Discussion Forum » Code_Saturne » Pressure Fluctuations

http://cfd.mace.manchester.ac.uk/twiki/bin/view/Main/PressureProblem

My problem is very simple: when I impose a fluctuating mass flow rate using usclim in a LES or URANS simulation, I obtain non-physical pressure fluctuations all over the channel , which can actually lead even to a positive pressure gradient. It seems there is a connection between the derivative of the mass flow I impose and the pressure gradient I obtain.

My problem is that theoretically I would expect obviously the pressure gradient to fluctuate but never to switch the sign as long as the mass flow rate is positive!!

-- RuggeroPoletto - 2011-01-18

Solved (at least for now!)

-- RuggeroPoletto - 2011-01-18

how?

-- JuanUribe - 2011-01-18

Basically in the case of unsteady flow the NS equation becomes:

dU / dt + Convective = - dp / dx + diffusion

so the pressure gradient may result positive in case the velocity is time dependent!!

The problem came in my mind because of the pressure fluctuations obtained using the DF-SEM, which prescribe a fluctuating massflow rate (and so inlet velocity) to the simulation. At the moment we are thinking of rescaling the whole velocity field ...

I'll let you know further results!

-- RuggeroPoletto - 2011-01-18

Topic revision: r3 - 2011-01-18 - 11:22:54 - RuggeroPoletto

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