scholarly journals Noise Characteristics Analysis of the Horizontal Axis Hydrokinetic Turbine Designed for Unmanned Underwater Mooring Platforms

2019 ◽  
Vol 7 (12) ◽  
pp. 465 ◽  
Author(s):  
Zhigao Dang ◽  
Zhaoyong Mao ◽  
Baowei Song ◽  
Wenlong Tian
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Pressure Fluctuations ◽  
Noise Pollution ◽  
Horizontal Axis ◽  
Acoustic Analogy ◽  
Noise Emission ◽  
Suction Surface ◽  
Noise Characteristics ◽  
Hydrokinetic Turbine

Operating horizontal axis hydrokinetic turbine (HAHT) generates noise affecting the ocean environment adversely. Therefore, it is essential to determine the noise characteristics of such types of HAHT, as large-scale turbine sets would release more noise pollution to the ocean. Like other rotating machinery, the hydrodynamic noise generated by the rotating turbine has been known to be the most important noise source. In the present work, the transient turbulent flow field of the HAHT is obtained by incompressible large eddy simulation, thereafter, the Ffowcs Williams and Hawkings acoustic analogy formulation is carried out to predict the noise generated from the pressure fluctuations of the blade surface. The coefficient of power is compared with the experimental results, with a good agreement being achieved. It is seen from the pressure contours that the 80% span of the blade has the most severe pressure fluctuations, which concentrate on the region of leading the edge of the airfoil and the suction surface of the airfoil. Then, the noise characteristics around a single turbine are systematically studied, in accordance with the results of the flow field. The noise characteristics around the whole turbine are also investigated to determine the directionality of the noise emission of HAHT.

Multiple-arrayed pressure measurement for investigation of the unsteady flow structure of a reattaching shear layer

2002 ◽  
Vol 463 ◽  
pp. 377-402 ◽  
Author(s):  
INWON LEE ◽  
HYUNG JIN SUNG
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Vortical Structure ◽  
Single Point ◽  
Pressure Fluctuations ◽  
Vortical Flow ◽  
Recirculation Region ◽  
Stream Velocity ◽  
Vortical Structures ◽  
Wall Pressure Fluctuations

Spatio-temporal characteristics of wall pressure fluctuations in separated and reattaching flows over a backward-facing step were investigated through an extensive pressure-velocity joint measurement with an array of microphones. The experiment was performed in a wind tunnel with a Reynolds number of 33 000 based on the step height and the free-stream velocity. Synchronized wavelet maps showed the evolutionary behaviour of pressure fluctuations and gave further insight into the modulated nature of large-scale vortical structures. To see the relationship between the flow field and the relevant spatial mode of the pressure field, a new kind of wavenumber filtering, termed ‘spatial box filtering’ (SBF), was introduced and examined. The vortical flow field was reconstructed using every single-point velocity measurement by means of the conditional average based on the SBF second mode of pressure fluctuations. The flow field showed a well-organized spanwise vortical structure convected with a speed of 0.6U0 and a characteristic ‘sawtooth’ pattern of the unsteady trace of reattachment length. In addition to the coherent vortical structures, the periodic enlargement/shrinkage process of the recirculation region owing to apping motion was analysed. The recirculation region was found to undergo an enlargement/shrinkage cycle in accordance with the lowpass-filtered component of pressure fluctuations. In addition, such modulatory behaviour of the vortical structure as the global oscillation phase was discussed in connection with the conditionally averaged flow field.

Effects of speed and road condition on annoyance caused by motorcycle noise emission

2021 ◽  
Vol 263 (1) ◽  
pp. 5748-5753
Author(s):  
Omid Samani ◽  
Anna Martius ◽  
M. Ercan Altinsoy
Keyword(s):  
Traffic Noise ◽  
Noise Pollution ◽  
Clear Understanding ◽  
Noise Emission ◽  
Noise Characteristics ◽  
Vehicle Category ◽  
Road Condition ◽  
Noise Measurements

Recently much attention has been drawn to the noise emission of two-wheelers and motorcycles. Considering the high levels of noise pollution and annoyance caused by motorcycles, it is necessary to evaluate the contribution of their noise emission to the overall traffic noise. Furthermore, this emission must be included in traffic noise studies and noise maps. In order to have a clear understanding of the noise characteristics of this vehicle category, extensive studies are required. This paper aims to investigate the effects of speed and road condition on annoyance caused by motorcycle noise emission. For this purpose, noise measurements are carried out for various engine speeds, and road conditions. These stimuli are used later in a perceptual experiment to realize the effect of each parameter on the caused annoyance. Stimuli are reproduced in the laboratory where participants can determine their annoyance toward each stimulus. Finally, based on the outcome of the perceptual experiment and analysis of psychoacoustic parameters, a conclusion is drawn to clarify how annoyance and noise emission alter in response to the changes in speed and road condition.

