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Translational reference frame

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Old   June 14, 2001, 19:54
Default Translational reference frame
  #1
Jay
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Hi! there,

Could you introduce the "Translational reference frame"? and how the N-S equations are changed?

or tell me some reference/paper that I can read?

Thank you very much.

Ray
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Old   June 15, 2001, 00:18
Default Re: Translational reference frame
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Dan Williams
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Aren't the NS equations invariant under a galilean transformation? You could check for yourself by just apply the transformation to velocity that "V.b = V.a + V.b wrt.a" Seems to me that no additional acceleration terms would appear in the momentum equations, as the translating velocity (V.b wrt a) just disappears when you take the derivatives.

Note that this is definitely not the case for a rotating domain.
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Old   June 15, 2001, 11:46
Default Re: Translational reference frame
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kalyan
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NS equations with no body forces are also Galilean invariant under rotation since rigid body type motions do not lead to additional stresses.
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Old   June 16, 2001, 04:49
Default Re: Translational reference frame
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clifford bradford
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yeah but who cares about the case when there's no body force?
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Old   June 18, 2001, 10:40
Default Re: Translational reference frame
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kalyan
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In most LES papers, people claim that their (subgrid) model is Galilean invariant by just showing its invaraince under translational motion. Some such models do not have invariance under rigid body rotation. Subgrid terms should be invariant under any type of rigid body motion. Even when you have density change and bouyancy effects, it is worthwhile checking if the model is Galilean invariant in the limit of microgravity.
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