CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

problems with simple algorithm(by patankar)

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

Reply
 
LinkBack Thread Tools Display Modes
Old   August 19, 2009, 12:18
Default problems with simple algorithm(by patankar)
  #1
New Member
 
E jav
Join Date: Aug 2009
Posts: 3
Rep Power: 10
jav1984 is on a distinguished road
I have some questions about SiMPLE algorithm based on Patankar's book.
on page 123 step 2 of algorithm:solving u* and v*(for 2D problem).to writing a fortran
code for this algorithm I have a confusing problem.if we note at eq. 6.8 & 6.9 the nodes that
are involved in two equations are not the same!(because the first eq is
written for sataggerd grid at x direction,the second is at y directin)
for example in the coefficient aE(for solving ue)there is FE=rho*uE(u*E)
we konw that UE is velocity in main point that is not calculated in this
eq.shoud I interpolate UE=0.5*(ue+uc)?
2-in coefficient aN there is Fb=rho*Vb,my outcome(guess)isvb is unknwon which should be guessed at the first
and after solving u*,we should enter the coefficient of anb based on
calculated v*,then use these V* adgain for coeficeint u* and repete
this to converge).is my guess(the sentence in pranteses) true? if it is true
we know that the nodes that their velocity entered in these two eq are
not the same! what shoud I do?
3-how should I apply boundary condition for staggered grid?(for example
at enterance we know velocity for main point)
4-if we have a solid in our domain shoud we define gamma as an array or as a parameter?
(we should attribute gamma=infinity for solid )

please help me
thanks
jav1984 is offline   Reply With Quote

Old   November 3, 2017, 21:57
Default
  #2
New Member
 
Francisco Angel
Join Date: Dec 2012
Posts: 21
Rep Power: 7
francisco.angel is on a distinguished road
Quote:
Originally Posted by jav1984 View Post
I have some questions about SiMPLE algorithm based on Patankar's book.
on page 123 step 2 of algorithm:solving u* and v*(for 2D problem).to writing a fortran code for this algorithm I have a confusing problem.if we note at eq. 6.8 & 6.9 the nodes that are involved in two equations are not the same!(because the first eq is written for sataggerd grid at x direction,the second is at y directin) for example in the coefficient aE(for solving ue)there is FE=rho*uE(u*E) we konw that UE is velocity in main point that is not calculated in this eq.shoud I interpolate UE=0.5*(ue+uc)?
Yes, that would be an approach, but the simple average approximation is not too good, due to that you use schemes like upwind for example, that Patankar discusses in a previous chapter.

[QUOTE=jav1984;226857]
2-in coefficient aN there is Fb=rho*Vb,my outcome(guess)isvb is unknwon which should be guessed at the first and after solving u*,we should enter the coefficient of anb based on calculated v*,then use these V* adgain for coeficeint u* and repete this to converge).is my guess(the sentence in pranteses) true? if it is true we know that the nodes that their velocity entered in these two eq are not the same! what shoud I do?
[QUOTE]

I didn't understand you quite well, but basically you have (rho*vn)*vn the vn inside the parenthesis is the guessed value that you ends up in the aN coefficient, the second vn is the unknown, the SIMPLE algorithm is an iterative procedure so you keep updating velocities and consequently a's (coefficients). Remember that all flow terms could require a scheme like SIMPLE.

[QUOTE=jav1984;226857]
3-how should I apply boundary condition for staggered grid?(for example at entrance we know velocity for main point)
[QUOTE]

It depends on the boundary condition, if you know the value of velocity you just use it like always in the momentum equations, in the continuity equation you use this correct value instead of u* + ( p' - p' i-1)d to generate an equation for the pressure correction values adyacent to the boundary.

[QUOTE=jav1984;226857]
4-if we have a solid in our domain shoud we define gamma as an array or as a parameter?
(we should attribute gamma=infinity for solid )

It's not so easy to to treat an inmersed solid, you can approximate the solid boundary to match some grid lines and apply the v=0 (no slip) boundary condition at those grid lines.

please help me
[QUOTE]
thanks
francisco.angel 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
unsteady flow problems Daniel FLUENT 0 January 26, 2009 00:54
Problems with Fluent on simple 1D problems agg FLUENT 3 November 21, 2008 12:55
problems with VERY simple mesh Ralf Schmidt FLUENT 7 October 17, 2006 07:21
unstructured grid sreekanth Main CFD Forum 1 August 6, 2001 15:09
Inverse problems Aleksey Alekseev Main CFD Forum 0 May 12, 1999 15:38


All times are GMT -4. The time now is 23:32.