possessing mature conditions for large-scale mass production and economic viability. This invention provides a passive noise reduction framework based on rigid geometric contours constraining gas-phase accumulation regions, rather than a concrete product limited to a single gap or contour. Attached Figure Description

[0010] Figure 1 This is a three-dimensional schematic diagram of the overall appearance of the device of the present invention.

[0011] Figure 2 This is a structural schematic diagram of the basic uniform gap configuration of the present invention.

[0012] Figure 3 This is a structural schematic diagram of the advanced gradient gap configuration of the present invention.

[0013] Figure 4 This is a schematic diagram of the structure of the enhanced variable curvature coupling stepped configuration of the present invention.

[0014] Explanation of reference numerals in the attached figures:

[0015] 1-First rigid component; 2-Second rigid component; 3-Matching micro-gap; 4-Rigid geometric profile; 5-Microscale gas phase accumulation region; 6-Multi-level micro-scale expansion step. Detailed Implementation

[0016] It should be noted that existing acoustic structures have inherent shortcomings in terms of mass production assembly tolerances, micro-gap blockage, thermal expansion deformation, and long-term cavitation erosion. The passive noise reduction framework based on rigid geometric contour constraints on the gas phase accumulation region disclosed in this invention, and the adaptive optimizations made to address the aforementioned mass production defects (such as self-cleaning lips, conjugate fit, and filtration structure), are all applications of conventional engineering methods in the field and do not constitute a limitation on the core mechanism of this invention.

[0017] To make the technical solution and beneficial effects of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. 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.

[0018] This invention provides a passive noise reduction device and method for rigidly geometrically constraining a gas-phase accumulation region. Its core principle lies in: setting a micro-gap between the mating surfaces of a first and second rigid component; when an incident sound wave acts on this micro-gap, the local pressure fluctuates periodically with the sound field, forming a transient negative pressure zone during the rarefaction phase of the sound wave, drawing in ambient air and forming a stable microscale gas-phase accumulation region. This gas-phase accumulation region continuously undergoes generation, compression, expansion, and collapse processes under the drive of the sound field. Through internal gas friction, gas-solid interface friction, and microscale vortex fragmentation induced by interface instability during collapse, acoustic energy is irreversibly converted into heat energy, thereby achieving noise attenuation. The rigid geometric contour on the mating surface constrains the volume change rate, pressure gradient, and collapse location of the gas-phase accumulation region, allowing the acoustic damping characteristics to be accurately output according to the design target.

[0019] To address the microscale acoustic cavitation that may be caused by the collapse of gas-phase accumulation zones, an integrally molded micro-pit sacrificial array can be set in the collapse concentration zone to guide the collapse to occur in non-core functional areas, protecting the precision-fitted contours. After 2000 hours of accelerated aging verification, the device using this structure showed a noise reduction attenuation of ≤1.5dB, ensuring stable acoustic performance throughout its entire life cycle.

[0020] It needs to be further clarified that, in order to ensure that low-frequency sound waves can effectively penetrate deep into the micro-gap and excite the gas phase accumulation region, the depth of the micro-gap along the direction of sound wave propagation is... Should meet: ,in For the speed of sound, The minimum effective frequency is specified. In some embodiments, when the target low frequency is 200Hz, the micro-gap depth is preferably greater than 0.8m. For applications with limited depth, low-frequency compensation can be achieved by setting a micro-resonant cavity array at the end of the micro-gap. This design is a conventional acoustic impedance matching method in the art and does not constitute a limitation on the core mechanism of this invention.

[0021] The physical principles upon which this invention is based will be explained below.

[0022] In this invention, the "microscale gas accumulation region" refers to a gas-rich area formed within a micro-gap due to the local pressure dropping below ambient atmospheric pressure under the influence of an incident sound field. This gas accumulation region undergoes a periodic process of formation, compression, expansion, and collapse driven by alternating sound wave pressure.

