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MRFZonesC questions what is the mesh_V and why only Coriolis force no centrifugal force |
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#1 | |
Senior Member
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hi every one!
i have some question about MRFZones.C in void Foam::MRFZone::addCoriolis(fvVectorMatrix& UEqn) const: Quote:
wayne |
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#2 |
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
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Hi Wayne,
I think that in an absolute velocity formulation, the Coriolis force (2rwxU_relative) and centripet force (rwxwxr) can be written as: rwxU I hope this is helpful, Dragos |
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#3 |
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
Rep Power: 20 ![]() |
...and mesh_.V() retuns the cell volume
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#4 |
Senior Member
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Hi Dragos:
i don` think so.if we write the moment equ in rotating frame, the velocity is relative velocity (W),and in the absolute frame the equation is without the coriolis force and centrifugal force. in MRF: rho*D(W_relative)/Dt=F(total,including pressure,viscosity)+omega(omegar)-2* omega u in absolute frame: rho*D(U_absolute)/Dt =F according to you should be rho*D(U_aboslute)/dt= F+ * omega U i dont think it will be rho*D(W_aboslute)/dt= F+ * omega U for the solver just treat one velocity not two thanks alot yours wayne |
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#5 |
Senior Member
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i am sorry, there is a "*" before "omega U" for last two equ.it is typing error of mine
thanks wayne |
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#6 |
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
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I had a vague memory in the back of my mind when I wrote the above post, but I've just dug for it and here it is...
In the absolute velocity formulation and for a steadily rotating frame the flow equations can be written as follows: - continuity: ![]() - momentum: ![]() - energy: ![]() ![]() ![]() You can also check the fluent user manual for it. I hope this is helpful, Dragos |
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#7 |
Senior Member
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Hi Dragos
thanks a lot! i could understand it now! the relative velocity is as calculating in the memeber function relativeflux,so moment eqution should be div(phi,u),is that right? thanks waye |
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#8 |
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
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Hi Wayne,
This is exactly what it is written in the momentum predictor: ); </blockquote> Dragos |
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#9 |
Senior Member
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Hi Dragos
but why the flow pattern of the result looks like U is relative velocity wayne |
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#10 |
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
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well Wayne, if it is like that I agree with you: it is strange.
Can you post a picture with an example? Dragos |
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#11 |
Senior Member
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Hi dragos
the result of mixvessl2D in tut looks likes the U is absolute velocity ![]() |
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#12 |
Senior Member
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#13 |
Senior Member
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#14 |
Senior Member
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#15 |
Senior Member
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Hi sorry
i try a lot here is the result of mixvessl2D(vector on the rotor),you can see clearly the velocity profile relative to the omega ![]() and then is my case a 3d centrifugal impeller a vector plot of U in the impeller z=1/2thick ![]() b vector plot on the blade ![]() |
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#16 |
Senior Member
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mix2d
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#17 |
Senior Member
Dragos
Join Date: Mar 2009
Posts: 648
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![]() Well in the picture I can see, the vectors look ok to me! Be careful to have pictures with dimensions of less than 50kb. Dragos |
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#18 |
Senior Member
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a vector plot of U in the impeller z=1/2thick
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#19 |
Senior Member
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b vector plot on the blade
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#20 |
Senior Member
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c relative velocity (at the same conditon) calculated by CFX
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