Numerical simulation of the airflow over and heat transfer through a vehicle windshield defrosting and demisting system
A numerical model and technique are described to simulate the turbulent fluid flow over and heat transfer through a model of vehicle windshield defrosting and demisting systems. The simplified geometry and the dimensions of the numerical model are representative of vehicle system with accurate locations of the nozzles and outlet vents, including cabin features such as seating and the rear parcel shelf.
The three-dimensional geometry of the numerical model is created in Auto Cad (Release 14). Surface meshing and a computational mesh of 750,000 (tetrahedral) fluid cells is generated in the pre-processor of the CFD software used for the simulation of the fluid flow. Turbulence is modelled by using the k-ɛ turbulence equations together with the wall function method. This decision was made after comparing the k-ɛ model's performance with that of lower order models, and after considering the increased computer time requirements and decreased stability of more complex models, such as the Reynolds stress model. The numerical results of the study are very encouraging and compare favourably with measurements obtained from the actual vehicle by Thermograph and Hot Bulb probe techniques. The findings highlight some of the drawbacks of the existing design of the windshield systems and show that the maximum flow rates occur in the vicinity of the lower part of the windshield, progressing from the defroster nozzle in the dashboard.
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