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Aeroacoustics and Noise Mitigation

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A special issue of Aerospace (ISSN 2226-4310). This special issue belongs to the section "Aeronautics".

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 37091

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Dr. Hua-Dong Yao

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Department of Mechanics and Maritime Sciences, Chalmers University of Technology, Göteborg, Sweden
Interests: Fluid-induced acoustics; fluid-structure interaction; fluid mechanics; turbulence modelling; renewable energy; fossil-free transport
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Special Issue Information

Dear Colleagues,

As the study of sound increasingly incorporates multidisciplinary physics, today aeroacoustics has been expanded from the study of sound generation alone to a process that partially or completely combines sound generation, propagation, and mapping at receivers. Moreover, aeroacoustics is not limited to flows such as external noise pollution, footprint, and indoor environment quality, but also deals with flow-structure interaction (FSI), aero-vibro-acoustics, and damage detection and health monitoring of structures, etc. Due to the common basis of mathematical algorithms and physics, theories and methods developed for aeroacoustics with air as the medium have been applied to other fluid media such as water. The application scenarios are also not limited to aircraft, but extend to, for example, ground vehicles, HVAC systems, wind turbines, ship propellers, and underwater vehicles. According to the instructions by ICAO, aircraft noise mitigation can be achieved by noise source controlling, air traffic management, operating procedures, land-use planning, and relevant regulations and policies. However, with the emergence of clean-energy air vehicles such as flying cars and drones, available technologies and policies should be updated to meet the new demands and situations of rural/urban air mobility.

This Special Issue is devoted to the topics relevant to aeroacoustics and FSI, especially noise mitigation: 1) airframe and propulsion, regarding external and cabin noise generation and exposure; 2) propulsor installation, propeller-wing interaction, and propeller-propeller interaction; 3) noise absorption technologies; 4) air traffic management, airport operating procedures and land-use planning, 5) rural/urban air mobility; 6) policies and certifications for new air vehicles; 7) environmental and psychoacoustic problems; 8) theories, modeling, computational and experimental methods, multidisciplinary design optimization, and applied machine-learning techniques; 9) other areas such as hydroacoustics and application scenarios (e.g., ducts, HVAC and wind turbines) as long as methods share a common knowledge base with aeroacoustics and can potentially be used for aircraft.

Dr. Hua-Dong Yao
Guest Editor

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Keywords

aeroacoustics
fluid-structure interaction
aero-vibro-acoustics
noise source reduction
sound absorption technology
air traffic management
land-use planning
airport operational procedures
policies and certifications
psychoacoustics

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Published Papers (12 papers)

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Editorial

Jump to: Research

3 pages, 167 KiB

Open AccessEditorial

Special Issue “Aeroacoustics and Noise Mitigation”

by Hua-Dong Yao

Aerospace 2023, 10(7), 594; https://doi.org/10.3390/aerospace10070594 - 29 Jun 2023

Cited by 1 | Viewed by 1213

Abstract

Aerospace, an open access journal operated by MDPI, recently released a Special Issue entitled “Aeroacoustics and Noise Mitigation” [...] Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

Research

Jump to: Editorial

15 pages, 11765 KiB

Open AccessArticle

Advances in Experimental Research on the Influence of Friction Powders on Acoustic Liners (Helmholtz Resonators)

by Constantin Sandu, Andrei-George Totu, Andrei-Tudor Trifu and Marius Deaconu

Aerospace 2023, 10(12), 1000; https://doi.org/10.3390/aerospace10121000 - 28 Nov 2023

Viewed by 1197

Abstract

This paper presents the technological advancement of using friction powders to increase the absorption of acoustic liners used in the reduction of tonal noise generated by aero-engines or for other applications related to Helmholtz resonators used in noise absorption of low frequencies. The experimental research was conducted during the European project ARTEM (2017–2022), and after. This concept was inspired by the discovery made by several historians of narrow neck bottles filled with ash in the old Christian churches. These artifacts were made with the purpose of absorbing low frequency noises. Based on this creative idea, the present authors proposed a new method of noise absorption capabilities of acoustic liners filled with various types and quantities of natural and artificial powders. Considering the positive results the ARTEM project offered, COMOTI continued testing this concept by using even finer cork powders manufactured with a new technology. Measurements in Kundt tubes showed that noise absorption increased significantly in broadband for low frequencies (over 0.9 at high frequencies and 0.6 at low frequencies, 500 Hz). Some of the researched powders can be used in the field of bladed machines to reduce the aerodynamic noise of an aircraft or in the automotive industry where the reduction of low frequency noises is necessary. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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19 pages, 7547 KiB

Open AccessArticle

Prediction of Aircraft Surface Noise in Supersonic Cruise State

by Xiaoguang Zhang, Huixue Dang and Bin Li

Aerospace 2023, 10(5), 439; https://doi.org/10.3390/aerospace10050439 - 8 May 2023