Computational Noise Prediction of a Centrifugal Fan

2007 ◽  
Author(s):  
Esra Sorguven ◽  
Yilmaz Dogan ◽  
Faruk Bayraktar ◽  
Ergin Arslan
Keyword(s):  
Pressure Fluctuations ◽  
Flow Simulation ◽  
Sound Intensity ◽  
Centrifugal Fan ◽  
Acoustic Analogy ◽  
Noise Emission ◽  
Band Frequency ◽  
Eddy Simulation ◽  
Acoustic Sources ◽  
Dependent Flow

In this study, computational aeroacoustics methods are employed to analyze the flow and the noise emission in a centrifugal fan. Unsteady flow inside the centrifugal fan is predicted with large eddy simulation. Acoustic sources are computed based on the results of the time-dependent flow simulation. The turbulent pressure fluctuations on the blades and on the volute of the fan are used as the source terms in the acoustic analogy of Ffowcs Williams and Hawkings. Propagation, diffraction and scattering of the acoustic sources inside the volute are computed with the boundary element method. Numerically obtained sound pressure level distribution in narrow band frequency spectrum is compared with experimental measurements at certain microphone points. The numerical and experimental sound intensity maps are also compared to validate the numerical prediction of directivity. Computational results agree well with the experimental data and provide an insight of the noise emission mechanisms.

scholarly journals Flow field and noise characteristics of manifold in natural gas transportation station

2019 ◽  
Vol 74 ◽  
pp. 70 ◽  
Author(s):  
Zhongya Su ◽  
Enbin Liu ◽  
Yawen Xu ◽  
Ping Xie ◽  
Chen Shang ◽  
...  
Keyword(s):  
Natural Gas ◽  
Flow Field ◽  
Noise Reduction ◽  
Simulation Analysis ◽  
Fluid Dynamic ◽  
Acoustic Analogy ◽  
Pressure Balance ◽  
Expansion Chamber ◽  
Flow Noise ◽  
Noise Characteristics

Manifolds play a role of pressure balance, buffering and rectification for different branch pipelines, the flow noise of manifolds has been a serious problem all this time in natural gas transmission station. By changing the number of outlet pipes of manifolds and the different positions of intake pipes, the distribution of the Sound Pressure Level (SPL) of the manifold flow noise is analyzed based on the Ffowcs Williams-Hawkings (FW-H) acoustic analogy theory and Large Eddy Simulations (LESs). The three-dimensional simulation analysis of the flow field shows that pressure pulsation is the mainly source of manifold noise, as the number of outlet pipe increases, the SPLs of fluid dynamic noise at the end of inlet pipes are significantly reduced by about 10 dB on average, when the inlet and outlet piping are oppositely connected, the SPL is 2 dB~3 dB lower than that in staggered connections. An expansion-chamber muffler is designed with the analysis of its noise reduction effect, the results show that after the muffler is installed, the noise reduction in the low-frequency ranges reaches up to 37.5 dB, which controls the maximum noise to around 82 dB.

DNS study of particle-bed–turbulence interactions in an oscillatory wall-bounded flow

2016 ◽  
Vol 792 ◽  
pp. 232-251 ◽  
Author(s):  
Chaitanya D. Ghodke ◽  
Sourabh V. Apte
Keyword(s):  
Flow Field ◽  
Turbulent Flows ◽  
Large Scale ◽  
Energy Transport ◽  
Pressure Fluctuations ◽  
Outer Region ◽  
Production Term ◽  
Non Gaussian ◽  
Particle Bed ◽  
Rough Beds

Particle-resolved direct numerical simulations (DNS) are performed to investigate the behaviour of an oscillatory flow field over a rough bed, corresponding to the experimental set-up of Keiller & Sleath (J. Fluid Mech., vol. 73 (04), 1976, pp. 673–691) for transitional and turbulent flows over a range of Reynolds numbers (95–400) based on the Stokes-layer thickness. It is shown that the roughness modulates the near-bed turbulence, produces streamwise horseshoe structures which then undergo distortion and breaking, and therefore reduces the large-scale anisotropy. A fully developed equilibrium turbulence is observed in the central part of the oscillation cycle, with two-component turbulence in the near-bed region and cigar-shaped turbulence in the outer region. A double averaging of the flow field reveals spatial inhomogeneities at the roughness scale and alternate paths of energy transport in the turbulent kinetic energy (TKE) budget. Contrary to the unidirectional, steady flow over rough beds, bed-induced production terms are important and comparable to the shear production term. It is shown that the near-bed velocity and pressure fluctuations are non-Gaussian, a result of critical importance for the modelling of incipient motion of sediment grains.

scholarly journals Numerical simulation of leakage flow field and acoustic characteristics for safety valve

2021 ◽  
Vol 336 ◽  
pp. 01007
Author(s):  
Fan Qian ◽  
Minghui Hu
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Pressure Fluctuation ◽  
Large Scale ◽  
Safety Valve ◽  
Sound Field ◽  
Wall Pressure ◽  
Small Scale ◽  
Acoustic Analogy ◽  
Wall Pressure Fluctuation

Aiming at the internal leakage problem of spring type nuclear safety valve at the sealing surface, the flow field and sound field characteristics at the leakage height of 0.5mm between the valve disc and the valve seat sealing surface were studied, and the numerical simulation was carried out based on large eddy simulation(LES) and mohring acoustic analogy method, and compare the effects of acoustic wall pressure fluctuation(AWPF) and turbulent wall pressure fluctuation(TWPF) as the excitation source on the external sound field of the valve. The simulation results show that: the change gradient of velocity field and pressure field at the leakage port of safety valve is significant and form vortices of different sizes. The small-scale vortices are mainly in the leakage port, while the large-scale vortices mainly exist in the flow channel; When the valve is leaking, the noise is mainly dominated by high-pressure injection noise, its spectrum curve shows wide-band characteristics, and the external noise of the valve is mainly caused by AW P F. The above research results can provide a theoretical basis for the safety valve online detection method.

