[wind81]

Hi, I would like to model the emission from the vehicle into the environment. May I know how to define the material which consists of NO, SO, CO and Particulate matter ?

[ghorrocks]

How you model it depends on what you are trying to achieve with the model. You can model it by a simple additional variable approach (simple, easy but does not account for variation in material properties due to composition changes) through to multi-component mixture models and multiphase models. What approach is appropriate depends on what you are trying to do.

So can you explain what you are trying to do, and why you are doing this?

[wind81]

Originally Posted by ghorrocks

How you model it depends on what you are trying to achieve with the model. You can model it by a simple additional variable approach (simple, easy but does not account for variation in material properties due to composition changes) through to multi-component mixture models and multiphase models. What approach is appropriate depends on what you are trying to do.

So can you explain what you are trying to do, and why you are doing this?

Hi, Ghorrocks thank you for your swift reply. In the study, I would like to investigate the pollution dispersion around the building under various wind speed. The pollution is come from the vehicle emission which consists of NO2, SO2, CO, PM10 and PM2.5. I have the concentration of each component from the vehicle and no reaction is involved in my study. May I know which is the appropriate approach to model the pollutant ? Through additional variable or variable composition mixture ? Thank you !

[ghorrocks]

You should be aware of the various modelling options and their implications - that way you can make the decision yourself with confidence. So read up in the documentation about the options so you understand them.

But if I guess what you are doing and trying to achieve, I would suspect material property effects and chemistry are not important in your case, so a simple additional variable approach would work well. To do this, add an additional variable; and in the domain set the additional variable to have a diffusive transport equation. So the only material property you need to define is the diffusivity of the material in air. Note that the diffusivity is just the molecular diffusivity and will be increased by any turbulence model - meaning that for most models the molecular diffusivity is irrelevant as turbulence is dominant. This means you can probably ignore diffusivity if your turbulence is high enough.

[wind81]

Originally Posted by ghorrocks

You should be aware of the various modelling options and their implications - that way you can make the decision yourself with confidence. So read up in the documentation about the options so you understand them.

But if I guess what you are doing and trying to achieve, I would suspect material property effects and chemistry are not important in your case, so a simple additional variable approach would work well. To do this, add an additional variable; and in the domain set the additional variable to have a diffusive transport equation. So the only material property you need to define is the diffusivity of the material in air. Note that the diffusivity is just the molecular diffusivity and will be increased by any turbulence model - meaning that for most models the molecular diffusivity is irrelevant as turbulence is dominant. This means you can probably ignore diffusivity if your turbulence is high enough.

Hi, Ghorrocks thank you for your advice.