Thermal Simulation of Automotive Lamps Using ANSYS Icepak

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:

PartsMost Preferred MaterialHeat deflection temperature range
Outer LensPlastics100°C -140°C
HousingPMMA90°C-120°C
ReflectorPMMA/Plastics90°C-120°C
BulbGlassN. A
BezelPlastics/PET+PBT90°C -140°C
Inner lensPlastics100°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.

Outer Lens

Figure 2: Lamp Parts

Icepak Simplification:

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

Conclusion:

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.

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Boundary-Layer Modeling using Inflation Layers

In contemporary Computational Fluid Dynamics, for practicing engineers and students, there lies an essential need for the know-how of “making a mesh better” to capture gradient information especially at the fluid-surface boundaries. Modeling the boundary layer becomes extremely important. Visualization of the mainstream flow is, of course, vital to understand the flow behavior. However to obtain a fairly accurate solution for a fluid flow problem, appropriate discretization or meshing of the fluid domain at the boundary layer holds the key.

What is Boundary Layer?

From theoretical fluid mechanics, we know that gradients of velocity and temperature exist within the boundary layer (Wikipedia). Obviously the fluid that is immediately in contact with the boundary will have the same velocity as the boundary. As we move away from the boundary, the velocity of the successive layers of the fluid will increase. Within the boundary layer, shear stresses are developed between layers of fluid moving at different velocities because of viscosity and the interchange of momentum as a result of turbulence. This can cause movement of fluid particles from one layer to the other. In all such flows where “the wall” participation brings considerable changes in the fluid flow, we observe that there is a non-linear variation in the velocity profile normal to the flow direction.

Boundary Layer Modeling using Inflation Layers
Typical profile of a boundary layer

Without accurately capturing these effects at the boundary, you wouldn’t have an accurate solution to such fluid flow problems. Hence, to ensure that you get a fairly accurate result, I will provide recommendations for meshing at boundaries.

Boundary Layer – Key Meshing Recommendations

Typically, the best way to capture effects in the boundary layer is by accommodating higher number of cells in the direction normal to the fluid flow. For mainstream flow, I wouldn’t expect gradients to change much. Hence I recommend reducing the mesh intensity in the flow direction. Within the boundary layer, I would suggest you to have elements with high aspect ratios (up to 100-1000); you can stack them in the direction normal to the wall.

You will need to choose element types that can be stacked one over the other. By doing so, you can marginally save the number of grid cells and time required for the computation. Apart from the conserving the mesh count, it is extremely important to model the boundary layer with sufficiently high quality of meshing elements. You will agree that a poor quality mesh will obviously result in a commensurate accuracy of the solution.

Modeling the Boundary Layer in ANSYS

In ANSYS Fluent, you can achieving cell/element stacking in the direction normal to the boundary using a feature called Inflation. Essentially, you can inflate the mesh with several layers from the surface of the boundary until you cover the boundary layer thickness fully. Tetrahedral elements, when subjected to high aspect ratios, suffer from poor geometric quality. In contrast, Prism elements, due to very high geometric anisotropy, even if they are subject to high aspect ratios, show no deterioration in the geometric quality.

Now, I will compare using prism elements to model the boundary layer instead of tetrahedral elements. Towards the end, I will draw comparison between these two types of elements.

Boundary Layer Modeling using Inflation Layers
Hybrid mesh with prism and tetrahedral elements

For a sample geometry, I have utilized the inflation feature to setup the growth of five inflation layers from the surface of the boundary. As you can see, prism elements are stacked over one another (inflated) in order to capture the boundary layer effects.

If the number of layers are specified as three, the meshing tool grows three layers of prism elements. Beyond the inflation layers, the rest of the fluid domain is meshed with tetrahedral elements. Therefore, the end result will be a hybrid mesh of prism and tetrahedral elements. You can control the inflation layers with parameters like growth rate.

The Benefits

Boundary Layer Modeling using Inflation Layers
Without Inflation

Boundary Layer Modeling using Inflation Layers
With Inflation

In the velocity contour plots, you can see the solution to the fluid flow problem with and without use of inflation. If you notice, the velocity gradients at the boundary are captured quite well when inflation is used. Do you work with applications that involve highly turbulent flows? In such cases, mesh inflation at the boundaries becomes extremely crucial.

In addition to capturing the boundary layer effects accurately, inflation also contributes to lesser element count and computational time. Considering this, I would advise you to use inflation for any wall bounded flow.

In this article, I explained the importance and the approach the use Inflation in the boundary layer. In my next article, I will describe ways to control the growth of the inflation layers using specific application(s).

P.S. If you’re interested, why don’t you attend one of our upcoming training courses for CFD and meshing?

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Fluid Dynamics – ANSYS 18 Innovations

ANSYS Release 18 is packed with lot of innovative features for computational fluid dynamics. This article summarizes the various advancements in the new release.

As always, ANSYS has delivered continuous product advancements. The latest release features several beneficial capabilities.

With ANSYS 18, engineers can create better, more accurate computational fluid dynamics (CFD) simulations. Therefore, engineers new to CFD will benefit from greatly expanded capabilities in easy-to-use ANSYS AIM, including support for transient flows, non-Newtonian fluid viscosity and fluid momentum. In addition, ANSYS 18 includes new features and functionality that enables engineers to solve CFD problems with more accuracy than ever before. Further breakthrough harmonic analysis delivers accurate turbomachinery simulations up to 100x faster. ANSYS 18 also introduces CFD Enterprise, the first solution designed for CFD experts in organizations who need to solve the toughest problems.

Here are the release highlights.

GUI & Advances in Post-Processing

The new release has better CAD import, enriched post-processing, well-organized realization of different volumetric domains and surface boundaries. Also the sophisticated solution monitoring and elegant post processing views make up for a delightful user experience with ANSYS 18.

Fluid Dynamics: Velocity vectors and pressure contour in a pump-valve operation, now displayed with enhanced graphics in ANSYS Fluent
Velocity vectors and pressure contour in a pump-valve operation, now displayed with enhanced graphics in ANSYS Fluent

Better Physical Models
  • Heat Transfer and Combustion. Monte-Carlo radiation model helps capture high temperature radiation in solid domains with better ray tracing implementation. Further on, enhanced flamelet modeling gets combustion analysis running better with ANSYS 18.
  • Multiphase Flow Models. Chemical mixing and other fluid blending processes benefit by the convergence and significant speedup improvements for free surface transient flow simulations with the Volume-of-Fluid (VOF) method.
  • Turbomachinery Enhancements. You can solve blade flutter cases more efficiently by using harmonic analysis. In addition, flank-milled blades can now be better modeled with ANSYS BladeModeler.
Solver Enhancements

Lastly with solver enhancements, mesh adaption of polyhedral meshes in ANSYS Fluent is now possible with its improved execution. Another aspect is that of overset meshing which is ready to better support the aerodynamic community.

Fluid Dynamics: Flow impact on an offshore structure - Robust free surface flow simulation with enhanced VOF model of ANSYS Fluent
Flow impact on an offshore structure – Robust free surface flow simulation with enhanced VOF model of ANSYS Fluent


Do you want to learn more about ANSYS 18 innovations for computational fluid dynamics? Join our webinar on March 23. There’s a lot to learn!

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