A NUMERICAL STUDY OF NOISE PROPAGATION FROM SURFACE-TREATED SUBMARINE USING ACOUSTIC ANALOGY

2021 ◽  
Vol 26 (4) ◽  
pp. 55-64
Author(s):  
Seunggi Kim ◽  
Jaiyoung Ryu
Keyword(s):  
Numerical Study ◽  
Acoustic Analogy ◽  
Noise Propagation

Numerical Study on Air-Reed Instruments With LES

2011 ◽  
Author(s):  
Kin’ya Takahashi ◽  
Masataka Miyamoto ◽  
Yasunori Ito ◽  
Toshiya Takami ◽  
Taizo Kobayashi ◽  
...  
Keyword(s):  
Numerical Study ◽  
Sound Field ◽  
Acoustic Analogy ◽  
Empirical Theory ◽  
Sound Sources ◽  
Aerodynamic Sound ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Semi Empirical ◽  
2D And 3D

The acoustic mechanisms of 2D and 3D edge tones and a 2D small air-reed instrument have been studied numerically with compressible Large Eddy Simulation (LES). Sound frequencies of the 2D and 3D edge tones obtained numerically change with the jet velocity well following Brown’s semi-empirical equation, while that of the 2D air-reed instrument behaves in a different manner and obeys the semi-empirical theory, so called Cremer-Ising-Coltman theory. We have also calculated aerodynamic sound sources for the 2D edge tone and the 2D air-reed instrument relying on Ligthhill’s acoustic analogy and have discussed similarities and differences between them. The sound source of the air-reed instrument is more localized around the open mouth compared with that of the edge tone due to the effect of the strong sound field excited in the resonator.

scholarly journals Numerical study of a control scheme on flow-induced cavity noise

2019 ◽  
Vol 283 ◽  
pp. 09002
Author(s):  
Lulu Liu ◽  
Jin Liu ◽  
Shijin Lyu
Keyword(s):  
Experimental Data ◽  
Cavity Length ◽  
Numerical Study ◽  
Numerical Procedure ◽  
Acoustic Analogy ◽  
Cavity Depth ◽  
Eddy Simulation ◽  
Control Scheme ◽  
Large Eddy ◽  
Flow Induced Noise

A numerical procedure for flow induced cavity noise is established in the paper. The procedure is based on large eddy simulation and FW-H acoustic analogy. The computational scheme is validated by comparing with experimental data. The change of flow induced noise along with cavity length, cavity depth and velocity is studied. A noise control scheme, which includes upright grille and oblique grille, is designed for reducing the flow-induced cavity noise. It turns out that the oblique grille shows superiority in the reduction of cavity noise by modifying the flow structure of the sheat layer.

Application of Numerical and Experimental Techniques for the Aero-Acoustic Characterisation of a Car Rear-View Mirror

2005 ◽  
Vol 4 (1-2) ◽  
pp. 185-212 ◽  
Author(s):  
Christoph Reichl ◽  
Christian Krenn ◽  
Martin Mann ◽  
Hermann Lang
Keyword(s):  
Acoustic Pressure ◽  
Cfd Simulation ◽  
Numerical Study ◽  
Pressure Fluctuations ◽  
Acoustic Analogy ◽  
Acoustic Characteristics ◽  
Rear View Mirror ◽  
Piv Method ◽  
Local Areas ◽  
Experimental Approaches

Numerical as well as experimental approaches are used to capture aero-acoustic characteristics of a car rear-view mirror. The numerical study splits up into several parts. Using an actual production mirror, particular emphasis must be put on the geometry preparation and mesh generation. Initially, a CFD simulation of the entire car aerodynamics is performed to extract the proper flow boundary conditions for the aero-acoustic simulation of a smaller section surrounding the mirror. Pressure fluctuations on the surfaces extracted during an LES generate the data base required for the aeroacoustic post-processing. The acoustic pressure at several monitoring points is then calculated using Lighthill's Acoustic Analogy. To include refraction effects of the nearby surfaces a direct BEM approach is also employed. Utilizing the PIV method, local areas of increased turbulence are identified experimentally. Microphone measurements with and without the exterior mirror are performed.