Cited by 4 | Viewed by 1796

Abstract

The aerodynamic noise of an aircraft leads to vibration fatigue damage to structures. Herein, a prediction method for aircraft surface noise under the comprehensive effect of mixed acoustic sources during flight, primarily surface aerodynamic, air intake, and tail nozzle jet noises, was studied. In the supersonic cruising state, the internal and external flow fields of the aircraft were solved using the Reynolds-averaged Navier–Stokes equations to obtain the statistical average solution of the initial turbulence. The non-linear disturbance equation was used to obtain the surface acoustic load of the aircraft. The calculation results revealed that the main source of aircraft surface noise is aerodynamic noise. The sound pressure level on the fuselage increases gradually from front to rear along the aircraft, and the OASPL at the air intake and tail nozzle is relatively large. The jet noise has little effect on the sound pressure level at the front of the fuselage and only contributes to the OASPL at the tail nozzle of the fuselage. The intensity of pressure pulsations from the engine exhaust in the tail section is 93.3% of the total intensity of pressure pulsations. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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17 pages, 6329 KiB

Open AccessArticle

A Numerical Study on the Flap Side-Edge Noise Reduction Using Passive Blowing Air Concept

by Yingzhe Zhang, Baohong Bai, Dakai Lin and Peiqing Liu

Aerospace 2023, 10(4), 360; https://doi.org/10.3390/aerospace10040360 - 7 Apr 2023

Cited by 4 | Viewed by 2041

Abstract

The flap side-edge is a vital contributor to airframe noise. In this study, we propose a novel flap side-edge noise reduction method based on the concept of active blowing air. A long slot is opened from the flap’s lower surface to the tip surface to induce a secondary jet flow, which is driven by the local pressure difference between the flap’s lower surface and the tip surface. The unsteady flow field around the flap side-edge was computed by the lattice Boltzmann solver PowerFLOW, and the far-field noise was predicted by the FW-H equation. It is demonstrated that the dominant features of the flap side-edge flow are the double vortex structures, and the new passive blowing air reduction method can achieve about 3.3 dB noise reduction. Moreover, the underlying noise reduction mechanism has been analyzed and revealed. It is shown that the secondary jet flow from the long slot on the flap side-edge would dissipate the flap side-edge vortex and displace the flap side-edge vortical structure away from the flap surface, thus resulting in a decrease in the pressure fluctuations on the flap side-edge surface. As a result, the flap side-edge noise was reduced. In contrast to the current active air blowing technique, the newly proposed blowing air technique is passive and quite simple and does not require an extra air source or control system. This novel flap side-edge noise reduction technology provides a new flow control strategy and noise reduction methodology and can be further optimized. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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17 pages, 9221 KiB

Open AccessArticle

Effect of Wavy Leading Edges on Airfoil Trailing-Edge Bluntness Noise

by Yudi Xing, Weijie Chen, Xingyu Wang, Fan Tong and Weiyang Qiao

Aerospace 2023, 10(4), 353; https://doi.org/10.3390/aerospace10040353 - 3 Apr 2023

Cited by 6 | Viewed by 2661

Abstract

Among the several noise-generation mechanisms of airfoil self-noise, trailing-edge bluntness noise is an important noise source, which is caused by the vortex shedding at blunt trailing edges. A numerical study on airfoil trailing-edge bluntness noise control using the bio-inspired wavy leading edges is presented in this paper. The high-fidelity, improved, delayed, detached eddy simulation (IDDES) method was used to calculate the flow field, and the acoustic analogy method was used for noise prediction. For both the blunt-trailing-edge airfoils, a baseline airfoil with a straight leading edge and a bio-inspired airfoil with a wavy leading edge were used in this study. The chord-based Reynolds number was 400,000, and there was no angle of attack. The numerical results show that the trailing-edge bluntness noise of the baseline airfoil was significantly reduced by the wavy leading edges. The sound pressure level reduction was about 3.7 dB at the characteristic frequency, and the maximum sound pressure level reduction was as high as 35 dB. The trailing-edge bluntness noise was decreased at all directional angles. The maximum overall sound pressure level reduction was 6.3 dB at 0°. In addition, by analyzing the pressure fluctuations, wake characteristics, turbulent vortex structures and spanwise correlation and coherence of the flow field, the noise-reduction mechanisms of the bio-inspired airfoil are deeply revealed. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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21 pages, 3269 KiB

Open AccessArticle

RANS-Based Aeroacoustic Global Sensitivity Study and Optimization of UAV Propellers

by Witold Klimczyk and Adam Sieradzki

Aerospace 2023, 10(3), 306; https://doi.org/10.3390/aerospace10030306 - 20 Mar 2023

