Buoyancy opposed flow over a heated hollow sphere

This study investigates the buoyancy-opposed turbulent flow over a heated hollow sphere placed inside a circular pipe by performing Large Eddy Simulation (LES). The Reynolds number ( R e ), based on the sphere diameter, and inlet velocity, was fixed at 16,000, while the Richardson number ( R i ) was varied from 0 to 2.21 to include both forced and mixed convection conditions. Argon was selected as the working fluid at an operating pressure of 3 MPa to reflect conditions relevant to the experimental data used for comparison. LES predictions were compared with available experimental and Numerical data. Detailed analysis was conducted on key flow and thermal characteristics, including the non-dimensional reattachment length ( L r / D ), separation angle ( θ s ), measured from the upstream stagnation point, turbulent kinetic energy ( T K E / U ∞ 2 ), Nusselt number ( N u ), and Strouhal number ( S t ). Moreover, Power Spectral Density (PSD) was performed on the co-efficient of lift ( C l ) to determine the vortex shedding frequency ( f v s ). The results demonstrated that, as R i increased, buoyancy effects increasingly opposed the main flow, resulting in longer reattachment lengths, shorter separation angles, and slightly smaller S t . This indicated that buoyancy caused the wake region to expand both in length and width. Furthermore, Proper Orthogonal Decomposition (POD) was performed on streamwise and cross-stream velocity components and it was found that the first 159 modes contained 90% of the total energy for R i = 1 . 84 . Further analysis suggested that variation in R i has little effect on the system’s dimensionality. • LES of buoyancy-opposed turbulent flow over a heated hollow sphere. • Re = 16,000; Ri varied from 0 to 2.21 for forced and mixed convection regimes. • Buoyancy enlarged wake region. • POD showed that Buoyancy does not affect system’s dimensionality significantly.