The purpose of this work is to investigate the maldistribution of fluid flow in a cantilevered tube bundle, specifically within a structure resembling a lead–bismuth fast reactor. This study employs a model featuring two distinct arrangements of 19 tubes, all with identical dimensions. The simulations are conducted using Computational Fluid Dynamics (CFD) software Fluent, with the methodology validated against experimental results from existing literature on flow over a single cylinder (Linton and Thornber in Phys Fluids 28:24,111, 2016 [1]). Both laminar flow and turbulent flow scenarios are analyzed using the laminar and Reynolds-Averaged Navier–Stokes (RANS) standard k-ε models, respectively. The inlet velocity is incrementally adjusted from low to high to observe the resulting flow characteristics. Throughout the investigation, significant maldistribution of fluid flow is noted, characterized by regions where velocity decreases and instances of periodic vortex shedding. Additionally, an increase in velocity gradient is observed in the successive rows of pipes, indicating complex interactions within the fluid dynamics of the system. These findings contribute to a deeper understanding of fluid behavior in structures, which is crucial for optimizing engineering design and enhancing safety measures. This study not only highlights the intricacies of flow patterns in tube bundles but also sets the stage for future research aimed at mitigating flow maldistribution issues in similar reactor configurations.