Lighting Systems play an important role in human factors of safe driving. It is an essential part of any vehicle and has undergone significant changes and advances in lighting technology over the years. Thermal aspects play a crucial role when it comes to the designing of automotive lights. Automotive lighting systems mainly consist of outer lens, inner lens, housing, reflectors, bulb, bezel, Led, PCB and light guide, etc.
Figure 1: Automotive headlamp
Out of the parts mentioned above, bulb and led are the two primary sources of lighting that generate a lot of heat energy. Hence it is essential to design the automobile lamps such that even at an extreme ambient temperature, the temperature on each part is maintained well below the critical limit. The critical limit is usually the heat deflection temperature & the maximum temperature on the parts of the lighting system should be well below their respective material HDT values.
The role of CFD simulation in Automotive lamp designing?
Coming to the main question – “What is the role of Computational Fluid Dynamics and software tools such as ANSYS in designing the automotive lighting system”?
CFD simulations can play a crucial role in optimizing various design parameters such as lamp size, the distance between bulb and lens, number of vents, vent location, and selection of materials according to the design requirements. The thermal simulation of automotive lamps comes under conjugate heat transfer type of analysis in which all the modes of heat transfer are essential to model. Radiation is the key source of heat transfer in lamps. Radiation affects the heat wattage from the filament or led source chip and increases the following – temperature of the bulb, reflector, housing, lens, etc. Hence, proper selection of the radiation model is important to get accurate results. Since many parts are interlinked, thermal conduction plays a crucial role in heat distribution especially when automotive lighting systems contain Led chips and PCB.
As all three modes of heat transfer are involved in this simulation, various parameters are needed to benchmark to get the correct results.
There are mostly three kinds of simulation done for Automotive lamps as follows:
Simulation of Headlamps:
The bulb of the headlamp consists of two filaments called High beam and Low beam filament. The Low beam filament is situated closer towards the lens and the High beam filament is placed closer towards the bulb holder. Generally, analysis of the former is more preferred than high beam one because when the Low beam filament is switched ON, the lamp parts get more heated. However, some companies also tend to perform analysis by turning ON both high beam and low beam filaments to predict the maximum temperature in the worst-case scenario.
Simulation of Taillamp:
Tail lamps are generally smaller in size as compared to headlamps, so to avoid high temperatures, they should be carefully designed. Tail lamps consist of tail function filament and stop function filament. Tail lamp simulation is done by turning ON both the tail function and stop function filament.
Simulation of Front turning lamp:
Headlamp consists of a signal turning bulb. Sometimes companies prefer to simulate the headlamps along with the front turning lamp. Often, two turning signal bulbs will be at the sides of headlamps. These two signal lamps may contain separate reflector parts and lens parts. The wattage of these bulbs is generally small, but as these signal bulbs are cramped to a smaller area, it may end up heating the lens and reflector way above HDT values. That is why engineers very often perform simulations for these lamps as well.
Table 1: Lamp Main parts and material description:
|Parts||Most Preferred Material||Heat deflection temperature range|
|Outer Lens||Plastics||100°C -140°C|
|Inner lens||Plastics||100°C -140°C|
The main aim of the simulation is to predict the temperature distribution in various lamp parts and to find out if the maximum temperature is greater or lesser than the Heat deflection temperature. This can help the design team to select the best material according to the design requirement. The simulation can also help the design team to decide the proper locations of air vents by predicting the air-flow path and location of maximum temperature.
Advantages of using ANSYS Icepak in Automotive light thermal simulation:
ANSYS Icepak is the most popular tool in the market when it comes to electronics cooling simulation. It uses Fluent as a solver which is one of the most reliable and popular solvers when it comes to CFD.
The top advantage of using ANSYS Icepak is that it saves us from the tedious task of generating fluid domain. It can automatically generate fluid domain using a cabinet or enclosure approach and creates hexahedral mesh easily. Using Icepak we can save a lot of time which we spend in generating fluid domain and creating a high-quality mesh. Moreover, ANSYS Icepak has various radiation models, such as S2S, DO, Ray, tracing models which can be used both for participating and non-participating mediums accordingly.
To show the capability of ANSYS Icepak in simulating automotive lighting systems, a quite simple model of an Automotive headlamp is developed using Spaceclaim. Please note that this cad design is in no way sponsored by or affiliated with any organization.
Figure 2: Lamp Parts
The Spaceclaim objects will be converted into icepack objects using the Icepak simplification feature available in Spaceclaim. Conversion to icepack objects is necessary and every geometry part must be converted to icepack objects through icepack simplification in space claim or design modeler.
Figure 3: Conversion of Spaceclaim parts to Icepak objects
Effort less meshing using ANSYS Icepak:
ANSYS Icepaks’ HD Mesher generates high-quality mesh even for complex geometries. The process of generating the mesh is extremely easy and less time-consuming. ANSYS Icepak generates the fluid domain automatically using the cabinet approach and saves a lot of time spent on pre-processing. The overall time required to perform the simulation reduces drastically. Referring to the current case, the overall time spent on meshing and generating high-quality mesh was ~ 15 mins and within 15 mins, 3 mesh trials were performed to identify and optimize assembly size and slack settings. Icepak automatically finds and generates the fluid domain based on empty spaces inside the cabinet/enclosure (with no solid bodies/hollow bodies). Figure 4 shows the mesh created in ANSYS Icepak.
Figure 4 – Mesh created in Icepak
Simulation and post-processing:
Simulation of a headlamp is done after giving necessary inputs/ boundary conditions required for running the simulation, such as bulb filament wattage, ambient temperature, radiation parameters, and material properties description, etc. Post-processing of simulation is done to generate temperature contours at various lamp parts. Figure 5 and Figure 6 show the temperature distribution in the bulb, lens, and housing. The temperature in the bulb is very high because the filament is enclosed in a glass bulb. As glass is a semi-transparent medium so radiation coming out from the heat source filament. Passes through the bulb and reaches the outer lens directly at the center of the lens.
Figure 5: Temperature distribution in the bulb
Figure 6: Temperature distribution in the housing and lens
The present work was an attempt to demonstrate ANSYS Icepak’s capabilities in solving a wide range of conjugate heat transfer problems across various domains and its ability to handle any complex modeling project. ANSYS Icepak is the most trusted software tool when it comes to electronics cooling simulation, but it can also be used in performing different types of conjugate heat transfer simulation which may not be necessarily related to electronics cooling. ANSYS Icepak not only saves us from the tedious work of creating fluid domain but its HD mesh algorithm generates high-quality mesh effortlessly. Icepak allows us for a great deal of control on meshing. One can mesh assemblies and subassemblies with different mesh sizes while maintaining an overall coarse mesh for the entire system. Moreover, ANSYS Icepak has almost all the popular turbulence models / radiations models which can be used according to the simulation requirement. The combination of these features makes ANSYS Icepak a great tool.