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May 16, 2014, 09:36 

#41  
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sandy
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Quote:
Thanks for your replay. In fact, I was running my case in the opposite way where I impose the inlet BC from the bottom at z=0 and flow should go out at the top where z=0.017 m. So when I shrink the domain length to half so less, liquid comes out smoothly not like when z=0.017. Any how the case now is working for the long domain when I swamped the BC upside down which I do not why???. If you have any explanation you can help me with because it is not logical... Could you please show me what was the inlet and walls BC you used for the case you ran and sent me? best wishes, Sandy, 

October 5, 2015, 11:22 

#42 
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Saideep
Join Date: Apr 2015
Location: INDIA
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Hi guys;
I presently have some sort of b.c issues that you had previously. Hope anyone can help me out. I am using interfoam solver and trying to inject two fluids simulataneously through alternate channels from the inlet {water, oil, water, oil} and expect a mixed flow{water+oil} at the outlet boundary as shown in figure. I fix pressure[Pa] at the inlet(x) and at the outlet(0). For velocity i use a "zeroGradient" at outlet and "pressureInletOutletVelocity" for inlet. When i have lower pressure injection for water relative to oil, everything seems to be fine as expected. But when i try to make all the inlet channels have the same pressure values, then initially everything looks fine but after some time of run, i have a backward flow at one of the inlet{that is the flow is going out of the domain at the inlet} and alpha gets out of range. Also the flow at the outlet changes it direction of flow. [Can be seen in the posted data. Negative sign at inlet is flow into domain, positive sign at outlet is outflow through the domain. Above one is something at initial time and the bottom data is at a later time]. Expression totalInflow_0 : sum=3.92639e15 Expression totalInflow_1 : sum=7.33046e16 Expression totalInflow_2 : sum=1.85515e17 Expression totalInflow_3 : sum=1.06606e15 Expression inflow_0_Water : sum=3.92639e15 Expression inflow_1_Water : sum=0 Expression inflow_2_Water : sum=1.85515e17 Expression inflow_3_Water : sum=0 Expression inflow_0_Oil : sum=0 Expression inflow_1_Oil : sum=7.33046e16 Expression inflow_2_Oil : sum=0 Expression inflow_3_Oil : sum=1.06606e15 Expression outflow_0_Water : sum=2.93572e15 Expression outflow_1_water : sum=2.28004e16 Expression outflow_2_Water : sum=1.86927e17 Expression outflow_3_water : sum=4.26874e22 Expression totalOutflow_0 : sum=2.96816e15 Expression totalOutflow_1 : sum=5.51016e16 Expression totalOutflow_2 : sum=1.05719e15 Expression totalOutflow_3 : sum=1.16767e15 Courant Number mean: 0.0292251 max: 0.300384 Interface Courant Number mean: 0.0116064 max: 0.23988  Expression totalInflow_0 : sum=1.11676e13 Expression totalInflow_1 : sum=2.21668e13 Expression totalInflow_2 : sum=5.45042e14 Expression totalInflow_3 : sum=1.20261e14 Expression inflow_0_Water : sum=1.11676e13 Expression inflow_1_Water : sum=0 Expression inflow_2_Water : sum=5.45042e14 Expression inflow_3_Water : sum=0 Expression inflow_0_Oil : sum=0 Expression inflow_1_Oil : sum=2.21668e13 Expression inflow_2_Oil : sum=0 Expression inflow_3_Oil : sum=1.20261e14 Expression outflow_0_Water : sum=1.9006e14 Expression outflow_1_water : sum=9.30047e15 Expression outflow_2_Water : sum=4.94652e16 Expression outflow_3_water : sum=2.04992e19 Expression totalOutflow_0 : sum=1.90947e14 Expression totalOutflow_1 : sum=1.34784e14 Expression totalOutflow_2 : sum=6.41545e15 Expression totalOutflow_3 : sum=4.47371e15 Courant Number mean: 0.00731049 max: 0.301158 Interface Courant Number mean: 0.00405459 max: 0.195399 Though i guess symmetry of my structure{spreads out the pressure} and the viscosity values(oil>water) have a role to play in the displacement i am not able to understand why there is an outflow through the inlet with positive pressure(gradient) and inflow at the region of outlet. Thanks; Saideep 

October 6, 2015, 07:04 

#43 
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Albrecht vBoetticher
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Do you have gravity acting in y direction? could you show the pressure distribution along a center slice cut through the domain?


