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

SIMPLE algorithm-Please help

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

Reply
 
LinkBack Thread Tools Display Modes
Old   October 6, 2009, 06:56
Post SIMPLE algorithm-Please help
  #1
New Member
 
Thiyagarajan dhayalan
Join Date: Jun 2009
Posts: 7
Rep Power: 8
Thiyaga is on a distinguished road
hi,
i tried to write a code for SIMPLE algorithm in Fortran but found it difficult. can anyone give a sample code on SIMPLE.my mail id is rajandhayalan@gmail.com
thank you
regards
Thiyaga.
Thiyaga is offline   Reply With Quote

Old   October 6, 2009, 09:56
Default
  #2
New Member
 
zoheb
Join Date: Mar 2009
Location: india, mumbai
Posts: 24
Rep Power: 8
zobekenobe is on a distinguished road
are you writing it with colocated grids and staggered grids
zobekenobe is offline   Reply With Quote

Old   October 7, 2009, 03:05
Post Simple
  #3
New Member
 
Thiyagarajan dhayalan
Join Date: Jun 2009
Posts: 7
Rep Power: 8
Thiyaga is on a distinguished road
hi,
thanks for the reply.iam using staggered grid.
reg
Thiyaga.
Thiyaga is offline   Reply With Quote

Old   October 8, 2009, 06:08
Default
  #4
New Member
 
Ammar Mushtaq
Join Date: Oct 2009
Location: Islamabad, Pakistan
Posts: 2
Rep Power: 0
Ammar Mushtaq is on a distinguished road
Send a message via Skype™ to Ammar Mushtaq
have u tried veersteeg's book, coz the algorithm in it is almost the code. I have implimented it in mathematica.
Ammar Mushtaq is offline   Reply With Quote

Old   October 9, 2009, 01:46
Default
  #5
New Member
 
Thiyagarajan dhayalan
Join Date: Jun 2009
Posts: 7
Rep Power: 8
Thiyaga is on a distinguished road
hi,
thx , i will try...
Thiyaga is offline   Reply With Quote

Old   October 17, 2009, 11:01
Default
  #6
Member
 
jk
Join Date: Jun 2009
Posts: 64
Rep Power: 8
jyothishkumar is on a distinguished road
Hi Ammar,

I tried with verteeg's book only. But the solution is blowing out (simple algorithm). Please check whether my following boundary conditions are correct:

firstof all i am using staggered grid (backward) and using Explicit scheme.

Assume it is a duct flow --> two walls on the upper and lower side (v velocity = 0), leftside --> inlet (u velocity) and rightside -->outlet (pressure outlet) but the u velocity grid would be the last on the right side

I have just created a dummy nodes outside the main domain (as mentioned in the book).
my domain size is 0.09m by 0.09m, height 0.08m. Grid size is 20 by 20
1. On the inlet i am giving u velocity = 0.1 m/s
2. On the outlet i am extrapolating this u velocity as given in the book
3. On the top and bottom wall my v velocity = 0
4. on the right side (just before the u node -- outlet) i am fixing the pressure as 0

I have doubt in the pressure correction (pprime) bc.

1. On all the sides i am setting the value of pprime = 0.

Withall this my solution is blowing out after few iterations (5 iterations)

Also for the simplicity i am keeping the value of meu and row as constant in all the equations (common row(density) taking out from the equations and canceling). I am not doing any averaging on this scalars. If you wish i can send my code also (its fully commented)
Your suggestion is highly appreciable.

thanks

jyo

Last edited by jyothishkumar; October 17, 2009 at 11:35.
jyothishkumar is offline   Reply With Quote

Old   October 17, 2009, 17:52
Default
  #7
Member
 
Join Date: Apr 2009
Posts: 35
Rep Power: 8
artemiss1984 is on a distinguished road
Dear friend. you should tell more details about your problem. your geometry.boundary conditions and...
maybe I can help you

Quote:
Originally Posted by Thiyaga View Post
hi,
i tried to write a code for SIMPLE algorithm in Fortran but found it difficult. can anyone give a sample code on SIMPLE.my mail id is rajandhayalan@gmail.com
thank you
regards
Thiyaga.
artemiss1984 is offline   Reply With Quote

Old   October 17, 2009, 18:15
Default
  #8
Member
 
Join Date: Apr 2009
Posts: 35
Rep Power: 8
artemiss1984 is on a distinguished road
what are the values of under-relaxation for velocity and pressure?
you should set the pprime value zero at the beginning of each iteration.
for B.cs usually the outlet boundary is difficult to set.

Quote:
Originally Posted by jyothishkumar View Post
Hi Ammar,

I tried with verteeg's book only. But the solution is blowing out (simple algorithm). Please check whether my following boundary conditions are correct:

firstof all i am using staggered grid (backward) and using Explicit scheme.

