Conservative Level Set Method Implementation and Verification in PHASTA

Abstract

Abstract. The implementation of the conservative level set method is presented for the open-source two-phase massively parallel finite-element based flow solver, parallel hierarchic adaptive stabilize transient analysis (PHASTA). During the development, multiple problems were identified and addressed, which are attributed to the use of low-order shape functions and tetrahedral elements. To calculate accurate interface normal vectors, the original level set distance field is regenerated at every time-step, unlike other approaches which advect both the original and conservative level set field. This novel reinitialization scheme minimizes the complexity of the solver and keeps the distance field inline with the correct interface location. This is essential for other parts of PHASTA, which rely on the distance field for calculating quantities relevant to bubble tracking, interfacial heat flux computation, etc. Although mass conservation is greatly improved compared to traditional level set method, some mass drift can still occur. A simple source term is introduced here which preserves the global void fraction. This can be adapted to control the mass of individual bubbles. Several tests are used to quantify the improvements over the original level set implementation in PHASTA-most notably the simulation of a turbulent swirling vertical annular flow.