Intrinsic relationship between the heat transfer and wake flow of liquid lead–bismuth eutectic over a circular cylinder

Lead–bismuth eutectic (LBE), with its low melting point, high thermal conductivity, and very low Prandtl number (Pr ∼ 0.025), is a promising coolant for lead-cooled fast reactors. The pronounced difference between the thermal and momentum diffusion of LBE results in a marked disparity between the evolution of temperature and velocity distributions, which fundamentally influences the flow and heat transfer around reactor components. This study numerically investigates the coupled thermal–hydraulic behavior of liquid LBE cross-flow past a high-temperature circular cylinder with temperature fixed at Tw = 800 K at a low Reynolds number of Rein = 150. The two-dimensional transient simulations are performed with the inlet temperature Tin varying from 400 to 700 K. A constant-property reference fluid is defined to compare the effect of temperature-dependent thermophysical properties. The numerical results indicate that variable properties significantly amplify the vortex-shedding frequency, lift, and drag fluctuations with the reduction of both velocity and thermal boundary layers, while shifting the separation points upstream. Increasing the wall-to-inlet temperature difference further amplifies the flow instability and convective heat transfer on the windward and lateral cylinder surfaces while shortening the vortex formation length. The underlying physics are explained through the interplay of temperature-dependent viscosity, local Reynolds number, and modified force balances in the boundary layer. The findings provide some insights into the fluid–thermal coupling of low-Pr flows.