Correlation of the effects of grazing flow on the impedance of Helmholtz resonators

1982 ◽  
Vol 72 (2) ◽  
pp. 550-555 ◽  
Author(s):  
B. E. Walker ◽  
A. F. Charwat
Keyword(s):  
Helmholtz Resonators ◽  
Grazing Flow

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 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.

Effect of extended necks on transmission loss performances of Helmholtz resonators in presence of a grazing flow

2018 ◽  
Vol 77 ◽  
pp. 228-234 ◽  
Author(s):  
He Zhao ◽  
Zhengli Lu ◽  
Yiheng Guan ◽  
Zhiqiang Liu ◽  
Guoneng Li ◽  
...  
Keyword(s):  
Transmission Loss ◽  
Helmholtz Resonators ◽  
Grazing Flow

Broadband liner impedance eduction for multimodal acoustic propagation in the presence of a mean flow

2016 ◽  
Vol 11 (2) ◽  
pp. 150-155
Author(s):  
R. Troian ◽  
D. Dragna ◽  
C. Bailly ◽  
M.-A. Galland
Keyword(s):  
Numerical Model ◽  
Flow Characteristics ◽  
Acoustic Propagation ◽  
Rational Fraction ◽  
Physical Parameters ◽  
Mean Flow ◽  
Linearized Euler Equations ◽  
Grazing Flow ◽  
Propagation Medium ◽  
Difference Time

Modeling of acoustic propagation in a duct with absorbing treatment is considered. The surface impedance of the treatment is sought in the form of a rational fraction. The numerical model is based on a resolution of the linearized Euler equations by finite difference time domain for the calculation of the acoustic propagation under a grazing flow. Sensitivity analysis of the considered numerical model is performed. The uncertainty of the physical parameters is taken into account to determine the most influential input parameters. The robustness of the solution vis-a-vis changes of the flow characteristics and the propagation medium is studied.

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