Spherical disturbance elements for compound enhancement in bionic fish-scale tubes: Wake control and thermo-hydraulic performance

Enhancing convective heat transfer in circular tubes is crucial for compact heat exchangers, but conventional passive structures often suffer from weak heat transfer in downstream recirculation zones. To address this limitation, a bionic fish-scale composite sphere enhanced heat transfer tube (CBS) is proposed by introducing hemispherical disturbance elements onto a bionic fish-scale substrate to control the wake recirculation zone. The effects of sphere diameter, concave/convex form, and arrangement pattern are systematically investigated. Using the SST k - ω turbulence model, flow and heat transfer of eight CBS configurations in a circular tube are numerically simulated for Re = 11225~33675. The enhancement mechanism is analyzed via field synergy, the energy penalty is evaluated by entropy generation, and the overall thermohydraulic performance is assessed using the performance evaluation criterion ( PEC ). Compared with the bionic fish-scale tube (CB), CBS simultaneously enhances heat transfer and reduces flow resistance over the entire Re range. The optimal configuration increases Nu by 14.03% and decreases f by 23.30% at Re = 33675. Sphere diameter dominates thermohydraulic performance, followed by concave/convex form, while arrangement pattern has the least effect. CBS_2 achieves the highest field synergy number Fc and a maximum PEC of 1.28 at Re = 11225, with the lowest total entropy generation ratio S / S 0 = 0.55. Mechanism-driven correlations for Nu and f are established, with prediction errors within ±5% for Nu / Nu CB and ±10% for f / f CB . The composite structure shows strong potential for compact tubular heat exchangers.