Mixed interface-tracking/interface-capturing technique for computation of moving objects in multiple fluids
Ungor, Mehmet Kerim
Akin, John Edward.
Doctor of Philosophy thesis
We present here for the first time a successful 3D implementation of the Edge-Tracked Interface Locator Technique (ETILT) over the Deforming Spatial-Domain/Stabilized Space-Time (DSD/SST) formulation thus allowing the simulation of moving objects in multiple fluid flows. While the DSD/SST technique allows us to track solid-fluid interfaces, ETILT lets us capture fluid-fluid interfaces accurately, forming one approach to Mixed Interface-Tracking/Interface-Capturing Technique (MITICT). Based on the well-known Volume-of-Fluid (VOF) method where the interface location is captured with an interface function governed by the advection equation, in ETILT an edge representation is formed over the nodal representation to increase accuracy. Several different approaches are discussed to project from the nodal level to the edge level and vice versa accurately and efficiently. The reverse projection from the edge to the node level is established through a penalty formulation which ensures that the accuracy obtained in the edge level is passed correctly to the node level. A 3D volume conservation scheme based on tetrahedral elements that uses accuracy gained in the edge representation is introduced to prevent the volume errors present in the standard Volume of Fluid (VOF) method. The different projection strategies, the 3D tetrahedral volume conservation scheme, and the MITICT formulation is tested through several numerical problems. The numerical scheme is evaluated using the well-known broken dam problem. The results not only agree very well with the literature, but prove to be insightful. The collapse of a cylindrical water column is computed to add the literature an easy to reproduce 3D benchmark problem in free surface flows. In order to deal with sharp corners and flows where the interface hits a wall, improvements are suggested and presented by the filling of a step mold problem. Lastly, the method's capability to model moving objects in multiple fluid environments is presented by the simulation of an oscillating cylinder through the interface between water and air.