| Simulation of flow fields, temperatures and defogging phenomena The CFD-simulation (Computational Fluid Dynamics) has increased in importance strongly and now even enables the treatment of complex systems. Up to now testing required real prototypes, now some of it can be done in simulation. The CFD-simulation is used in this project to predict temperatures and flow fields as well as defogging phenomena (condensation and evaporation of water) in lighting assemblies (automotive head and rear lamps). Thus problems like thermal damage to the plastics and visible water films may be detected and solved in an early stage of design. In particular, the use of clear lenses requires a proper system testing as any observer gains a deep insight into the system so that any deficiency becomes apparent. |
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| The temperatures in automotive head and rear lamps are influenced by inner heat sources (bulbs) and environmental heating (e.g. sun, motor). A proper model for predicting temperatures has to account for conduction and convection as well as for thermal radiosity. In particular, the thermal radiosity dominates the internal heating by the bulbs. Conventional models for thermal radiosity (view factor scaling, discrete ordinate method) do not sufficiently provide for specular radiosity at high reflective surfaces (reflectors). An adaptation of such a radiosity model to lighting assemblies is imperative to achieve an acceptable accuracy of the simulation results. |  |
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| Figure 1 compares simulated and measured temperatures on the outer side of the lens of a head lamp. While the thermography shows hot spots in areas, where the light passes the lens (especially high beam), the conventional radiosity model is not able to reproduce this. An improved radiosity model is necessary to achieve a sufficient accuracy. In addition to model improvements, the modelling of the bulbs thermal behaviour and the definition of environmental influences are basic aspects of this project. | ||
| Besides thermal problems, defogging phenomena are also examined. Defogging denotes the condensation of water vapour inside the lighting assemblies especially on the inner side of the lenses. An appropriate mathematical model was implemented into a conventional CFD-tool and validated to account for these defogging phenomena. This offers the possibility to determine those areas which tend to show condensation effects as well as to judge different strategies to solve the problem. All in all, the simulation helps to minimize time consuming and expensive measurements on prototypes and to detect and solve possible problems. Furthermore, detailed knowledge can be gained at an early stage of design and especially in those areas where measurements are not possible or at least hard to perform. | ||
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