The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can...The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers(MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.展开更多
Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The generation mechanism of flap side-edge noise is analyzed by numerical simulation on unsteady flow field using Very Lar...Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The generation mechanism of flap side-edge noise is analyzed by numerical simulation on unsteady flow field using Very Large Eddy Simulation （VLES）. Two kinds of flap side-edge shape modifications are proposed, and their frequency spectrum and directivity of far-field noise are compared with the baseline configuration using permeable integral surface Ffowcs Williams and Hawkings （FW-H） acoustic analogy method to investigate their effects on noise reduction. Via the numerical simulation of flow field and acoustic field, it proves that the flap side-edge noise is broadband noise in nature. The different shapes of flap side-edge change the pattern of flow field, vortex structures and the development of vortex, thus having influences on noise source distributions and characteristics of far-field noise. The result shows that at the given 5° angle of attack, the proposed flap side-edge shape modifications can reduce the overall sound pressure level （OASPL） by 1 to 2 dB without decreasing the lift and drag aerodynamic performances.展开更多
Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod wi...Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod with a diameter of 10 mm. The incoming flow velocity is 40 m/s and the corresponding Reynolds numbers based on airfoil chord and rod diameter are about 397000 and 26000, respectively. The far-field acoustic field is predicted using an acoustic analogy method which has been validated by the experiment. A straight leading edge airfoil and a wavy leading edge airfoil are simulated. The results show that wavy leading edge increases the airfoil lift and drag whereas the lift and drag fluctuations are substantially reduced. In addition, wavy leading edge can significantly change the flow pattern around the leading edge and a pair of counter-rotating streamwise vortices stemming from each wavy leading edge peak are observed.An averaged noise reduction of 9.5 dB is observed with the wavy leading edge at the azimuthal angle of 90°. Moreover, the wavy leading edge can mitigate noise radiation at all the azimuthal angles without significantly changing the noise directivity. The underlying noise reduction mechanisms are then analyzed in detail.展开更多
Numerical studies are conducted to explore the noise reduction effect of leading-edge tubercles inspired by humpback whale flippers.Large eddy simulations are performed to solve the flow field,while the acoustic analo...Numerical studies are conducted to explore the noise reduction effect of leading-edge tubercles inspired by humpback whale flippers.Large eddy simulations are performed to solve the flow field,while the acoustic analogy theory is used for noise prediction.In this paper,a baseline airfoil with a straight leading-edge and three bionic airfoils with tubercled leading-edges are simulated.The tubercles have sinusoidal profiles and the profiles are determined by the tubercle wavelength and amplitude.The tubercles used in this study have a fixed wavelength of 0.1c with three different amplitudes of 0.1c,0.15c and 0.2c,where c is the mean chord of the airfoil.The freestream velocity is set to 40 m/s and the chord based Reynolds number is 400,000.The predicted flow field and acoustic field of the baseline airfoil are compared against the experiments and good agreements are found.A considerable noise reduction level is achieved by the leading-edge tubercles and the tubercle with larger amplitude can obtain better noise reduction.The underlying flow mechanisms responsible for the noise reduction are analyzed in detail.展开更多
基金supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 52362049 and 52208446)the Natural Science Foundation of Gansu Province (Grant Nos. 22JR5RA344 and 22JR11RA152)+4 种基金the Special Funds for Guiding Local Scientifi c and Technological Development by the Central Government (Grant No. 22ZY1QA005)the Joint Innovation Fund Project of Lanzhou Jiaotong University and Corresponding Supporting University (Grant No. LH2023016)the Fundamental Research Funds for the Central Universities (2682023ZTZ010), the Lanzhou Science and Technology planning Project (Grant No. 2022-ZD-131)the key Research and Development Project of Lanzhou Jiaotong University (Grant No. LZJTU-ZDYF2302)the University Youth Fund Project of Lanzhou Jiaotong University (Grant No. 2021014)。
文摘The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers(MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.
