Fluids

Fluids

Fluent – How to Change Starting Flow Time/Time Step

    • Muchanical
      Subscriber

      Hello Everyone,


      I have an easy question and would be happy if someone can help me.


      I simulated a transient simulation with Fluent ending after 1 second with 100 timesteps. I saved the results named "ts-001.cdat", "ts-002.cdat", and so on. After the simulation, I closed the saved case-file. Now I want to continue this simulation from 1s to maybe 2s. If I open the transient case-file once again and initialize with the last timestep-number 100, it starts with a current time of 0s.


      So, how to change the starting current time to maybe 1s and how to write the result-files starting with "ts-101.cdat" and not with "ts-001.cdat"?
      This should make it as if I had the simulation run from 0s to 2s from the beginning. I want to avoid time-consuming renaming with a lot of another software.


      In the end, I want to attach the animation of the new simulation to the animation of the preceding simulation. I create the transient animation with CFD-Post


      Best regards,
      Mustafa


      PS 
      ts stands for timestep

    • Rob
      Ansys Employee

      You need to read in the data and then continue running. However, .cdat isn't a Fluent file, it's a cut down dataset for post-processing. You need a .dat file. 

    • Muchanical
      Subscriber

      Hello rwoolhou,


      thx for the reply.
      So, there is no possibility to change manually the starting timestep in Fluent? That would also be helpful in other situations...
      I didn't save the last result as *.dat-file. For the next time I will do it, thank you.

      Now my problem is, I saved only the *.cdat-files and the *.case-file. I have already searched for it but how can I export a *.cdat-file in CFD-Post to a .dat-file to read this with Fluent and continue the simulation as you said because I do not have any *.dat-file.


      I have tried to rename the ".cdat" to a ".dat" manually with typing in. One time it worked but another time there were many issues caused by data damaging. Would you prefer such a manual renaming even if Fluent is opening the renamed *.dat-file correctly?


      Best regards,
      Mustafa

    • DrAmine
      Ansys Employee
      You can set that via rampant variable.
    • Rob
      Ansys Employee

      .cdat is a cut down data set which is ONLY used in CFD Post: it can't be read back into Fluent.  The data file contains the current time step and flow time: so reading this in will allow you to restart from where you left off. 


      If you really want to just change the time in a model (usually for post processing) then read this    https://www.eureka.im/4995.html   Use at your own risk, and I won't elaborate on their comments as this is a public forum. I use the commands irregularly as needed. 

    • Muchanical
      Subscriber

      Thx @rwoolhou and @abenhadj. My first question is answered, so this discussion is solved.


      The commands (rpsetvar 'flow-time ##) and (rpsetvar 'time-step ##) are working where ## is the required value.


      @rwoolhou: Can you clarify why it is risky to use this, pls? Would it make a numerical difference to the results if I change the starting time with the above commands during starting a new simulation?


      Thx for the help.


      Best regards,
      Mustafa

    • Rob
      Ansys Employee

      Any time you use an rpsetvar command you're changing something in the simulation. The above are fairly safe, but could mess with the case-data links: if you mistype something you could also change something important. 

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