Bubble diameter control of baroclinic torque–mediated vortex topology and energy pathways in a helical-axial multiphase pump

Helical-axial multiphase pumping is increasingly employed in oil and gas, energy, and chemical industries, where efficient transport of gas–liquid mixtures without phase separation is critical. However, the internal flow is governed by complex vortex dynamics, strongly influenced by interfacial phenomena and bubble-scale physics. In particular, the role of bubble diameter in controlling vortex Topology through baroclinic torque mechanisms remains insufficiently understood. This study systematically investigates the influence of bubble diameter on the baroclinic torque–mediated vortex topology initiation, development, stretching, and breakdown in the pump. A high-fidelity numerical framework based on the Eulerian multiphase model coupled with the k–ω SST turbulence model is employed. Vortex dynamics are analyzed using density-gradient fields, the Q-criterion, helicity, and circulation metrics. The results show that bubble diameter basically controls vortex topology through modulation of density gradients and pressure-gradient misalignment, directly affecting baroclinic torque. Small bubbles suppress vortex formation due to strong interphase coupling, whereas large bubbles intensify vortex instability and dissipation due to phase segregation. An intermediate bubble diameter achieves optimal vortex stability and energy-transfer efficiency. This study establishes a mechanism-based structure linking bubble-scale physics to vortex topology evolution and pump performance, providing new insights for multiphase pump optimization.