Direct numerical simulations have been conducted to investigate the influence of shear effects on the Rayleigh-Bénard convection of liquid metal in a cuboid vessel within an aspect ratio of 4 under strong horizontal magnetic fields, where the Rayleigh number is fixed at ${10}^6$, Prandtl number $\text{Pr}=0.025$, Hartmann number varying from 1000 to 4000, and the wall shear Reynolds number ranging from 0 to 60 000. According the intensity of the shear effects, three typical flow regimes, i.e., competition regime, buoyancy-dominated regime, and shear-dominated regime, have been detected. In the buoyancy-dominated regime, multiple turbulent states emerge, with changes in magnetic field strength influencing the stability regions of these states and altering the large-scale circulation (LSC) structure. The underlying mechanisms governing these turbulent states have been thoroughly explained through elliptical instability analysis. During the competition regime, characteristic phenomena such as “vortex reconnection” and “vortex proliferation” occur, characterized by alternating four-vortex and five-vortex patterns, which influence the flow and heat transfer characteristics. And proper orthogonal decomposition analysis is employed to examine structural changes caused by instability, identifying dominant modes responsible for the observed changes in vortex patterns. When shear becomes dominant, the LSCs undergo reorganization, leading to reduced flow fluctuations and enhanced heat transfer performance. In addition, energy budget analysis reveals that increasing magnetic field strength extends the shear-dominated regime while contracting the energy competition phase.

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• High Hartmann number flows
• Rayleigh-Bénard convection
• Shear flows
• Turbulent convection
• Two-dimensional turbulence
• Vortex interactions