Numerical Study On The Fresh Air Supply Characteristics Of The Mesh Plate In The Train Compartment

My country's railway passenger cars have entered the era of high speed.Passengers' requirements for trains are not only limited to speed,but also higher requirements for train comfort.Indoor comfort is closely related to airflow organization.Whether the indoor airflow distribution is reasonable and whether the air breeze speed meets t he standard is closely related to the uniformity of the passenger car's air conditioning and ventilation system.The long-distance nature of high-speed trains determines the variability of the outdoor environment of the train,and the indoor load also has instability.If the air supply is stable,passengers will feel cold when the indoor load is small,and when the indoor load is large,the passengers will feel cold.It feels sultry.Therefore,the air outlet uniformity of the air supply duct is inevitable related to the change of the indoor load and the air supply state parameters.In this paper,taking the journey of a train on the Beijing-Guangzhou line in one day in July as an example,the meteorological parameters of 16 stations through which the train passes are studied,and the range of the envelope load caused by the change of external environment is calculated,and the maximum and minimum ventilation volume when the bus is fully loaded is finally determined.Three illustrative air supply volumes wer e selected for simulation experiments.Based on the solid model,the air supply duct model of the air-conditioned bus reduced by three times was established,and the simulation analysis was carried out in Fluent by the method of computational fluid dynamic s.Firstly,the air duct is simulated and calculated with three types of air supply,and the variance is calculated according to the obtained wind speed of each air outlet.The result shows that the air duct is not uniform under the three different air sup ply quantities.At the air outlet at the bottom of the main air duct,the end that is closer to the air supply outlet has more wind,and the far end has less wind.According to the principle of uniform air supply,a solution to optimize the uniformity of t he air duct was determined,that is,to improve the uniformity of the air duct by adding a baffle at the lower part of the air outlet of the air duct and reducing the exit area of the main air duct.By calculating the variance value of the wind speed at th e outlet of the air duct before and after the optimization,the optimal height of the baffle and the size of the outlet at the end of the main air duct are determined.In order to verify that the optimized scheme of the air supply duct can improve the uniformity of the indoor air distribution,the air supply model including the indoor environment was established again.First of all,simulate the same with three types of air supply to obtain the velocity cloud diagram of the indoor air distribution.A cross section of the front,middle,and rear of the train compartment was selected,and the average speed of the cross section was observed and analyzed.The results showed t hat the average speed of the front end of the compartment was the largest,followed by the middle and the smallest at the rear.The experimental results are consistent with the simulation results of the air supply duct.Then apply the optimized air duct to simulate again,select the cross section at the same position in the front,middle,and rear of the train,and calculate the average speed.The result shows that the average speed of the front,middle,and rear in the train compartment tends to be equal.The simulation study in this paper can show that the uniformity of the air supply duct is closely related to the quality of the indoor air distribution.Adding a baffle at the bottom of the air outlet of the air supply duct can effectively improve the uniformity of the indoor air distribution.However,even after the uniformity of airflow distribution is improved,the indoor breeze speed will exceed the standard when the air supply is too large,the indoor personnel will have a clear sense of blowing,and the comfort of passengers will be poor.It is recommended to apply dynamic load calculation when designing and calculating the air supply volume of air-conditioned passenger cars.The steady-state load calculation method may make passengers feel that the a ir volume is small or too large,which will affect the riding experience.