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krsp June 14, 2012 08:07

Flow around cylinder, forcing term
Hi everyone,

I am a new FOAM user and I am trying to model an oscillating (sinusoidal) flow around a free circular cylinder in 2D. I have some trouble, trying to add a forcing term to the UEqn. (I use a pimpleFoam solver).

The UEqn looks like this:

================================================== ======
dimensionedVector forcing(
(Um1*omega*Foam::cos(omega*runTime.value()) + slope)*forceDir

fvVectorMatrix UEqn
+ fvm::div(phi, U)
+ turbulence->divDevReff(U)
- forcing
if (ocorr != nOuterCorr-1)
if (momentumPredictor)
solve(UEqn == -fvc::grad(p)); // forcing is included in UEqn
================================================== ======

It all runs fine with no errors, however the velcity accelerates. This means that if Um1 is eg. 0.2 m/s, then in the beginning Ux oscillates between (-0.2 ; 0.2). But after some time it increases/decreases to oscillate between eg. (0 ; 0.4), (0.2 ;0.6), (0.4 ; 0.8) etc.
I'm thinking, that a pressure gradient is developing, but I don't know why..

I have zeroGradient conditions for both velocity and pressure at inlet+outlet. The top and bottom boundaries are both slip.

Does anyone have an idea of, what I have done wrong? (I use OpenFoam 1.6-ext).

Thanks in advance :)

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