scholarly journals Numerical studies of transmission loss performances of asymmetric Helmholtz resonators in the presence of a grazing flow

2018 ◽  
Vol 38 (2) ◽  
pp. 244-254 ◽  
Author(s):  
Zhengli Lu ◽  
Weichen Pan ◽  
Yiheng Guan
Keyword(s):  
Mach Number ◽  
Gas Turbines ◽  
Stokes Equations ◽  
Transmission Loss ◽  
Helmholtz Resonator ◽  
Transmission Losses ◽  
Resonant Frequencies ◽  
Helmholtz Resonators ◽  
Grazing Flow ◽  
Maximum Transmission

As a typical noise-attenuating device, Helmholtz resonators are widely implemented in aero-engines and gas turbines to decrease the transmission of acoustic noise. However, an asymmetric Helmholtz resonator could be designed and implemented due to the limited space available in the engines. To examine and optimize the noise-attenuating performances of the asymmetric resonator, comparison studies are performed. For this, a two-dimensional frequency-domain model of a cylindrical duct with a grazing flow is developed. An asymmetric Helmholtz resonator is attached as a side branch. The model containing the linearized Navier–Stokes equations is validated first by comparing the predicted results with the experimental ones available in the literature. Further validation is conducted by comparing the results of an asymmetric resonator with the analytical ones available in the literature. The effects of (1) neck offset distance from the center of the resonator cavity denoted by [Formula: see text] and (2) the grazing flow Mach number [Formula: see text] are evaluated. It is shown that as the grazing flow Mach number is increased, the resonant frequencies and the maximum transmission losses are dramatically varied for a given [Formula: see text]. As [Formula: see text] is increased from 0 to 0.5 and [Formula: see text], the resonant frequencies and the maximum transmission losses are increased. However, when [Formula: see text] is lower than 0.07, i.e. [Formula: see text], the transmission loss performances are almost unchanged with [Formula: see text] increased. The optimum design of the asymmetric resonator is shown to give rise to the resonant frequency being shifted by 10% and 2–5 dB more transmission loss at higher Mach number. Finally, visualization of vortex shedding formed at the neck of the asymmetric resonator confirms that acoustical energy is transformed into kinetic energy and absorbed by the surrounding air. This study opens up a numerical design approach to optimize an asymmetric resonator.

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 Aeroacoustic Attenuation Performance of a Helmholtz Resonator with a Rigid Baffle Implemented in the Presence of a Grazing Flow

2020 ◽  
Vol 2020 ◽  
pp. 1-16 ◽  
Author(s):  
Di Guan ◽  
Dan Zhao ◽  
Zhaoxin Ren
Keyword(s):  
Mach Number ◽  
Transmission Loss ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Loss Peak ◽  
Mean Flow ◽  
Theoretical Formulation ◽  
Grazing Flow ◽  
Maximum Transmission ◽  
Rigid Baffle

To broaden its’ effective frequency range and to improve its transmission loss performance, a modified design of a Helmholtz resonator is proposed and evaluated by implementing a rigid baffle in its cavity. Comparison is then made between the proposed design and the conventional one by considering a rectangular duct with the resonator implemented in the presence of a mean grazing flow. For this, a linearized 2D Navier-Stokes model in frequency domain is developed. After validated by benchmarking with the available experimental data and our experimental measurements, the model is used to evaluate the effects of (1) the width Lp of the rigid baffle, (2) its implementation location/height Hg, (3) its implementation configurations (i.e., attached to the left sidewall or right sidewall), (4) the grazing mean flow Mu (Mach number), and (5) the neck shape on a noise damping effect. It is shown that as the rigid baffle is attached in the 2 different configurations, the resonant frequencies and the maximum transmission losses cannot be predicted by using the classical theoretical formulation ω2=c2S/VLeff, especially as the grazing Mach number Mu is greater than 0.07, i.e., Mu>0.07. In addition, there is an optimum grazing flow Mach number corresponding to the maximum transmission loss peak, as the width Lp is less than half of the cavity width Dr, i.e., Lp/Dr≤0.5. As the rigid plate width is increased to Lp/Dr=0.75, one additional transmission loss peak at approximately 400 Hz is produced. The generation of the 12 dB transmission loss peak at 400 Hz is shown to attribute to the sound and structure interaction. Finally, varying the neck shape from the conventional one to an arc one leads to the dominant resonant frequency being increased by approximately 20% and so the secondary transmission loss peak by 2-5 dB. The present work proposes and systematically studies an improved design of a Helmholtz resonator with an additional transmission loss peak at a high frequency, besides the dominant peak at a low frequency.

