
[Sponsors] 
October 9, 2015, 20:22 
Incompressible solver for unsteday flow in SU2

#1 
New Member
Join Date: Oct 2015
Posts: 3
Rep Power: 4 
I am a beginner of SU2. For my research, the flow is lowmach, incompressible flow. However, I found in SU2_AIAA_ASM2013 that it says SU2 only vaild for steadystate only.
Also, this threads, http://www.cfdonline.com/Forums/su2...lesolver.html And all incompressible test cases officially provided by SU2 developers are all steady cases. Recently, I tried a case, a rigid beam in channel. I can't get the right flow field. The velocity distribution are totally different with ABAQUS/CFD at the same physical time with same material parameters. So, here, can anybody tell more details about SU2's incompressible solver using Artificial Compressibility method? This bothers me for a long while. 

October 16, 2015, 07:08 

#2 
Senior Member
Vino
Join Date: Mar 2013
Posts: 128
Rep Power: 7 
Hi Bravo,
you can do both steady and unsteady flow simulation of incompressible flows using SU2. 

October 16, 2015, 08:42 

#3 
New Member
Join Date: Oct 2015
Posts: 3
Rep Power: 4 
Hi Vino, thanks for your reply. Can I ask some further questions?
For unsteady incompressible flow, are both the Time stepping and Dual Time stepping good enough? When I do the unsteady flow, it needs thousands of internal iterations in one external iteration to get a good result. Is this common? 

October 19, 2015, 01:54 

#4 
Senior Member
Vino
Join Date: Mar 2013
Posts: 128
Rep Power: 7 
Bravo, its very common to use 1000 internal iterations if you are using explicit time marching, because of CFL limitations. You can go ahead with implicit time marching with very high CFL to get it done in Less that 100 iterations. This is a general idea. explore for your particular applications.


October 19, 2015, 10:31 

#5  
New Member
Join Date: Oct 2015
Posts: 3
Rep Power: 4 
Quote:
Thank you again! You suggestion is helpful to CFD beginners as me! 

October 30, 2015, 15:26 
Incompressible solver for unsteday flow in SU2

#6  
New Member
Juan J. Alonso
Join Date: Jan 2013
Posts: 4
Rep Power: 7 
Quote:
Indeed, as Vino says, SU2 can handle both steadystate and unsteady problems. Let me clarify the content of the discussion a bit further. If you choose an explicit time step, that means that every cell in the mesh gets advanced forward in time with the same time step, explicitly: no inner iterations required. This time step is the smallest allowable time step in the entire grid (by the CFL condition) which is normally found in the smallest cells in the mesh. For viscous problems, this time step is usually very, very small, which means that, to cover a given amount of physical time (say you want to see what the flow does over a physical time period of 1 second) you may need to do a very large number (in the thousands to tens of thousands or more) of time steps. But this works. In general, it is more efficient to solve for the unsteady solution using an implicit timeadvancement scheme such as the BDF2 (Backwards Difference Formula, 2nd order in time) in SU2. Using BDF2, the advancement of the solution in each physical time step is cast as an implicit solution that requires a number of inner iterations to converge as far as needed (from about 50100 if you have an inviscid problem with multigrid, to ~1,000 for RANS without multigrid). You have to tweak the parameters of the scheme to get as fast an inneriteration convergence as possible, to minimize the overall cost of the unsteady simulation. You also have to decide how far to converge each inner iteration:2 orders of magnitude is typically enough. Good luck! Juan 

February 21, 2017, 07:15 
Incompressible solver for unsteday flow in SU2

#7 
New Member
Cosmin
Join Date: Sep 2016
Posts: 1
Rep Power: 0 
Hi,
I have been using SU2 for a number of flow problems involving incompressible formulation for steady state case, which provided extremely good results. After that, I wanted to try an unsteady simple case (i.e. flow around a cylinder ) in order to get the frequency of the vortex shedding in the wake of the cylinder but with no success whatsoever (i.e. validation). The boundary conditions are the same, just like in the TestCase (i.e. farfield and noslip). I am using a physical time of 20s and a time step of 0.05 s with a 200 internal interations/external iteration (dualtime stepping with implicit euler for time advancement) => 400 iterations. The simulation is done for Re =100 using two different flow numerical methods (i.e. JST/ ROE). The methods provided different results in terms of Lift coefficient amplitude, but neither of them is in accordance with benchmark results (approx. cl=0.3). I also use 3 levels of multigrid (V_cycle). I have attached also 4 pictures with my results. Therefore, the next question: 1) Is there some kind of another scaling factor?Or am I missing something?or is just not possible to do transient incompressible problems? Lift JST.png Drag JST.png Drag ROE.png Lift ROE.png Thank you, 

April 12, 2017, 23:22 
Turbulence intensity plotting

#8 
New Member
jini
Join Date: Mar 2017
Posts: 2
Rep Power: 0 
How to plot the turbulent intensity in paraview?


Tags 
incompressible flow, su2 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Solver for an incompressible, turbulent flow with heat transfer  tH3f0rC3  OpenFOAM Running, Solving & CFD  8  February 22, 2018 01:28 
Transition SST komega and solver choice for incompressible flow over wing  Aeronautics El. K.  FLUENT  0  August 4, 2014 18:33 
How is the accuracy using VOF (pressure based solver) on supersonic flow  air_fun  Fluent Multiphase  0  June 18, 2014 13:06 
Incompressible, Unsteady Cylinder Flow  startingcfd  Main CFD Forum  1  March 15, 2011 02:12 
Incompressible flow solver (staggered grid)  J. Ehrhard  Main CFD Forum  1  October 8, 1998 19:47 