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Recent Advances in Flow-Induced Noise

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 30614

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Prof. Dr. Cheolung Cheong

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Guest Editor

School of Mechanical Engineering, Pusan National University, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan 46241, Korea
Interests: aeroacoustics; noise

Dr. Hanshin Seol

E-Mail Website
Guest Editor

Korea Research Institute of Ships & Ocean Engineering, Daejeon 34103, Korea
Interests: propeller noise, cavitation

Special Issue Information

Dear Colleagues,

Since Lighthill (1952) defined aerodynamic noise sources mathematically, the related areas of aeroacoustic research have made remarkable progress in understanding the noise generation mechanism in applications such as jet, fan, and turbomachinery flows and in developing high-fidelity computational aeroacoustic techniques. Recent advances in the related research areas may be highlighted in terms of two points. One is the extension of the relevant physical theory from aerodynamic noise to flow-induced noise. Lighthill developed his theory for the request of reducing jet noise in the aeronautics industry in the 1950s. Although most research funding still comes from the aeronautics industry, the application areas have become broader (e.g., high-speed vehicle noise, home appliance noise, wind-turbine noise, etc.). Recently, the underwater acoustic waves radiated from ships and submarines have gained a great deal of attention due to environmental issues. The investigation into this issue inevitably requires the extension of aerodynamic noise theory to include flow noise (e.g., cavitation noise). Another reason for the increase in interest is the dramatically increased computation resources available for the numerical investigation of aerodynamic noise generation and fluid dynamics. The increasingly resolved computation results of flow-induced noise help develop our understanding of noise generation mechanisms, which enlarges our current knowledge of flow-induced noise. In this respect, this Special Issue is devoted to the application of fundamental aerodynamic noise theory and computational flow-induced noise techniques.

Prof. Dr. Cheolung Cheong
Dr. Hanshin Seol
Guest Editors

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Keywords

aeroacoustics
flow-induced noise
fan noise
cavitation noise
underwater propeller noise
automobile wind noise
airframe noise

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Published Papers (9 papers)

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Research

18 pages, 30227 KiB

Open AccessArticle

Noise Reduction Effect of Superhydrophobic Surfaces with Streamwise Strip of Channel Flow

by Chen Niu, Yongwei Liu, Dejiang Shang and Chao Zhang

Appl. Sci. 2021, 11(9), 3869; https://doi.org/10.3390/app11093869 - 25 Apr 2021

Cited by 1 | Viewed by 2024

Abstract

Superhydrophobic surface is a promising technology, but the effect of superhydrophobic surface on flow noise is still unclear. Therefore, we used alternating free-slip and no-slip boundary conditions to study the flow noise of superhydrophobic channel flows with streamwise strips. The numerical calculations of the flow and the sound field have been carried out by the methods of large eddy simulation (LES) and Lighthill analogy, respectively. Under a constant pressure gradient (CPG) condition, the average Reynolds number and the friction Reynolds number are approximately set to 4200 and 180, respectively. The influence on noise of different gas fractions (GF) and strip number in a spanwise period on channel flow have been studied. Our results show that the superhydrophobic surface has noise reduction effect in some cases. Under CPG conditions, the increase in GF increases the bulk velocity and weakens the noise reduction effect. Otherwise, the increase in strip number enhances the lateral energy exchange of the superhydrophobic surface, and results in more transverse vortices and attenuates the noise reduction effect. In our results, the best noise reduction effect is obtained as 10.7 dB under the scenario of the strip number is 4 and GF is 0.5. The best drag reduction effect is 32%, and the result is obtained under the scenario of GF is 0.8 and strip number is 1. In summary, the choice of GF and the number of strips is comprehensively considered to guarantee the performance of drag reduction and noise reduction in this work. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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19 pages, 4821 KiB

Open AccessFeature PaperArticle

Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

by Yasir Al-Okbi, Tze Pei Chong and Oksana Stalnov

Appl. Sci. 2021, 11(6), 2593; https://doi.org/10.3390/app11062593 - 15 Mar 2021

Cited by 4 | Viewed by 4185

Abstract

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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18 pages, 23947 KiB

