# On the alpha Eqn of VOF method when using Immersed boundary method in OpenFOAM

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 October 1, 2013, 21:03 Alpha Eqn of VOF method when using Immersed boundary method in OpenFOAM #1 Senior Member   David Long Join Date: May 2012 Location: Germany Posts: 104 Rep Power: 14 Hi, I am interested in the implementation of Immersed Boundary (IB) / fictitious-domain method in OpenFOAM, and also read some related papers/pretensions like: 1. Zeljko Tukovic, Hrvoje Jasak (2012). Immersed boundary method in OpenFOAM (7th OF workshop) 2. Oscar M. Curet, et al (2010). A versatile implicit iterative approach for fully resolved simulation of self-propulsion. Computer Methods in Applied Mechanics and Engineering I thought it might not be so difficult to extend the use of IB method with volume of fluid (VOF) method, e.g an enhanced version of interFoamsolver which supports immersed rigid body in the fluid domain. Look to the original alpha Eqn of VOF method in OF: in IB method the solid phase is considered as "fluid" but with some constraint conditions to enforce the "fluid" moving as a rigid body. I wouldn't repeat the momentum and constraint equations here (one can see in the 2. paper) here. However, there are some problems I am facing: 1. If the immersed solid body is moving in the fluid domain and has different density (e.g. rocks or steel), how do we account for the changes to the P Eqn while momentum Eqn remains the same? 2. Most importantly, if there are two fluid phases (e.g air and water) and we introduce VOF method along with IB method, how do we change the alpha Eqn so that we can capture the interface between air and water, as well as the interface between fluid and immersed solid body? Because within the solid body, both alpha1 and alpha2 (alpha2 = 1 - alpha1) should be set as Zero, if we see the solid phase is alpha3, and set its value alpha3 = 1 within the solid body and alpha3 = 1 outside, how can we modify the alpha Eqn account for the 3rd phase alpha3? Any hints (especially related papers on VOF + IB in CFD) or recommendation will be highly appreciated. Thanks for your attention. Cheers, David Last edited by keepfit; October 4, 2013 at 22:55.

 January 29, 2014, 15:57 #2 New Member   Andrew Ho Join Date: Jan 2014 Posts: 6 Rep Power: 12 Hi David, Have you made any progress on this front? I'm also interested in creating a two phase VOF, moving immersed boundary simulation.

 January 30, 2014, 04:59 General moving objects #3 Senior Member   Fabian Roesler Join Date: Mar 2009 Location: Germany Posts: 213 Rep Power: 18 Hi for the third phase you have to add another phase fraction alpha3 so alpha, the sum of all phase fractions is still one. This is done in multiphaseInterFoam. I once read some articles about immersed rigid body in fluid domains. Flow 3D has a certain technique called FAVOR to simulate general moving objects. They have some articles about their method published free. Maybe these articles can clarify some of your questions. I do not have access to my literature database so I can not give you any more details. Have a look to these links: http://www.flow3d.com/pdfs/tp/genera...-flow-9-05.pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.186.5829&rep=rep1&type=pdf Cheers Fabian

 January 30, 2014, 05:41 #4 Senior Member   Pablo Higuera Join Date: Jan 2011 Location: Auckland Posts: 627 Rep Power: 19 There is a very interesting and slightly more recent thread on the Fictitious Domain method: http://www.cfd-online.com/Forums/ope...1-x-2-2-x.html

 January 31, 2014, 14:32 #5 New Member   Andrew Ho Join Date: Jan 2014 Posts: 6 Rep Power: 12 Thanks guys for the responses, I will have a closer look at this fictitious domain method, since it might do the job. Fabian, I'll have a look at those papers as well. cheers!

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