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Transient rotor stator vs none

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Old   November 21, 2018, 04:21
Default Transient rotor stator vs none
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Marcello Asciolla
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I have a quick question, maybe very stupid, but I have to know the answer.
I know that frozen rotor and stage mixing plane interfaces are approximations, very useful for a steady solution, but what about the transient rotor stator interface? Is it an approximation too?
Is this is true, is it possible the use of "none" for an interface between a rotating domain and a steady one, maybe for a more precise solution?
I want to know if this option could be used for this case, what does "none" mean exactly for the solver and what could be the difference between this kind of interface and transient rotor stator one.
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Old   November 21, 2018, 05:14
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transient rotor stator interface Actually means that if you have a rotating domain, mesh will actually be rotating. The angle of the rotating domain can change over time.
I think that there are no approximations for transient rotor-stator,
as it involves all the physics.
and it has a disadvantage to usually being very computationally expensive like all transient simulations are.


The frozen rotor connection cannot do that as the mesh position is fixed in space, this is an approximation and it depends on the case if this is ok or not


case:
let say you want to simulate a wind turbine and you are interested in what is going on with the flow when the blade passes the pole.
well this can only be done in transient with the help of transient rotor stator interface as the inflowing air is involved and the blade passage.
this was just an example

there is way way more examples where transient rotor stator interface should be used than the frozen rotor stator, but the extra complexity and computational time are in most cases not worth it, hence approximation.

.....
This is something similar to turbulent models being approximations, if we could, we would always use Direct Numerical Simulations or at least LES or DES models, but we can't because it is not worth the effort and computational time, hence approximation.

We encounter approximations in all numerical simulations as the real world is just too complex. Usually, this is ok.
But the person preparing simulations needs to know what can, he or she neglect in the simulation otherwise the results can be very wrong
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Old   November 21, 2018, 06:01
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Transient rotor stator solves the full transient Navier Stokes equations with a moving mesh. But the Navier Stokes equations are an approximation, the turbulence model is an approximation, the mesh is an approximation of the geometry and CFX's coupled solver uses a numerical model which approximates the Navier Stokes equations - so be careful calling it "exact". It really is a whole heap of approximations on top of each other.
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Old   November 21, 2018, 07:50
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Marcello Asciolla
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I am sorry, maybe "approximation" is the wrong word, but I wanted to mean if there is the neglection of physical effects in transient rotor stator model, because I misunderstood the behavior of the solver when the option "none" is selected and I thought that in this case it was intended to the use for a simulation with all the physical effects, but I was wrong.
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Old   November 21, 2018, 16:44
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Which option are you asking about the "none" option? I assume it is in the interface setup. Frame change model or pitch change?
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