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estimate of physical time step

sriluta

Hey, how can I estimate the physical time step of my unsteady Simulation in general ? So iam investigating 15 Stators, without a rotor ( therefore no rotation speed is set), with a very high fluctuating inflow. I started the unsteady Simulation with the initial solution of my steady state  Simulation. 

So iam using Omnis, open solver, density-based solver, the implicit time integration mode. I Started a first unsteady Simulation with the default settings ( physical time step: 0.001 s). 

One option would be with the Courant number formula,  but how do I found out  the characteristic size of  my mesh cell ? 

I read on another site that a good guideline would be 1/20th of the time it takes a fluid to pass through a component. In my case: 0.72m long channel, flow velocity: 800 m/s -->( 0.72m)/(800m/s) = 0.0009* 1/20= 0.000045s 

At the end of the day I have to do a Time Step independence study anyway.

greetings Hussein

  • sriluta
    0

    ah I think I find the characteristic size of my mesh cell in mesh/mesh quality fields/cell volume and there I can found the minimum 

  • domen
    +1 in reply to sriluta

    Hi, it's a very good question. The time step depends on which phenomena you want to capture. Anyway, each time step need to converge very well, otherwise you are going to cumulate relatively high error and the results won't make much sense. For this you need to choose a time step that is anyway not too large. 

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