Implementing a Multiphase Flow Modelling Capability in the High-Fidelity Software CHAPSim2

The accurate simulation of boiling and related multiphase flow phenomena is critical across a wide range of industrial applications, including energy systems, chemical processing, and thermal engineering. In nuclear industry, in particular, boiling heat transfer plays a crucial role in the operation of nuclear reactors, such as the boiling water reactor, where improved modelling can significantly reduce overly conservative design constraints, thereby lowering construction costs and increasing operational efficiency. This work focuses on developing multiphase flow capabilities in the Direct Numerical Simulation (DNS) software CHAPSim2 to address the growing need for high-fidelity simulations of boiling and related processes. The development will lay solid groundwork for further extensions of the software for detailed modelling of boiling heat transfer in the future. A Volume of Fluid (VOF) module is implemented, coupled with a high-accurate algebraic interface capturing algorithm. Unlike the traditional VOF methods that rely on geometrical interface reconstruction, this approach represents the interface using a continuous hyperbolic tangent function, ensuring the moving interface to be captured with geometrical faithfulness and compact thickness. The solver is systematically validated against several well-established benchmark cases, including, for example, the classical Zalesak’s rotation problem [1] and rising bubble in a quiescent fluid [2]. [1] S. T. Zalesak, Fully multidimensional flux-corrected transport algorithms for fluids. Journal of Computational Physics, 31 (1979) 335–362 [2] S. Hysing, S. Turek, N. Kuzmin, E. Parolini, E. Burman, S. Ganesan, & L. Tobiska, Quantitative benchmark computations of two-dimensional bubble dynamics. International Journal for Numerical Methods in Fluids, 60 (2009) 1259–1288