# buoyantBoussinesqPimpleFoam gives incorrect results for non-steady laminar flows

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 February 28, 2012, 14:00 buoyantBoussinesqPimpleFoam gives incorrect results for non-steady laminar flows #1 New Member   Join Date: May 2010 Posts: 1 Rep Power: 0 Sponsored Links Hello everybody, We consider classical 2D Rayleigh-Benard 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 non-dimensional 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/OFconv4.2-3.8.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, time-integrators, mesh did not give correct results. Have anybody compared any of these solvers with time-dependent (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: 266 Rep Power: 11 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   slan Join Date: Nov 2010 Location: Eindhoven Posts: 16 Rep Power: 8 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: 9 Which version of the OF do you use? Is it 1.6-ext or 'original' 1.6 supported by OpenCFD?

March 6, 2012, 12:17
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slan
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Quote:
 Originally Posted by smajer Which version of the OF do you use? Is it 1.6-ext or 'original' 1.6 supported by OpenCFD?
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.

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