Numerical Simulation Research On Defrosting Characteristics Of A Automotive Windshield

With the vigorously economic growth, the automobile has become a necessity of transportation. Meanwhile, the automobile air condition has been widely applied in automobile industry. Moreover, automobile AC’s defrosting system is very significant for the safely driving and comfortably sitting. Every year, the traffic accidents caused by the front windshield’s frosting, which blurs the driver’s sight, have frequent occurrences. Hence, the researching on the front windshield’s defrosting performance has theoretic meaning and engineering application value.This thesis firstly researches the simplification of front windshield model and explores the numerical simulation method and testing method applicable for the real vehicle’s front windshield. Utilizing the thin model provided by STAR-CCM+ to solve the defrosting process, utilizing infrared imager to acquire the every 5 minutes’ temperature change values of the surface of front windshield and contrasting the simulation values and testing values to verify the accuracy of SST k-ω turbulence model and thin model’s defrosting simulation calculations, make a well preparation for the subsequent demonstration of numerical simulation.With the finalizing of simulation method, this thesis then takes the sedan’s passenger compartment as the simulation object. Through numerical simulation, the airflow movement in defrosting duct and passenger compartment, the velocity field of inner side surface of front windshield, temperature field and frost thickness distribution of the outside surface of front windshield will be obtained. For better analyzing and evaluating the front windshield’s defrosting characteristics, the research measures the defrosting performance by testing the defrosting rate of Zone A and Zone A’ and Nusselt Number. The result indicates that the velocity distribution on the inner side of front windshield is inhomogeneous. At the right part, lower-left part and upper-middle part of the inner side of front wind shield exists a low velocity zone respectively. These low velocity zones partly is located at the Zone A and Zone A’, which causes a serious impact on the defrosting of these zones. Therefore, the defrosting performance must be optimized by researching the influencing factors of the structure of the air duct, flux and temperature of air duct inlet and the angle of defrosting grilles. The study found:i): The scheme 2 proposed for the defrost duct structure enlarges the outward airflow at the driver’s side and broadens the sight-available zone’s velocity. Furthermore, it brings more homogeneous velocity distribution, more smooth inner air flow, less loss of airflow and less ’blind area’ to contribute to a better defrosting performance.ii) The higher temperature nearby the air duct inlet and sharper temperature difference between warm airflow and front windshield, the more heat exchange will be done between them and the higher speed will happen with the defrosting. However, higher temperature of air duct inlet means the heater core with higher capacity must be used. Comprehensively considering from the defrosting performance and energy saving, T14 is a relatively ideal scheme.iii) It is true that larger flux at the air duct inlet can produce better defrosting performance. But higher capacity and rotational speed with blower shall be required, which, however, will cause much noise. Comprehensively considering from the defrosting performance and noise reduction, M9 is a relatively ideal scheme.iiii) The different angles of defrosting grilles will make the different flow distribution. It is found that a negative angle scheme is better than positive angle scheme with respect to defrosting performance. Among the negative angle schemes, the scheme A1 can achieve the best defrosting performance. Hence, the grille should be regularly fixed with an angle of-15 o in the initial design scheme.Finally, analyzing and evaluating the different schemes’ defrosting performance helps to find the influencing law of defrosting in respects of flux and temperature nearby the inlet and the angle of grille and further achieves the optimized defrosting scheme, which provides a reference for optimizing the defrosting performance with automobiles.