SimScale CAE Forum

VIP Latrine Optimization Challenge – Post-Processing Air Change Rate


VIP Latrine Optimization Challenge with Neven Subotic Stiftung (Foundation)

Link to post-processing state:

Step-by-step Tutorial: Post-processing for Air Change Rate

To ensure that the minimum required air change rate is obtained, a post-processing state has been created in the post-processing software Paraview, which does as much as possible to make this an easy process for the user, however certain inputs are required for accurate results. The overall process is opening the state, selecting the downloaded results, changing the clip filters to isolate certain surfaces and volumes and then read out the air change rate value (ACR) in number changes per hour (1/h).

Download and extract the results

The first step is to download and extract your results from SimScale, to do this, simply select the run in which you wish to download and select the download icon.

Figure 1: Selecting the required run and downloading using the download icon.

You will need to extract the zip folder before continuing.

Opening the State

As previously mentioned the state is there to make your job easier, you simply need to open the state, select the case, modify the volume and read out the ACR value. So to start, open Paraview (the state was created using version 5.5, other versions might produce warning messages but shouldn’t be a problem) and open the state, when prompted, load the case from file, and select the case.foam file from your extracted run.

Figure 2: open a state.

Figure 3: Choose file names of select the case.foam file in the extracted directory you have downloaded. Finally, select ok.

Modify the Internal Volume

There is a required air refresh rate for VIP Latrines of 6 refreshes per hour, to calculate this change rate, you need two parameters, volume flow rate and the volume of the reference space. Here we slice a surface across the drop holes and vent pipes and reduce the surface using clips Reduce Surface. This surface is used to evaluate the flow rate and should be checked to ensure that the vent pipe disks are not cut by the clips.

Figure 3: Disks not cut by the Reduce Surface filters.

Next, the volume needs to be set so that it represents only the volume within the walls as depicted below, this does not have to be accurate, however, should not be used to increase volume to give a bigger ACR. the top should be level with the bottom of the roof and the sides should extend to the wall fully, including about half of the wall vent volumes as shown. The bottom should extend to just include a small part of the holes.

Figure 4: Entire internal volume, up to the roof part and down to the floor, extending approximately 50% into the walls.

Reading the ACR

Finally after the adjustments have been made it is safe to take the ACR rate in the right-hand panel as the final ACR for this design and wind direction.

Figure 5: ACR value in a number of refreshes per hour to use in the cost function.

The recommendation is to ensure that the ACR is kept above 6, however, to allow an error margin 8 refreshes should be the minimum that the design achieves for all wind direction. The overall task is to minimise the cost calculated in the CAD model but to exceed this minimum of 8 ACR calculated using CFD.

VIP Latrine Optimization Challenge – Import CAD, Meshing and Simulation Setup




Hi, I just signed up to try the challenge and this modelling environment.
My current issue is that I don’t have permission to download the post-processing state…

Kind regards,


Hi Kevin!

I am sure my colleague Darren (@1318980) can help you out here. :slight_smile: Thanks a lot for participating in the workshop and happy SimScaling!



Hi @kevin_ft, Just ammended, please let me know if you still have issues.



hi everyone,
i am also participated in this challenge. i am done with simulation and for post processing i am download results and trying to simulated in paraview but there is some problem

  1. in results file case state file content 0 kb

and when we select this case state file and open but its not open in paraview software.

please help me
thanks you


Hi Rohit,

please share the project either with Darren (@1318980) and me privately. We’ll have a look if the setup or the settings are the cause of this issue.




Hi @ROHIT_SR, I would expect case.foam to be of 0 size, this is because it actually doesnt hold the results, it simply tells the reader, in this directory, there are results, and by knowing the openfoam directory layout it opens the result. When you open the case.foam in paraview can you screenshot what you see?



and just to confirm your doing; load state file> .psvm > select other file > case.foam?


when i open this file in para view there nothing on screen .

another problem is, when i am trying to open google drive link there is also some problem.

thank you,



@ROHIT_SR if you select the case.foam in paraview, is the path correct?