Numerical Assessment of 2D Aeroacoustic Simulations for Landing Gear

2018 ◽  
Author(s):  
Sultan I. Alqash ◽  
Kamran Behdinan
Keyword(s):  
Acoustic Field ◽  
Numerical Study ◽  
Near Field ◽  
Three Dimensional ◽  
Aerodynamic Noise ◽  
Design Stage ◽  
Acoustic Analogy ◽  
Ansys Fluent ◽  
2D Flow ◽  
Field Noise

Landing gears (LG) are primarily designed to support the entire loads of an aircraft during landing, taxiing, and taking off. From aerodynamic design prospective, many of the LG components are exposed to the air flow giving rise to what so-called aerodynamic noise. Numerical study of complex systems such as LG as a three-dimensional (3D) model is not only CPU and memory consuming, but also it is way beyond the demand of industries for quick estimate during the design stage [1–3]. To understand the underlying physics of the flow induced noise, a two-dimensional (2D) flow past a circular cylinder is simulated using ANSYS Fluent. Two different Reynolds numbers, Re = 150 and 90000 are examined. For low Re, two distinct numerical conditions relevant to steady and unsteady flow are simulated and compared to examine the effect of the time dependency on the acoustic field. At high Re, the acoustic field is computed using the built-in Ffowcs William and Hawkings (FW-H) acoustic analogy solver in Fluent. The results show the importance of including the unsteady state term to extract the flow data. The far-field noise prediction is found to be highly dependent on the location of the near-field data.

An Investigation Into Acoustics and Vibraton of CPAP Devices: Numerical Prediction of Centrifugal Fan Acoustics and Vibration

2013 ◽  
Author(s):  
Xuan-Tung Vuong ◽  
A. M. Al-Jumaily ◽  
Robert Paxton
Keyword(s):  
Numerical Study ◽  
Centrifugal Fan ◽  
Acoustic Analogy ◽  
Flow Induced Vibration ◽  
Upper Airways ◽  
Sound Sources ◽  
Human Interface ◽  
Obstructive Sleep ◽  
Unsteady Simulation ◽  
Cpap Devices

Continuous Positive Air Pressure (CPAP) devices are used to generate pressurized airflow to relieve upper airways and allow Obstructive Sleep Apnea (OSA) patients to breathe comfortably and easily. The airflow path in these devices consists of several components including but is not limited to inlet and outlet ducts, a centrifugal fan, a humidifier and a human interface. These components contribute significantly to the noise generated by the airflow. This research paper present a numerical study of a centrifugal fan performed with commercial ANSYS software package to predict the sound and vibration produced by the centrifugal fan. The methodologies are following: first, the unsteady flow field is computed using the CFD model to obtain aerodynamic quantities and sound sources. Then, the finite element method (FEM) is used to predict the flow-induced vibration using the predicted aerodynamic quantities. Finally, the Ffowcs-William and Hawkings’s (FW-H) acoustic analogy is used to predict the acoustic pressure at the far-field using the sound sources from the unsteady simulation.

Numerical Study of Noise from Isotropic Turbulence

1997 ◽  
Vol 05 (03) ◽  
pp. 317-336 ◽  
Author(s):  
A. Witkowska ◽  
D. Juvé ◽  
J. G. Brasseur
Keyword(s):  
Isotropic Turbulence ◽  
Numerical Study ◽  
Acoustic Power ◽  
Turnover Time ◽  
Turbulence Structure ◽  
Sound Generation ◽  
Acoustic Analogy ◽  
Eddy Simulation ◽  
Stationary Turbulence ◽  
Theoretical Predictions

A numerical study of sound radiation by isotropic turbulence is carried out by combining turbulence simulation with Lighthill's acoustic analogy. In the first study we analyze sound generation by decaying isotropic turbulence obtained both with 643 Direct Numerical Simulation (DNS) and 163 Large Eddy Simulation (LES). Both simulations lead to similar results for acoustic power, in agreement with the numerical results of Sarkar and Hussaini, but slightly different from theoretical predictions of Proudman and Lilley. In the second study we analyze sound generation by forced stationary turbulence, simulated with 1283 DNS using a forcing scheme which preserves turbulence structure. The acoustic power computed from the stationary turbulence is in good agreement with results obtained for decaying isotropic turbulence. The acoustic spectrum shows that the characteristic frequency of the generated sound is approximately four times the inverse eddy turnover time. The contributions of different turbulence scales to the generated noise are computed separately from filtered velocity fields. For the low Reynolds number turbulence analyzed, the scales which most contribute to noise generation are 2–3 times smaller than the energy-containing scales and lie between the energy and dissipation-rate spectral peaks.

Compressible Reynolds-Averaged Navier-Stokes Analysis of Wind Turbine Turbulent Flows Using a Fully-Coupled Low-Speed Preconditioned Multigrid Solver

2014 ◽  
Author(s):  
M. S. Campobasso ◽  
M. Yan ◽  
J. Drofelnik ◽  
A. Piskopakis ◽  
M. Caboni
Keyword(s):  
Turbulence Model ◽  
Static Pressure ◽  
Navier Stokes ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Noise Propagation ◽  
Low Speed ◽  
Analysis And Design ◽  
Reynolds Averaged Navier Stokes ◽  
Fully Coupled

