# convergence of pressure-adjusting icoFoam solver

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 December 10, 2012, 11:52 convergence of pressure-adjusting icoFoam solver #1 Member   Join Date: Jul 2012 Posts: 31 Rep Power: 6 Hi everybody, i am currently trying to solve the flow of fluid in a simple geometry with one velocity inlet and two pressure outlets. I want to implement a modified icoFoam solver that adjusts the pressure values at the outlets based on certain criteria (e.g., to achieve a certain predescribed flow split). My main problem is that PISO seems to converge terribly slow. E.g., if I use a constant inlet velocity and constant pressure values at the outlets (i.e., steady-state), a relatively steady state is reached after around ten time steps, but both inlet pressure and outlet fluxes do not reach a constant value even after 100 time steps, although the changes are small in the end. Unfortunately, it seems that that many time steps are necessary whenever I change the outlet pressures. So here are my questions: - why does it take so long to converge? is there a way to accelerate this? I used timestep = 0.001; piso corrector steps did not have a significant effect. Is it allowed to use PISO in this way? Anyone who has something to chip in, please feel free! thx in advance Last edited by kpax; December 13, 2012 at 12:10.

 December 13, 2012, 12:13 #2 Member   Join Date: Jul 2012 Posts: 31 Rep Power: 6 just a small update: i also tried timestep = 0.0001s and constant inlet velocity. the inlet pressure converged to a constant value after around 1000 time steps!! this cant be right. edit: the result of checkMesh: Checking geometry... Overall domain bounding box (-0.00500013 0.0737801 0.0766678) (0.0261582 0.0874276 0.0917605) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (-9.2092e-17 -2.65308e-16 -5.09871e-17) OK. Max cell openness = 2.76457e-16 OK. Max aspect ratio = 6.53503 OK. Minumum face area = 1.51201e-09. Maximum face area = 5.16808e-08. Face area magnitudes OK. Min volume = 2.2457e-13. Max volume = 5.80311e-12. Total volume = 3.88672e-07. Cell volumes OK. Mesh non-orthogonality Max: 59.2528 average: 17.1145 Non-orthogonality check OK. Face pyramids OK. Max skewness = 1.52552 OK. Coupled point location match (average 0) OK. seems alright doesnt it? maybe non-orthogonality could be a problem? Last edited by kpax; December 14, 2012 at 06:14.

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