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Imposing a fluctuating BC at the outlet

sriluta

Hey, maybe someone can explain me that. I am investigating a cascade flow in a turbine with very high pressure fluctuations. At the inlet domain I have a unsteady boundary condition.Now I am looking for a boundary condition for my outlet. I don't quite understand the following: I have a certain outlet area, i.e. the distance from the blade to the outlet. I extend this outlet range for example by 2 times. Then I start a simulation with a fixed boundary condition at the new outlet. If the flow now passes the first outlet but has not yet reached the second outlet, I extract the time-dependent condition there during the simulation and this extracted condition is then my outlet boundary condition at the desired location in the simulations.

greetings

  • domen
    0

    Hi, maybe I didn't get it right, but basically you want to impose a BC inside the domain. You want to impose static pressure on old_outlet, while the outlet is at new_outlet.
    If it's a cascade, and the area and radius don't change, I would use the new outlet for BC and the old outlet for extracting info on the thermodynamic conditions. 

  • sriluta
    0 in reply to domen

    exactly, you understood correctly.

    So In principle, it is a question of proving that the fluctuations in the domain are damped, if this is the case, I could apply a fixed outlet condition, which would be my preference. If we talk about fixed outlet condition, then we are talking about a fixed static pressure in the outlet, so it does not change with time, right ?

    Another option would be to have a fixed BC at the outlet. This would only be ok, as I said, if all fluctuations up to the outlet have been damped. To check this would be e.g. some simulations with different outlet lengths and see if the results depend on the length of the outlet area and maybe I can find the length needed to damp all fluctuations.

    To your Statement so option 1 , what you you mean by extracting info on the  thermodynamic conditions from the old outlet ?  i don't quite understand how to do this, to extract the time-dependent condition there :(

    and yes, the area and radius don't change

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