Assume it is a duct flow --> two walls on the upper and lower side (v velocity = 0), leftside --> inlet (u velocity) and rightside -->outlet (pressure outlet) but the u velocity grid would be the last on the right side

I have just created a dummy nodes outside the main domain (as mentioned in the book).
my domain size is 0.09m by 0.09m, height 0.08m. Grid size is 20 by 20
1. On the inlet i am giving u velocity = 0.1 m/s
2. On the outlet i am extrapolating this u velocity as given in the book
3. On the top and bottom wall my v velocity = 0
4. on the right side (just before the u node -- outlet) i am fixing the pressure as 0

I have doubt in the pressure correction (pprime) bc.

1. On all the sides i am setting the value of pprime = 0.

Withall this my solution is blowing out after few iterations (5 iterations)

Also for the simplicity i am keeping the value of meu and row as constant in all the equations (common row(density) taking out from the equations and canceling). I am not doing any averaging on this scalars. If you wish i can send my code also (its fully commented)
Your suggestion is highly appreciable.

thanks

jyo
artemiss1984 is offline   Reply With Quote

Old   October 18, 2009, 00:56
Default pprime initialisation
  #9
Member
 
jk
Join Date: Jun 2009
Posts: 64
Rep Power: 8
jyothishkumar is on a distinguished road
Hi Artmiss,

I did the initialization of pprime. My urf for u and v, pressure is 0.3.

for the outlet boundary since i am giving the pressure outlet (0 value -- gauge) my pprime would be zero at the outlet as there are no corrections

my u and v velocities are going very high values and finally diverges.


any suggestions

thanks

jyo
jyothishkumar is offline   Reply With Quote

Old   October 18, 2009, 07:58
Default
  #10
New Member
 
Join Date: Oct 2009
Posts: 7
Rep Power: 7
amirbabak1979 is on a distinguished road
Dear jyo,

Put The relaxation factor for U and V around 0.3-0.4 and for Pressure around 0.1. You should notice that relaxation factor for pressure should be less than for U and V ones.

The other thing is before you wanna call your pressure boundary and solver
you should put pprime=0.0 in the main Do of your program.

hope it will work.


Quote:
Originally Posted by jyothishkumar View Post
Hi Artmiss,

I did the initialization of pprime. My urf for u and v, pressure is 0.3.

for the outlet boundary since i am giving the pressure outlet (0 value -- gauge) my pprime would be zero at the outlet as there are no corrections

my u and v velocities are going very high values and finally diverges.


any suggestions

thanks

jyo
amirbabak1979 is offline   Reply With Quote

Old   October 18, 2009, 15:25
Default
  #11
Member
 
Join Date: Apr 2009
Posts: 35
Rep Power: 8
artemiss1984 is on a distinguished road
Dear friend. perform the suggestions of Mr. babak.The SIMPLE algorithm is very sensitive to urf's especially when Re increased.Don't use the values suggested in commercial soft wares. I doubt the reality of convergence with this urf's!
for final check tell me the method of calculation of u and v at solid boundaries.it is important


Quote:
Originally Posted by jyothishkumar View Post
Hi Artmiss,

I did the initialization of pprime. My urf for u and v, pressure is 0.3.

for the outlet boundary since i am giving the pressure outlet (0 value -- gauge) my pprime would be zero at the outlet as there are no corrections

my u and v velocities are going very high values and finally diverges.


any suggestions

thanks

jyo
artemiss1984 is offline   Reply With Quote

Old   October 19, 2009, 04:15
Default
  #12
Member
 
jk
Join Date: Jun 2009
Posts: 64
Rep Power: 8
jyothishkumar is on a distinguished road
Thanks and i will do that
jyothishkumar is offline   Reply With Quote

Old   October 21, 2009, 08:40
Default
  #13
Member
 
jk
Join Date: Jun 2009
Posts: 64
Rep Power: 8
jyothishkumar is on a distinguished road
Hi,

Again i have restructured my grid pattern in the following manner. I am now giving pressure inlet and pressure outlet boundary. Even on the wall (top and bottom) also i have my pressure and u velocity grid to coincide. This way i am sure about the pprime values at the boundary. Now my pprime value on the left and right side (inlet and exit) boundary will be zero. On the wall i am doing pwall = p(i,1) = 2*p(i,2) - p(i,3), similarly i am doing for pprime also. One more thing that i want to clarify is that i am fixing the value of row and meu everywhere (in the scalar grid points). Is that fine what i am doing. (still on the process of writing the code) Any suggestions ?

thanks

jyo
jyothishkumar is offline   Reply With Quote

Reply

Tags
simple

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
SIMPLE algorithm in 3D cylindrical coordinates zouchu Main CFD Forum 1 January 20, 2014 18:02
SIMPLE algorithm jika Main CFD Forum 2 October 22, 2009 06:46
About Phase Coupled SIMPLE (PC-SIMPLE) algorithm Yan Kai Main CFD Forum 0 April 18, 2007 03:48
About Phase Coupled SIMPLE (PC-SIMPLE) algorithm Yan Kai FLUENT 0 April 13, 2007 23:17
SIMPLE algorithm Jonathan Castro Main CFD Forum 3 December 10, 1999 05:59


All times are GMT -4. The time now is 18:37.