Design relation and end correction formula for multi-orifice Helmholtz resonators with intrusions

2015 ◽  
Vol 230 (6) ◽  
pp. 939-947 ◽  
Author(s):  
Chintapalli VSN Reddi ◽  
Chandramouli Padmanabhan
Keyword(s):  
Resonance Frequency ◽  
Boundary Element ◽  
Computational Cost ◽  
Low Frequency ◽  
Frequency Noise ◽  
Cross Sectional ◽  
Impedance Boundary ◽  
Correction Formula ◽  
Helmholtz Resonators ◽  
Design Relation

Helmholtz resonators are used to control low-frequency noise in cavities. One of the ways to reduce the resonance frequency of a resonator without changing its volume is to introduce an intrusion. Similarly, the introduction of multiple orifices can increase the resonance frequency without changing the resonator volume. These features provide an ability to accommodate slight changes in the cavity/enclosure frequencies during the design process. However, one has to rely on extensive three-dimensional finite element or boundary element simulations to predict the resonator characteristics with the introduction of these features. To reduce the computational burden, a design relation, between the first resonance frequency of a single orifice intruded resonator with that of a multi-orifice intruded resonator, is proposed in this paper. In developing this design relation, the total cross-sectional area of the resonator with multiple orifices is the same as that of the single orifice resonator. It is shown that this design relation is independent of the shape/size of the orifices and resonator cavity. Using this relation, a new end correction formula for the orifice lengths of multi-orifice intruded resonators has been proposed. The end correction formula can be used to calculate the reactance of multi-orifice intruded Helmholtz resonators analytically. These expressions are derived by carrying out extensive simulations of the resonators using the boundary element method. Limited experiments have been carried out to validate the proposed approach. The use of these expressions will reduce the computational cost of simulating cavities embedded with resonators as one can avoid modeling the resonators and use impedance boundary conditions instead.

scholarly journals Numerical investigation on low-frequency noise damping performances of Helmholtz resonators with an extended neck in presence of a grazing flow

2021 ◽  
pp. 146134842110205
Author(s):  
Weiwei Wu ◽  
Yiheng Guan
Keyword(s):  
Resonant Frequency ◽  
Stokes Equations ◽  
Transmission Loss ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Frequency Noise ◽  
Frequency Range ◽  
Helmholtz Resonators ◽  
Numerical Predictions ◽  
Grazing Flow

In this work, modified designs of Helmholtz resonators with extended deflected neck are proposed, numerically evaluated and optimized aiming to achieve a better transmission loss performance over a broader frequency range. For this, 10 Helmholtz resonators with different extended neck configurations (e.g. the angle between extended neck and the y-axis) in the presence of a grazing flow are assessed. Comparison is then made between the proposed resonators and the conventional one, i.e. in the absence of an extended neck (i.e. Design A). For this, a two-dimensional linearized Navier Stokes equations-based model of a duct with the modified Helmholtz resonator implemented was developed in frequency domain. The model was first validated by comparing its numerical predictions with the experimental results available in the literature and the theoretical results. The model was then applied to evaluate the noise damping performance of the Helmholtz resonator with (1) an extended neck on the upstream side (Design B); (2) on the downstream side (Design C), (3) both upstream and downstream sides (Design D), (4) the angle between the extended neck and the y-axis, i.e. (a) 0°, (b) 30°, and (c) 45°, (d) 48.321°. In addition, the effects of the grazing flow Mach number (Ma) were evaluated. It was found that the transmission loss peaks of the Helmholtz resonator with the extended neck was maximized at Ma = 0.03 than at the other Mach numbers. Conventional resonator, i.e. Design A was observed to be associated with a lower transmission loss performance at a lower resonant frequency than those as observed on Designs B–D. Moreover, the optimum design of the proposed resonators with the extended neck is shown to be able to shift the resonant frequency by approximately 90 Hz, and maximum transmission loss could be increased by 28–30 dB. In addition, the resonators with extended necks are found to be associated with two or three transmission loss peaks, indicating that these designs have a broader effective frequency range. Finally, the neck deflection angles of 30° and 45° are shown to be involved with better transmission loss peaks than that with a deflection angle of 0°. In summary, the present study sheds light on maximizing the resonator’s noise damping performances by applying and optimizing an extended neck.

scholarly journals Development of a Slit-Type Soundproof Panel for a Reduction in Wind Load and Low-Frequency Noise with Helmholtz Resonators

2021 ◽  
Vol 11 (18) ◽  
pp. 8678
Author(s):  
Byunghui Kim ◽  
Seokho Kim ◽  
Yejin Park ◽  
Marinus Mieremet ◽  
Heungguen Yang ◽  
...  
Keyword(s):  
Transmission Loss ◽  
Numerical Study ◽  
Shape Change ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Wind Load ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Helmholtz Resonators ◽  
Commercial Program

With the rapid increase in automobiles, the importance of reducing low-frequency noise is being emphasized for a comfortable urban environment. Helmholtz resonators are widely used to attenuate low-frequency noise over a narrow range. In this study, a slit-type soundproof panel is designed to achieve low-frequency noise attenuation in the range of 500 Hz to 1000 Hz with the characteristics of a Helmholtz resonator and the ability to pass air through the slits on the panel surface for reducing wind load. The basic dimension of the soundproof panel is determined using the classical formula and numerical analysis using a commercial program, COMSOL Multiphysics, for transmission loss prediction. From the numerical study, it is identified that the transmission loss performance is improved compared to the basic design according to the shape change and configuration method of the Helmholtz resonator. Although the correlation according to the shape change and configuration method cannot be derived, it is confirmed that it can be used as an effective method for deriving a soundproof panel design that satisfies the basic performance.

