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#1 |
New Member
Join Date: May 2022
Posts: 18
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Hello everyone,
I am learning the RANS equations for incompressible flows. I am not sure to understand the classical development of RANS equations as given in the attached figure. 1) Why eq(4) is simplified compared to eq(3) ? 2) I think that eq(4) is the conservative form of the equation while eq(3) is the non-conservative form. Is that true ? 3) The author introduces a "null term" to obtain eq(4). This null term is ![]() ![]() ![]() Thanks ! |
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#2 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,704
Rep Power: 66 ![]() ![]() ![]() |
Yeah nothing is being simplified.
(3) is indeed the convective form and (4) would be the conservation form if the derivation is correct. If (3) & (4) is supposed to be the Navier-Stokes then your author has mixed up a u with a v, or a y with an x. This null term is of course the divergence free incompressibility constraint. The sum must go to zero ![]() ![]() |
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#3 |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,813
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Quote:
Where do you find these equations? To be honest, I don't like that... I suppose they should illustrate the momentum equations in quasi-linear and divergence form but why the diffusive term has only one component? |
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#4 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,704
Rep Power: 66 ![]() ![]() ![]() |
Yeah I don't like it either. Either we are not looking at the navier-stokes or this is a really interesting derivation.
Not only is (3) questionable, they should be adding the entire continuity equation and not just the solenoidal condition if they want to go to the conservative form. And even then, where are all the other missing terms...? |
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Tags |
equation, navier-stokes, rans, simplification |
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