Experimental Study of Advanced Helmholtz Resonator Liners with Increased Acoustic Performance by Utilising Material Damping Effects

In aero engines, noise absorption is realised by acoustic liners, e.g., Helmholtz resonator (HR) liners, which often absorb sound only in a narrow frequency range. Due to developments of new engine generations, an improvement of overall acoustic damping performance and in particular more broadband noise absorption is required. In this paper, a new approach to increase the bandwidth of noise absorption for HR liners is presented. By replacing rigid cell walls in the liner’s honeycomb core structure by flexible polymer films, additional acoustic energy is dissipated. A manufacturing technology for square honeycomb cores with partially flexible walls is described. Samples with different flexible wall materials were fabricated and tested. The acoustic measurements show more broadband sound absorption compared to a reference liner with rigid walls due to acoustic-structural interaction. Manufacturing-related parameters are found to have a strong influence on the resulting vibration behaviour of the polymer films, and therefore on the acoustic performance. For future use, detailed investigations to ensure the liner segments compliance with technical, environmental, and life-cycle requirements are needed. However, the results of this study show the potential of this novel liner concept for noise reduction in future aero-engines.

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Passive Damper LP Tests for Controlling Combustion Instability

Volume 1: Combustion and Fuels, Education ◽

10.1115/gt2006-90874 ◽

2006 ◽

Cited By ~ 7

Author(s):

M. A. Macquisten ◽

A. Holt ◽

M. Whiteman ◽

A. J. Moran ◽

J. Rupp

Keyword(s):

Combustion Instability ◽

Vortex Formation ◽

Helmholtz Resonator ◽

Acoustic Energy ◽

Combustion Instabilities ◽

Design Rules ◽

Acoustic Damping ◽

Passive Damper ◽

Combustion Systems ◽

Combustion Tests

The drive to low emissions from GT combustors has pushed manufacturers towards leaner combustion systems. Lean combustion systems are susceptible to thermo acoustic or combustion instabilities, which can significantly limit the operation of the GT in terms of performance and emissions. Combustion instability is the result of coupling between fluctuations in the heat release rate and pressure waves. The occurrence of instability dependent on (a) satisfying the Rayleigh criterion and (b) the growth must exceed the losses of acoustic energy. The growth of instability can be controlled by increasing the level of acoustic damping via a Helmholtz resonator and through viscous damping. Design rules for a passive damper have been developed through the EU funded project called PRECCINSTA (Prediction and control of combustion instabilities in tubular and annular combustion systems) by the University of Cambridge. These design rules are for a doubled-skinned perforated liner where a biasing flow is used to dissipated sound energy. The sound dissipation mechanism is via vortex formation. These design rules were then validated against atmospheric and intermediate pressure combustion tests at Rolls-Royce for self-excited and forced excited oscillations. This paper summaries these tests and gives the results for a simple perforated liner as a passive acoustic damper.

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Investigation on the Acoustic Performance of Multiple Helmholtz Resonator Configurations

Acoustics Australia ◽

10.1007/s40857-021-00231-8 ◽

2021 ◽

Author(s):

K. Mahesh ◽

R. S. Mini

Keyword(s):

Helmholtz Resonator ◽

Acoustic Performance

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Acoustic Energy Balance During the Onset, Growth and Saturation of Thermoacoustic Instabilities

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2020-16158 ◽

2020 ◽

Author(s):

R. Gaudron ◽

D. Yang ◽

A. S. Morgans

Keyword(s):

