Monte Carlo Radiation Model Setup in Ansys Fluent

Hello, my name is Jesus Ramirez and I am part of the technical staff of AUSEN Engineering. Today I am going to show you how to model solar radiation in an automotive headlamp assembly. Let's talk about this.

For cars parked in uncovered areas or standing on highways for long periods of time, solar rays entering the headlamp are focused by the lens in certain areas inside which produce thermal hotspots.

The overall heat up of the assembly and thermal hotspots produces stresses due to thermal expansions and mechanical constraints. Moreover, the thermal hotspots can also possibly harm electronic or other plastic components, which are used inside the headlamp.

In this video, the headlamp assembly is modeled in an air volume with the boundaries maintained at a temperature of 20°C. Two wall supplies of 1200W per square meter heat flux are used to simulate the effect of the sun's rays shining on the headlamp.

The rays will travel into the headlamp through the front cover, which is from polycarbonate with an absorption coefficient of 0. 5. The rays will travel into the headlamp through the front cover, which is from polycarbonate with an absorption coefficient of 0. 5. The rays will be focused on the headlamp modeled as blood plastics and participate by absorbing, reflecting, and emitting radiation.

The ring vessel is modeled with an emissivity of 0.16, meaning 84 percent of the incident radiation is reflected. So, let's see how we can do the model of this geometry. This is the geometry of the headlamp that we are going to use. So, let's start with the modeling.

To analyze radiation, the first thing that we need to do is to enable the energy equation. We have the energy equation already. Now, we want to change the viscous model to laminar. In this case, we are not interested in solving or modeling near-wall effects or turbulent behavior.

So, we can use the laminar approach. After that, we want to include the radiation model. We are going to use the Monte Carlo approach. We are going to change this value to 20 for the sake of the speed of the simulation for this demonstration.

It is important to recall that the Monte Carlo model is a statistical radiation model that tracks the photons through the system. The size of this sample is determined by the target number of histories.

In general, the larger the number of histories, the more accurate the simulation at the expense of computational time. In this video, we are going to use a relatively low number, but in practice, this number may need to be increased. We are going to drag and drop some of these materials.

We will get some chercher a modeling for these. Today, we have an interesting combi model, but let's move back here for the real modeling to resolve the problem parameters.

The Monte Carlo model is expensive, and in contrast, the surface-to-surface model assumes all radiation to be diffused and so will capture the specular nature of the focusing of rays by the lens.

These are some of the reasons that for this case in particular, using the Monte Carlo model is the better approach. With these changes, we will click OK, and some warnings will be available. Material properties or models have changed.

This is something that we do internally because of the model that we selected. So, let's keep moving. I have created two materials: glass and plastic. You can see that the material is very well designed and the focus is very good. I have created two materials: glass and plastic.

I have created two materials: glass and plastic. These are materials that I have created in a science of properties. You can know more about this in our other videos. What I am going to do right now is to assign cell zones.

Basically, when I go here into the cell zones, I have different solids created. For example, if I select Bessel, this is open, and basically, what I'm going to do is to change the material name here to material for plastic. I will click apply, and now plastic has been assigned to the vessel.

Also, let me see what else I can do. Let me try to do it faster. Now, I have best selected. I'm going to click right, right-click, and select copy. I'm going to set, and then I'm going to copy the solid for yr to other solids. So, I don't need to double-click, enter, and change the materials.

I will copy the best, and it stops. I will assign that to the holder, the house, in today's vessel, the refurbished vessel, and the rim. And I will click in copy and then click OK. Now, I am going to design the reflector to the rim vessel and to the sitting still rim, and we click in copy.

The vessel cell zone conditions were copied to the other cell zones. Okay, and close. Finally, I will open the lens right and need to be sure that glass is selected. Nothing to do here. Well, indeed, there is something that I need to do. So, let me double-click here again.

I need to click here, participate in radiation, because I want the lens to participate in radiation. Now, I will click apply and close. Let's create the boundary conditions. In this case, the geometry or the mesh has to be selected to be the boundary condition.

So, in this case, the geometry or the mesh has a large number of faces, and several of them have the suffix shadow. These shadows of faces are automatically created in Fluent because the faces are two-sided, meaning that the face has two separate boundaries, one on each side.

