On sound transmission loss across a Helmholtz resonator in a low Mach number flow duct

Tang, Shiu Keung

doi:10.1121/1.3409481

Cited by 32 publications

(21 citation statements)

References 24 publications

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“…The mean flow may induce tonal sound as indicated in existing literatures (such as Nelson et al 28 and Ziada et al, 29 but the narrow sidebranch tube width may weaken such lock-on effect. 7 These are left to further study.…”

Section: Resultsmentioning

confidence: 99%

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Narrow sidebranch arrays for low frequency duct noise control

Tang

2012

The Journal of the Acoustical Society of America

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The present study investigates the sound transmission loss across a section of an infinitely long duct where one or more narrow sidebranch tubes are installed flushed with the duct wall. The finite-element method is used to compute the wave propagation characteristics, and a simplified theoretical analysis is carried out at the same time to explain the wave mechanism at frequencies of high sound reduction. Results show that the high sound transmission loss at a particular frequency is due to the concerted actions of three consecutive sidebranch tubes with the most upstream one in the resonant state. The expansion chamber effect of the setup also plays a role in enhancing sound attenuation at non-resonance frequencies. Broadband performance of the device can be greatly enhanced by appropriate arrangements of tube lengths and/or by coupling arrays on the two sides of the duct.

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Section: Resultsmentioning

confidence: 99%

“…The Helmholtz resonators 7 and the plenum chambers 8 are typical examples. There are many derivatives proposed as well.…”

Section: Introductionmentioning

confidence: 99%

Narrow sidebranch arrays for low frequency duct noise control

Tang

2012

The Journal of the Acoustical Society of America

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“…The effect of the grazing flow is evaluated and shown in Figure 5. It can be seen that the maximum TL 31 is decreased from 39 to 11 dB by approximately 28 dB, as the grazing flow Mach number is increased from 0 to 0.10, as the neck offset distance is set to five different values. The resonant frequency corresponding to the maximum TL is found to shift by approximately 10% to higher values with increased M u but less than 0.07.…”

Section: Resultsmentioning

confidence: 99%

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

Pan

Guan

2018

Journal of Low Frequency Noise, Vibration and Active Control

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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 e c =a s and (2) the grazing flow Mach number M u 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 e c =a s. As e c =a s is increased from 0 to 0.5 and M u ! 0:1, the resonant frequencies and the maximum transmission losses are increased. However, when M u is lower than 0.07, i.e. M u 0:07, the transmission loss performances are almost unchanged with e c =a s 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.

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“…Different authors [1][2][3][4][5][6][7][8] have studied two-and three-dimensional resonators under grazing flow using scale-resolving simulations such as Direct Numerical Simulation (DNS) and many experimental studies on Helmholtz resonators can be found in the literature. [9][10][11][12][13][14][15][16] It is shown that a Helmholtz resonator typically has a linear regime at low and moderate sound pressure levels (< 130dB). For this regime, it is expected that linearized governing equations can be used to model the acoustic behavior.…”

Section: Introductionmentioning

confidence: 99%

“…A few experimental studies on slit resonators exist, but they consider a relatively large perforation 16 or acoustic waves under normal incidence 3,6 . In order to provide the necessary validation data for the numerical simulations, a dedicated experimental campaign on a slit resonator under grazing flow has been carried out within the framework of this paper.…”

Section: Introductionmentioning

confidence: 99%

Combined Numerical and Experimental Study of a Slit Resonator Under Grazing Flow

Denayer

Tournadre

Roeck

et al. 2014

20th AIAA/CEAS Aeroacoustics Conference

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This study compares two numerical methods based on the Linearized Navier-Stokes equations (LNSE) for the simulation of a resonator in presence of a cold mean flow: a time domain Runge-Kutta Discontinuous Galerkin (RKDG) code and a frequency-domain high-order continuous Finite Element Method (pFEM). The results are compared to experimental data from a dedicated experimental campaign on a slit resonator. It was shown that the simulations predict the correct trends, but some discrepancies have been observed. The origin of these differences has to be investigated further. Different impedance measurement techniques are applied to the numerical and experimental data to obtain the acoustic impedance of the slit resonator. Within their respective range of validity, reasonable agreement is found between the different techniques. Nomenclature B Width of the duct, [m] Z Acoustic impedance, [Rayl] c Speed of sound, [m/s] z Specific impedance, [-] f Frequency, [Hz] z i Location of microphone i, [m] k Acoustic wave number, [m −1 ] δ Flow boundary layer thickness, [m] H Back cavity depth, [m] δ ij Kronecker delta function, [-] L Length of the test section, [m] Acoustic monopole source amplitude, [P a] M Mach number, [-] κ Thermal conductivity, [W/(m.K)] p Pressure, [P a] λ Acoustic wavelength, [m] R +/− Reflection coefficient of scatter matrix, [-] µ Dynamic viscosity, [kg/(m.s)] S Cross section of the channel, [m 2 ] ν Kinematic viscosity, [m 2 /s] S c Surface of perforation, [m 2 ] τ Viscous stress tensor, [P a] T Absolute temperature, [K] Φ Dissipation function, [W/m 3 ] T +/− Transmission coefficient of the scatter matrix, [-] ρ Density, [kg/m 3 ] u Velocity vector, [m/s] ω Angular frequency, [rad/s] x Vector of the cartesian coordinate position, [m]

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On sound transmission loss across a Helmholtz resonator in a low Mach number flow duct

Cited by 32 publications

References 24 publications

Narrow sidebranch arrays for low frequency duct noise control

Narrow sidebranch arrays for low frequency duct noise control

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

Combined Numerical and Experimental Study of a Slit Resonator Under Grazing Flow

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