Energy Balance ◽

Network Models ◽

Acoustic Energy ◽

Dimensionless Numbers ◽

Weakly Nonlinear ◽

Acoustic Damping ◽

Thermoacoustic Instabilities ◽

Wide Range ◽

Acoustic Absorption Coefficient ◽

Flame Describing Function

Abstract Thermoacoustic instabilities can occur in a wide range of combustors and are prejudicial since they can lead to increased mechanical fatigue or even catastrophic failure. A well-established formalism to predict the onset, growth and saturation of such instabilities is based on acoustic network models. This approach has been successfully employed to predict the frequency and amplitude of limit cycle oscillations in a variety of combustors. However, it does not provide any physical insight in terms of the acoustic energy balance of the system. On the other hand, Rayleigh’s criterion may be used to quantify the losses, sources and transfers of acoustic energy within and at the boundaries of a combustor. However, this approach is cumbersome for most applications because it requires computing volume and surface integrals and averaging over an oscillation cycle. In this work, a new methodology for studying the acoustic energy balance of a combustor during the onset, growth and saturation of thermoacoustic instabilities is proposed. The two cornerstones of this new framework are the acoustic absorption coefficient Δ and the cycle-to-cycle acoustic energy ratio λ, both of which do not require computing integrals. Used along with a suitable acoustic network model, where the flame frequency response is described using the weakly nonlinear Flame Describing Function (FDF) formalism, these two dimensionless numbers are shown to characterize: 1) the variation of acoustic energy stored within the combustor between two consecutive cycles, 2) the acoustic energy transfers occurring at the combustor’s boundaries and 3) the sources and sinks of acoustic energy located within the combustor. The acoustic energy balance of the well-documented Palies burner is then analyzed during the onset, growth and saturation of thermoacoustic instabilities using this new methodology. It is demonstrated that this new approach allows a deeper understanding of the physical mechanisms at play. For instance, it is possible to determine when the flame acts as an acoustic energy source or sink, where acoustic damping is generated, and if acoustic energy is transmitted through the boundaries of the burner.

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Nonlinear behavior of Helmholtz resonator with a compliant wall for low frequency, broadband noise control

Journal of Vibration and Acoustics ◽

10.1115/1.4052870 ◽

2021 ◽

pp. 1-29

Author(s):

Maya Pishvar ◽

Ryan L Harne

Keyword(s):

Dynamic Response ◽

Low Frequency ◽

Nonlinear Behavior ◽

Helmholtz Resonator ◽

Broadband Noise ◽

Sound Attenuation ◽

Wall Material ◽

Modeling Framework ◽

Compliant Wall ◽

Broadband Sound

Abstract Low frequency sound attenuation is often pursued using Helmholtz resonators (HRs). The introduction of a compliant wall around the acoustic cavity results in a two-degree-of-freedom (2DOF) system capable of more broadband sound absorption. In this study, we report the amplitude-dependent dynamic response of a compliant walled HR and investigate the effectiveness of wall compliance to improve the absorption of sound in linear and nonlinear regimes. The acoustic-structure interactions between the conventional Helmholtz resonator and the compliant wall result in non-intuitive responses when acted on by nonlinear amplitudes of excitation pressure. This paper formulates and studies a reduced order model to characterize the nonlinear dynamic response of the 2DOF HR with a compliant wall compared to that of a conventional rigid HR. Validated by experimental evidence, the modeling framework facilitates an investigation of strategies to achieve broadband sound attenuation, including by selection of wall material, wall thickness, geometry of the HR, and other parameters readily tuned by system design. The results open up new avenues for the development of efficient acoustic resonators exploiting the deflection of a compliant wall for suppression of extreme noise amplitudes.

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Design of Acoustic Liner in Small Gas Turbine Combustor Using One-Dimensional Impedance Models

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4040765 ◽

2018 ◽

Vol 140 (12) ◽

Cited By ~ 1

Author(s):

Daesik Kim ◽

Seungchai Jung ◽

Heeho Park

Keyword(s):

Gas Turbine ◽

Side Wall ◽

Acoustic Energy ◽

Gas Turbine Combustor ◽

Design Guideline ◽

Acoustic Damping ◽

Thermoacoustic Instabilities ◽

Acoustic Dissipation ◽

Acoustic Liner ◽

Bias Flow

The side-wall cooling liner in a gas turbine combustor serves main purposes—heat transfer and emission control. Additionally, it functions as a passive damper to attenuate thermoacoustic instabilities. The perforations in the liner mainly convert acoustic energy into kinetic energy through vortex shedding at the orifice rims. In the previous decades, several analytical and semi-empirical models have been proposed to predict the acoustic damping of the perforated liner. In the current study, a few of the models are considered to embody the transfer matrix method (TMM) for analyzing the acoustic dissipation in a concentric tube resonator with a perforated element and validated against experimental data in the literature. All models are shown to quantitatively appropriately predict the acoustic behavior under high bias flow velocity conditions. Then, the models are applied to maximize the damping performance in a realistic gas turbine combustor, which is under development. It is found that the ratio of the bias flow Mach number to the porosity can be used as a design guideline in choosing the optimal combination of the number and diameter of perforations in terms of acoustic damping.

