Analysis And Optimization On The Cabin Flow Field Of A Two-seater Convertible

In the automotive flow field,the longitudinal vortex structure has an essential effect on aerodynamic drag and aeroacoustic noise,and a number of flow control methods have to be implemented based on flow characteristics.The flow field of opencabin vehicles such as convertibles is different from that of a conventional car,with there is still a lack of understanding,especially a lack of clear knowledge of the overall vortical structure.The aerodynamic performance of a convertible is affected by air movement and vortical movement around the body,thereby it is meaningful to reveal the flow field and vortical structure characteristics of convertibles.This paper conducts numerical simulations and wind tunnel experiments to investigate the flow field characteristics,vortical structure analysis,and cabin flow field optimization.Determining the overall and local vortical structure characteristics of the convertible to clarify the formation mechanism of the dominant vortices.Exploring methods to improve the cabin flow field characteristics of the convertible based on the wake topology obtained.Firstly,the state and transient numerical calculations are carried out to explore the flow field characteristics of the convertible.The numerical simulations,force measurement experiments,and tuft experiments are combined to verify and analyze the flow structures around the convertible,where the results show that they are in good agreement.The typical flow characteristics of the convertible are obtained by analyzing the velocity streamlines of representative cross-sections,with the generation mechanism of cabin backflow revealed.Meanwhile,the reason of high aerodynamic drag of the convertible is elucidated by analyzing the turbulent kinetic energy dissipation and pressure difference.Then,the vortex criterion and vorticity analysis are applied to clarify the dominant vortices around the body and to elucidate the formation mechanism and motion characteristics of the A-pillar vortex,the Windshield Vortex,and the Nook Vortex.The A-pillar Vortex is triggered by the side flow,the flow over the door into the cabin,and the flow over the windshield.A part of the A-pillar Vortex enters the cabin due to external forces and crashes the side wall of the seater,resulting in an average wind speed increasing nearby the occupant’s head.The flow close to the windshield step is induced by two nearby vortical cores to form a high-intensity Nook Vortex,which continuously breaks into small vortices to crash the A-pillar Vortex.The Windshield Vortex is triggered off by the velocity shear layer,and both numerical simulations and smoke flow experiments show that it oscillates up and down streamwise,crashing the A-pillar Vortex and impacting the wake development.The wake topology of a twoseater convertible is obtained after analyzing and summarizing the longitudinal vortices,which deepens the understanding of the spin direction,shape,and development path of the dominant vortices around the body,providing a supporting for future work on drag reduction,noise reduction,and comfort of the convertible.Finally,the effect of the deflector configuration on improving the cabin flow field is determined.It is found that although the conventional method stops the propagation of cabin backflow,it increases the air velocity nearby the occupant’s head,with an optimization effect of-43.5%,which deteriorated cabin comfort in general.Then the deflectors are designed to guide the cabin backflow.The optimization effects of two deflectors with different spacing and a single deflector are studied.The analysis of the flow field details and the monitoring points prove that a single deflector could reduce the air velocity nearby the occupant’s head without adding additional aerodynamic drag,with an optimization effect of 11.9%.