Research On Aerodynamic Drag Reduction Characteristics Of High-Speed EMU Based On Air Suction-Blowing Combination

With the continuous improvement of the operating speed of High-speed Electric Multiple Units(EMUs),aerodynamic drag gradually dominates the operating resistance,and the resulting energy consumption poses new challenges to energy conservation and environmental protection.At present,traditional drag reduction methods such as optimizing exterior design have reached the extreme,and the optimization space for reducing the aerodynamic drag of high-speed EMUs is becoming increasingly limited.As a new development direction of drag reduction,active flow control technology will have great prospects if it is applied to the aerodynamic drag reduction of high-speed EMUs.In order to further reduce the aerodynamic drag of high-speed EMUs,an active flow control drag reduction method combining air suction and blowing is proposed at EMU head and tail.In this paper,the aerodynamic drag characteristics of the high-speed EMU with 400km/h steady-state operation are studied by using the numerical calculation method based on Realizable k-εfor a three-car simplified model,and the drag reduction effect and mechanism of the air suction-blowing combination are analyzed.The main research contents and results are as follows:(1)The aerodynamic characteristics of the original train model are explained and analyzed from the aspects of surface air pressure,boundary layer development law,wall shear stress and the change of surrounding flow field.Combined with the composition and distribution of aerodynamic drag,the setting of suction and blowing ports is focused on the front and rear of the EMU.(2)When the forward suction and blowing is applied to the rear of the EMU,it only has a reducing effect on the pressure drag of the tail car,while the friction drag slightly increases.As the mass flow rate of the suction and blowing is increased,the aerodynamic drag reduction rate of the tail car gradually increases,but the increment of the drag reduction rate gradually decreases.Under the same mass flow rate of the suction and blowing,the more dispersed the arrangement of the suction ports on the upper edge of the windshield,and the closer the blowing ports are to the lower edge of the windshield,the smaller the pressure drag of the tail car.Under the same mass flux of the suction and blowing,the more the number of suction-blowing ports,the better the pressure drag reduction effect of tail car.When the mass flux of the air suction and blowing is 40.834 kg/(m~2s)and setting 6 rows of air suction and blowing ports,the aerodynamic drag reduction rate of 13.32%for the tail car can be achieved.(3)When the reverse suction and blowing is applied to the head of the EMU,there is a certain reduction effect on the pressure and friction drag of the head car,but the pressure drag reduction is more significant.As the air mass flow rate is increased,the aerodynamic drag reduction rate of the head car gradually increases.Under the same mass flow rate of the suction and blowing,the more dispersed the arrangement of the suction and blowing ports above and below the windshield,the lower the pressure drag of the head car.Under the same mass flux of the suction and blowing,the more the number of suction-blowing ports,the more significant the pressure drag reduction effect of the head car.When the mass flux of air suction and blowing is 40.834 kg/(m~2s),the aerodynamic drag reduction rate of 39.85%can be reached by setting 6 rows of suction and blowing ports for the head car.This research provides a reference for the aerodynamic drag reduction of the next generation of EMUs,and is of great significance for breaking through the limitations of traditional aerodynamic drag reduction.