Towards boiling crisis simulation : the level set method

The accurate prediction of the so-called Departure from Nucleate Boiling is a crucial point in the safety analysis of nuclear reactor cores. Nowadays, the DNB evaluation is based on experimental correlations using numerical results of averaged two-phase flow models. A natural goal is therefore to replace this rough procedure by a direct numerical simulation of the boiling crisis. The physical model now involves the motion of two phases separated by an interface and the main difficulty is to simulate this interface. Although there are many unresolved issues concerning the modelling of the entire boiling crisis phenomenon (such as triple points, nucleation, etc.), we focus merely on the numerical aspects of solving its hydrodynamics. Our goal is to devise a numerical algorithm for computing the motion of two compressible phases separated by an interface (with surface tension effects) through which mass, momentum, and energy exchanges occur. It is based on the level set method introduced by Osher and Sethian (1988) which views the interface as the zero level set of a so-called “level set function”. Contrary to other methods, e.g. front tracking, the point is not to follow precisely the interface but rather to “capture” it on a fixed Eulerian mesh. The level set function is evolved by a new equation of Hamilton-Jacobi type. The main advantages of this method are its ability to deal with complex interface topologies and its versatility even for three-dimensional computations.