Cited by 4 | Viewed by 2433

Abstract

Modeling of Unmanned Aerial Vehicles (UAV) propellers in a global, multidisciplinary aeroacoustic optimization was investigated. The modeling consists of three aspects: geometry, aerodynamics, and aeroacoustics. Firstly, a parametric geometry model was established using chord, twist, and sweep distributions along the radius, defined by splines to ensure smoothness. Additionally, airfoil parameters including maximum camber and its position, as well as the position of maximum thickness, were added. Secondly, a blade geometry-resolved aerodynamic model based on steady RANS was established. A two-equation SST turbulence model was used for compressible flow with periodic boundary conditions. Thirdly, an aeroacoustic model for far-field tonal noise calculation was defined, based on the Ffowcs Williams and Hawkings analogy and a RANS solution. A global sensitivity analysis was performed to establish the importance of individual design variables. Consequently, surrogate modeling-based optimization strategy was devised to efficiently establish Pareto front of propeller geometries in multi-objective aeroacoustic optimization. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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14 pages, 3316 KiB

Open AccessArticle

Multidisciplinary Optimization Design of Low-Noise Propellers

by Dongwen Xue, Qun Yan, Zhuohan Li and Kai Wei

Aerospace 2023, 10(3), 254; https://doi.org/10.3390/aerospace10030254 - 7 Mar 2023

Cited by 4 | Viewed by 4095

Abstract

In this paper, a multidisciplinary optimization design method and its verification of low-noise aircraft propellers considering aerodynamics, noise, and structural strength were carried out to further reduce the aerodynamic noise of the aircraft propellers. The Vortex Lattice Method-based Lift Surface Method and the Frequency-Domain-based Hanson Method were deployed to evaluate the aerodynamic performance and far-field noise of the propeller with validation by benchmark test result comparison, respectively. Integrating both of the aforementioned methods, the constraints, and a genetic algorithm with coding, a joint program was successfully proposed so that the aircraft propeller performance could be optimized comprehensively. In this program, the design variables contain blade structural strength-constrained distribution patterns of the chord length, twist angle, and dihedral angle along the blade radius. A maximum amount of noise reduction was settled as an optimization target. Meanwhile, it ensured no penalty for aerodynamic thrust and efficiency. The optimized propeller was successfully delivered by performing the developed program. Its structure examined strength tests such as static load and dynamic response, and its aerodynamic and aeroacoustic performances were tested at an aeroacoustic wind tunnel. As a result, the optimized propeller reduced its far-field noise emission peak by 2.7 dB at the first BPF under typical conditions and performed a maximum noise reduction of 4 dB for lower-thrust operations compared with the baseline propeller. For the latter operation, noise reduction at the second BPF was also obviously observed. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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19 pages, 7439 KiB

Open AccessArticle

Micro Turbojet Engine Nozzle Ejector Impact on the Acoustic Emission, Thrust Force and Fuel Consumption Analysis

by Grigore Cican, Tiberius-Florian Frigioescu, Daniel-Eugeniu Crunteanu and Laurentiu Cristea

Aerospace 2023, 10(2), 162; https://doi.org/10.3390/aerospace10020162 - 10 Feb 2023

Cited by 9 | Viewed by 5606

Abstract

This paper explores the implementation of an ejector to a micro turbojet engine and analysis of the advantages in terms of acoustic and thrust/fuel consumption. Starting with the analytical equations and a series of numerical simulations, the optimal ejector geometry for maximum thrust was obtained. The ejector was manufactured and integrated with the Jet Cat P80 micro turbo engine for testing. The purpose of this article is to report on an improved geometry that results in no significant increase in the frontal area of the turbo engine, which could increase drag. The tests were completed using various functioning regimes, namely idle, cruise and maximum. For each of them, a comparative analysis between engine parameters with and without an ejector was performed. During the experiments, it was observed that, when the ejector was used, the thrust increased for each regime, and the specific consumption decreased for all regimes. The stability of the engine was tested in transient regimes by performing a sudden acceleration sequence, and one carried out the operating line and the modification of temperature values in front of the turbine for both configurations. For each regime, the acoustic noise was monitored at a few points that were different distances from the nozzle, and a decrease was identified when the ejector was used. The advantages of using the ejector on the Jet Cat P80 turbo jet engine are an increased thrust, a lower specific consumption and a reduced noise level, and at the same time, the integrity of the engine in stable operational states and transient operating regimes is not affected. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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15 pages, 1909 KiB

Open AccessArticle

Mass-Conserved Solution to the Ffowcs-Williams and Hawkings Equation for Compact Source Regions

by Zhiteng Zhou, Yi Liu, Hongping Wang and Shizhao Wang

Aerospace 2023, 10(2), 148; https://doi.org/10.3390/aerospace10020148 - 6 Feb 2023