[0023] It should be noted that the formation of the transient negative pressure zone is not due to the direct generation of equivalent macroscopic static pressure from acoustic pressure. Within a micrometer-scale gap, the alternating airflow induced by acoustic waves is strongly constrained by a rigid wall. During the extremely short duration of the rarefied phase of the acoustic wave, local gas separates from the wall due to inertial effects, forming a microscale low-pressure zone. Its instantaneous pressure value can be far lower than the acoustic pressure amplitude of the rarefied phase. This phenomenon can be compared to the narrow-slit nonlinear effect in acoustics: when acoustic waves pass through a micro-gap much smaller than the thickness of the viscous boundary layer, the inertial and viscous effects of the gas particles couple, generating instantaneous pressure fluctuations in a localized region that are far higher than the pressure gradient of the free acoustic field. This device utilizes precisely this microscale transient dynamic effect, rather than the direct pressure conversion in the macroscopic free acoustic field.

[0024] Under standard operating conditions (temperature 23±2℃, atmospheric pressure 101.325 kPa, air medium), heat exchange within the micro-gap is sufficient, the number of gas moles is approximately constant, and the behavior of the microscale gas accumulation region satisfies the ideal gas law:

[0025]

[0026] in, The pressure within the gas phase accumulation region, The volume of the gas phase accumulation region. The number of moles of gas. Let be the ideal gas constant. This refers to the thermodynamic temperature. Sound pressure fluctuations cause periodic changes in the gap volume, and pressure is inversely proportional to volume.

[0027]

[0028] The pressure gradient in the gas accumulation region is determined by the slope of the rigid geometric profile:

[0029]

[0030] Under periodic excitation of the sound field, the volume change rate With sound wave frequency It is directly related to the geometric profile of the gap and the pressure difference inside and outside the gas accumulation zone. Determined by the ideal gas law and geometric constraints, the correspondence between structural parameters and macroscopic acoustic impedance is established. The acoustic energy dissipation power can be expressed as:

[0031]

[0032] The aforementioned mechanical work is ultimately dissipated into the environment as heat through molecular collisions during gas viscous shearing and vortex breaking, constituting an irreversible thermodynamic process. The equivalent acoustic damping coefficient increases with increasing incident sound pressure level, resulting in adaptive damping output.

[0033]

[0034] When the gas-phase accumulation zone collapses at the end of compression, the gas-solid interface breaks down and induces microscale vortex structures, which further dissipate residual acoustic energy through fluid viscosity. This process and the dynamics of the gas-phase accumulation zone are different stages of the same physical process, together constituting a complete acoustic energy dissipation mechanism.

[0035] Based on the aforementioned physical principles, the basis for determining the key parameters is further elaborated. Table 1 shows the transient negative pressure peak and gas phase accumulation zone formation state corresponding to different gap widths, as measured by bench tests (according to GB / T6881.2-2017 reverberation chamber method) at an incident sound pressure level of 100 dB. It should be noted that the stable formation of the gas phase accumulation zone does not require the transient negative pressure peak to always be higher than a certain fixed threshold, but rather depends on the combined effects of the negative pressure duration, gap geometric constraint, and gas intake compensation. In smaller gaps, although the peak negative pressure is relatively low, the stronger wall constraint effect and slower gas leakage result in a longer negative pressure maintenance time, thus allowing for the stable formation of a gas phase accumulation zone.

[0036] Table 1: Correspondence between gap width and gas accumulation region formation state under incident sound pressure level of 100 dB

[0037] Gap width (mm) Peak value of transient negative pressure (kPa) Formation state of gas phase accumulation region 0.02 1.8 Stable formation 0.06 2.8 Stable formation 0.10 3.5 Highest activity 0.15 2.2 Stable formation 0.20 1.2 It can still be maintained

[0038] When the incident sound pressure level drops to 85 dB, only devices with a gap width in the range of 0.08 mm to 0.15 mm can trigger a gas phase accumulation zone with the assistance of a pre-negative pressure guiding structure. The above data shows that the transient negative pressure peak value has a non-linear relationship with the gap width, and the peak value appears in the range of 0.08 mm to 0.12 mm, which is the preferred operating range of the device of the present invention.

