Research On Aerodynamic Characteristics Of Convertible Car

As the rapidly development and improvement of the economy and load condition,the automobile has been an indispensable riding tool for the human.More and more people tend to pursue the personalization of vehicles while the guarantee of the performance,fuel economy and safety.The convertible cars can not only satisfy people's personalized needs,but also give the passengers a comfortable outdoor experience,while gain a higher drag coefficient for the unique body type.The open cockpit can't cut off the noise by isolating or sealing,which cause a bad effect on the passengers' experience easily.Therefore,the prediction and optimization of the aerodynamic performance must be conducted in the design stage of the convertible cars.The flow characteristics and aerodynamic noise of convertible cars have been comprehensive researched in Fluent which is a CFD fluid simulation platform,based on the theory of computational fluid dynamics and aero-acoustics.Firstly,the paper explores the reason of the high drag coefficient from the vehicle body structure,airflow velocity,pressure distribution of air velocity and some other aspects,to obtain the local factor which has high effects on the drag coefficient.The law of the flow field speed distribution along with the vehicle speed has been summarized by the comparison of flow field distributions under different speeds.Then,the airflow velocity of the head area is evaluated quantitatively to determine the local area which is vulnerable to the airflow,and the relevant measures are presented to find that the wind deflector behind the back cushion can reduce the airflow velocity near the rear occupant effectively,while leads to the increasing of the drag coefficient.And the notchback body can not only improve the flow field environment,but also has little impact on the aerodynamic drag.Furthermore,the location of the main sound source is determined by the preliminary prediction of the convertible sound source position by broadband noise source model during the study of noise disciplines.The noise spectrum characteristics of different speed and different collecting points are researched based on the large eddy simulation(LES),the results show that most of the convertible noise is wideband noise.The sound pressure level shows linear relationship with the vehicle speed.Aerodynamic resistance and aerodynamic noise are two different kinds of fluid mechanics phenomena,the drag resistance and noise are multi-objective optimized based on the global optimization.The factors which have big influence on the aerodynamic characteristics and their variable ranges are determined by comprehensively analyzing the distribution characteristics of the steady state and transient flow field.And the response law between the correlation factors,aerodynamic drag and noise is obtained based on the approximate model of the aerodynamic optimization framework.The multi-island genetic algorithm is applied to conduct the global optimization to obtain vehicle parameters with low resistance,low noise and relatively good cockpit flow environment.The research about the aerodynamic resistance,the aerodynamic noise mechanism of the convertible car and the multidisciplinary aerodynamic modeling optimization method can not only provide theoretical support for the aerodynamic optimization of the convertible car,but also put forward a feasible method for the optimized designing of low-resistance and low-noise automobile.