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-   -   MRFZonesC questions what is the mesh_V and why only Coriolis force no centrifugal force (http://www.cfd-online.com/Forums/openfoam-solving/58976-mrfzonesc-questions-what-mesh_v-why-only-coriolis-force-no-centrifugal-force.html)

waynezw0618 April 1, 2008 02:09

hi every one! i have some
 
hi every one!
i have some question about MRFZones.C
in void Foam::MRFZone::addCoriolis(fvVectorMatrix& UEqn) const:

Quote:

const labelList& cells = mesh_.cellZones()[cellZoneID_];
const scalarField& V = mesh_.V();Q1:what is the mesh_.V()?
....

forAll(cells, i)
\ {
Usource[cells[i]] -= V[cells[i]]*(Omega ^ U[cells[i]]);
Q2:here coriolis force is equal to "omega u",but i think it should be "1/2 * omega u" and also there is no centrifugal force which is "omega(omegar)",so if i want to calculate the flow in the turbins? would i need to modify the them both?
}

thanks
wayne

dmoroian April 1, 2008 07:12

Hi Wayne, I think that in an
 
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

dmoroian April 1, 2008 07:13

...and mesh_.V() retuns the ce
 
...and mesh_.V() retuns the cell volume

waynezw0618 April 1, 2008 10:17

Hi Dragos: i don` think so.
 
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

waynezw0618 April 1, 2008 10:20

i am sorry, there is a "*" be
 
i am sorry, there is a "*" before "omega U" for last two equ.it is typing error of mine

thanks
wayne

dmoroian April 2, 2008 02:22

I had a vague memory in the ba
 
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:
where the relative velocity is:
and the transport velocity is:

You can also check the fluent user manual for it.

I hope this is helpful,
Dragos

waynezw0618 April 2, 2008 04:29

Hi Dragos thanks a lot! i
 
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

dmoroian April 2, 2008 04:40

Hi Wayne, This is exactly wha
 
Hi Wayne,
This is exactly what it is written in the momentum predictor:


tmp<fvvectormatrix> UEqn
(
<blockquote>fvm::div(phi, U)
+ turbulence->divR(U)
);
</blockquote>

Dragos

waynezw0618 April 3, 2008 00:08

Hi Dragos but why the flow p
 
Hi Dragos
but why the flow pattern of the result looks like U is relative velocity

wayne

dmoroian April 3, 2008 01:09

well Wayne, if it is like that
 
well Wayne, if it is like that I agree with you: it is strange.
Can you post a picture with an example?

Dragos

waynezw0618 April 3, 2008 02:41

Hi dragos the result of mixv
 
Hi dragos
the result of mixvessl2D in tut looks likes the U is absolute velocity
http://www.cfd-online.com/OpenFOAM_D...your_image.gif

waynezw0618 April 3, 2008 02:57

http://www.cfd-online.com/Open
 
http://www.cfd-online.com/OpenFOAM_D...your_image.gif

waynezw0618 April 3, 2008 03:18


 


waynezw0618 April 3, 2008 03:19

http://www.cfd-online.com/Open
 
http://www.cfd-online.com/OpenFOAM_D...ges/1/7177.jpg

waynezw0618 April 3, 2008 03:35

Hi sorry i try a lot here i
 
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
http://www.cfd-online.com/OpenFOAM_D...your_image.gif
and then is my case a 3d centrifugal impeller
a vector plot of U in the impeller z=1/2thick
http://www.cfd-online.com/OpenFOAM_D...your_image.gif
b vector plot on the blade
http://www.cfd-online.com/OpenFOAM_D...your_image.gif

waynezw0618 April 3, 2008 03:44

mix2d http://www.cfd-online.c
 
mix2d
http://www.cfd-online.com/OpenFOAM_D...ges/1/7180.jpg

dmoroian April 3, 2008 03:49

http://www.cfd-online.com/Open
 
http://www.cfd-online.com/OpenFOAM_D...part/happy.gif Lots of tries!
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

waynezw0618 April 3, 2008 03:50

a vector plot of U in the impe
 
a vector plot of U in the impeller z=1/2thick
http://www.cfd-online.com/OpenFOAM_D...ges/1/7182.jpg

waynezw0618 April 3, 2008 03:58

b vector plot on the blade ht
 
b vector plot on the blade
http://www.cfd-online.com/OpenFOAM_D...ges/1/7184.jpg

waynezw0618 April 3, 2008 03:59

c relative velocity (at the s
 
c relative velocity (at the same conditon) calculated by CFX
http://www.cfd-online.com/OpenFOAM_D...your_image.gif


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