scholarly journals Effects of Parameters of Helmholtz Resonator on Transmission Loss of Hybrid Muffler

2018 ◽  
Vol 7 (3.17) ◽  
pp. 151
Author(s):  
Thiha Zaw ◽  
Aminudin Abu ◽  
Noor Fawazi ◽  
A M. Wahab
Keyword(s):  
Transfer Matrix ◽  
Transfer Matrix Method ◽  
Matrix Method ◽  
Transmission Loss ◽  
Helmholtz Resonator ◽  
Transmission Losses ◽  
Expansion Chamber ◽  
Low Frequencies ◽  
Helmholtz Resonators ◽  
Resonator Cavity

Expansion chamber and Helmholtz resonators are widely used in noise control. In this paper, they are combined to use as a hybrid muffler. The analysis is done to investigate the influence of the parameters of Helmholtz resonator on transmission loss. The transfer matrix method is used in the analysis. The result of transmission loss from the transfer matrix method is validated with the result from experimental two-load method using four microphones impedance tube. After had the transmission loss of the hybrid muffler been validated, the study was proceeded to investigate the effects of parameters of Helmholtz resonator on the transmission loss. The root mean square value of transmission loss were also calculated to compare the transmission losses clearly. In this paper, we investigated the effect of length of the neck of Helmholtz resonator, the effect of diameter of the neck of Helmholtz resonator, the effect of the length of the Helmholtz resonator cavity and the effect of the diameter of the Helmholtz resonator cavity for stationary medium. It is found that the transmission loss is increased when the diameter of the neck of Helmholtz resonator is increased. When the length of the neck is reduced, the transmission loss is increased. The transmission loss can also be increased by reducing the diameter of resonator cavity. It is better to increase the transmission loss at low frequencies by increasing the length of the resonator cavity.  

Numerical study for increasement of low frequency sound insulation of double-panel structure using sonic crystals with distributed Helmholtz resonators

2019 ◽  
Vol 33 (14) ◽  
pp. 1950138
Author(s):  
Myong-Jin Kim
Keyword(s):  
Free Space ◽  
Transmission Loss ◽  
Numerical Study ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Sound Insulation ◽  
The Finite Element Method ◽  
Helmholtz Resonators ◽  
Sonic Crystal ◽  
Sonic Crystals

Numerical simulations of the sound transmission loss (STL) of a double-panel structure (DPS) with sonic crystal (SC) comprised of distributed local resonators are presented. The Local Resonant Sonic Crystal (LRSC) consists of “C”-shaped Helmholtz resonator columns with different resonant frequencies. The finite element method is used to calculate the STL of such a DPS. First, the STLs of LRSC in free space and the DPS with LRSC are calculated and compared. It is shown that the sound insulations of the local resonators inserted in the double panel are higher than that in free space for the same size of the SCs and the same number of columns. Next, STL of the DPS in which the SC composed of three columns of local resonators having the same outer and inner diameters but different slot widths are calculated, and a reasonable arrangement order is determined. Finally, the soundproofing performances of DPS with distributed LRSC are compared with the case of insertion of general cylindrical SC for SC embedded in glass wool and not. The results show that the sound insulation of the DPS can be significantly improved in the low frequency range while reducing the total mass without increasing the thickness.

scholarly journals Research of Acoustically Improved Helmholtz Resonator

2021 ◽  
Vol 7 (1) ◽  
pp. 270-278
Author(s):  
J. Li ◽  
J. Shan ◽  
Z. Guo ◽  
A. Levtsev
Keyword(s):  
Transmission Loss ◽  
Three Dimensional ◽  
Helmholtz Resonator ◽  
Acoustic Characteristics ◽  
Helmholtz Resonators ◽  
Extension Tube ◽  
Section Shape ◽  
In Series ◽  
Combined Structure ◽  
The One

The three-dimensional acoustic finite element method is used to predict the transmission loss of the Helmholtz resonance muffler. The results are in good agreement with the experimental results, indicating the applicability and accuracy of the numerical method used in this paper. On the one hand, in order to reduce the resonance frequency without changing the shape of the resonator, the connecting tube is extended to the inside of the resonator, and the influence of the extension length and the cross section shape of the extension tube on the acoustic characteristics of the resonator is discussed in detail. On the other hand, in order to broaden the muffled frequency band of the traditional Helmholtz resonators, the resonators are combined in series and parallel, and the influence of the combined structure on the acoustic characteristics is discussed in detail.

