Optimization Of Airflow Organization And Study On Thermal Comfort For Railway Double Decker Passenger Cars

In recent years,with the improvement of living standards,passengers’requirements for the thermal comfort of railway vehicles are also increasing.The comfort degree of the environment in the passenger compartment directly affects the quality of passengers’travel,because the heating ventilation and air conditioning system is one of the systems that directly regulate the environment in the passenger compartment,it is necessary to analyze and study the thermal comfort of the air conditioning system and inner flow field in the passenger compartment.In this thesis,the air distribution of the railway double decker passenger car is simulated mainly by the method of Computational Fluid Dynamics（CFD）,and the comfort of the passenger compartment in two extreme environments in summer and winter is analyzed,as well as the distribution of the passenger car inner flow field under the failure of air conditioning,and the countermeasures are given.First of all,the air supply system of railway double decker passenger car is simulated and analyzed by numerical calculation method,and the influence of air supply angle and the number of throttle plates at the air duct air inlet of each layer on the air volume distribution of each layer of passenger compartment is studied respectively.It shows that adjusting the air supply angle of the fresh air inlet can fine-tune the air volume proportion of each floor passenger compartment.And when the number of air duct air inlet throttle plates in the middle passenger compartment increases from zero to three,the change of air volume in the middle passenger room is-15.5%.When the number of air duct air inlet throttle plates in the upper passenger compartment is increased from zero to four,the change of the air volume in the upper passenger compartment is-10.5%.By adjusting the air supply angle and the number of throttle plates at the air ducts of each floor for many times,a comprehensive optimization scheme is determined to make the air volume proportion of each floor cabin meet the design standard as much as possible.Different obstacles are set at the air outlet of the air duct to change the outflow coefficient,so as to achieve the purpose of air uniformity at each air outlet of each floor of the passenger compartment.Secondly,the calculation method of temperature field in the railway double decker passenger car is introduced.When the external environment is 35.0℃in summer,the temperature distribution in the passenger compartment when the air supply temperature is17.0℃,19.0℃and 21.0℃is calculated respectively.It is found that when the air supply temperature is 19.0℃,the temperature in the passenger compartment is basically within the standard range.When the external environment is-17.2℃in winter,the temperature distribution in the passenger compartment when the air supply temperature is 21.0℃,23.0℃and 25.0℃is calculated respectively.It is found that the temperature in the passenger compartment is basically in the standard range when the air supply temperature is 23.0℃.In addition,in winter conditions,the temperature near the area of 0.10 m above the floor of the middle-level compartment of railway double decker passenger car is relatively low,resulting in a large vertical temperature difference within the range of 0.10～1.10 m above the floor in the passenger compartment,which is found to be caused by the air distribution pattern of up-supply up-return in the middle-level compartment.The temperature distribution in the middle-level compartment has been improved by the addition of branch ducts and diversion plates to direct part of the air volume from the main ducts to the area at the bottom of the passenger compartment and reduce backflow.Then,the single index of air speed,temperature,CO₂ concentration and relative humidity in the passenger compartment and the comprehensive index of Effective Temperature Difference,Air Duffusion Performance,Predicted Mean Vote,Predicted Percent Dissatisfied were used to analyze the thermal comfort of the passenger compartment respectively.Based on the principal component analysis and Predicted Mean Vote（PMV）,a comprehensive evaluation model for thermal comfort was established with considering all parts of passengers’bodies,and comprehensive PMV values of people in each level passenger compartment were analyzed.The results showed that the average PMV values of upper-level,lower-level,A-end and B-end compartments in summer were 0.592,0.628,0.664 and 0.577,respectively.The average PMV values of upper-level,lower-level,A-end and B-end in winter are-0.681,-0.687,-0.726 and-0.712,respectively.After calculation,it is found that more than 85%of the passengers are satisfied with the thermal environment in the passenger compartment.Finally,the distribution of temperature and CO₂ concentration in the passenger compartment after the failure of one air conditioner and two air conditioners was analyzed under the background of air conditioner failure conditions in two extreme environments in summer and winter.As for the temperature in the passenger compartment after the air conditioner fails in summer,the temperature in the passenger compartment can reach a maximum of 57.8°C,and emergency measures need to be taken,while the temperature in the passenger compartment can be maintained at a minimum of about 3.7°C after the air conditioner fails in winter.In terms of CO₂ concentration,whether the air conditioning failure occurs in summer or winter,the CO₂ concentration in the passenger compartment will increase and the air quality will decrease.Aiming at the flow field after both air conditioners fail in summer,the influence of opening the passenger car door on the flow field is analyzed,and it is verified that opening the passenger car door after the air conditioner fails in summer is an effective emergency response measure.