Three-Dimensional Unsteady Flow Field due to IGV-Rotor Interaction in the Tip Region of an Axial Compressor Rotor Passage

2001 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang ◽  
Qingguo Zhang
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Large Scale ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Low Energy ◽  
Suction Surface ◽  
Compressor Rotor ◽  
Flow Mixing

This paper reports an experimental study of the three-dimensional unsteady flow field due to IGV-rotor interaction in the tip region of an axial compressor rotor passage. The measurements were conducted on a low-speed large-scale axial compressor using a 3-component Laser Doppler Velocimetry. Both experimental method and measurement techniques are presented in details. The results indicate that the tip corner flow of the IGV suction surface has deeper effects on the downstream flow than the IGV wake in the tip region. The interaction and the flow mixing among the IGV wake, the IGV comer flow and the rotor leading-edge flow occur at the inlet of a rotor passage, which make the rotor inlet flow three-dimensional, turbulent and unsteady. The low-energy fluids from the upstream tend to accumulate toward the rotor pressure surface after they enter a rotor passage. In the procedure, the interaction and the flow mixing among the rotor tip leakage vortex and the low-energy fluids occur in the rotor passage.

scholarly journals LEVELS, TRENDS AND EXPOSURE DOSES OF NOISE EMITTED BY SMALL SCALE ENTERPRISES IN ABEOKUTA, SOUTH-WESTERN NIGERIA

2019 ◽  
Vol 17 (1) ◽  
pp. 49-66
Author(s):  
O. OGUNTOKE ◽  
O. SHOLANKE ◽  
A. C. OJO
Keyword(s):  
Large Scale ◽  
Noise Exposure ◽  
Weighted Average ◽  
Noise Pollution ◽  
Policy Formulation ◽  
Small Scale ◽  
Noise Levels ◽  
Noise Emission ◽  
Machine Operators ◽  
The Impact

Monitoring of noise levels and their impact are common in large scale and corporate industrial establishments while the small scale industries have not received sufficient attention. Consequently, the present study examined the levels and pattern of noise emission from small-scale enterprises that are generally ignored from compliance monitoring of the relevant agencies. The study utilises the results of noise emission quantification, determination of safe distance to the selected small-scale enterprises and impact on human as input for noise policy formulation. Three types of small-scale enterprises sampled from seventy-five (75) sites in Abeokuta were selected for noise measurement using a portable noise meter. Questionnaire and field observation were employed to assess the impact of noise on machine operators and their apprentices. Mean noise emission from the aluminum slitting machines ranged from 103.9 – 118.4 d(BA), iron welding machines; 97.0 – 108.8 d(BA) and food grinding machines; 91.6 to 108.2 d(BA). Daily Noise Dose (DND) from these three types of machine workshops were 800 – 19230% (aluminum slitter), 200 – 2400% (iron welder), and 100 – 3305% (food grinder). Time Weighted Average (TWA) for 8 hours noise exposure values were 94.0 – 107.8, 88.0 – 98.8 and 85.0 – 100.2 respectively. The spatial dimension of noise emission from the studied machines showed that acceptable levels were obtained at 20 meters from the machines sites. As predictors of variations in noise emission, the age of the machines explained 8.3 – 13.6%, 17.2 – 17.8% and 29.1 – 55.4% of noise emitted by food grinders, aluminum slitters and iron welders. The capacities of the studied machines predicted 7.9 – 13.5%, 18.4 – 30.5 and 43.9 – 56.3% of the noise emitted by iron welders, aluminum slitter and food grinders respectively. While the noise levels at the sites of the machines were significantly higher than the permissible limit, 25% of the workers were exposed for upwards of 10 hours daily and 30% for more than five years. The array of health problems; stress, dizziness, tinnitus, sleep disturbance and speech interference, experienced by the machines operators may not be unconnected to their non-use of Personal Protective Equipment (PPE) to minimize noise hazard. Policy formulation for public protection from noise pollution should prescribe limit for small scale enterprises, enforce noise level compliance, monitor wearing of appropriate PPE by machine operators and maintained a minimum of 20 meters between the sites of these machines and other human activities.         

Large-scale flow field visualization for aneurysm treatment

2001 ◽  
Vol 9 (1) ◽  
pp. 3-7
Author(s):  
Damon Liu ◽  
Mark Burgin ◽  
Walter Karplus ◽  
Daniel Valentino
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Aneurysm Treatment ◽  
Large Scale Flow

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

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