[0039] To verify the robustness of acoustic performance under mass production tolerances, three samples of 0.08mm, 0.10mm, and 0.12mm were selected from the same batch of injection molds and with the same process parameters, using a nominal gap of 0.10mm as the benchmark. Tests were conducted at a sound pressure level of 100dB. All three samples stably formed a gas phase accumulation region, with an average insertion loss fluctuation of ≤2.5dB in the mid-to-high frequencies, indicating that the noise reduction function was fully realized. This data demonstrates that the present invention possesses excellent robustness within IT7-level mass production tolerances and does not exhibit any engineering defects that would lead to failure due to micron-level deviations.

[0040] Furthermore, regarding the frequency dependence of gas-phase accumulation region collapse, experiments show that under conditions of incident sound pressure level ≥100dB and frequency ≥500 Hz, the gas-phase accumulation region can completely undergo the processes of generation, compression, expansion, and collapse within one acoustic cycle. Collapse-induced micro-vortex dissipation becomes the main contributor to sound energy attenuation. At lower frequencies (50 Hz~500Hz), the gas-phase accumulation region mainly exhibits periodic expansion and compression, and the collapse phenomenon is relatively weakened. At this time, low-frequency damping is mainly provided by the micro-resonant cavity array, and the two work together to achieve full-band noise reduction coverage.

[0041] The key structural features of the present invention will be described in detail below.

[0042] Rigid geometric profiles refer to intentionally formed geometric features on mating surfaces that differ from ideal smooth planes, including but not limited to steps, grooves, protrusions, and surface undulations. Their function is to regulate the acceleration, deceleration, separation, and reattachment of airflow by locally altering the cross-sectional shape of micro-gap, thereby constraining the growth direction, collapse location, and pressure pulsation intensity of the gas accumulation zone. In this invention, rigid geometric profiles include both macro-scale mating surface configurations (such as uniform gaps, gradually varying gaps, and variable curvature mating surfaces) and micro-scale surface microstructures (such as micro-vortex dissipation structures and micro-toothed damping surfaces), together constituting a full-scale spatial constraint system for micro-scale gas accumulation zones.

[0043] The pre-negative pressure guiding structure addresses the technical problem of insufficient sound pressure level under idling, low-speed, and low-frequency operating conditions, which hinders the spontaneous formation of a gas phase accumulation zone. This structure utilizes local pressure fluctuations generated by pipeline vibration, fluid pulsation, or the structure's own micro-vibration to create a transient negative pressure zone under conditions where the sound pressure level is not lower than 85 dB and the frequency is not lower than 50 Hz, thus achieving automatic triggering and maintenance of the gas phase accumulation zone. In one specific implementation, the pre-negative pressure guiding structure is a wedge-shaped guiding surface located at the inlet of the mating micro-gap. The angle between the wedge-shaped guiding surface and the mating surface is 10°–30°, and its length along the main incident direction of the sound wave is 2 mm–5 mm. The gap width at its front end is slightly larger than that at its rear end, forming a converging flow channel. When pipeline vibration or fluid pulsation causes gas to flow through this converging flow channel, the flow velocity increases and the pressure decreases, thereby forming a local negative pressure zone at the junction of the rear end of the wedge-shaped guiding surface and the micro-gap, assisting in the triggering of the gas phase accumulation zone. This structure is part of the rigid geometry, integrally formed with the rigid component, and requires no additional parts.

[0044] It should be noted that the "auxiliary triggering under conditions where the sound pressure level is not lower than 85dB" mentioned in claim 4 refers to the ability to achieve auxiliary triggering under typical conditions covering the main target noise reduction frequency band (e.g., 100Hz to 8kHz). For extreme low-frequency conditions below 50Hz, those skilled in the art can meet the triggering conditions by increasing the convergence ratio of the guide structure or introducing additional vibration excitation, according to actual needs. This adaptive adjustment does not change the core working principle of pre-negative pressure guide.

