Development of a CFD Model for Simulating Headlamp Humidity Clearing 2001-01-0861

The use of vented automotive lamps while reducing cost can also result in moisture intrusion through the vent openings into the lamp. If the lamp internal air humidity approaches 100% water vapor may condense on the lens inner surfaces which detracts from the lamp appearance and quality of the light output. Headlamps are required to pass a humidity clearing test which is specified by the FMVSS108 procedure[1]. Prior to the use of CFD predictive tools, lamp venting design was basically a trial and error process which could sometimes require several different prototypes before passing the test. Now by using CFD the venting design can be optimized without the need for prototypes which results in reduced design cost and faster time to market. By utilizing a combined external/internal flow CFD model with coupled heat and mass transfer, lamp vents can be placed in regions that will maximize the removal rate of humidity from the lamp interior. A headlamp FMVSS108 CFD model has been developed and the predicted lamp internal humidity correlated to within +/-10% of experimental humidity measurements. With further CFD code developments and increased computing speed it will be possible to explicitly model the formation and removal of water vapor in automotive lamps, thus allowing the designer to optimize the vent location to minimize the risk of condensation occurring. This virtual design method will reduce design cost and dependence on prototypes while improving lamp performance.