Open AccessArticle

Numerical Study on the Route of Flame-Induced Thermoacoustic Instability in a Rijke Burner

by Nannan Dang, Jiazhong Zhang and Yoshihiro Deguchi

Appl. Sci. 2021, 11(4), 1590; https://doi.org/10.3390/app11041590 - 10 Feb 2021

Cited by 11 | Viewed by 2600

Abstract

The self-excited thermoacoustic instability in a two-dimensional Rijke-type burner with a center-stabilized premixed methane–air flame is numerically studied. The simulation considers the reacting flow, flame dynamics, and radiation model to investigate the important physical processes. A finite volume-based approach is used to simulate reacting flows under both laminar and turbulent flow conditions. Chemical reaction modeling is conducted via the finite-rate/eddy dissipation model with one-step reaction mechanisms, and the radiation heat flux and turbulent flow characteristics are determined by using the P-1 model and the standard k-ε model, respectively. The steady-state reacting flow is first simulated for model verification. Then, the dynamic pressure, velocity, and reaction heat evolutions are determined to show the onset and growth rate of self-excited instability in the burner. Using the fast Fourier transform (FFT) method, the frequency of the limit cycle oscillation is obtained, which agrees well with the theoretical prediction. The dynamic pressure and velocity along the tube axis provide the acoustic oscillation mode and amplitude, also agreeing well with the prediction. Finally, the unsteady flow field at different times in a limit cycle shows that flame-induced vortices occur inside the combustor, and the temperature distribution indicates that the back-and-forth velocity changes in the tube vary the distance between the flame and honeycomb in turn, forming a forward feedback loop in the tube. The results reveal the route of flame-induced thermoacoustic instability in the Rijke-type burner and indicate periodical vortex formation and breakdown in the Rijke burner, which should be considered turbulent flow under thermoacoustic instability. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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20 pages, 4406 KiB

Open AccessArticle

Estimation of the Noise Source Level of a Commercial Ship Using On-Board Pressure Sensors

by Hongseok Jeong, Jeung-Hoon Lee, Yong-Hyun Kim and Hanshin Seol

Appl. Sci. 2021, 11(3), 1243; https://doi.org/10.3390/app11031243 - 29 Jan 2021

Cited by 7 | Viewed by 2989

Abstract

The dominant underwater noise source of a ship is known to be propeller cavitation. Recently, attempts have been made to quantify the source strength using on-board pressure sensors near the propeller, as this has advantages over conventional noise measurement. In this study, a beamforming method was used to estimate the source strength of a cavitating propeller. The method was validated against a model-scale measurement in a cavitation tunnel, which showed good agreement between the measured and estimated source levels. The method was also applied to a full-scale measurement, in which the source level was measured using an external hydrophone array. The estimated source level using the hull pressure sensors showed good agreement with the measured one above 400 Hz, which shows potential for noise monitoring using on-board sensors. A parametric study was carried out to check the practicality of the method. From the results, it was shown that a sufficient recording time is required to obtain a consistent level at high frequencies. Changing the frequency resolution had little effect on the result, as long as enough data were provided for the one-third octave band conversion. The number of sensors affected the mid- to low-frequency data. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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16 pages, 9123 KiB

Open AccessArticle

The Application of a Linear Microphone Array in the Quantitative Evaluation of the Blade Trailing-Edge Noise Reduction

