| Different material properties,structural sizes and shapes in complex vehicle systems produce different thermal responses to environmental loads,which results in significant dynamic non-uniform characteristics in the vehicle thermal environment.On the one hand,during the short-term operation of the automobile,the unevenly distributed environmental loads such as external solar radiation and temperature,as well as the irregularly moving airflow of the ventilation system are applied to the interior of the passenger cabin together,and the thermal environment inside the occupant cabin presents obvious differences in space-time distribution,leading to inconsistencies in skin temperature response and thermal comfort between occupants in different locations and between different parts of the occupant’s body.On the other hand,during the long-term service,automobile is always affected by the dynamic non-uniform thermal environment.Under the cumulative effect of non-uniform distributed environmental loads,the appearance defects of different parts in different regions of the automobile appear significantly inconsistent in time sequence and quantity.It can be seen that the dynamic nonuniform thermal environment of vehicle plays an important role in both occupant thermal comfort and vehicle weathering resistance.However,there is currently a lack of systematic analysis methods for the dynamic and non-uniform thermal environment of the vehicle.The steady-state analysis method used in the past is difficult to accurately predict and control the dynamic non-uniform thermal-flow characteristics of cabin and thermal comfort of the passenger which vary with time and position.There is also a lack of effective numerical analysis methods for studying the differential distribution in thermal environment of vehicles in longterm service.Therefore,it is urgent to systematically study the characteristics of automotive thermal environment under environmental loads in long and short periods,and its experimental and numerical analysis methods,and master the effects and rules of dynamic non-uniform thermal environment on occupant thermal comfort and heat transfer of automotive parts.In this paper,based on experimental research and numerical calculation method,occupantvehicle system in dynamic non-uniform thermal environment is regarded as the main research object,a systematic analysis method of vehicle dynamic non-uniform thermal environment in long and short periods is proposed,and a test platform for studying vehicle thermal environment characteristics in short period is established.A numerical calculation method for dynamic thermal-flow characteristics of occupant cabin based on buoyancy model is established,and a numerical calculation method for objective evaluation of full-time occupants dynamic thermal comfort based on thermal regulation of human body is proposed.The influence and regularity of dynamic non-uniform thermal environment on thermal comfort of occupants in different seating positions and different parts of their body in a short time are studied.A one-year natural exposure test of the whole vehicle was carried out to characterize the environmental load distribution and annual cumulative value of the components inside and outside the vehicle under long-term service.A numerical calculation method based on multi-layer structure model is put forward to rapidly predict the dynamic non-uniform environmental loads of the vehicle.The influence of physical parameters on the environmental load distribution of auto-parts and its laws are studied.Key technical issues mentioned above are tackled with the following specific contents:(1)The concept of dynamic environmental load in long and short periods,as well as the systematic analysis method of vehicle dynamic non-uniform thermal environment are put forward.This method can realize the test,numerical analysis and parametric characterization of vehicle dynamic non-uniform thermal environment characteristics and rules in long and short periods.Considering the difference of heat conduction between layers of materials with different thermophysical attributes,a dynamic heat transfer model of multi-layer structure is proposed.Considering the significant difference of solar incident angle,solar radiation and radiation heat transfer in different parts of vehicle curved structure,the mathematical model of solar radiation intensity of vehicle curved structure,as well as the dynamic radiation heat transfer model inside and outside of vehicle are established.The theoretical model of heat transfer among vehicle system,human body and environment is refined.A test platform is established to study the dynamic non-uniform characteristics of vehicle thermal environment under short-term cooling conditions,and a characterization method of dynamic non-uniform characteristics of vehicle thermal environment parameters is proposed.