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The effect of type of sound damper material in the Helmholtz resonator to the output power spectrum of acoustic energy Harvester

Journal of Physics Theories and Applications ◽

10.20961/jphystheor-appl.v3i2.38148 ◽

2019 ◽

Vol 3 (2) ◽

pp. 50

Author(s):

Hedwigis Harindra ◽

Agung Bambang Setio Utomo ◽

Ikhsan Setiawan

Keyword(s):

Energy Harvesting ◽

Power Spectrum ◽

Electric Power ◽

Energy Harvester ◽

Helmholtz Resonator ◽

Acoustic Energy ◽

Acoustic Energy Harvesting ◽

Wasted Energy ◽

Second Peak ◽

Output Electric Power

Acoustic energy harvesting is one of many ways to harness acoustic noises as wasted energy into useful electical energy using an acoustic energy harvester. Acoustic energy harvester that tested by Dimastya (2018) which is consisted of loudspeaker and Helmholtz resonator, produced two-peak spectrum. It is suspected that the first peak is due to Helmholtz resonator resonance and the second peak comesfrom the resonance of the conversion loudspeaker. This research is to experimentally confirm the guess of the origin of the first peak. The experiments are performed by adding silencer materials on the resonator inner wall which are expected to be able to reduce the height of first peak and to know how they affect the output electric power spectrum of the acoustic energy harvester. Three different silencer materials are used, those are glasswool, acoustic foam, and styrofoam, with the same thickness of 12 cm. The results show that glasswool absorbs sound more effectively than acostic foam and styrofoam. The use of glasswool, acoustic foam, and styrofoam with 12 cm thickness lowered the first peak by 90% (from 39 mW to 0,5 mW), 82% (from 39 mW to 0,7 mW), and 82% (from 39 mW to 0,7 mW), respectively. Based on these results, it is concluded that the guess of the origin of the first peak is confirmed.

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Swirler geometry effects (dh/do ratio) on synthetic gas flames. Part 2: dynamic flame behaviour at external y altered acoustic conditions

Energetika ◽

10.6001/energetika.v67i1.4536 ◽

2021 ◽

Vol 67 (1) ◽

Author(s):

Harun Yilmaz ◽

Omer Cam ◽

Ilker Yilmaz

Keyword(s):

Boundary Conditions ◽

Pressure Sensors ◽

Acoustic Energy ◽

Acoustic Boundary Conditions ◽

Acoustic Damping ◽

Pressure Profiles ◽

Flame Response ◽

Scale Variable ◽

A Minor ◽

Flame Behaviour

In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic damping (energy loss) is not that effective, and, as a result, thermo-acoustic flame instabilities occur. In this study, effects of the swirler dh/do ratio (at different swirl numbers) on dynamic flame behaviour of the premixed 20%CNG/30%H2/30%CO/20%CO2 mixture under externally altered acoustic boundary conditions and stability limits (flashback and blowout equivalence ratios) of such mixture were investigated in a laboratory-scale variable geometric swirl number combustor. Therefore, swirl generators with different dh/do ratios (0.3 and 0.5) and geometric swirl numbers (0.4, 0.6, 0.8, 1.0 1.2 and 1.4) were designed and manufactured. Acoustic boundary conditions in the combustion chamber were altered using loudspeakers, and flame response to these conditions was perceived using photodiodes and pressure sensors. Dynamic flame behaviour of respective mixture was evaluated using luminous intensity and pressure profiles. Results showed that the dh/do ratio has a minor impact on dynamic flame behaviour.

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Preparation of Polyvinylidene Fluoride (PVDF) Triboelectric Nanogenerators with Different Polymer

Materials Science Forum ◽

10.4028/www.scientific.net/msf.814.91 ◽

2015 ◽

Vol 814 ◽

pp. 91-95

Author(s):

Cheng Wang ◽

Hao Yu ◽

Tao Huang ◽

Chao Tan

Keyword(s):

Polymer Films ◽

Polyvinylidene Fluoride ◽

Low Cost ◽

Mechanical Energy ◽

Flexible Polymer ◽

Surrounding Environment ◽

Nanofiber Membranes ◽

External Consistency ◽

Low Wear ◽

Triboelectric Nanogenerators

Triboelectric nanogenerators have recently been used to harvest mechanical energy from surrounding environment which is of great significance in the field of energy conversion. Electrospinning provides a simple, low cost and versatile method for the generation of 1D nanostrucutures. Nanofiber membranes have many advantages over the commonly used dense film for designing the riboelectric nanogenerators, such as the low wear resistance caused from the internal and excellent external consistency of the electrospinning membranes. In this paper, we produce a variety of polymer films by electro-spinning, and fabricate Polyvinylidene Fluoride (PVDF) triboelectric nanogenerators with different polymer films afterwards. We except to explore the TEG power generation effect, and influencing factors, and then determine the best combination of the results of TEG (PVDF-PHBV). Such a flexible polymer TEG generates output voltage of up to 112 V at a power of 0.045W.

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