Numerical Instability Study of Supercritical Water Flowing Upward in Two Heated Parallel Channels

Abstract

A three-dimensional (3D) numerical simulation has been carried out using a RANS model in CFD ANSYS CFX v15.0 to investigate the out of phase oscillation instability between two heated parallel channels with supercritical water flowing upward. Spatial and temporal grid sizes effects on flow instability are studied first. High sensitivity of the CFD code on time step size is investigated, while spatial grid size refinement influence is not noteworthy. Oscillatory instability boundaries of three experimental cases are predicated by CFD code with the standard k-e turbulence model. Chatoorgoon’s 1D nonlinear SPORTS code is also used to determine the instability boundary for comparison purposes. These new numerical results are compared with experimental data and previous numerical results. In general, there is a good agreement between numerical instability results of this paper and the experiments. Certain instability thresholds difference is observed among different numerical simulations, and possible reasons are pointed out. A previous finding that CFD results clearly yield better predictions of the instability boundary than a 1D solution is disputed in this paper.