(2)Using the built-up vehicle thermal environment test platform,The dynamic nonuniform thermal environment test in a short time is carried out,and the dynamic variation and distribution of air temperature and flow rate in the occupant cabin,as well as the skin temperature response of the occupant body under the dynamic non-uniform thermal environment are characterized in detail.To solve the problem of insufficient calculation accuracy in the process of natural and forced convection,and to more accurately reflect the influence of buoyancy and density on the airflow and temperature distribution in the occupant cabin during the process of natural convection and forced convection,a numerical calculation method based on buoyancy model and variable density air property for the dynamic "heat-flow" characteristics of the occupant cabin is established.The dynamic error analysis shows that the air temperature simulation errors of multiple observation points around the front and rear occupants are all within 10%.Through different cross-sections of the occupant cabin,the distribution characteristics of air temperature in the occupant cabin and the distribution rules of environmental loads on the inner wall are analyzed in detail,as the occupants enter the cabin.The laws of airflow and temperature change around the occupants are mainly explored,and the differences of cooling response between inner wall and air are compared in detail from two aspects: cooling time sequence and range.The analysis results show that the distribution of air temperature in the occupant cabin gradually changes from the layered distribution of air temperature rising from bottom to top to the distribution of air temperature decreasing from bottom to top,and it is still in the non-uniform distribution state,after air conditioning is switched on.The study on "heat-flow" characteristics of occupant cabin can provide scientific guidance for thermal management and optimization of efficient and comfortable air conditioning.(3)In view of the difficulty of PMV-PPD method in evaluating dynamic thermal comfort and local thermal comfort of occupants,and the inadequacy of objective evaluation accuracy of dynamic thermal comfort caused by lack of accurate analysis of whole body skin temperature in full time,based on theoretical research on thermal regulation and thermal comfort of human body at home and abroad,a numerical calculation method for objective evaluation of occupant’s thermal comfort under dynamic non-uniform thermal environment in full time is proposed.Combining the dynamic response of air flow velocity and air temperature around 21 sections of each occupant during air conditioning refrigeration,the thermal response model of the occupant is coupled with the thermal-flow model of the occupant cabin.The dynamic response characteristics of skin temperature and thermal regulation response of the occupants are calculated,and the thermal sensation index and thermal comfort index of the occupants are evaluated.Distribution characteristics of skin temperature and thermal comfort of the occupants in different sections were compared and analyzed,and the difference distribution and dynamic change law of thermal sensation and thermal comfort of passengers in different seats are emphatically studied.The results show that the errors of skin temperature simulation values of front and rear occupants are mostly within 5%,which provides a reliable basis for accurately evaluating the thermal comfort differences of different sections of the occupants.(4)A one-year natural exposure test and appearance defect inconsistency test of the whole vehicle were carried out to perform detailed characterization of the non-uniform thermal environment distribution,dynamic temperature change law,and annual cumulative values of the internal and external parts in the vehicle,and the environmental load spectra of the entire vehicle throughout the year were obtained.The experimental results show that the environmental load distribution is closely related to the time sequence and regional distribution of vehicle appearance defects,which provides an important basis for revealing the nonequilibrium weathering mechanism between parts from the perspective of environmental load.There are still some serious deficiencies in the long-term dynamic environmental load characterization test,such as long test cycle and limited measuring points,which make it difficult to quickly and comprehensively grasp the distribution of the environmental load in the whole vehicle.Therefore,a numerical calculation method which can quickly predict the dynamic non-uniform environmental load of the vehicle under all weather conditions is proposed,combined with the heat transfer model of the multi-layer structure.The distribution characteristics of the environmental loads inside and outside the car and their day-night variation laws are studied,and the influence of the optical properties of the window glass,the physical parameters of the auto-parts,the parking direction and the position of the vehicle on the differential distribution of the environmental loads are focused on.The results show that the environmental load intensity and diurnal temperature difference of the local parts can be significantly reduced by adjusting the vehicle physical parameters,and the vehicle will suffer from greater environmental load stimulation as facing the equator.In this paper,the principles,methods,experiments,and numerical technical analysis of the dynamic and non-uniform thermal environment of automobiles in long and short periods are studied,and some phased achievements are obtained.The research has solved some key common technical issues,including the system analysis method of the dynamic and nonuniform thermal environment of the automobile,the dynamic "heat-flow" characteristic analysis of the passenger cabin based on the buoyancy model,the thermal response of the occupant in a short period,the dynamic heat transfer of the multilayer structure,as well as the numerical method of environmental load distribution under long-term service.It provides common laws and design principles for the study of dynamic and non-uniform thermal environment characteristics of automobiles in long and short periods,enriches and perfects the existing automobile thermal environment research system,and shows good theoretical and engineering application value. |
