Research On The Influence Of Windshield Schemes On Aerodynamic Performance Of High-speed Trains

With the rapid development of high-speed railway in China,the running speed of high-speed trains has been constantly improved.When the trains are running at high speed,aerodynamic drag becomes the main source of the drag for the high-speed trains,and aerodynamic noise becomes the main source of noise for high-speed trains.Therefore,how to reduce the aerodynamic drag and noise of the high-speed trains has become an important issue concerning energy conservation and environmental protection.Due to the important influence of the connection section on the aerodynamic performance of the high-speed trains,it is necessary to analyze the aerodynamic performance of the different windshields.The research results can also provide reference for the design and optimization of the high-speed train windshields in the future.In this paper,three marshalling high-speed train models are established by using 3d modeling software.High-speed train windshields can be summarized into five categories: internal windshields,closed external windshields,closed half windshields,slit half windshields and excursion half windshields.The specific parameters of two kinds of half windshield are defined: the slit width coefficient of the slit half windshields and the excursion coefficient of the excursion half windshields.The steady flow fields of the high-speed trains with different windshields are calculated by using the Reynolds averaged method.According to the calculation results,we analyze the basic characteristics of the flow fields,aerodynamic drag and lift of the trains.The results of the basic characteristics of the flow fields show that the external windshields block the outflow field and the cavity flow field in the windshields,which leads to the decrease of the air flow velocity in the cavity and the negative pressure on the end faces.Therefore,external windshields are beneficial to the air inlet of the air conditioner.The research on aerodynamic drag of the different windshields shows that the drag reduction effect of the internal windshields is the worst,and the drag reduction effect of the closed external windshields is the best.The aerodynamic drag coefficient of the closed external windshields is about 20% lower than that of the internal windshields.The drag reduction effects of slit half windshields and excursion half windshields are not as good as that of closed half windshields.The aerodynamic drag of the high-speed trains increases with the increase of the slit width or excursion.Therefore,the slit width and excursion of the half windshields should be controlled as far as possible when the windshields are designed and manufactured.The research on aerodynamic lift coefficients of different windshields shows that the head car aerodynamic lift coefficients of the different windshields have little difference.The tail car aerodynamic lift coefficient of the closed external windshields is the minimum and its value is 0.023 at 300km/h.The difference of aerodynamic lift coefficient among the other windshields is very small.The unsteady flow fields around the trains are simulated by large eddy simulation method,and the pulsating pressure on the train surface is obtained.We convert the pulsating pressure into frequency domain information,and then we analyze the dipole sound source distribution on the train surface.The surface noise of high-speed trains with the same windshields is studied to analyze the general rule of aerodynamic noise distribution on the whole trains.The results show that the surface sound pressure level increases with the increase of the running speed.At the same speed,the sound pressure level of the train surface decreases with the increase of frequency.The sound pressure level of the surface dipole sound source at the connection section is larger than that of the whole trains,and the difference is about 20dB~40dB in the low frequency range at 300km/h.Therefore,the connection section is an important noise source of the whole trains.By comparing the sound pressure level of the trains with different windshields,it is found that the noise reduction effects of the closed external windshields and closed half windshields are significant.The noise reduction effects of the slit half windshields and excursion half windshields are not good.The noise reduction effect of the internal windshields is the worst.At a speed of 300km/h,compared with the internal windshields,the surface sound pressure level of the closed external windshields decreases by 25dB~40dB,and that of the closed half windshields decreases by 15dB~30dB.We analyze the influence of specific parameters on the aerodynamic performance of the trains,and the results show that the slit width coefficient has little effect on the maximum pressure level of the surface dipole sound source near the windshield.The maximum pressure level near the windshield increases with the increase of the excursion coefficient when the excursion coefficient is less than 0.04.FW-H far-field noise model is adopted to calculate the far-field aerodynamic noise in the windshield cross profile,and then its attenuation law is analyzed.The surface sound pressure levels of the five different windshields all decrease with the increase of the distance between the measuring point and the car body surface.The variation trend conforms to the law of logarithmic attenuation.By comparing the sound pressure levels of different windshields at a distance of 5 m from the car body surface,it is found that the noise reduction effect of closed external windshields is the best,followed by that of the closed half windshields.The noise reduction effects of the slit half windshields and the excursion half windshields are not good,and the noise reduction effect of the internal half windshield is the worst.