[0045] A micro-cavity array is used to further extend low-frequency noise reduction capabilities and achieve full-band coverage. This array employs a quarter-wavelength tube, a Helmholtz resonator, or a micro-slit plate structure. The cavity diameter is 3 mm–10 mm, the depth is 2 mm–8 mm, and the aperture is 0.5 mm–2 mm. The resonant frequency covers the low-frequency range of 50 Hz–500 Hz, forming a complementary coupling with the damping mechanism of the gas phase accumulation region (mainly acting on mid-to-high frequencies and howling frequencies). In one specific implementation, the opening end of the micro-cavity array is directly connected to a mating micro-gap through micro-holes with apertures of 0.5 mm–2 mm, allowing sound pressure fluctuations within the micro-gap to directly excite the resonator. The micro-holes are located downstream of the mating micro-gap (near the sound outlet), and can be arranged in single or multiple rows along the gap width direction. The center-to-center distance between adjacent micro-holes is 1.5–3 times the cavity diameter. Alternatively, the opening of the resonator array faces directly towards the external sound field, utilizing the flexible vibration of the component walls to achieve acoustic coupling with the damping of the gas phase accumulation region within the micro-gap. Preferably, the resonant cavity opening is located downstream of the mating micro-gap to capture residual acoustic energy dissipated through the gas phase accumulation region, forming a cascaded dissipation effect. The resonant cavity array is integrally formed with the rigid component, requiring no additional assembly. Through acoustic impedance matching design, the device achieves uniform noise reduction across the entire frequency range of 50 Hz to 16 kHz.

[0046] The self-cleaning micro-lip is used to ensure stable noise reduction performance throughout the entire life cycle. This structure utilizes the local high-pressure pulse generated at the moment of collapse of the gas phase accumulation zone to form a reverse micro-purge airflow at the gap inlet, automatically expelling micro-dust particles that have invaded the gap.

[0047] The microporous filtration and self-cleaning microlip structure of this invention is designed for dust (particle size 1μm~100μm) and oil stains in normal industrial environments. For extreme working conditions containing fibers, large hard particles, and heavy carbon deposits, those skilled in the art can add a pre-cyclone filter at the system inlet. This does not change the core acoustic control principle of micro-gap cavitation damping and can completely eliminate the risk of noise reduction failure caused by micro-gap blockage.

[0048] In a preferred embodiment, the self-cleaning micro-lip has a wedge-shaped cross-section, with its tip pointing towards the interior of the mating micro-gap. The angle between the wedge surface and the mating surface is 30°–60°, preferably 45°. When the gas phase accumulation zone collapses near the lip, the generated high-pressure pulse, guided by the wedge-shaped surface, forms an instantaneous jet pointing towards the outside of the gap inlet. The peak jet velocity can reach 5 m / s–15 m / s, sufficient to blow away micro-dust particles attached to the inlet edge. The lip is continuously arranged along the gap edge, covering more than 70% of the entire inlet circumference. The self-cleaning micro-lip is integrally formed with the rigid component, requiring no additional maintenance. Accelerated aging tests have verified that after 2000 hours of continuous operation in an environment with a dust concentration of 50 mg / m³, the gap size change is ≤0.005 mm, and the noise reduction attenuation is ≤1.5 dB.

[0049] A conjugate acoustic guide surface is used to reduce the device's sensitivity to installation location. This surface is an integrated extension of the outer contour of a rigid component, designed using a Bézier curve or a variable curvature spline surface. Its curvature variation causes incident sound waves to converge towards the entrance region of the mating microgap after reflection or diffraction. In one specific implementation, the conjugate acoustic guide surface is one or more segments of circular arc or parabolic cylinder, with its focal point or directrix located near the microgap entrance. This focuses the energy of incident sound waves from different directions into the microgap, enhancing the triggering intensity of the gas phase accumulation zone. Experiments show that without the conjugate guide surface, the noise reduction decreases by approximately 5 dB to 8 dB when the sound wave incident angle deviates by 30° from the direction directly opposite the microgap entrance; while with the conjugate guide surface, the noise reduction decreases by less than 2 dB at the same incident angle deviation.

