Numerical Simulation of Thermal Striping Phenomena in a T-Junction Piping System Using Large Eddy Simulation

Abstract

At the Japan Atomic Energy Agency (JAEA), the simulation code "MUGTHES (MUlti Geometry simulation code for THErmal-hydraulic and Structure heat conduction analysis in boundary fitted coordinate)" has been developed to evaluate thermal striping phenomena that are caused by the turbulence mixing of fluids at different temperatures. In this paper, numerical schemes for thermal-hydraulic simulation employed in MUGTHES are described, including the LES model. A simple method to limit numerical oscillation is adopted in energy equation solutions. A new iterative method to solve the Poisson equation in the BFC system is developed for effective transient calculations. This method is based on the BiCGSTAB method and the SOR technique. As the code validation of MUGTHES, a numerical simulation in a T-junction piping system with the LES approach was conducted. Numerical results related to velocity and fluid temperature distributions were compared with existing water experimental data and the applicability of numerical schemes with the LES model in MUGTHES to the thermal striping phenomenon was confirmed.

Thermal Mixing in T-Junction Piping System Related to High-Cycle Thermal Fatigue in Structure

“…Before application of MUGTHES to thermal striping phenomena on the CIP, numerical simulation of the JAEA WATLON experiment 5,8) which was a water experiment for the T-junction piping system (T-pipe) was conducted from the viewpoint of code development and validation. In the authors' previous work 10) (hereinafter called the ''previous simulation''), preliminary confirmation of the applicability of MUGTHES to the WATLON experiment was obtained.…”

“…As for the energy equation, however, a non-conservative law form is employed to eliminate unphysical temperature fluctuation in uniform temperature field due to error of the velocity field. 10) In the non-conservation law form, a velocity component is put outside of the spatial gradient in the advection term and then the advection term in energy equation is always zero in the uniform temperature distribution. The filtered equations for the LES are shown in tensor form by using the Einstein summation rule as follows.…”

“…The second order central differential scheme is used for the advection term in the momentum equation. As for the pressure solver, an iterative method BiCGSTAB+SOR was previously developed 10) and is used in this study. Details of the method are given in the literature.…”

“…Details of the method are given in the literature. 10) In brief, the SOR technique is inserted into the standard BiCGSTAB method.…”

“…Thus, thermal striping may be an issue for the CIP and has been recognized as one of the most important issues in design and safety of the JSFR. [2][3][4] In JAEA, experiments [4][5][6][7][8] and numerical analyses 3,[9][10][11] have been performed in order to evaluate thermal striping phenomena and to establish an evaluation ÓAtomic Energy Society of Japan method for the high-cycle thermal fatigue in JSFR. As for the evaluation method, Kasahara et al 12) proposed a thermal fatigue evaluation method based on power spectrum density (PSD) of temperature fluctuation in a fluid and a frequency transfer function from the fluid temperature fluctuation to thermal stress in the structure.…”