October 6, 2015, 13:37 

#44 
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Saideep
Join Date: Apr 2015
Location: INDIA
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Hi vonboett;
Thanks for your reply. The gravity has been turned off. I taught rather than plots the attached pics make sense in following order. Just let me know if you find it the other way round. I was using an injection pressure: 10000Pa {all inlets} and outlet Pressure: 0Pa. You can notice a negative Ux that starts to occur at the 1st inlet causing an outflux. [numbering 0 to 3 from bottom to top] see fig1 and fig2 which are successive time steps data. fig2.png fig3.png Also attached is a plot at the outlet end where the velocities turn negative which start to cause an inflow at the outlet region[fig3]. U_xoutletend.png Coming to pressure, it looks quite physical initially[fig4] {last time step before it starts to behave bad}: p1.jpg and at the time where it bursts out[fig5] In the last figure please look at the legend values. p2.jpg Overall it makes sense of the flow behavior but why is there a change in the direction of flow and sudden pressure burst throughout the domain? I notice that this happens when the water injection pressure >= oil injection pressure but not the other way round. Sorry for the long post; Thanks; Saideep 

October 7, 2015, 03:43 

#45 
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Andrea Ferrari
Join Date: Dec 2010
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If you have multiple fluids at the inlet i guess that setting a fixed value boundary condition for pressure in both fluids is not a good idea. The pressure inside the two fluids is, in theory, different due to capillary pressure but you are trying to fix the same value. I think this is the problem. I have observed similar behavior at the outlet when both fluids leave the domain at the same time.
I would switch to a velocity fix boundary condition and leave the pressure free to adjust depending on the fluid at the inlet. Or fix the pressure only at the inlet where you have fluid 1 (or fluid 2). Hope this help Andrea 

October 7, 2015, 07:20 

#46 
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Albrecht vBoetticher
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what is your alpha boundary condition at the inlet and outlet? Could you take a look if you get negative concntrations or values grater 1 for alpha?
Try out outlet { type inletOutlet; inletValue uniform 0; value uniform 0; } for alpha1 together with a pressureInletOutletVelocity and zeroGradient for U at inlet? 

October 7, 2015, 09:24 

#47 
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Saideep
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Thanks Andrea and vonboett;
@Andrea: Actually i started with fixed velocity values for the inlets which is an ideal case. Due to the shape of the model{throats arent symmetric at the ends of the model} I am not able to maintain a constant pressure at inlets of specific phase injection channels{which i am interested in, to calculate the grad(P)_oil/water}, so i switched to fixed pressure boundaries. May be an alternative could be is to extend my model{i.e. include throats at the top and bottom also so that it could symmetric at all inlet channels}. @vonboett: I am using the following bc for alpha. left_0 { type fixedValue; value uniform 1; /*phase1= water*/ } left_1 { type fixedValue; value uniform 0; /*phase0 = oil*/ } /*continue to other inlets also*/ and outlet channels with zeroGradient and equilibrium contact angle over the surface of the solid. Do you mean inletOutlet and outletInlet for U at inlet and P at oulet respectively or for alpha? And yes once this happens nothing remains to be computed accurately in terms of volume fraction, alpha[increases every step of calculation c.a. 4000], pressure etc. Thanks a lot Adrea and vonboett for your insight on this; Saideep 

October 8, 2015, 05:38 

#48 
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Albrecht vBoetticher
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I am curious about what happends with pressureInletOutletVelocity for U at the outlets
and { type inletOutlet; inletValue uniform 0; value uniform 0; } for alpha at the outlets... 

October 12, 2015, 12:05 

#49 
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Saideep
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Hi and sorry for my late reply.
It practically made not difference. Data written as output: /*ve sign is inflow into the domain*/ Expression totalInflow_0 : sum=1.92084e13 Expression totalInflow_1 : sum=4.19385e13 Expression totalInflow_2 : sum=1.78747e13 Expression totalInflow_3 : sum=1.6061e14 /*+ve shall be the outflow through the outlet*/ Expression totalOutflow_0 : sum=6.52957e15 Expression totalOutflow_1 : sum=1.24967e14 Expression totalOutflow_2 : sum=7.9281e15 Expression totalOutflow_3 : sum=5.53935e15 Max(alpha1) = 176.701 I used a fixed P at inlet for water at 10500Pa and for oil at 10000 Pa. Inlet and outlet velocities mentioned as pressureInletOutletVelocity. Also changed the alpha outlet bc to inletOutlet{I still dont understand why you meant to use this over here but made no difference}!! Any further ideas. Thanks!! Saideep 

October 13, 2015, 06:40 

#50 
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Albrecht vBoetticher
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Hi Saideep,
I work with turbulent open channel flows and there it can happen that you get some inflow at the outlet in some parts for some moment, and therefore I like to use inletOutlet for alpha to make sure that it sucks in atmospheric air and not water from the downstream. If you use U { type inletOutlet inlet value uniform (0 0 0) value uniform (0 0 0) } at the outlet you should at least get rid of inflow at the outlet. Just as a test to see that everything else is right, how about specifying the inflow velocity at the inlets and use p_rgh zeroGradient at the outlet (as well as alpha zeroGradient)? Cheers, Albrecht 

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