hi every one� i have some
 

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

thanks
wayne

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

...and mesh_.V() retuns the ce
 

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

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×(omega×r)-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

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

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

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

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

Hi Dragos but why the flow p
 

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

wayne

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

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

http://www.cfd-online.com/Open
 

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

 

http://www.cfd-online.com/Open
 

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

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

mix2d http://www.cfd-online.c
 

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

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

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

b vector plot on the blade ht
 

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

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

http://www.cfd-online.com/Open
 

http://www.cfd-online.com/OpenFOAM_D...ges/1/7188.jpg

b absolute velocity (at the sa
 

b absolute velocity (at the same conditon) calculated by CFX

http://www.cfd-online.com/Open
 

http://www.cfd-online.com/OpenFOAM_D...ges/1/7190.jpg

Hi i am sorry.too too much t
 

Hi
i am sorry.too too much try maybe.and also there is no velocity(U=0)in hub and shroud boundays in my result.but i think there should be angular velocity like mixvessl2d'rotor.
i do not know why,can you help me ?

I agree something is strange i
 

I agree something is strange in picture a and b. It looks like you are rotating the impeller in opposite direction to the one presented from cfx. However, what you show in a and b cannot be relative velocities since they are not along the blades (as seen in the first picture from cfx).

Dragos

i agree with " they are not al
 

i agree with " they are not along the blades",and they do not normal to the blade too.
and also there is velocity in the hub and the shroud (which is up and down boundary of the impeller).

what is wrong with it?
wayne

and also there is velocity in
 

and also there is velocity in the hub and the shroud (which is up and down boundary of the impeller)
--->
and also there is no velocity in the hub and the shroud (which is up and down boundary of the impeller)

sorry.

and look at next two picture (
 

and look at next two picture (1 is foam ,2 is CFX)
1
http://www.cfd-online.com/OpenFOAM_D...your_image.gif
2
http://www.cfd-online.com/OpenFOAM_D...your_image.gif
you can find in foam calculation before the flow goes in to the blade it does not rotate,which is quiet differet from CFX result.
it also happened in the inlet boundary
so i guess it may be because of the faceSet or boundary condition,i am not quiet sure.
what is your idea?
wayne

foam http://www.cfd-online.co
 

foam
http://www.cfd-online.com/OpenFOAM_D...ges/1/7194.jpg

cfx http://www.cfd-online.com
 

cfx
http://www.cfd-online.com/OpenFOAM_D...ges/1/7196.jpg

I still think the impeller in
 

I still think the impeller in foam computation spins in opposite direction to the one in cfx.
foam: +0z
cfx: -0z
Most likely this is due to the fact that you did not impose rotation on the hub.

Dragos

Hi I still think the impelle
 

Hi
i have checked that,the direction of rotation is the same in foam and cfx.or please look at the last two images,especially in cfx,the velocity vectors around axis (central of the blue circle in the underside of the cfx image,where the inlet pipe is nearby)are anticlockwise,if i impose a opposite direction,there would be an clockwise rotation for it near the inlet pipe,the roatation dirction of fluid in the inlet pipe and nearby will not intensively affect by the downstream.
so any other reasons?
_________________________________________________
Q2: how to impose the rotation on the hub? for the hub is wall,and MRFZones has boundary correction function which has impose the rotation to the boundary,and what will i do ? faceset(add hub and shroud to faceset or not delelet the boundary as what in the mixvessl2D?

by last, i mean in cfx result,
 

by last, i mean in cfx result, there is a rotation around the axia in evidence,the rotation direction is the same as i have imposed,but there is no rotation in Foam result.
i think it will a rotation of opposite diretion if i have spined a oppsite one

wayne

Can you display the MRFZones d
 

Can you display the MRFZones dictionary here?

Hi i am not working with my c
 

Hi
i am not working with my computer now.and i remember the omega is defined as [0 0 -1] 75.88
(impeller`s rotation speed is 725rpm, direction in -z).you could look at the "cfx" image carefully.at the right corner,z is to the inner,and the vector arround the inlet is clockwise.and angular velocity is in the -z.

wayne

This is why I want to see your
 

This is why I want to see your dictionary, because my impression is that you have a rotation axis defined as

axis axis [0 0 0 0 0 0 0] (0 0 1);

in foam. So please post it when you will be able to.

Hi i am sorry for i am aw
 

Hi
i am sorry for i am away for the passed few days. and now i am back to my office.
i have check for that right now,and you are right, i gave a wrong rotation axis dirction.i will modified it.
by how to impose the rotation to the boundary? do i need a faceSet?or others?

No you don't have to impose th
 

No you don't have to impose the velocity on the rotating wall. You just specify a normal wall "fixedValue" condition. If it is inside the rotating zone, then it will now how to impose the velocity correctly.

I'm glad you found the error,
Dragos

Hi how to impose? i try to m
 

Hi
how to impose?
i try to make a faceset like:

name IMPELLLER;//name of the cellzone
action new;
topoSetSources
(
boundaryToFace
{
}
);

and then modify the MRFZones Dictionary as:

5 //number of my rotating boundary..
（
IMPELLER //my cellZone
{
patches (HUB);//HUB is one of the rotating zone
origin origin [0 1 0 0 0 0 0] (0 0 0);
axis axis [0 0 0 0 0 0 0] (0 0 -1);
omega omega [0 0 -1 0 0 0 0] 75.92;
}
....//other rotating boundary such as shroud blade and so on
)

and specify all normal wall "fixedValue"

is that right?

wayne

and here is the vector of U on
 

and here is the vector of U on "HUB" whichi is rotating
http://www.cfd-online.com/OpenFOAM_D...ges/1/7233.jpg