CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

MRFZonesC questions what is the mesh_V and why only Coriolis force no centrifugal force

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 1, 2008, 02:09
Default hi every one! i have some
  #1
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
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
waynezw0618 is offline   Reply With Quote

Old   April 1, 2008, 07:12
Default Hi Wayne, I think that in an
  #2
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 647
Rep Power: 11
dmoroian is on a distinguished road
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 is offline   Reply With Quote

Old   April 1, 2008, 07:13
Default ...and mesh_.V() retuns the ce
  #3
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 647
Rep Power: 11
dmoroian is on a distinguished road
...and mesh_.V() retuns the cell volume
dmoroian is offline   Reply With Quote

Old   April 1, 2008, 10:17
Default Hi Dragos: i don` think so.
  #4
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
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 is offline   Reply With Quote

Old   April 1, 2008, 10:20
Default i am sorry, there is a "*" be
  #5
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
i am sorry, there is a "*" before "omega U" for last two equ.it is typing error of mine

thanks
wayne
waynezw0618 is offline   Reply With Quote

Old   April 2, 2008, 02:22
Default I had a vague memory in the ba
  #6
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 647
Rep Power: 11
dmoroian is on a distinguished road
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
dmoroian is offline   Reply With Quote

Old   April 2, 2008, 04:29
Default Hi Dragos thanks a lot! i
  #7
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
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
waynezw0618 is offline   Reply With Quote

Old   April 2, 2008, 04:40
Default Hi Wayne, This is exactly wha
  #8
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 647
Rep Power: 11
dmoroian is on a distinguished road
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
dmoroian is offline   Reply With Quote

Old   April 3, 2008, 00:08
Default Hi Dragos but why the flow p
  #9
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
Hi Dragos
but why the flow pattern of the result looks like U is relative velocity

wayne
waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 01:09
Default well Wayne, if it is like that
  #10
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 647
Rep Power: 11
dmoroian is on a distinguished road
well Wayne, if it is like that I agree with you: it is strange.
Can you post a picture with an example?

Dragos
dmoroian is offline   Reply With Quote

Old   April 3, 2008, 02:41
Default Hi dragos the result of mixv
  #11
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
Hi dragos
the result of mixvessl2D in tut looks likes the U is absolute velocity

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 02:57
Default http://www.cfd-online.com/Open
  #12
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:18
Default
  #13
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:19
Default http://www.cfd-online.com/Open
  #14
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:35
Default Hi sorry i try a lot here i
  #15
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
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

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:44
Default mix2d http://www.cfd-online.c
  #16
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
mix2d

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:49
Default http://www.cfd-online.com/Open
  #17
Senior Member
 
dmoroian's Avatar
 
Dragos
Join Date: Mar 2009
Posts: 647
Rep Power: 11
dmoroian is on a distinguished road
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
dmoroian is offline   Reply With Quote

Old   April 3, 2008, 03:50
Default a vector plot of U in the impe
  #18
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
a vector plot of U in the impeller z=1/2thick

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:58
Default b vector plot on the blade ht
  #19
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
b vector plot on the blade

waynezw0618 is offline   Reply With Quote

Old   April 3, 2008, 03:59
Default c relative velocity (at the s
  #20
Senior Member
 
wayne.zhang
Join Date: Mar 2009
Location: Shanghai, Shanghai, P.R.China
Posts: 307
Rep Power: 9
waynezw0618 is on a distinguished road
Send a message via MSN to waynezw0618 Send a message via Skype™ to waynezw0618
c relative velocity (at the same conditon) calculated by CFX

waynezw0618 is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Centrifugal force/ Rotating Wall david FLUENT 4 January 2, 2014 07:30
centrifugal force sue FLUENT 0 November 25, 2008 04:01
cyclone separator- centrifugal force kumar FLUENT 2 May 29, 2008 03:33
Cyclone separator-centrifugal force aPpA FLUENT 0 July 6, 2005 14:22
Coriolis force Saturn FLUENT 5 September 30, 2004 15:56


All times are GMT -4. The time now is 10:53.