Study On Variable Cross-section Duct Air Supply System With Spiral Duct Used In Trains

The variable cross-section duct air supply system with spiral duct is a new kind of air supply system in trains. It integrates the characteristics of cross-section duct and flexibility of spiral duct, especially suitable for trains, which have limit space and special demand for uniform air distribution. While domestic application and research is relatively less , there is no applicable design method.Design method and air distribution characteristics are studied with theoretical analysis, CFD method and experimental test, in order to guide the design of air supply system.First, the influence of spiral duct on the resistance characteristics of the variable cross-section duct and the design method is theoretically analyzed. Four methods to adjust air volume are provided. Design method by changing the flow coefficient is put forward under the condition of limited space in some trains. The uni-dimension process of the perforate plate considered the accuracy of calculation and the convenience for producing.Then, resistance characteristics of two specifications of spiral ducts and relevant local resistance are tested. Influencing factors are analyzed. The experiment provides the data for determining flow coefficient, as well as the CFD simulation.CFD method is used to analyze the characteristics of the duct after the design calculation. The simulated and computed results fit well to each other. The differences of air volume of each opening obtained by the two methods do not exceed 10%.Prototype test carried out on multifunction air-conditioning experiment platform is used to verify the reliability of the design method and the CFD method. The test result shows that the maximum deviation value of all openings air volume is 6% compared with the calculated value, and is 9% compared with the CFD simulation. The design of air volume is met. It not only verifies the correctness of the design method put forward in this paper, but also proves the feasibility of utilizing the CFD method to analyze the air supply system of this kind. At last, design method when the space is not limited is put forward and the air supply system is improved accordingly. The new system is verified with the CFD method.