Analysis of Moisture and Natural Convection Inside an Automotive Headlamp by Using CFD

摘要

Since an automotive headlamp is very complicated structure, CFD (Computational Fluid Dynamics) had the problem of being very difficult. Especially, if radiation is taken into consideration, the memory required for calculation is huge. In the present study, the first aim was to develop the new calculation technology that was called FSI-DM, that is a unique technique, in which the calculation mesh generated in the fluid were made discontinuous on the solid and fluid surface. In this FSI-DM, radiative heat transfer was calculated with using the coarse mesh generated on the solid surface to reduce memory size in order to use practical, and it enable us to predict velocity and temperature on the inner parts of an automotive headlamp comparatively accurately. Next, FSI-DM was further extended so that it would be able to be applied for moisture condensation on the lens surface. In order to express moisture condensation, moisture transfer model was developed using analogy that was formed between the temperature equation and the diffusion equation. This analogy model for moisture was applied to the spherical lamp and actual headlamp with a complicated structure, and it shows that plastic which was constitute headlamp emits moisture when lighting the bulb and that misting occurs when the lens surface is rapidly cooled. Furthermore, the same thing checked also in the experiment qualitatively but quantitative evaluation.