[0050] Based on the above principles and structural features, this invention employs a three-tiered configuration: the basic configuration uses uniform, equal-thickness micro-gap to achieve basic noise reduction in the mid-to-high frequencies; the advanced configuration uses gradually changing or stepped gaps, where the stepped gaps increase or decrease progressively along the main incident direction of the sound wave to broaden the effective frequency band and enhance damping strength; the reinforced configuration uses a combination of variable curvature surfaces and multi-level shrinking and expanding steps to introduce sound wave deflection, phase interference, and nonlinear strong damping, achieving deep broadband noise reduction. The entire device is integrally molded from a single material, adaptable to injection molding, die casting, and machining processes, requiring no additional acoustic materials and can be used directly as a structural component.

[0051] To further counteract gap drift caused by thermal expansion and reduce assembly alignment difficulty, in some embodiments, an integrally formed conjugate guide slope (angle 3°~5°) is provided at the end of the mating surface. Except for the micro-gap area of ​​the mating surface, a clearance step of more than 0.5mm is provided on the non-working surface, and the parallelism is automatically calibrated during assembly. At the same time, a combination of two materials with complementary coefficients of thermal expansion can be used to control the gap change within 0.002mm in the whole temperature range (-40℃~150℃), and the noise reduction performance fluctuation is less than 1dB.

[0052] The width of the micro-gap directly determines the ability to form a gas accumulation zone and the pressure holding characteristics. Bench tests (based on the reverberation chamber method of GB / T 6881.2-2017) showed that when the gap is less than 0.02 mm, the flow resistance is too high to form an effective transient negative pressure; when it is greater than 0.2 mm, gas leakage is too rapid, making it impossible to maintain a stable gas accumulation zone. These ranges remain effective within a temperature range of -40℃ to 150℃.

[0053] To demonstrate that the noise reduction effect originates from the dynamics of the gas-phase accumulation zone rather than structural resonance or viscous dissipation, a comparative experiment was designed. The same device was used for comparative testing in air and a degassed liquid medium. The degassed liquid medium consisted of deionized water boiled and maintained at a slight boil for 30 minutes, then covered with a low-volatility oil film and sealed to room temperature, with a measured dissolved oxygen content below 1 ppm. Under these conditions, no observable gas cavities could form within the microgap. Simultaneously, to eliminate the influence of changes in acoustic boundary conditions, a control experiment was conducted: an impermeable flexible film was wrapped around the device to block the microgap from the atmosphere, while maintaining ambient air pressure inside. The results showed that when only the connection was blocked without evacuation, the noise reduction decreased by less than 2 dB; however, in the degassed liquid medium environment, the noise reduction significantly decreased and the damping characteristics fundamentally changed. These comparative experiments demonstrate that the core contribution of this invention originates from the dynamic effect of the gas-phase accumulation zone, rather than structural resonance or simple viscous boundary layer dissipation.

[0054] The following parallel embodiments further illustrate the specific implementation of the present invention. All embodiments were performed under standard test conditions: temperature 23±2℃, atmospheric pressure 101.325 kPa, incident sound pressure level 100 dB, air medium, and sample size. The testing standard is based on GB / T 6881.2-2017, the reverberation chamber method. All noise reduction values ​​are calculated based on the insertion loss measured according to this standard, using an average energy distribution over 1 / 3 octave band within the effective noise reduction frequency band.

[0055] Example 1: Basic configuration (uniform gap)

[0056] This embodiment demonstrates the specific application of the core principle in basic acoustic damping function. The first rigid member 1 and the second rigid member 2 form a mating structure, producing a uniform and stable micro-gap 3 with a width set at 0.10 mm. The surface roughness of the mating surfaces is...

[0057] Ra≤0.8 μm. A continuous and uniform microscale gas phase accumulation region 5 is generated under acoustic field excitation, primarily achieving stable attenuation of mid-to-high frequency noise from 1kHz to 8kHz, with an average insertion loss of 15dB to 18dB. The basic configuration is injection molded from 30% glass fiber reinforced PA66, suitable for mild operating conditions such as household appliance housings and conventional air ducts.

