In order to understand the mechanism by which a pantograph can generate aerodynamic noise and grasp its farfield characteristics,a simplified double-strip pantograph is analyzed numerically.Firstly,the unsteady flow f...In order to understand the mechanism by which a pantograph can generate aerodynamic noise and grasp its farfield characteristics,a simplified double-strip pantograph is analyzed numerically.Firstly,the unsteady flow field around the pantograph is simulated in the frame of a large eddy simulation(LES)technique.Then the location of the main noise source is determined using surface fluctuating pressure data and the vortex structures in the pantograph flow field are analyzed by means of the Q-criterion.Based on this,the relationship between the wake vortex and the intensity of the aerodynamic sound source on the pantograph surface is discussed.Finally,the far-field aerodynamic noise is calculated by means of the Ffowcs Williams-Hawkings(FW-H)equation,and the contribution of each component to total noise and the frequency spectrum characteristics are analyzed.The results show that on the pantograph surface where vortex shedding or interaction with the wake of upstream components occurs,the pressure fluctuation is more intense,resulting in strong dipole sources.The far-field aerodynamic noise energy of the pantograph is mainly concentrated in the frequency band below 1500 Hz.The peaks in the frequency spectrum are mainly generated by the base frame,balance arm and the rear strip,which are also the main contributors to the aerodynamic noise.展开更多
A series of metal-Al_(2)O_(3)catalysts were prepared simply by the conventional impregnation with Al_(2)O_(3)and metal chlorides,which were applied to the dehydration of fructose to 5-hydroxymethylfurfural(HMF).An agr...A series of metal-Al_(2)O_(3)catalysts were prepared simply by the conventional impregnation with Al_(2)O_(3)and metal chlorides,which were applied to the dehydration of fructose to 5-hydroxymethylfurfural(HMF).An agreeable HMF yield of 93.1%was achieved from fructose at mild conditions(100℃and 40 min)when employing Cr(III)-Al_(2)O_(3)as catalyst in 1-butyl-3-methylimidazolium chloride([Bmim]Cl).The Cr(III)-Al_(2)O_(3)catalyst was characterized via XRD,DRS and Raman spectra and the results clarified the interaction between the Cr(III)and the alumina support.Meanwhile,the reaction solvents([Bmim]Cl)collected after 1st reaction run and 5th reaction run were analyzed by ICP-OES and LC-ITMS and the results confirmed that no Cr(III)ion was dropped off from the alumina support dur-ing the fructose dehydration.Notably,Cr(III)-Al_(2)O_(3)catalyst had an excellent catalytic performance for glucose and sucrose and the HMF yields were reached to 73.7%and 84.1%at 120℃for 60 min,respectively.Furthermore,the system of Cr(III)-Al_(2)O_(3)and[Bmim]Cl exhibited a constant stability and activity at 100℃for 40 min and a fa-vorable HMF yield was maintained after ten recycles.展开更多
基金This work is funded by National key R&D Program China(2016YFE0205200)National Natural Foundation of China(U1834201).
文摘In order to understand the mechanism by which a pantograph can generate aerodynamic noise and grasp its farfield characteristics,a simplified double-strip pantograph is analyzed numerically.Firstly,the unsteady flow field around the pantograph is simulated in the frame of a large eddy simulation(LES)technique.Then the location of the main noise source is determined using surface fluctuating pressure data and the vortex structures in the pantograph flow field are analyzed by means of the Q-criterion.Based on this,the relationship between the wake vortex and the intensity of the aerodynamic sound source on the pantograph surface is discussed.Finally,the far-field aerodynamic noise is calculated by means of the Ffowcs Williams-Hawkings(FW-H)equation,and the contribution of each component to total noise and the frequency spectrum characteristics are analyzed.The results show that on the pantograph surface where vortex shedding or interaction with the wake of upstream components occurs,the pressure fluctuation is more intense,resulting in strong dipole sources.The far-field aerodynamic noise energy of the pantograph is mainly concentrated in the frequency band below 1500 Hz.The peaks in the frequency spectrum are mainly generated by the base frame,balance arm and the rear strip,which are also the main contributors to the aerodynamic noise.
基金The authors thank the financial support for this study by the National Natural Science Foundation of China(Nos.21106057 and 21376111)Society Devel-opment Fund of Zhenjiang(SH2012009)Advanced Talents of Jiangsu University(10JDG143).
文摘A series of metal-Al_(2)O_(3)catalysts were prepared simply by the conventional impregnation with Al_(2)O_(3)and metal chlorides,which were applied to the dehydration of fructose to 5-hydroxymethylfurfural(HMF).An agreeable HMF yield of 93.1%was achieved from fructose at mild conditions(100℃and 40 min)when employing Cr(III)-Al_(2)O_(3)as catalyst in 1-butyl-3-methylimidazolium chloride([Bmim]Cl).The Cr(III)-Al_(2)O_(3)catalyst was characterized via XRD,DRS and Raman spectra and the results clarified the interaction between the Cr(III)and the alumina support.Meanwhile,the reaction solvents([Bmim]Cl)collected after 1st reaction run and 5th reaction run were analyzed by ICP-OES and LC-ITMS and the results confirmed that no Cr(III)ion was dropped off from the alumina support dur-ing the fructose dehydration.Notably,Cr(III)-Al_(2)O_(3)catalyst had an excellent catalytic performance for glucose and sucrose and the HMF yields were reached to 73.7%and 84.1%at 120℃for 60 min,respectively.Furthermore,the system of Cr(III)-Al_(2)O_(3)and[Bmim]Cl exhibited a constant stability and activity at 100℃for 40 min and a fa-vorable HMF yield was maintained after ten recycles.