Cited by 4 | Viewed by 2215

Abstract

A mass-conserved formulation for the Ffowcs-Williams–Hawkings (FW–H) integral is proposed to suppress contributions of spurious mass flux to the far-field sound at very low Mach numbers. The far-field condition and compact-source region assumptions are employed. By using higher-order derivatives of Green’s function, an expansion of the integrand in the monopole term is performed. This expansion transforms the mass-flux like monopole term into a series including different orders of velocity moment. At very low Mach numbers, the zero-order term is exactly the contribution from the spurious mass flux. The proposed mass-conserved formulation is confirmed by using an unsteady dipole, a two-dimensional (2D) incompressible convecting vortex, a circular-cylinder flow, and a co-rotating vortex pair. Additional spurious mass flux is added to the unsteady dipole, 2D incompressible convecting vortex, and flows over a circular cylinder; and the spurious mass flux of the co-rotating vortex pair comes from the residual of an incompressible-flow simulation. The far-field sound is found to be sensitive to spurious mass flux in the unsteady dipole and 2D incompressible convecting vortex cases. Then, the computation of the monopole-term expansion with the flow over a circular cylinder is presented. Fast convergence performance was observed, suggesting that the expansion requires little extra computational resources. Finally, FW–H boundary dependence is observed in the co-rotating vortex-pair case and eliminated by using the proposed mass-conserved formulation. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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16 pages, 4857 KiB

Open AccessArticle

Acoustic Experimental Technology for Aircraft Nacelle Liner

by Qun Yan, Dongwen Xue, Qinqin Mu, Jiafeng Yang, Xiang Gao and Wenchao Huang

Aerospace 2023, 10(1), 56; https://doi.org/10.3390/aerospace10010056 - 5 Jan 2023

Cited by 4 | Viewed by 3383

Abstract

An aircraft nacelle acoustic liner is a key mean of aircraft noise reduction. The success of its design depends strongly on the development of experimental technology, which is generally divided into two stages: impedance eduction and the modal verification of acoustic performance. The comparative study summarizes the impedance eduction technology based on the in-situ method and the straight forward method, and the acoustic modal measurement and control technology, as well as their applications in the design of the acoustic liner of an engine intake and exhaust ducts. The results show that the in-situ method has higher accuracy at low frequencies, and the accuracies of both methods are decreased in the high frequency range. Both methods show an acceptable accuracy and good applicability in the mid-frequency range. A modal generator was designed and used to emit separate and pure acoustic modes in sequence, and a comparative test was carried out on the two types of acoustic liner. Compared with the seamed acoustic liner, the seamless acoustic liner significantly improved its noise reduction effect at the multi-acoustic modes and target frequencies, which further increases the overall reduction up to 5.2 dB. Through research, reliable and validated technologies of acoustic performance tests for a nacelle acoustic liner were established. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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15 pages, 9394 KiB

Open AccessArticle

Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan

by Martin Ottersten, Hua-Dong Yao and Lars Davidson

Aerospace 2022, 9(12), 846; https://doi.org/10.3390/aerospace9120846 - 19 Dec 2022

Cited by 4 | Viewed by 3079

Abstract

In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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22 pages, 14708 KiB

Open AccessArticle

Effects of Aeroelastic Walls on the Aeroacoustics in Transonic Cavity Flow

by Stefan Nilsson, Hua-Dong Yao, Anders Karlsson and Sebastian Arvidson

Aerospace 2022, 9(11), 716; https://doi.org/10.3390/aerospace9110716 - 14 Nov 2022

Cited by 4 | Viewed by 2786

Abstract

The effects of elastic cavity walls on noise generation at transonic speed are investigated for the generic M219 cavity. The flow is simulated with the Spalart–Allmaras (SA) improved delayed detached-eddy simulation (IDDES) turbulence model in combination with a wall function. The structural analysis software uses a modal formulation. The first 50 structural normal mode shapes are included in the simulation, spanning frequencies of 468–2280 Hz. Results are compared with those from a reference simulation with rigid cavity walls. A spectral analysis of pressure fluctuations from a microphone array above the cavity evinces a distinct tone at 816 Hz, which is absent in the reference simulation. Furthermore, the power of the 4th Rossiter mode at 852 Hz is depleted, implying a significant energy transfer from the fluid to the structure. Spectral proper orthogonal decomposition (SPOD) is employed for analyses of cavity wall pressure fluctuations and wall displacements. The SPOD mode energy spectra show results consistent with the spectra of the microphone array with respect to the tone at 816 Hz and the depletion of the energy at the 4th Rossiter mode. Furthermore, the SPOD mode energy spectra show energy spikes at additional frequencies, which coincide with structural eigenfrequencies. Full article

(This article belongs to the Special Issue Aeroacoustics and Noise Mitigation)

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