SimScale CAE Forum

Solar radiation value through bus windows

Hi everyone.

I’m new in this world. I want to simulate the air inside a bus.
The bus will increase its temperature due to the solar radiation through the windows. And the vehicle is refrigereted with a cold air inlet (5cm X 5cm) from top to bottom. These are my questions:

  1. What SOLVER should I use?
    laminar / k-epsilon / k-omega SST?
    steady-state / transient?
    Boussinesq approximation on / off?

  2. What boundary condition do I have to use for the solar radiation through the windows? heat flux in W/m2?
    Which value or number? 50 W/m2?
    I don’t know where I can find this information. If anyone knows, I will be grateful.

My cases can be found in my profile.


1 Like

Hi @sl_pez,

Interesting application indeed! To answer your queries,

  1. Solver:
    Any turbulence solver, may be the K-omega SST one
    Steady state should be sufficient for your application as this is computationally not so expensive
    Bousinessq approximation off - this is used when quite some density variation is seen in the analysis

  2. Boundary condition:
    Please note that it is not possible to include radiation in our fluid solvers. So the equivalent value can be calculated to be defined as surface heat flux (W/m2). Please try to search on some literature for an approximate value that can be specified for the radiation.

I hope this helps! Please feel free to contact us for other queries.


1 Like

Thank you for all the information.:+1:

And why can’t the k-epsilon model be used?Is it better k-omega SST?


Either one of these models can be used. To be more precise you will have to study all the differences between the two to choose the best one for your application. k-omega SST is generally good for wall shear conditions.

I have more questions:

  1. If I want to see the evolution of the temperature and velocity through time but also at the end, should I use a steady-state or transient model?
    I have different simulations. For example, in a case, a change the velocity value. It is 3 m/s from 0 to 30 minutes, then 2 m/s from 30 to 60 minutes, and finally 1 m/s till the end.

  2. If the element size is 0.025m, what must the time step size be?

Thank you.

Hey @sl_pez,

To answer your queries,

  1. In this case you will have to run a transient analysis to get the results with respect to time. The inlet velocity value can be defined using a table upload. 60 minutes would be a long time to run a transient simulation for. If the mesh is large then the simualtion run could take a very long time.

  2. The time step value depends also on the velocity of flow. Please refer the CFL condition and calculate the initial time step value accordingly. The minimum cell size can be obtained from the mesh refinements defined.