Case study: Correlation between boundary and finite element determination of large silencer transmission loss

2021 ◽  
Vol 69 (4) ◽  
pp. 276-287
Author(s):  
Kangping Ruan ◽  
T.W. Wu ◽  
D.W. Herrin
Keyword(s):  
Finite Element ◽  
Boundary Element Method ◽  
Boundary Element ◽  
Cross Sections ◽  
Transmission Loss ◽  
Cutoff Frequency ◽  
Low Frequency ◽  
Cross Sectional ◽  
Element Determination ◽  
Element Method

Silencers used in the power generation industry generally have large ducts entering and leaving the silencer. With large cross-sectional dimensions, the plane wave cutoff frequency will be exceeded at a low frequency so that transmission loss can no longer be evaluated by assuming constant sound pressure over a cross-section. More sophisticated calculation and processing approaches are necessary. In this research, the boundary element method is used in conjunction with a reciprocal identity method to determine the transmission loss for rectangular and circular cross-sections: the two configurations that cover most real-world designs. The boundary element method is compared to a finite element method strategy where the transmission loss is determined using an automatically matched layer boundary condition at the inlet and outlet. This approach can be used in most commercial software. Although these two approaches have little in common, transmission loss results compare well with one other. Validation by comparison is helpful because analytical solutions are only available for simple axisymmetric cases. Methods are compared for practical configurations like parallel-baffle silencers and reactive silencers.

Optimization of metamaterials with complex neck shapes for aircraft cabin noise improvement

2021 ◽  
Vol 263 (2) ◽  
pp. 3963-3974
Author(s):  
Tenon Charly Kone ◽  
Sebastian Ghinet ◽  
Raymond Panneton ◽  
Anant Grewa
Keyword(s):  
Transmission Loss ◽  
Low Frequency ◽  
Optimization Method ◽  
Frequency Noise ◽  
Low Frequencies ◽  
Helmholtz Resonators ◽  
Cabin Noise ◽  
Resonance Frequencies ◽  
In Series ◽  
Small Form Factor

More frequently, recent low-frequency noise control techniques commonly implemented in aerospace and ground transportation as well as in building applications are based on acoustic metamaterial concepts. The technologies proposed in the literature, using layered porous materials with embedded Helmholtz resonators (HR), exhibited considerable potential when tuned at tonal, multi-tonal or narrow frequency bands. Our recent investigations have shown that the acoustical performance of these metamaterials can be further improved by the use of resonators with complex shaped necks. These necks can be designed and optimized to minimize the HR resonance frequencies (small form factor) and maximize the sound transmission loss (STL) performance. This paper presents the developed design optimization method for HRs with complex neck shapes recessed within the HR cavity. The HRs were embedded in a layer of porous material. The implemented approach was based on the transfer matrix methods (TMM) in series and in parallel coupled to a multi-objective optimization. Complex optimum neck shapes were obtained allowing for a shift towards the low frequencies of the resonator resonance with a good STL performance. Moreover the STL calculated using the TMM approach were observed to be in excellent agreement with the finite element method numerical results.

Multi-tonal low frequency noise control using Helmholtz resonators with complex cavity designs for aircraft cabin noise improvement

2021 ◽  
Vol 263 (2) ◽  
pp. 3975-3986
Author(s):  
Tenon Charly Kone ◽  
Sebastian Ghinet ◽  
Raymond Panneton ◽  
Thomas Dupont ◽  
Anant Grewal
Keyword(s):  
Noise Control ◽  
Transmission Loss ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Sound Insulation ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Helmholtz Resonators ◽  
Resonance Frequencies

The noise control at multiple tonal frequencies simultaneously, in the low frequency range, is a challenge for aerospace, ground transportation and building industries. In the past few decades, various low frequency noise control solutions based on acoustic metamaterial designs have been presented in the literature. These solutions showed promising performance and are considered a better alternative to conventional sound insulation materials. In the present investigation, it was noticed that subdividing the cavity of a Helmholtz resonator allowed the control of multi-tonal noise at several resonance frequencies simultaneously and a shift of the resonance peaks towards the low frequencies. This paper proposes concepts of Helmholtz resonators with subdivided cavities to improve the sound transmission loss (STL) performance and simultaneously control the noise at several tonal frequencies. HRs with cylindrical shaped cavities were embedded in a layer of porous material. The STL of the metamaterial noise insulation configuration was predicted using serial and parallel assemblies of transfer matrices (TMM) incorporating a thermo-viscous-acoustic approach to accurately account for the viscous and thermal losses of acoustic wave propagation within the metamaterial. The STL calculated using the proposed TMM approach were observed to be in excellent agreement with the finite element method (FEM) numerical results.

Low-Frequency Noise Reduction of Rocket Fairings Using Horn-Shaped-Neck Helmholtz Resonators

2019 ◽  
Vol 56 (1) ◽  
pp. 273-282 ◽  
Author(s):  
Xiuyan Cheng ◽  
Xiangyu Chen ◽  
Jili Rong ◽  
Bochao Fan ◽  
Nisu A.
Keyword(s):  
Noise Reduction ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Helmholtz Resonators
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