# Interfoam Droplet under shear test case

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 January 25, 2009, 22:52 Hi Everyone, I am in the pr #1 Member   Adam Donaldson Join Date: Mar 2009 Location: Ottawa, Ontario, Canada Posts: 37 Rep Power: 9 Hi Everyone, I am in the process of validating an alternative multiphase solver, and one of my test cases has been giving me some problems. To determine if the issue was related to my solver, or the case, I have tried solving it using interFoam (and interDyMFoam). Alas, I obtain the same incorrect results. I was hoping someone might be able to shed some light on the problem. In the classical droplet under shear case, a Capillary number of 0.1 should result in a deformation parameter, D=(L-S)/(L+S) = 0.109375, where L and S are the longest and shortest radii in the shear plane. Interfoam and my new solver both give a value of D = 1.68 (give or take). This is significantly higher than expected. When I try the case with a higher capillary number (0.3), the droplet doesn't reach a steady state (It eventually elongates and breaks) I am working on a 3D grid, 128x64x128, with dimensions of [-4 to 4],[-2 to 2], [-4 to 4]. A droplet with radius = 1 is placed in the center of the domain. The top and bottom boundaries are walls, where the top has an imposed velocity of +4 in the x direction, while the bottom has a velocity of -4 in the negative x direction. The remainder of the velocity field is initialized with Ux = Z (i.e. a shear rate of 1). The two boundaries on the left and right are cyclic, and the front and back are set to zero-gradient for all variables. Both fluids have a density of 4 kg/m3, and a viscosity of 1 kg/ms (0.25 m2/s). The surface tension is = 10 kg/s2. Under these conditions, the Capillary number for the droplet is = 0.1. If anyone has successfully completed this test case using interFoam, I would love to hear from you with details on how you set the case up, and what you think might be causing the shear stress to be poorly accounted for.

 July 10, 2009, 15:54 #2 New Member   sesha Join Date: Mar 2009 Posts: 23 Rep Power: 9 Hi, I am trying to solve the exact problem. I am not sure if you have met with any success. I was able to get something done for a 2D case with some accuracy, i.e., 1 cell in the z direction. I also found this over estimation issue. For a 2D it is not that bad. I am trying to set up a 3D case but am getting into problems while running it. Check my other latest post today.

 July 10, 2009, 15:57 #3 New Member   sesha Join Date: Mar 2009 Posts: 23 Rep Power: 9 Adona, You should try the inflow-outflow condition on the left and right face instead of the cyclic boundary conditions. This might be the problem.

May 3, 2010, 18:46
#4
Member

Join Date: Nov 2009
Posts: 48
Rep Power: 8
Hello sir,

I am a new user in openfoam.. I want to simulate the droplet which falls on surface ( solid or liquid ). Could you please help me and tell me how do i have to define a droplet in openFoam and which solver do i have to use...

I would also be so grateful if you can help me simulate the one that u done.

thanks

Mehran

Quote:
 Originally Posted by adona058 Hi Everyone, I am in the process of validating an alternative multiphase solver, and one of my test cases has been giving me some problems. To determine if the issue was related to my solver, or the case, I have tried solving it using interFoam (and interDyMFoam). Alas, I obtain the same incorrect results. I was hoping someone might be able to shed some light on the problem. In the classical droplet under shear case, a Capillary number of 0.1 should result in a deformation parameter, D=(L-S)/(L+S) = 0.109375, where L and S are the longest and shortest radii in the shear plane. Interfoam and my new solver both give a value of D = 1.68 (give or take). This is significantly higher than expected. When I try the case with a higher capillary number (0.3), the droplet doesn't reach a steady state (It eventually elongates and breaks) I am working on a 3D grid, 128x64x128, with dimensions of [-4 to 4],[-2 to 2], [-4 to 4]. A droplet with radius = 1 is placed in the center of the domain. The top and bottom boundaries are walls, where the top has an imposed velocity of +4 in the x direction, while the bottom has a velocity of -4 in the negative x direction. The remainder of the velocity field is initialized with Ux = Z (i.e. a shear rate of 1). The two boundaries on the left and right are cyclic, and the front and back are set to zero-gradient for all variables. Both fluids have a density of 4 kg/m3, and a viscosity of 1 kg/ms (0.25 m2/s). The surface tension is = 10 kg/s2. Under these conditions, the Capillary number for the droplet is = 0.1. If anyone has successfully completed this test case using interFoam, I would love to hear from you with details on how you set the case up, and what you think might be causing the shear stress to be poorly accounted for.

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