Improving the Accuracy of CFD Method for Windscreen Deicing
Examensarbete för masterexamen
Applied mechanics (MPAME), MSc
During winter, ice formed on the windscreen has to be removed before driving the vehicle. It is not safe to drive the vehicle without clear visibility on the windscreen. The defroster system in passenger cars melts ice on the windscreen. During the development of defroster systems, car manufacturers conduct physical tests to measure their performance. The performance of various design models are predicted through physical tests which consumes large amount of time. At Volvo Cars, Computational Fluid Dynamics(CFD) is used extensively to analyse the performance of various attributes of the car which reduces substantial amount of development time. The objective of the master thesis is to improve the accuracy of the current CFD method in predicting the melting pattern of ice over the windscreen. The Volvo V40 model is used to analyse the performance of the defroster models. The Volvo V40 CAD model is surface meshed using ANSA meshing software which is then followed by generating the volume mesh using Harpoon meshing software. Boundary layers are generated at the cabin surface interface with the windscreen. In addition to it, three layers of windscreen and ice are modelled as prism layers using Fluentmesh to accurately predict the temperature and melting pattern at the external boundary of ice. Steady state defroster ow is analysed to predict that the ow coming out from the defroster nozzles is uniformly distributed over the windscreen. The steady state ow simulation are carried out using realizable k and k SST turbulence model for modeling the turbulent ow in the defroster domain. It is found that the realizable k turbulence model performed better than the k ! SST turbulence model in solving the defroster ow field. Having known the distribution of the defroster ow, transient thermal analysis is performed by use of Solidification and Melting model and modified various boundary conditions. By varying the thermal properties of air from constant to a polynomial function of temperature and followed by modifying the boundary conditions of certain walls like A-pillar, instrument panel and front doors from adiabatic to temperature thermal boundary condition (using a transient temperature profile) there is some amount of improvement in the performance of the transient CFD model. However, consideration of radiation effect on certain walls did not have any in uence in the transient simulation results. Moreover the selection of unsteady first order discretization scheme predicted the melting of ice quicker occur over the windscreen than unsteady second order scheme. The melting pattern obtained using unsteady first order scheme correlates better to the physical test results. Finally with the consideration of heat energy supplied across the heater instead of specifying the transient temperature profile at the inlet of HVAC unit, accuracy of the transient model improved significantly. It is believed that by taking into account source terms like gravitational force, buoyancy force in the solidification and melting model in addition to the implementation of sliding of partially melted ice occur over the windscreen can lead to further improvement in the performance of transient CFD models.
Strömningsmekanik och akustik , Hållbar utveckling , Strömningsmekanik , Materialvetenskap , Fluid Mechanics and Acoustics , Sustainable Development , Fluid mechanics , Materials Science