Implementation of the lax-wendroff method in Cobra-TF For solving two-phase flow transport equations

COBRA-TF (Coolant Boiling in Rod Arrays-Two Fluid), or CTF, is a subchannel code used to cany out the reactor core thermal hydraulic solution in both standalone and coupled multi-physics applications. CTF applies the first-order upwind spatial discretization scheme to solve two-phase flow conservation equations. In this work, the second-order Lax-Wendroff (L-W) scheme was implemented in CTF to solve two-phase flow transport equations to improve numerical accuracy in both temporal and spatial discretization. To avoid the oscillation issue, the nonlinear flux limiter VA (Van Albada) was employed for the convective terms in the transport equations. Assessments were carried out to evaluate the performance of the implemented second- order L-W scheme. It was found that the L-W scheme performs better than the upwind scheme for single-phase and two-phase flow problems in terms of numerical accuracy and computational efficiency.