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Objective The jet noise generated by the main circuit breaker switching valve of high-speed railway EMU is excessively high, which seriously affects passenger comfort. Therefore, it is essential to study effective noise reduction measures. Method Field experiments are conducted to measure the jet noise of the switching valve, revealing a noise level as high as 96 dB with noticeable intermittency and pulsation. Using LES (large eddy simulation), a mathematical model for simulating the jet noise of the switching valve is established. Four different nozzle shapes are selected, and their flow velocity distribution nephograms are computed. The calculated jet flow results are imported into LMS.Virtual.Lab software, and the acoustic boundary element method is employed to simulate the jet noise fields of the four nozzles. The simulated 1/3-octave frequency spectrum values for them are compared with experimentally measured values. Finally, four existing industrial mufflers and a developed new structural composite material muffler are selected and tested for their noise reduction effectiveness on the switching valve. Result & Conclusion Generated by main circuit breaker disconnection, the jet noise of the switching valve is closely related to the shape of the exhaust port and falls into the mid-to-high-frequency noise range. All five mufflers can significantly reduce the jet noise from the switching valve, with the new structural composite material muffler demonstrating the best noise reduction effect, achieving a reduction of up to 20 dB.

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[Objectives] The characteristics and influencing factors of the radiated noise generated by the blowdown of sewage from underwater vehicles is investigated.[Methods] The flow field analysis and the quantitative calculation of radiated noise of large-diameter air jet were carried out based on Large Eddy Simulation(LES)and FW-H equation calculation method.[Results] The calculated and experimental results show that the radiated noise is mainly related to the pressure difference between the blowdown pressure and the back pressure,and is basically not affected by the blowdown back pressure. As the pressure difference increases,the radiated noise becomes larger. As the sanitary pressurized tank is blown out,the radiated noise experiences a breakthrough and increases significantly due to air jet under the water. Moreover, the spectrum shows a low frequency characteristic. The radiated noise is mainly concentrated in the range of 0-1 500 Hz and there are significant peaks appears in the spectrum,and there is a significant peak.[Conclusions] A reasonable measure to weaken the radiated noise during the process of blowdown is to control the pressure difference and prevent the appearing of the high pressure air jet under the sea.

Jet noise is the dominating component of aircraft aerodynamic noise, and causes severe environmental pollution and health threats. Yet lack of a fundamental understanding of how turbulent eddies generate noise radiation poses great challenges in designing accurate noise prediction methodologies and efficient noise reduction devices. The progresses and limitations of the studies on the turbulent noise source identification and noise source mechanisms in open literature are reviewed. Judging by the cause-effect reasoning that the turbulent fluctuations generate acoustic perturbations, it seems promising to develop physically more accurate models and governing equations to separate the acoustic and turbulent fluctuations in future research. By explicitly formulating the former as the generalized function of the latter, the dynamic process how turbulent eddies generate noise radiations is revealed.

In order to meet the airworthiness standards and safety requirements of civil aviation aircraft within the full flight envelope, the engine needs to be designed with a large safety margin to meet the most stringent noise requirements. Therefore, the engine performance potential cannot be taken full use of. A self-adaptive mutation strategy is proposed to improve the traditional gray wolf algorithm. Along with the adjustment of optimization mode during the optimization process, the global optimization performance is improved. Integrated optimization control of performance and jet noise is studied based on the improved grey wolf optimization algorithm according to different flight requirements. The control variable is optimized to improve the engine performance while guaranteeing the safety and noise limits. Simulation results show that the thrust is increased by 13.45% under the maximum thrust mode, the fuel assumption is reduced by 3.19% under the least fuel consumption mode, and the temperature of the turbine is reduced by 2.07% under the lowest turbine inlet temperature mode. [ABSTRACT FROM AUTHOR]

[Objectives] In order to study the underwater jet noise characteristics,[Methods] the Lighthill acoustic analogy is carried out to compute the underwater free jet flow sound field characteristic of axisymmetric nozzle, with applying of FLUENT simulation software and large eddy simulation, the real flow field of submerged axisymmetric nozzle is simulated, and the jet noise is measured by the reverberation method.[Results] The results show that the core length of steady flow field is independent of flow rate, and the length is about 8 times the diameter of the nozzle. The radiation power of jet noise is proportional to the velocity of eight times. The power spectrum of jet noise is different with the flow velocity in the low frequency. In the high frequency, the difference is significantly reduced. The radiated noise energy is mainly concentrated in the low frequency. With the increase of flow velocity, the main contribution of jet noise moves to high frequency.[Conclusions] In terms of computing simulation of jet noise, the large eddy simulation and Lighthill acoustic analogy combined analysis is an effective means.

The aerodynamic characteristics of muzzle noise are studied based on experimental and numerical research on jet noise induced by complex flows discharging from a large caliber small arms with a muzzle brake. The measured noise data are analyzed to distinguish the muzzle shock wave from muzzle impulse noise by the wavelet transform method. The muzzle noise is numerically simulated by a CFD-CAA hybrid method. The feasibility of the proposed method is proven by comparing the simulated results with the test results. In addition, the distribution of shock wave in muzzle brake and the directivity of muzzle noise field are analyzed based on the numerical simulation. The results indicate that the muzzle noise has a wide spectrum with high sound energy and complex components. It is found that the muzzle brake causes the lateral diversion of flow field around the muzzle, thus affecting the distribution of muzzle flow noise. [ABSTRACT FROM AUTHOR]

This definition takes the direction of the vorticity into account and can accelerate the the transition from Reynolds-averaged Navier-Stokes (R A N S) region to large-eddy-simulafoon (LES) region. A n isolated jet w k h Mach number of 0.9 and Reynolds number of 1.1 m i l o n based on the nozzle daameter js simulated. The flow quantities and nojse from two meshes are compared. The two meshes both provide reasonable results, but the results from the hne mesh are closer to the measurements. Beside nojse from iive integral surfaces of dense mesh are compared. It js proved that the numerical methods are competent to predict jet-noise. W h e n the freest ream Mach number increases to 0.2, the length of potendal core increases and the turbulent kinedc energy (T K E) and the and the far-field nojse decrease. The changes of of far-field nojse due to Hight velodty by our simulations are similar to the measurements. Tlis method can be extended to predict llgght velodty effects on jet nojse. [ABSTRACT FROM AUTHOR]