Numerical Study of Self-Excited Oscillations and Aeroacoustic Sources of Jet Flows in High Temperature Gas Reactor Cores

Abstract High-temperature gas-cooled reactors (HTGRs) improve thermodynamic efficiency due to high operating temperatures and the use of chemically inert gas coolants promotes the longevity of the reactor components. However, the use of high speed gaseous coolants in such reactors can face flow- and acoustic-induced vibration issues. Previous operational experience in gas-cooled reactors have shown a history of these issues, ultimately resulting in economic losses due to project delays, unscheduled maintenance, and reactor shutdowns. Despite the advantages of HTGRs, limited data on the complex flow-sound-structure interactions in gas-cooled reactors complicate the design of future systems. Given the difficulties of creating comprehensive experimental test facilities, high-fidelity simulations have emerged as essential tools. In this study, the self-excited fluid-resonant conditions of a subsonic jet exiting the HTGR reactor core and impinging on the reactor plenum was numerically investigated. Focusing initially on a two-dimensional planar jet with impingement length-to-jet width ratios (L/H) of 7 and 10, a fully coupled, compressible CFD simulation was performed. The resulting flow field was post-processed to extract the acoustic field, and Howe’s integrand identified aeroacoustic energy exchange regions. It was found that the simulations captured the self-excited oscillations of an impinging planar jet at the different L/H. The Strouhal number based on the jet width (StH) closely matched the Rossiter model predictions and experimental data, while three anti-symmetric vortex cores in the vorticity field confirmed oscillations at the n = 3 jet-stage. Helmholtz decomposition revealed high acoustic particle velocities at the jet inlet and impingement region, indicating significant aeroacoustic energy exchange in these regions. The preliminary findings of this study demonstrate that CFD can be a valuable tool for investigating fluid-resonant conditions in HTGR systems.