|
[Sponsors] |
How do I make steady state SIMPLE solver to transient? |
![]() |
|
LinkBack | Thread Tools | Search this Thread | Display Modes |
![]() |
![]() |
#1 |
Member
Join Date: Feb 2019
Posts: 69
Rep Power: 7 ![]() |
I am referring to the book by H.K.Versteeg and he mentioned the following modifications,
1) Adding a^0_P to the central coefficient a_P 2) Pressure correction equation must include the unsteady continuity equation effect (rho^0-rho)*DV/Dt. However, since I am using incompressible flow, I just assume this as zero. 3) The time-stepping procedure creates an extra loop outside the main iteration cycles of SIMPLE. I am confused by the third step as I thought that the iteration step of SIMPLE to convergence can be used as the time-stepping procedure. However, my thought is not correct as the solver produces different convergence result when different dt is used, which I think is the solver converging after making that particular timestep. (Smaller dt gives a less varied result) Hence, does this mean that for n-number of timesteps, I need to make n-number of SIMPLE solver convergence? If yes, how do I add this time-stepping loop outside the SIMPLE solver? The SIMPLE solver already gives me the corrected momentum & pressure for the next timestep already and thus, what do I need to do outside the SIMPLE loop while inside the time-stepping loop? |
|
![]() |
![]() |
![]() |
![]() |
#2 | ||
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,728
Rep Power: 66 ![]() ![]() ![]() |
Quote:
Quote:
Once you add the transient terms from step 1), which will also contain a dt in it, you get a very similar linear system that needs to be solved the same way. At the end of this you get the solution at the next time-step. Then you just keep repeating this until you get to your desired solution time. The main cycles of SIMPLE needs to converge iteratively for a single time-step. Then you just march it forward in time . Last edited by LuckyTran; April 20, 2020 at 11:21. |
|||
![]() |
![]() |
![]() |
![]() |
#3 | |
Member
Join Date: Feb 2019
Posts: 69
Rep Power: 7 ![]() |
Quote:
My algorithm looks something like this, for t=1:NumberTime time=dt*t; u0=u; v0=v; p0=p; [u,v,p]=SIMPLE(u0,v0,p0) end Is this correct? I don't think so as my solver basically stuck at the first successful timestep. After one timestep when the SIMPLE produces the converged result, this converged result get "reused" by SIMPLE which basically just converge the result further. As the result is already converged, the result remains the same for the subsequent timesteps. There is something wrong with my understanding as I don't get how to shift it to the next timestep! |
||
![]() |
![]() |
![]() |
![]() |
#4 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,830
Rep Power: 73 ![]() ![]() ![]() |
Quote:
Have a look to the Ferziger, Peric, Street textbooks, there is a chapter devoted to the transient method. Furthermore, you could also think to use a fractional time step. |
||
![]() |
![]() |
![]() |
![]() |
#5 |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,728
Rep Power: 66 ![]() ![]() ![]() |
You will need to keep a copy of the same initial solution at every SIMPLE iteration as well as the latest implicit solution.
You probably just didn't do 1) correctly if your solution isn't going anywhere. |
|
![]() |
![]() |
![]() |
![]() |
#6 | ||
Senior Member
duri
Join Date: May 2010
Posts: 245
Rep Power: 17 ![]() |
Quote:
Are you using three sets of variable for n, n-1 and old. The old variable is not same as n-1 except for the first iteration of each time step. At each iteration n-1 should be replaced by n till the convergence. After convergence old variable should be replaced with converged solution. Quote:
|
|||
![]() |
![]() |
![]() |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
Convergence in steady state simulations vs transient ones | cardioCFD | CFX | 5 | January 21, 2018 10:59 |
Solver for transonic flow? | Martin Hegedus | OpenFOAM Running, Solving & CFD | 22 | December 16, 2015 04:59 |
error message | cuteapathy | CFX | 14 | March 20, 2012 06:45 |
TUI Transient solver to Steady solver | mbell10 | FLUENT | 1 | February 2, 2011 08:53 |
Constant velocity of the material | Sas | CFX | 15 | July 13, 2010 08:56 |