文摘Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The generation mechanism of flap side-edge noise is analyzed by numerical simulation on unsteady flow field using Very Large Eddy Simulation （VLES）. Two kinds of flap side-edge shape modifications are proposed, and their frequency spectrum and directivity of far-field noise are compared with the baseline configuration using permeable integral surface Ffowcs Williams and Hawkings （FW-H） acoustic analogy method to investigate their effects on noise reduction. Via the numerical simulation of flow field and acoustic field, it proves that the flap side-edge noise is broadband noise in nature. The different shapes of flap side-edge change the pattern of flow field, vortex structures and the development of vortex, thus having influences on noise source distributions and characteristics of far-field noise. The result shows that at the given 5° angle of attack, the proposed flap side-edge shape modifications can reduce the overall sound pressure level （OASPL） by 1 to 2 dB without decreasing the lift and drag aerodynamic performances.
基金supported by the National Natural Science Foundation of China (Nos.51776174,51476134,51276149 and 11602290)State Key Laboratory of Aerodynamics of China Aerodynamics Research and Development Center (No.SKLA20160201)+1 种基金Key Laboratory of Aerodynamic Noise Control of China Aerodynamics Research and Development Center (No.ANCL20170201)China-Europe IMAGE (Innovative Methodologies and Technologies for Reducing Aircraft Noise Generation and Emission) program (No.688971-IMAGE-H2020MG-20141015)
文摘Large Eddy Simulation（LES） is performed to investigate the airfoil broadband noise reduction with wavy leading edge under anisotropic incoming turbulence. The anisotropic incoming turbulence is generated by a rod with a diameter of 10 mm. The incoming flow velocity is 40 m/s and the corresponding Reynolds numbers based on airfoil chord and rod diameter are about 397000 and 26000, respectively. The far-field acoustic field is predicted using an acoustic analogy method which has been validated by the experiment. A straight leading edge airfoil and a wavy leading edge airfoil are simulated. The results show that wavy leading edge increases the airfoil lift and drag whereas the lift and drag fluctuations are substantially reduced. In addition, wavy leading edge can significantly change the flow pattern around the leading edge and a pair of counter-rotating streamwise vortices stemming from each wavy leading edge peak are observed.An averaged noise reduction of 9.5 dB is observed with the wavy leading edge at the azimuthal angle of 90°. Moreover, the wavy leading edge can mitigate noise radiation at all the azimuthal angles without significantly changing the noise directivity. The underlying noise reduction mechanisms are then analyzed in detail.
基金This work is supported by the National Natural Science Foundation of China(No.52106056,51776174 and 51936010)the National Science and Technology Major Project of China(No.2017-II-0008-0022)+2 种基金the Fundamental Research Funds for the Central Universities(No.31020210QD706)the National Key Laboratory of Science and Technology on Aerodynamic Design and Research(No.614220121050103)the Key Laboratory of Aerodynamic Noise Control(No.ANCL20210104).
文摘Numerical studies are conducted to explore the noise reduction effect of leading-edge tubercles inspired by humpback whale flippers.Large eddy simulations are performed to solve the flow field,while the acoustic analogy theory is used for noise prediction.In this paper,a baseline airfoil with a straight leading-edge and three bionic airfoils with tubercled leading-edges are simulated.The tubercles have sinusoidal profiles and the profiles are determined by the tubercle wavelength and amplitude.The tubercles used in this study have a fixed wavelength of 0.1c with three different amplitudes of 0.1c,0.15c and 0.2c,where c is the mean chord of the airfoil.The freestream velocity is set to 40 m/s and the chord based Reynolds number is 400,000.The predicted flow field and acoustic field of the baseline airfoil are compared against the experiments and good agreements are found.A considerable noise reduction level is achieved by the leading-edge tubercles and the tubercle with larger amplitude can obtain better noise reduction.The underlying flow mechanisms responsible for the noise reduction are analyzed in detail.
