| With the rapid development of the automobile industry,the car not only brings convenience to people’s life,but also leads to a series of problems,such as traffic congestion,energy shortage and environmental pollution.The progress of science and technology makes connected vehicles becoming a hot spot in the field of international intelligent transportation,and leading the direction of intelligent transportations’ development,which also led to human-vehicle-road-environment system to the direction of informatization,intelligence and environmental protection.Relevant research shows that cars traveling in a platoon in intelligent transportation system can not only improve road’s capacity,reduce the occurrence of traffic accidents,but also reduce fuel consumption and exhaust emissions,improve the level of road traffic safety.Therefore,this paper uses the numerical simulation method to study the energy-saving platoon of passenger cars in connected vehicles environment.In this paper,a new realistic generic car model,Driv Aer model,is used to study the aerodynamic characteristics.The model is different from the highly simplified Ahmed model and SAE model,which makes the test results closer to the actual situation of life.XFlow software was used for numerical simulation experiment.The main features of this new generation CFD simulation software are described from three aspects: spatial discrete mode,turbulence model selection and numerical algorithm selection.Its theoretical basis is introduced from the mesoscopic dynamics model,the lattice Boltzmann method and the basic theory of the large eddy simulation method.This paper assumes that the research in connected vehicles environment is ideal,that is,cars has a good communication,ignoring the vehicle operation delay and other interference factors.In this paper,we first study the influence of automobile shape on the driving of platoon.Because cars on the road have different shapes of its body,this chapter chooses estateback,notchback and fastback to study.The selected Driv Aer model is identical in front but with different tail shapes.Firstly,the simulation of one vehicle is carried out,and then the simulation of two vehicles is carried out.Through the comparative analysis of the speed field and the pressure field of one vehicle and two vehicles,the mechanism of the drag reduction of the platoon is revealed.The results show that the wake structure of the vehicle platoon with different shapes is not the same,but the drag reduction mechanism of it is consistent.When cars travel in platoon,the front flow field interacts with the rear flow field,and the presence of the rear flow field causes the tail vortex area of the vehicle to decrease slightly.The flow field of the front vehicle is significantly reduced,the rear end of the car to reduce the strength of the vortex,the two cars in platoon of the aerodynamic drag coefficient are reduced.On the basis of this study,we use the notchback to study the influence of spaces on platoon,set the simulation speed to 22m/s,and choose 11 kinds of distances between 0L and 3L(L: body length),and carries on the numerical simulation experiment to the two cars platoon and the three cars platoon.The velocity fields and pressure fields of the vehicle wake are analyzed from 0.5L,1L and 3L.The relationship of spaces and the aerodynamic resistance of two cars platoon and three cars platoon is obtained,and the relationship of spaces and the fuel economy of two cars platoon and three cars platoon is obtained,too.So,we use the notchback to study the influence of speeds on platoon,and use the two cars platoon by the space of 1L,and 7 kinds of speeds between 60km/h~120km/h is selected in this research.The pressure field of one car and two cars platoon are analyzed by the speed of 16m/s,22m/s and 34m/s,and obtain the relationship of fuelsaving rate and speed.The research of this paper provides a theoretical basis for the determination of vehicle space and speed in a platoon in connected vehicles environment,and provides a theoretical basis for the future research work. |