[0058] Example 2: Advanced configuration (gradual gap)

[0059] This embodiment demonstrates the specific application of the core principle in broadband acoustic damping. By linearly shrinking the micro-gap 3 from 0.12 mm to 0.05 mm along the main incident direction of the sound wave, with a shrinkage length of 20 mm, different positions correspond to different gas phase accumulation zones with varying stiffness and acoustic impedance, forming continuous acoustic energy dissipation and phase interference. This effectively broadens the noise reduction bandwidth to 315 Hz–12.5 kHz, with an average insertion loss of 18 dB–22 dB.

[0060] The advanced configuration features a pre-negative pressure guiding structure integrally formed at the micro-gap inlet. This pre-negative pressure guiding structure is a wedge-shaped guiding surface with an angle of 15° to the mating surface, a length of 3 mm along the main incident direction of the sound wave, a front gap width of 0.15 mm, and a rear gap width of 0.12 mm. It can assist in triggering the gas phase accumulation zone under low sound pressure conditions of 85 dB. This embodiment is die-cast from ADC12 aluminum alloy and is suitable for medium-noise operating conditions such as pump body shells, chassis covers, and general industrial pipelines.

[0061] Example 3: Reinforced configuration (variable curvature + step)

[0062] This embodiment demonstrates the specific application of the core principle in deep broadband noise reduction. The mating surface employs a continuously variable curvature surface, with the radius of curvature smoothly transitioning from 20 mm at the inlet to 5 mm at the outlet along the main incident direction of the sound wave, while maintaining a constant rate of curvature change. Simultaneously, a three-stage micro-expansion step 6 is configured, sequentially along the main incident direction of the sound wave: the first step shrinks the mating micro-gap from 0.10 mm to 0.06 mm; the second step maintains a constant width of 0.06 mm; and the third step expands the mating micro-gap from 0.06 mm to 0.12 mm. Each step has a width of 0.8 mm, and the step surface is perpendicular to the mating surface. This shrink-constant-expansion configuration can induce local vortex shedding and pressure abrupt changes when the gas phase accumulates in the step region, significantly enhancing nonlinear damping. The enhanced configuration achieves an average insertion loss of 22 dB to 28 dB across the entire frequency band from 315 Hz to 16 kHz. It is precision machined from 45# steel using CNC and is suitable for extreme operating conditions such as engine compartments, hydraulic lines, industrial fans, and high-pressure ducts, where conditions are high temperature, high sound pressure, and high oil content.

[0063] Example 4: Reinforced configuration + conjugate guide surface

[0064] Based on the reinforced configuration, a conjugate acoustic guide surface is incorporated around the periphery of the device. This surface is an integrated extension of the rigid component's outer contour, designed using a Bezier curve, capable of focusing, deflecting, and redistributing energy from incident sound waves. Experiments show that, in the reinforced configuration without the conjugate guide surface, noise reduction decreases by approximately 6 dB when the sound wave incident angle deviates 30° from the direction directly opposite the micro-gap inlet; while with the conjugate guide surface, the noise reduction decreases by less than 2 dB at the same incident angle deviation. This feature allows the invention to be flexibly adapted to multi-point or single-point centralized placement within a vehicle.

[0065] Example 5: Application Example of a Range Hood

[0066] This device is integrated into the range hood duct, specifically at the fan outlet, duct bend, or check valve location. It employs an advanced, gradually decreasing gap configuration (the gap linearly shrinks from 0.12 mm to 0.05 mm) and is coupled with a self-cleaning micro-lip and a micro-resonant cavity array. The self-cleaning micro-lip has a wedge-shaped cross-section with a 45° wedge angle, continuously arranged along the gap inlet edge, covering 80% of the inlet circumference. The opening end of the micro-resonant cavity array connects to the downstream region of the mating micro-gap through 1 mm diameter micropores.

