Modeling And Experimental Research On Coastdown Resistance Of Light Duty Vehicle In High Altitude Condition

As an important means of transportation,the vehicle has become an essential part of people's daily life.Under the background of low-carbon life,people pursue the vehicle safety and reliability,at the same time,people pay more attention on power,economy and exhaust emission of vehicle.With the aggravation of environmental pollution and the enhancement of environmental protection consciousness,many countries have enacted more stringent vehicle emission regulations.At the same time,the research of automobile emission is more detailed and thorough,and the change law of the automobile's performance has gradually become a hot research topic,countries established the altitude environment simulation laboratory is gradually increasing.Before the vehicle performance or exhaust emissions testing,the vehicle's coastdown resistance data is one of the key premise,and under the condition of ensuring the manpower,material resources and financial resources to be reduced as far as possible,how to obtain the more accurate coastdown resistance under the altitude environment is more difficult.With the computer technology and the development of turbulence model,Computational Fluid Dynamics(Computational Fluid Dynamic,referred to as CFD)is more and more applied to the vehicle development process,this paper is based on CFD technology to carry out research.In this paper,the combination of test and simulation method is adopted.In order to study the variation of automotive coastdown resistance at different altitudes.So in this paper,a three dimensional solid model of a kind of SUV is established by using Catia.First,the model computing domain is gridded by using Hypermesh and then three-dimensional numerical simulation of steady flow was carried out for the Car model by using CFD of software Fluent.At last,the variation of coastdown resistance at four different altitudes and three different velocity is obtained,and the simulation results show that: The air resistance coefficient of the vehicle is basically unchanged at different altitude,which lays the foundation for the following coastdown resistance correction method.In this paper,coastdown tests are also conducted for four light-duty vehicles at different altitudes and temperatures,then the real coastdown resistance and the modified resistance are obtained.Test results show that: the modification method of automotive coastdown resistance presented in this paper can modify the automotive coastdown resistance at 0m and 20? to that at various altitudes and temperatures preciously,and the error is less than ECE method;besides,the modification method can be used for different kinds of vehicles;by using this method the cost and time of automotive test can be saved.