Host: The Japan Society of Mechanical Engineers
Name : The 30th International Conference on Nuclear Engineering (ICONE30)
Date : May 21, 2023 - May 26, 2023
During the lifetime of a nuclear reactor, the coolant inside the pressure vessel can experience different flow regimes. Laminar and turbulent flow regimes are widely studied and have several models that can be applied. However, the mechanism of laminar-turbulent transition is less well understood. Understanding such transition is crucial since it can be essential during transients such as reactor startup or accidents. It can also play an important role in advanced reactors that operate at low flow conditions. In this work, we perform a parametric numerical study to identify how the Reynolds Number (Re), Pitch-to-diameter ratio (P/D), and domain length (L) affect the laminar-turbulent transition region. We focus on squared array rod bundles. The simulations are carried out using the spectral-element code NekRS and a Direct Numerical Simulation (DNS) approach [1, 2]. We imposed a no-slip condition on the walls. The P/D ranged from 1.05 to 1.20, while the Re varied from 250 to 3500. We analyze the temporal and spatial behavior of the instabilities as a function of P/D and (Re) in detail, including the Power Spectral Density (PSD) method [3].