by Weijie Chen, Luqin Mao, Kangshen Xiang, Fan Tong and Weiyang Qiao

Appl. Sci. 2021, 11(2), 572; https://doi.org/10.3390/app11020572 - 8 Jan 2021

Cited by 3 | Viewed by 1985

Abstract

This paper concerns the application of a linear microphone array in the quantitative evaluation of blade trailing-edge (TE) noise reduction. The noise radiation from the blades with straight and serrated TEs is measured in an indoor open-jet wind tunnel. The array data are processed using the inverse method based on the Clean algorithm based on spatial source coherence (Clean-SC). In order to obtain correct application and achieve the best effect for the microphone array test, the computing software for array data reduction is firstly developed and assessed by Sarradj’s benchmark case. The assessment results show that the present array data processing method has a good accuracy with an error less than 0.5 dB in a wide frequency range. Then, a linear array with 32 microphones is designed to identify the noise source of a NACA65(12)-10 blade. The performance of the Clean-SC algorithm is compared with the Clean algorithm based on point spread functions (Clean-PSF) method for experimentally identifying the noise sources of the blade. The results show that there is about a 2 dB error when using the Clean-PSF algorithm due to the interference of different aerodynamic noise sources. Experimental studies are conducted to study the blade TE noise reduction using serrated TEs. The TE noise for the blade with and without sawtooth configurations is measured with the flow speeds from 20 m/s to 70 m/s, and the corresponding Reynolds numbers based on the chord are from 200,000 to 700,000. Parametric studies of the sawtooth amplitude and wavelength are conducted to understand the noise reduction law. It is observed that the TE noise reduction is sensitive to both the amplitude and wavelength. The flow speed also affects the noise reduction in the serrated TEs. To obtain the best noise suppression effect, the sawtooth configuration should be carefully designed according to the actual working conditions and airflow parameters. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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27 pages, 15425 KiB

Open AccessArticle

Numerical Investigation of Tip Vortex Cavitation Inception and Noise of Underwater Propellers of Submarine Using Sequential Eulerian–Lagrangian Approaches

by Garam Ku, Cheolung Cheong, Ilryong Park and Hanshin Seol

Appl. Sci. 2020, 10(23), 8721; https://doi.org/10.3390/app10238721 - 5 Dec 2020

Cited by 10 | Viewed by 3401

Abstract

In this study, the high-fidelity numerical methods are developed to investigate the tip vortex cavitation (TVC) inception and noise of underwater propellers, namely, Model-A and Model-B, which are designed to investigate the effects of sweep angle on cavitation inception and noise. In addition, the entire body of the DARPA Suboff submarine is included to consider the effects of the inflow distortion originating from the boundary layer flow of the submarine body on the cavitating flow of the propellers. The Eulerian approach consisting of Reynolds-averaged Navier–Stokes (RANS) solver and the vortex model is coupled with the Lagrangian approach using the bubble dynamics equations and the acoustic analogy for nuclei initially distributed in inlet flow. First, three-dimensional incompressible unsteady RANS simulations are performed to predict the hydrodynamic flow field driven by underwater propellers installed on a DARPA Suboff submarine body. The Scully vortex model and dissipation vortex model (DVM) are used to regenerate the tip vortex dissipated by artificial numerical damping and low grid resolution around the vortex core center, which is identified by using minimum λ₂-criterion in the swirling flow field originating from the propeller blade tip. Then, tip vortex cavitation inception is simulated by applying the bubble dynamics equations to nuclei initially distributed in the inflow region. The volume and location of each nucleus are obtained by solving the bubble dynamics equations on the flow field obtained using the Eulerian method. Finally, the cavitation noise is predicted by modeling each bubble with a point monopole source whose strength is proportional to its volume acceleration. The validity of the present numerical methods is confirmed by comparing the predicted acoustic pressure spectrum with the measured ones. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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30 pages, 20168 KiB

Open AccessFeature PaperArticle

Numerical Investigation of Tip-Vortex Cavitation Noise of an Elliptic Wing Using Coupled Eulerian-Lagrangian Approaches

by Garam Ku, Cheolung Cheong and Hanshin Seol

Appl. Sci. 2020, 10(17), 5897; https://doi.org/10.3390/app10175897 - 26 Aug 2020

Cited by 10 | Viewed by 3911

Abstract

In this study, a numerical methodology is developed to investigate the tip-vortex cavitation of NACA16-020 wings and their flow noise. The numerical method consists of a sequential one-way coupled application of Eulerian and Lagrangian approaches. First, the Eulerian method based on Reynolds-averaged Navier–Stokes equation is applied to predict the single-phase flow field around the wing, with particular emphasis on capturing high-resolution tip-vortex flow structures. Subsequently, the tip-vortex flow field is regenerated by applying the Scully vortex model. Secondly, the Lagrangian approach is applied to predict the tip-vortex cavitation inception and noise of the wing. The initial nuclei are distributed upstream of the wing. The subsequent time-varying size and position of each nucleus are traced by solving spherically symmetric bubble dynamics equations for the nuclei in combination with the flow field predicted from the Eulerian approach. The acoustic pressure at the observer position is computed by modelling each bubble as a point source. The numerical results of the acoustic pressure spectrum are best matched to the measured results when the nuclei number density of freshwater is used. Finally, the current numerical method is applied to the flows of various cavitation numbers. The results reveal that the cavitation inception determined by the predicted acoustic pressure spectrum well matched the experimental result. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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22 pages, 9184 KiB

