| When drivers are handling the vehicles,they have to get 90?99% of traffic information by visualization,and a clear vision is necessary to guarantee the driving safety and comfort.Under rainfall conditions,rainwater accumulates on the surface of side windows and exterior mirrors to form water film,streams,or droplets,refracting and blocking light,blurring the driver's vision,and leading to more traffic hazards.Therefore,it is of vital importance to accurately predict the water phase distribution of the side windows when the car is driven in the stormy environment,and to make a reasonable evaluation of the degree of water pollution.It also matters to analyze the change pattern under different driving environments,and to carry out optimal design to improve the clarity of the field of vision in such case.However,currently,the studies on automobile aerodynamics mostly revolve around the fields of aerodynamic drag,aero-acoustic,and crosswind stability.Both domestic and foreign scholars have not yet conducted in-depth research on water contamination in the side window area.At the same time,as the logistics industry is highly competitive,an increasingly number of vehicles are required to cope with all-weather driving environment because of the more stringent requirements on the timeliness of transported goods.Therefore,in this paper,with heavy-duty commercial vehicles as the research object,by applying both numerical simulation and experimental verification method,a systematic study was conducted on the water contamination in the side window area.The main points are as follows:Firstly,the theoretical basis of Euler-Lagrange Method(ELM)and Euler-Liquid Film Model(ELFM)was elaborated,focusing on the theories and solution methods involved in air-raindrops,air-liquid film,liquid film-raindrops,and liquid film-wall surface interactions.Predicated on the generalization of the relationship between rainfall intensity,visibility and traffic speed limit regulations,seven typical rainfall intensities applicable to the study of water contamination in automobile side window areas were proposed.In light of the rainfall theories such as Gamma raindrop spectrum and Best raindrops"terminal velocity,the functional relationships between rainfall intensity and raindrop size,spacing and raindrops"terminal velocity were derived and established,and the relevant rainfall parameters were simplified and solved to realize the simulation of different rainfall environments in multiple working conditions.Finally,the Euler-Lagrange method was employed to construct the natural rainfall environment,and the numerical simulation results of different raindrop diameters were compared with the measured values at experiments.The errors of raindrops'terminal velocity calculation fell within 5 %.Secondly,to address the problems encountered in the current commercial vehicle water contamination test,a rain and wind coupling test system was built.By optimizing the design of nozzle form and arrangement,rainwater homogenization network aperture and other parameters,the terminal velocity of raindrops and the diameter of raindrops did not match with the real situation.In terms of numerical simulation,ELM-ELFM were used to establish a numerical simulation method applicable to water contamination in the side window area of heavy commercial vehicles.Two-way coupling calculation of body wall surface-droplet-liquid film-air in the process of vehicle-raindrop-air interaction was realized,and the rationality and accuracy of the numerical simulation method were verified through comparison with the test.Then,a study was carried out to address the limitations of using the volume of rainwater to evaluate the degree of water contamination in the side window area.Firstly,the side window view area was divided based on ergonomics,and then the average thickness of water film and the percentage of water phase distribution were quantified by using volume integration and gray scale processing methods to construct a comprehensive evaluation method of water contamination in the side window area of commercial vehicles covering each view area of the side window and the exterior mirror surface.Based on this,an analysis was made on the mapping relationship between the average thickness of water film,the water phase distribution ratio in each area and the driving speed and rainfall intensity,which provides an important design basis for the assessment of water contamination in the side window area at the vehicle development stage.In addition,the influence of the side wind environment on water contamination in the side window was carried out,and the numerical simulation of the wind-rain coupled environment was achieved using the transverse pendulum model method.The focus was on the distribution law of raindrop particles in different side wind environments,and the variation of the average thickness of water film and water phase distribution ratio in each area with different wind-rain coupling parameters and its internal mechanisms were elaborated.The results showed that the leeward environment caused the airflow to reduce the drag force of the raindrop particles,and the raindrop particles continue to move in the original direction under the dominance of the inertial force;the windward environment caused rearview mirror wake vortex airflow velocity to increase,prompting more particles to move with the vortex hit the side window.Finally,a study was carried out on the control of water contamination in the side window area of heavy commercial vehicles.The control boundary method was employed to distinguish the primary and secondary influencing factors of water pollution in the side window area.It was found that the splash of raindrops on the surface of the rearview mirror,reflection and liquid film shedding were the main sources of pollution.To ensure the calculation accuracy while improving the calculation efficiency,a sub-domain calculation method was constructed predicated on data mapping theory,which improved the efficiency by 65 % compared with the whole-field calculation method.On this basis,the average thickness of water film and the percentage of water phase distribution in the lateral view area,exterior mirror view area and exterior mirror surface were minimized as the optimization objectives.The thickness of rearview mirror housing,housing inward tilt angle,bracket height and housing turning angle were used as design variables to determine the weight coefficients among multiple objectives based on the entropy weight-AHP combined weighting method.The interactive orthogonal test design and improved GAR-TOPSIS method were employed to optimize the water pollution problem in the side window area,with the optimal design scheme obtained.After optimization,the average thickness of water film in the lateral view area,rearview mirror view area and rearview mirror surface was reduced by 50.4 %,85.4 % and 59.8 %,respectively,and the water phase distribution ratio was reduced by 13.8 %,49.3 % and 14.9 %,respectively.In summary,in this paper,both automotive aerodynamics and multiphase flow theory were applied to provide an effective prediction tool for the study of water pollution in the side window area.A systematic study was carried out on the particle distribution of raindrops and water film motion law in the side window area under different working condition.This provides reference research ideas and methods for the advancement of dynamic field of view calibration and the optimization of water pollution in the side window area of commercial vehicles. |
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