| The passenger compartment of a car is the only active space for drivers and passengers.When the air conditioning and windows are closed,the temperature in the passenger compartment of the car running in the summer sun can reach 70℃,which is far beyond the comfort and tolerance of human beings.Therefore,ensuring the comfort of the environment in the passenger compartment is the focus of all car manufacturers.Limitations of electric vehicle driving mileage put forward higher requirements for power design accuracy of air conditioning system.To accurately design the power of the air conditioning system,more accurate understanding of the cooling effect of the crew cabin is required.This paper simulates and optimizes the cooling process of an electric vehicle crew compartment,and then makes an environmental compartment test on the sample,which verifies that the simulation has some errors.Because of the higher accuracy requirement of electric vehicle for air conditioning system design,this paper tries to improve the simulation method to increase the simulation accuracy.Firstly,according to the 3D CATIA digital model of an electric vehicle,a simulation model was built based on the passenger compartment and air conditioning system.In order to ensure the convergence of simulation and the sufficiency of calculation resources,the model was simplified reasonably on the basis of CATIA model: the small features of the secondary position of the model were erased,and the porous medium model was used to replace the air filter core and evaporator core.The air inlet of the air conditioning box was used as the model inlet and the circulation outlet of the passenger compartment is used as the model outlet.After the calculation,the distribution of flow field and temperature field in the air-conditioning box,air duct and passenger compartment were obtained,and the average air temperature of the airconditioning surface outlet was extracted as the evaluation standard of the cooling effect of the passenger compartment.Secondly,the computer-aided optimization was carried out for the problem that the average air outlet temperature of the main driving side,the central side and the co driving side was quite different from each other in the simulation results of occupant compartment cooling.The length and width of the cross section of the air duct on each blowing surface and the location of the diversion point were selected as the design variables of this optimization,and seven design variables were parameterized by the grid deformation software — Sculptor to control the deformation of the air duct grid.In the ISIGHT optimization platform,the optimal Latin square test design method was used to select 30 sample points as the optimization scheme.After invoking sculptor software through ISIGHT platform to adjust the mesh according to the scheme sample points,the deformed mesh was imported into STAR-CCM+ model for simulation calculation.After the calculation,the average temperature of each outlet in each optimization scheme was extracted,and the scheme with the minimum temperature difference of each outlet was selected as the optimal scheme.The optimized scheme reduced the sum of the temperature difference between the main driving side and the central side and the temperature difference between the co-driving side and the central side from 1.89℃ to 0.09℃.As a result,the effectiveness of the computer-aided optimization method was verified.Finally,after making of the air duct samples,verification tests were carried out under the same conditions according to the simulation boundary conditions in the environment cabin.Comparing the average temperature of the air outlet in the result of the optimal scheme with the measured value in the verification test,it was found that the average error between the simulation result of the optimal scheme and the test result was 8.4%.As the air conditioning system has a great influence on the driving mileage of electric vehicles,it was attempted to improve the simulation method to increase the accuracy of the simulation.Since the internal structure and heat transfer mechanism of the evaporator were not considered in the conventional threedimensional fluid simulation,the one-dimensional simulation software KULI was used to build the heat transfer model of the air side and the refrigerant side of the airconditioning box.The velocity distribution of the evaporator core inlet in the results of the conventional three-dimensional simulation(the optimal scheme)was extracted and inputted into the KULI model as the boundary condition.More accurate velocity and temperature distribution at the outlet of evaporator core were obtained after simulation.Then a new three-dimensional simulation model was established,which only included the air-conditioning box behind the core of the evaporator,the air duct and the passenger compartment.The more accurate exit temperature and velocity nephogram of evaporator core in one-dimensional simulation results were taken as the new entrance boundary conditions of simulation.The average temperature of each outlet in one-dimensional / three-dimensional simulation is obtained eventually.Compared with the results of one-dimensional / three-dimensional simulation,it was found that the average error of the air temperature of the three outlets is only 4.6%.It is concluded that the accuracy of this one-dimensional / three-dimensional simulation is higher than that of the conventional three-dimensional simulation. |
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