Research On Experimental Scene Of Exterior Water Management In Automotive Climatic Wind Tunnel

The automotive climatic wind tunnel（CWT）can achieve experimental research on Exterior Water Management（EWM）by restoring the natural rainfield.However,with the indepth study of EWM,many researchers found that there were some shortcomings in the EWM experiment.Due to the limitation of the CWT spraying system,the spraying amount can only meet the requirements of rainfall intensity,but the distribution,speed and size of raindrops can not be completely controlled.It may impact the results of EWM,affecting the reliability of the experiment.Therefore,in order to analyze the influence of the CWT rainfield on the EWM experiment and improve the rainfield,the experimental scene of the EWM is studied in this paper.In this paper,the rainfield of the EWM problem is divided into three levels according to the short-term rainfall intensity.Based on the M-P raindrop size distribution and the raindrop velocity formula,the parameters of the rainfield under natural conditions are determined.On this basis,an EWM numerical simulation model is established,which accords with the natural rainfield,and the reliability of the model is verified by combining the simplified model with the experimental data.Based on the size of the actual CWT and the parameters of the spraying system,the experimental scene of EWM in the CWT is built.By comparing the results of the two models,including the surface water film distribution on the front windshield and side windows and the distribution of raindrops around the body,the impact of the rainfield in CWT on the results of EWM is analyzed in detail.The results show that the thickness of surface water film on the front windshield and side window under the CWT is smaller than that under natural conditions.This difference is more obvious under heavy rainfall.Compared with the water film thickness of the side window,the water film thickness of the front windshield glass is much different from the results obtained under natural conditions.However,the distribution of water film on the surface is in good agreement with the natural results.Combined with the distribution of raindrops in the rainfield around the body,the mechanism is analyzed.At the same time,in order to further analyze the influence of the raindrop parameters on the EWM experimental results,the experimental results are analyzed by changing the speed and size of the raindrops sprayed by the spraying system.The results show that the size of the raindrop sprayed by the spray system has little influence on the results,but the speed of raindrop has a great influence on the results.After the raindrop size increased,the average thickness of the water film on the front windshield increased,but the average thickness of the water film on the side windows remained unchanged.When the raindrop velocity increased,the average thickness of the water film on the front windshield and side windows decreased significantly.Therefore,it is imperative to ensure the consistency of the raindrop speed in the experiment.Finally,the improvement measures for the experimental scene of EWM in the CWT are proposed.By changing the nozzle distribution of the spraying system,the overall uniformity of the rainfield in the CWT is improved.Compared with the initial conditions,the average deviation rate of rainfield which is the self-made evaluation index decreased by 10.8%,55.9%,and 52.5%,respectively.By changing the nozzle axis,on the basis of keeping the water film distribution of the front windshield and side windows unchanged,the difference between the water film thickness and that of the natural conditions is significantly reduced.Under the three rainfall levels,the difference in the water film thickness of the side windows was reduced by5.2%,3.5%,and 0.5%,respectively,and the water film thickness of the front windshield was reduced by 3.3%,9.9%,and 10.0%,respectively.And the distribution of rainwater around the body is more reasonable.The improvement mechanism is further studied by analyzing the movement of raindrops.This study provides reference ideas and methods for the follow-up EWM experiments.