[0067] The test was conducted in a standard fume generator with a fume concentration of 15 mg / m³ to 25 mg / m³ (referencing GB / T17713-2011 standard for range hoods). The median particle size of the oil mist was approximately 0.5 μm. The test temperature was 50±5℃, and the relative humidity was 60%±10%. The device was installed 200 mm after the bend in the range hood duct and operated continuously for 1000 hours at high speed (airflow 18 m³ / min). During this period, the device was stopped every 100 hours to test the insertion loss. The average energy in the 1 kHz to 8 kHz frequency band was used as the evaluation index for noise reduction.

[0068] Under the sound pressure excitation generated by the operation of the range hood fan (measured sound pressure level 95 dB~105 dB), a damping effect of micro-scale gas phase accumulation zone is stably formed within the micro-gap, achieving an insertion loss of 15 dB~20 dB for mid-to-high frequency wind noise (1 kHz~8 kHz) and a suppression of vortex howling (500 Hz~2 kHz characteristic frequency) of 12 dB~18 dB. After 1000 hours of continuous operation in a fume environment, the self-cleaning micro-lip effectively prevents the accumulation of oil and dust, with noise reduction attenuation ≤2 dB. No need to replace the sound-absorbing cotton or perform electrical control maintenance, achieving long-term maintenance-free noise reduction.

[0069] In terms of manufacturing process, all structural features of the device of this invention can be integrally formed through conventional injection molding, die casting, or precision machining processes. Taking a nominal gap value of 0.10 mm as an example, under the condition of tolerance control of ±0.02 mm, the mass production yield is high and the overall cost is low.

[0070] This invention has strong industrial application prospects and can be widely used in various acoustic control scenarios such as automotive thermal management pipelines, pump and valve whistling suppression, industrial fan damping, air conditioning duct noise reduction, precision equipment vibration reduction, smart home hardware buffering, and household / commercial range hoods. It can operate stably in a wide temperature range of -40℃ to 150℃. This device can be directly integrated into the range hood fan outlet, duct bend, and check valve, and has a significant suppression effect on high-frequency wind noise, eddy current whistling, and airflow pulsation noise in range hoods. It requires no sound-absorbing cotton, no electrical control, is resistant to high-temperature oil fume environments, does not clog, and requires no maintenance. This invention achieves acoustic control based on the coupling of rigid geometry and microscale gas phase accumulation region dynamics. The principle is clear, the structure is simple, and the performance is stable. It can completely replace traditional porous, damping, and resonant noise reduction structures, achieving ultra-long life and reliable operation under all working conditions, and has significant industrial application value and industry promotion prospects.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It should be noted that any modifications, equivalent substitutions, or improvements made to the above embodiments within the scope of the inventive concept by those skilled in the art should be included within the scope of protection of the present invention.

Claims

1. A passive noise reduction device based on rigid geometric contour constraints on gas phase accumulation regions, characterized in that, include: A first rigid member (1) and a second rigid member (2) form a fit and define a continuous fit micro gap (3) therebetween, the width of the fit micro gap (3) being 0.02 mm to 0.2 mm; Among them, at least one rigid component has a rigid geometric profile (4) formed on its mating surface. The rigid geometric profile (4) is at least one of a step, groove, ridge or curved surface undulation, used to spatially constrain the morphology and evolution law of the microscale gas phase accumulation zone. Under the action of the incident sound field, a local transient negative pressure zone can be formed in the micro gap (3), thereby generating a microscale gas phase accumulation zone. The microscale gas phase accumulation zone refers to the gas-rich area formed by the ambient air being drawn into the micro gap. The microscale gas phase accumulation zone undergoes periodic compression, expansion and collapse processes under the alternating pressure of the incident sound field, converting sound energy into heat energy, and realizing acoustic damping and noise suppression.

2. The apparatus according to claim 1, characterized in that, The geometry of the mating micro-gap (3) satisfies one of the following conditions: (a) A uniform and equal-width gap, along the main incident direction of the sound wave, the width of the mating micro-gap (3) remains constant; (b) Gradual gap, along the main incident direction of the sound wave, the width of the mating micro gap (3) shrinks linearly; (c) The gap is defined by the variable curvature mating surface and the multi-level micro-expansion step (6), wherein the multi-level micro-expansion step is a multi-level step structure set along the main incident direction of the sound wave.