So, this is how we handle interfaces. Basically, what we are going to use is the copy function to set up the boundary conditions faster. So, let's start here in the boundary condition. Let's go to wall and select vessel enclosure. Double-click. Let's wait for some seconds, and we will put here.

So, what we are going to do is we are going to turn out so that the material will be changed to plastic. We are going to change the material to plastic and change the material to plastic. Right. And here in radiation, we will keep the boundary condition type as opaque.

The internal emissivity as one and the diffuse fraction of one. Right. So, we will click apply. Right. So, now the boundary condition has been applied to this one. Okay. So, now we are going to change the material to this one.

So, now, with this boundary condition already done, I will right-click and copy. I will select everything and click here and OK. Now, close this and one moment. Okay. Perfect. Now, let's select our enclosure lens right. It should be here. Double-click. So, let's wait.

Let's change the material to glass. Right. In radiation, this will be semi-transparent, and the diffuse fraction to zero. Okay. Then, we click in apply. So, again, with I'm going to use some copy. With this guy selected, right-click, copy.

And what I am going to do here is to select here the enclosure lens shadow. Let me check for that here. Okay. And click copy and click OK. And we're clicking close. Now, let's select the close rim vessel. Double-click here.

So, the thermal material will be plastic, and in the radiation, it will be opaque. The internal emissivity will be changed to 0.16, and the diffuse fraction to 0. 1. And we will click apply. Right. Then, with this guy selected, we are going to copy this.

And we are going to select the enclosed rim vessel shadow, the holding rim, the holder rim vessel, right, the holder rim vessel shadow, and the whole thing rim vessel shadow. Let me check. We have everything as it is.

So, enclosure vessel shadow, holder rim vessel, holder rim vessel shadow, housing rim vessel, okay, this one, and set, okay, click copy, click OK, that's good. Now, let's do something similar for enclosure one here. So, we will open it and enter here in thermal temperature. Let's just see. Okay.

Let me say I feel like we are on here. Emm, thin the so, let's change the temperature previously. And for radiation, we are going to click boundary source. So, we will have a direct irradiation of 1200. The beam direction will be minus 0.848 here in minus 0.53 here. Okay.

So, let's keep this and click in apply. So, now, with this one, I am going to solve the case. And for solving the case, what I'm going to do is go into methods. And I'm going to retain the default settings. Also, I'm going to go here to solution residuals.

So, I am going to click in show advanced options and check that scale is selected, right? And click OK. Cool. So, we are going to create a report definition. So, I am going to new, right? So, face report, face maximum, right? So, I am going to call this max temp.

And basically, I am going to select temperature here, right? Static temperature. And I am going to do is to select enclosure inner vessel from here. Enclosure inner vessel. Okay. So, click OK. And that's it. Okay. So, remember to write the case. And now, let's go to run the calculations.

So, we click here and run calculations. I am going to number of iterations will be 99. Yes. So, click in calculate. And we click yes because I want to initialize the case before running. Okay. And let's run the calculations. And let's wait until the case finishes.

Once the simulation finishes, we can see some post-processing. So, here, there is a clear hot spot, right? And we can see the location of this hot spot compared with the lens location, right? So, this is something that we can see. And we can not only evidently see the hot spot, right?

That is a control temperature. Also, if we want, we can do another kind of analysis, right? So, let's go here. So, new. Let's call this like contour. Right. So, let's select basically the block here. Right. So, also the vessel. Okay. So, let's go here. Okay. So, let's go here. Until here.

Maybe this and this. Right. So, here, we are going to select radiation. And here, we are going to select radiation intensity normalized by standard deviation. So, we will click here. So, I believe something. I didn't select one. Okay. Yes. So, maybe I'm going to select everything.

And I am going to deselect enclosure one. Look for it. Here. And I'm going to deselect that input surface. This one. See? Okay. Now, it looks much, much better. Right?

So, this is the standard elevation, generally less than 30. But here, we still see basically values that it sees this value in any small area, which isn't desirable. Right? We don't want this. So, maybe increase the number of histories in the Monte Carlo radiation model.

We lower the standard deviation. And for sure improve the results. However, the simulation will be more expensive computationally speaking. Right? So, well, this is like a demonstration of how to set up the Monte Carlo analysis, Monte Carlo radiation model.

So, thank you very much for your attention. Bye-bye. Bye.