Numerical Simulation of the Acoustic Pressure Field in an Annular Combustion Chamber With Helmholtz Resonators

2004 ◽  
Author(s):  
S. M. Camporeale ◽  
A. Forte ◽  
B. Fortunato ◽  
M. Mastrovito ◽  
A. Ferrante
Keyword(s):  
Combustion Chamber ◽  
Gas Turbines ◽  
Acoustic Pressure ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Acoustic Frequency ◽  
Helmholtz Resonators ◽  
Lean Premixed Flames ◽  
Lower Magnitude

In modern gas turbines in which lean premixed flames are used to obtain low NOx emissions, large pressure oscillations may arise inside the combustor due to thermoacoustic combustion instability at frequencies corresponding to the natural acoustic frequency of the system. Such pressure fluctuations, that may cause structural damages, need to be damped in order to avoid a reduction of the operational range of the gas turbine. In this work Helmholtz resonators connected to the external envelope of the combustion chamber are examined as passive systems for damping the low frequency acoustic pressure in the case of an annular combustor. The acoustical behavior of the combustor has been first investigated by means of the Finite Element method, obtaining its acoustic eigenmodes and eigenfrequencies in order to tune the Helmholtz resonators on the frequency to be damped. In order to characterize the resonator, preliminary tests have been carried out on a simplified system composed of a Helmholtz resonator applied at the end of an impedance tube. Then the eigenmodes of the system obtained by connecting one or more resonators to the annular chamber and the damping effects obtained by varying the geometry, the number and the position of the resonators are analyzed. It appears that the peak of acoustic pressure characterizing the combustion chamber splits into two peaks of lower magnitude when the Helmholtz resonators are applied and the peak frequencies are correlated to the overall volume of resonant cavities, whilst lower effects are obtained by varying the position and the number of resonator units.

scholarly journals An Experimental and Numerical Study on the Effect of Spacing between Two Helmholtz Resonators

Acoustics ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 97-117
Author(s):  
Abhishek Gautam ◽  
Alper Celik ◽  
Mahdi Azarpeyvand
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Pressure Field ◽  
Transmission Loss ◽  
Numerical Study ◽  
Pressure Level ◽  
Impedance Tube ◽  
Acoustic Performance ◽  
Helmholtz Resonators ◽  
Maximum Transmission

This study investigates the acoustic performance of a system of two Helmholtz resonators experimentally and numerically. The distance between the Helmholtz resonators was varied to assess its effect on the acoustic performance of the system quantitatively. Experiments were performed using an impedance tube with two instrumented Helmholtz resonators and several microphones along the impedance tube. The relation between the noise attenuation performance of the system and the distance between two resonators is presented in terms of the transmission loss, transmission coefficient, and change in the sound pressure level along the tube. The underlying mechanisms of the spacing effect are further elaborated by studying pressure and the particle velocity fields in the resonators obtained through finite element analysis. The results showed that there might exist an optimum resonators spacing for achieving maximum transmission loss. However, the maximum transmission loss is not accompanied by the broadest bandwidth of attenuation. The pressure field and the sound pressure level spectra of the pressure field inside the resonators showed that the maximum transmission loss is achieved when the resonators are spaced half wavelength of the associated resonance frequency wavelength and resonate in-phase. To achieve sound attenuation over a broad frequency bandwidth, a resonator spacing of a quarter of the wavelength is required, in which case the two resonators operate out-of-phase.

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.

Acoustic Behavior Prediction and Analysis of Resonators in the Presence of Low Mach Number Flow

2020 ◽  
Vol 28 (03) ◽  
pp. 1950015
Author(s):  
Hongpu Huang ◽  
Zhenlin Ji ◽  
Kangjian Han
Keyword(s):  
Mach Number ◽  
Resonance Frequency ◽  
Flow Velocity ◽  
Stokes Equations ◽  
Transmission Loss ◽  
Numerical Procedure ◽  
Low Mach Number ◽  
Resonance Frequencies ◽  
Number Flow ◽  
Low Mach Number Flow

The frequency-domain linearized Navier–Stokes equations (LNSEs) are used to describe the sound field of Helmholtz resonators and concentric perforated tube resonators in the presence of low Mach number flow. The numerical procedure of LNSEs method is performed in three steps, computational fluid dynamics (CFD) calculation, data transfer and acoustics calculation. The transmission loss predictions of the resonators exhibit good agreement with measurements published in the literature. The results show that the low Mach number flow shifts the resonance frequencies of resonators and changes the acoustic attenuation behavior, which may be attributed to the change of acoustic impedance of the opening and orifices. In order to weaken the effect of flow on the resonance frequency, the modified configurations of resonators are proposed by using the conical tubes to reduce the flow velocity passing the opening and orifices. Numerical results demonstrated that the influence of flow velocity on the resonance frequency of the modified resonators is less sensitive than the original configurations.

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