The high-fidelity aeromechanical analysis and design of multi-megawatt horizontal axis wind turbines can be performed by means of Reynolds-averaged Navier-Stokes codes. The compressible or incompressible formulation of the fluid equations can be used. One of the objectives of the paper is to quantify the effects of flow compressibility on the aerodynamics of large turbine rotors with particular attention to the tip region of a 82 m rotor blade featuring a relative Mach number of about 0.3 near rated conditions. Noticeable local static pressure variations due to compressibility are observed. Such variations point to the better suitability of compressible solvers for turbine aerodynamics, not only when the solver is used for direct aeroacoustic simulation of the near field noise propagation, but also when it is used to provide the surface static pressure to be used as input for acoustic analogy noise propagation codes. On the numerical side, a novel numerical approach to low-speed preconditioning of the mean flow and turbulence model equations for the fully coupled integration of the flow equations coupled to a two-equation turbulence model is presented and implemented in a compressible Navier-Stokes research code for the steady and yawed wind-induced time-dependent flows analyzed herein.

Tonal Noise Generation in an Inlet Vaned Axial Blower at Several Axial Gaps

2006 ◽  
Author(s):  
K. M. Argu¨elles Di´az ◽  
J. M. Ferna´ndez Oro ◽  
C. Santolaria Morros ◽  
R. Ballesteros Tajadura
Keyword(s):  
Source Term ◽  
Noise Source ◽  
Numerical Study ◽  
Axial Flow ◽  
Single Stage ◽  
Axial Distance ◽  
Noise Generation ◽  
Acoustic Analogy ◽  
Tonal Noise ◽  
Specific Contribution

The main objective is the numerical study of the noise generation in a single stage axial flow blower. For the present work, just the discrete noise generation (tonal noise) is dealt with. A numerical methodology based on a generalization of Lighthill’s aero-acoustic analogy, the so-called Ffowcs Williams and Hawkings aero-acoustic analogy (FFWH), is developed. The numerical methodology has been tested with two different operational configurations of the blower: a first one, with a reduced axial gap between the rows of the stage (i.e. 50 mm) and a second one with a higher axial distance (i.e. 70 mm). The specific contribution of every tonal noise source term will be analyzed for both configurations.

A Numerical Study of the Unsteady Flow Field and Tonal Hydrodynamic Sound of a Centrifugal Pump

2015 ◽  
Author(s):  
Jian-Cheng Cai ◽  
Jie Pan ◽  
Andrew Guzzomi
Keyword(s):  
Centrifugal Pump ◽  
Cfd Simulation ◽  
Numerical Study ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Broad Band ◽  
Sound Radiation ◽  
Acoustic Analogy ◽  
Eddy Simulation ◽  
Surface Dipole

In this paper, the 3-D unsteady turbulent flow inside a centrifugal pump is investigated by computational fluid dynamics (CFD) in ANSYS CFX, using Detached Eddy Simulation (DES) as the turbulence approach. The pump has a single end-suction and a single volute discharge. The impeller is semi-open (unshrouded with baseplate) and has five backswept blades and pump-out back blades. The CFD model of the pump consists of the inlet, the impeller, and the volute. A sliding mesh technique has been applied to the interfaces in order to allow unsteady interactions between the rotating impeller and the stationary parts. These unsteady interactions generate pressure fluctuations over the volute casing and blade surfaces that are hydroacoustic dipoles according to Lighthill’s acoustic analogy theory. The pressure fluctuation spectra at the volute tongue show that pressure fluctuations are generated mainly by the discrete components related to the impeller rotation at low frequencies, especially the blade-passing frequency (BPF) component. This component is approximately 1% of the reference dynamic pressure 0.5ρν22 where ν2 is the circumferential velocity at the impeller outlet. The discrete components with frequency larger than 4 times BPF are no longer obvious in the spectra. Compared to the experimental results, the CFD simulation predicts much lower amplitudes for the broad band pressure fluctuations. This is reasonable, because DES combines a classical Reynolds averaged Navier Stokes (RANS) simulation with elements of Large Eddy Simulation (LES), and both RANS and LES use average methods which filter out the high frequency fluctuations. Nevertheless, CFD is capable of accurately predict the BPF component. The pressure fluctuations on the casing and blade surfaces are extracted and modelled as the stationary and rotary dipoles, respectively, according to the Ffowcs Williams and Hawkings (FW-H) equation of the acoustic analogy theory. After Fast Fourier Transform, the spectra of the pressure fluctuations are obtained, and are used to predict the tonal hydrodynamic sound radiation at BPF and its low order harmonics. The sound radiation of casing surface dipoles is calculated by extracting the tonal components, and performing a surface integration with the fundamental solution to Helmholtz equation as the kernel. A frequency domain formulation of the FW-H equation with the moving surface dipole is employed to predict the tonal blade noise. The results from these acoustical simulations show that the sound power generated by the casing surface dipole is three orders of magnitude higher than that of the blade surface dipole, and the main hydroacoustic sources are located at the volute tongue.

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