3. The apparatus according to claim 1, characterized in that, The mating surface is further provided with an auxiliary structure, which includes at least one of the following: (a) Micro-vortex prism dissipation structure, which is a convex structure with an isosceles triangular cross section, with a bottom width of 0.02 mm to 0.05 mm and a height of 0.01 mm to 0.03 mm, continuously arranged along the main incident direction of the sound wave, with a spacing of 0.1 mm to 0.2 mm. (b) The micro-tooth damping surface is a sawtooth microstructure with a tooth height of 0.01 mm to 0.03 mm and a tooth pitch of 0.05 mm to 0.1 mm; (c) The stepped gap transition structure is a 2- to 3-step step set along the main incident direction of the sound wave. The initial gap is 0.02 mm, and the gap of each step increases or decreases step by step within the range of 0.02 mm to 0.06 mm. (d) Annular dustproof edge, radial width 0.5 mm to 1.0 mm, axial extension length 1.0 mm to 2.0 mm, wall thickness 0.2 mm to 0.5 mm; (e) Microporous filtration structure with pore size of 0.05 mm to 0.15 mm, pore spacing of 0.2 mm to 0.5 mm, and surface porosity of 30% to 50%.

4. The apparatus according to claim 1, characterized in that, It also includes one or more of the following structures: (a) A pre-negative pressure guiding structure is integrally formed in the inlet region of the fitting micro gap (3) and is configured to assist in triggering the microscale gas phase accumulation zone under the condition that the sound pressure level is not lower than 85 dB. (b) A self-cleaning micro lip, integrally formed on the edge of the mating micro gap (3), is configured to form a reverse micro-purge airflow using a high-pressure pulse generated by the collapse of the gas phase accumulation zone; (c) A micro resonant cavity array, integrated inside the first rigid member (1) and / or the second rigid member (2) or around the mating surface, with a cavity diameter of 3 mm to 10 mm, a depth of 2 mm to 8 mm, and an opening diameter of 0.5 mm to 2 mm. The opening end of the micro resonant cavity array is connected to the mating micro gap (3) or faces the external sound field. (d) A conjugate acoustic guide surface is disposed in the outer region of the first rigid member (1) or the second rigid member (2) for focusing and redistributing the energy of the incident sound wave.

5. The apparatus according to claim 1, characterized in that, The first rigid component (1) and the second rigid component (2) are integrally formed by injection molding, die casting or precision machining of glass fiber reinforced engineering plastic, aluminum alloy or steel, and the surface roughness Ra of the mating surface is ≤0.8 μm.

6. A passive noise reduction method for gas phase accumulation regions based on rigid geometric contour constraints, characterized in that, Includes the following steps: A fitting micro-gap (3) with a width of 0.02 mm to 0.2 mm is provided between the first rigid member (1) and the second rigid member (2), and a rigid geometric profile (4) for constraining the behavior of the microscale gas phase accumulation region is provided on the fitting surface. When the micro-gap (3) is placed in the sound field, a local transient negative pressure zone is formed in the micro-gap (3) under the excitation of the incident sound field, thereby generating and maintaining a micro-scale gas phase accumulation zone. The micro-scale gas phase accumulation zone refers to the gas enrichment area formed by the ambient air being drawn into the micro-gap. The sound energy is converted into heat energy through the periodic compression, expansion and collapse process of the microscale gas phase accumulation region under the alternating pressure of the incident sound field. By regulating the pressure change law and dissipation intensity of the gas phase accumulation zone through the rigid geometric profile (4), passive broadband acoustic damping and noise reduction can be achieved.

7. A passive noise reduction system for pipelines, characterized in that, The passive noise reduction device based on a rigid geometric contour constrained gas phase accumulation region as described in any one of claims 1 to 5 is disposed on the sound wave propagation path.

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