Open AccessArticle

Numerical and Experimental Study on the Flow-Induced Noise Characteristics of High-Speed Centrifugal Pumps

by Qiaorui Si, Chunhao Shen, Xiaoke He, Hao Li, Kaile Huang and Jianping Yuan

Appl. Sci. 2020, 10(9), 3105; https://doi.org/10.3390/app10093105 - 29 Apr 2020

Cited by 13 | Viewed by 3344

Abstract

The development of low-noise pumps is essential to design quiet fluid delivery systems. Due to the complicated internal flow, the flow-induced noise characteristics of high-speed centrifugal pumps have not been well understood. Taking engine cooling pumps as an example model, experimental measurements are performed in a semi-anechoic room and a CFD/CFA calculation method is proposed to study the fluid-borne noise and radiated noise characteristics. In the speed range of 5000–6750 r/min, both the pump head and the dimensionless radiated noise characteristics conform to similar laws, and the highest efficiency point pump presents the lowest noise level. Consistent with the experimental results, the predicted radiated noise of the model pump presents dipole characteristics at the required flow rate condition. Moreover, the spectrum of fluid borne noise at pump outlet shows broadband characteristics but with obvious discrete peaks, which are not only related to the fluid pressure pulsation characteristics (6f₀ and the multiple) at the low-frequency region, but also to the frequency of the structural mode (3000–6000 Hz region). Rotor-stator interaction of the pump flow field between the impeller and volute is the main reason of flow-induced noise; unstable flow also contributes to the broadband components in the noise spectrum. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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17 pages, 7827 KiB

Open AccessArticle

Optimization of the Orifice Shape of Cooling Fan Units for High Flow Rate and Low-Level Noise in Outdoor Air Conditioning Units

by Se Min Park, Seo-Yoon Ryu, Cheolung Cheong, Jong Wook Kim, Byung Il Park, Young-Chull Ahn and Sai Kee Oh

Appl. Sci. 2019, 9(23), 5207; https://doi.org/10.3390/app9235207 - 29 Nov 2019

Cited by 19 | Viewed by 5166

Abstract

Demand for air conditioners is steadily increasing due to global warming and improved living standards. The noise, as well as the performance of air conditioners, are recognized as one of the crucial factors that determine the air conditioners’ values. The performance and noise of the air conditioner are mostly determined by those of its outdoor unit, which in turn depend on those of the cooling fan unit. Therefore, a cooling fan unit of high-performance and low noise is essential for air-conditioner manufacturers and developers. In this paper, the flow performance and flow noise of the entire outdoor unit with an axial cooling fan in a split-type air-conditioner were investigated. First, a virtual fan tester constructed by using about 18 million grids is developed for highly resolved flow simulation. The unsteady Reynolds-Averaged Navier–Stokes equations are numerically solved by using finite-volume computational fluid dynamics techniques. To verify the validity of the numerical analysis, the predicted P–Q curve of the cooling fan in a full outdoor unit is compared with the measured one. There was an excellent agreement between the two curves. The further detailed analysis identifies the coherent vortex structures between the fan blade tip and fan orifice, which adversely affect the flow performance and causes flow noise. Based on this analysis, the optimization of fan orifice was carried out using the response surface method with three geometric parameters: inlet radius, neck length, and outlet angel of the orifice. The optimum layout for the high flow rate is proposed under the understanding that the increased flow rate can be converted to noise reduction. The additional computation using the proposed optimum orifice shows that the flow rate is increased by 4.6% at the operating point. Finally, the engineering sample was manufactured by using the optimum design, and the measured data confirmed that the flow rate were increased by 2.1%, the noise reduction was made by 2.8 dBA, and the power consumption is reduced by 4.0% at the operating rotational speed. Full article

(This article belongs to the Special Issue Recent Advances in Flow-Induced Noise)

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