Colloquium: Jacob Ashwin Abraham (FPT)

This thesis investigates flow and heat transport phenomena in pipe and Pressurized Water Reactor (PWR) rod bundle geometries using high-fidelity Direct Numerical Simulation (DNS). Since conventional system codes like RELAP5 and SPECTRA rely on pipe flow correlations, this study evaluates their applicability to rod bundle geometries, which exhibit complex flow patterns such as secondary vortices, gap street vortices, and inter-subchannel coupling. To address these challenges, simulations were conducted on pipe, square subchannel, and 2×2 subchannel configurations, with a P/D ratio of 1.3263 and a Bulk Reynolds number (Re) of 5300. The Nek5000 spectral element solver was employed to analyze these geometries with high accuracy. Results demonstrate significant differences in turbulence structures and heat transfer between the configurations, with the 2×2 subchannel geometry providing a better representation of rod bundle flow dynamics. This work highlights the importance of geometry-specific modeling for improving reactor safety and design and establishes a foundation for future research in advanced thermal-hydraulic analysis.

Supervisor: Dr. Marc Gerritsma