
[Sponsors] 
buoyantBoussinesqPimpleFoam gives incorrect results for nonsteady laminar flows 

LinkBack  Thread Tools  Display Modes 
February 28, 2012, 14:00 
buoyantBoussinesqPimpleFoam gives incorrect results for nonsteady laminar flows

#1 
New Member
Join Date: May 2010
Posts: 1
Rep Power: 0 
Hello everybody,
We consider classical 2D RayleighBenard convection in a domain with aspect ratio sqrt(2)x1 (sqrt(2) is half of the length of the periodicity cell according to linear theory). At the lower and upper boundaries we set slip conditions ("Rayleigh conditions"), at the left and right boundaries there are also slip conditions (so there are no traveling waves and mean horizontal flow). For the nondimensional parameters Pr=11.5968, Ra=56931 there must be a periodic solution (we have already obtained it by means of our own pseudospectral method). The flow modeled with our pseudospectral code (64x64) can be seen here http://sibgat.imec.msu.ru/convOF/lin...lines3_c_1.avi It can be considered as "exact" solution. Now we take the hotroom case and transform it to the described problem, setting RASModel to laminar and corresponding dimensional parameters to h = 0.1 (height) L = 0.1*sqrt(2) (horizontal length) blockMeshDict (60 40 1) nu = 1.567e−6 beta = 3.072e−6 Tb = 277.2 (temperature at the lower boundary) Tu = 276.8 (at the upper boundary) Tref = Tb This gave wrong results in buoyantBoussinesqPimpleFoam, as can be seen here http://sibgat.imec.msu.ru/convOF/OFconv4.23.8.mpeg This regime obviously converges to steady mode. BuoyantBoussinesqPisoFoam in OF 1.6 gave chaotic motion which does not seem to converge to periodic motion. Playing with tolerances, nCorrectors, timeintegrators, mesh did not give correct results. Have anybody compared any of these solvers with timedependent (periodic for instance) laminar flow? I hope very much there is a solution to this problem... Thank you! 

February 29, 2012, 07:22 

#2 
Senior Member
Olivier
Join Date: Jun 2009
Location: France, grenoble
Posts: 252
Rep Power: 9 
hello,
This is an interesting test case, so if you can share your final conclusion & tests, this will be very estimate. In the hotroom case, in fvSchemes, almost all div scheme use Gauss upwind ... Maybe try with less diffusive 2nd order scheme ? regards, olivier 

March 2, 2012, 10:06 

#3 
New Member

Hi,
I also met some problem with buoyantBoussinesqPimpleFoam solver for transient laminar flows. What I am modelling is the benchmark problem  flow over a cylinder. I set RASModel to laminar and switch off the turbulent. Make Reynold number to 75 and temperature is set to 289 K in the whole domain. All turbulent parameters in the 0 subdirectory are set to 0, e.g. alphat, epsilon, k, kappat, nut. Boundaries: left_inlet ( T=289 K, p_rgh buoyantPressure 0); right_outlet ( T zeroGradient, p_rgh buoyantPressure 0), up and down are symmeyPlane. The weird thing is that the temperature near the backward of the cylinder decreases. And the velocity field also goes wrong. http://profile.imageshack.us/user/shuiquanlan/ Last edited by aaron_lan; March 2, 2012 at 10:26. 

March 5, 2012, 08:52 

#4 
New Member
Sinisa Majer
Join Date: Oct 2009
Location: Zagreb, CROATIA
Posts: 8
Rep Power: 8 
Which version of the OF do you use? Is it 1.6ext or 'original' 1.6 supported by OpenCFD?


March 6, 2012, 12:17 

#5 
New Member

I am using the latest version 2.1.0. I am still struggling with this mixed convection over cylinder problem. With buoyantBoussinesqPimpleFoam solver, I modeled natural convection in a cavity and natural convection over a cylinder successfully. But when I come to the forced convection over a cylinder, simulations go wrong. The situation for mixed convection (combine natural convection and forced convection over a cylinder) is worse.


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Backup results in steady simulation  Li  CFX  0  July 9, 2007 05:39 
using steady state results for unsteady flow  siva appanna  Main CFD Forum  3  February 20, 2006 06:29 
Unsteady laminar flows  Seeker Philip  FLUENT  1  July 14, 2005 07:50 
Difference results between Steady and Unsteady?  Giang T Vu  FLUENT  6  May 22, 2004 06:37 
Any desired level of accuracy in laminar flows?  gorka  Main CFD Forum  6  April 1, 2003 14:41 