Wave‐vector filtering and flow noise reduction in finite structures

1993 ◽  
Vol 93 (4) ◽  
pp. 2287-2287
Author(s):  
Y. F. Hwang
Keyword(s):  
Noise Reduction ◽  
Wave Vector ◽  
Flow Noise ◽  
Finite Structures

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

2021 ◽  
Vol 11 (9) ◽  
pp. 3869
Author(s):  
Chen Niu ◽  
Yongwei Liu ◽  
Dejiang Shang ◽  
Chao Zhang
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Noise Reduction ◽  
Channel Flow ◽  
Superhydrophobic Surface ◽  
Sound Field ◽  
Flow Noise ◽  
Slip Boundary ◽  
Eddy Simulation ◽  
Reduction Effect

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.

Research on acoustic behaviors of water pipelines with guide vanes

2022 ◽  
pp. 107754632110623
Author(s):  
Xianzhong Wang ◽  
Ning Li ◽  
Min Yu ◽  
Hongzhou Lin ◽  
Lili Ye
Keyword(s):  
Noise Reduction ◽  
Guide Vane ◽  
Experimental Methods ◽  
Guide Vanes ◽  
Experimental Platform ◽  
Flow Noise ◽  
Water Pipelines ◽  
Flow Speeds ◽  
Radiation Noise ◽  
Reduction Effect

In this paper, the pipeline with guide vanes was taken as the research object, the flow noise was studied based on the hybrid calculation method, then the acoustic-structure coupling method was introduced to study the vibration and radiation noise, and then explored the best position of the guide vanes. Based on the pipeline experimental platform and improved experimental methods, it was found that the guide vanes had a better noise reduction effect on the elbows; based on that, a simulation study was carried out on the elbow with guide vanes, and the mechanism of the guide vanes on the velocity field and pulsating pressure of the pipeline was explored. Finally, the noise reduction effect at different positions of the guide vanes under different flow speeds was studied. The results indicated that the guide vane at the middle of the elbow had the best effect on improving the flow field and reducing noise in the working conditions studied in this article, providing a calculation basis for the design of the guide vane.

scholarly journals Study on flow noise characteristics of Bionic cylinder based on acoustic analogy

2021 ◽  
Vol 336 ◽  
pp. 01003
Author(s):  
Zixian Cui ◽  
Hao Song ◽  
Qi Li ◽  
Buchao An ◽  
Lin Su
Keyword(s):  
Noise Reduction ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Cylinder Surface ◽  
Acoustic Analogy ◽  
Fluctuating Pressure ◽  
Flow Noise ◽  
Noise Characteristics ◽  
Reduction Effect ◽  
Serrated Structure

The drag and noise reduction of the flow around a cylinder is one of the important topics in hydrodynamics and acoustics. In this paper, three typical bionic cylinders are designed based on the serrated structure on the surface of shark skin. Using Large eddy turbulence model and Lighthill’s acoustic analogy method, the flow noise characteristics of smooth cylinder and three kinds of bionic cylinders at different Reynolds numbers were compared, and the structure of cylinder surface was optimized. The results show that the main source of the flow noise around a cylinder is dipole noise, which is caused by the periodic fluctuating pressure on the cylinder surface.The bionic cylinder can reduce the amplitude of the fluctuating pressure, improve the wake flow field and reduce the wake vorticity, so as to reduce the noise. Among the three kinds of bionic cylinder, V-shaped bionic cylinder has the best noise reduction effect, and the critical value of S/H of V-shaped cylinder is about 2.5. When s / h > 2.5, V-shaped bionic cylinder has no effect of noise reduction.

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.

scholarly journals Numerical Study on Noise Reduction of Gas Extinguishing Nozzle Using Adsorbent

2018 ◽  
Vol 7 (3.33) ◽  
pp. 152
Author(s):  
Hak Sun Kim ◽  
Yo Hwan Kim ◽  
In Ju Hwang ◽  
Youn Jea Kim
Keyword(s):  
Noise Reduction ◽  
Sound Pressure ◽  
Reference Model ◽  
Numerical Study ◽  
Fire Suppression ◽  
Design Parameters ◽  
Flow Noise ◽  
Fire Extinguishing ◽  
Ansys Cfx ◽  
Suppression Process

Currently, gas-based firefighting systems tend to release fire extinguishing agent at pressures of around 100 bar or more for quick firefighting. The flow noise produced by the agent discharge is approximately 140 dB, which is similar to fireworks. This powerful sound pressure level (SPL) results in equipment failure during the fire suppression process, accelerating the movement studies to reduce flow noise. Most previous studies have selected design parameters such as packing density, porosity, and absorbent arrays, but these factors alone do not address noise reduction issues. The methods used in this study constitute the thickness of the absorber in the nozzle. The sound absorber plays an important role in absorbing sound pressure by flow noise depending on its shape. In this study, numerical analysis was performed using ANSYS CFX ver. 18.1 to investigate the characteristics of flow noise and sound absorption. The thickness of the absorber shall be reduced or increased by 1 mm in relation to 86 mm. In particular, if the absorber diameter increases by 2 mm in the newly designed model, SPL is shown at 121.55 dB, down 9.3 % from the reference model.  

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