The Impact of Time Dependent Magnetic Field on Cu–Water Nanofluid

ABSTRACT The main aim of this study is to investigate the effect of time‐dependent magnetic field on natural convection of Cu–water nanofluid in a square cavity. The left wall of the cavity is hot, while the right wall is kept cold and the remaining walls are assumed to be adiabatic. The governing 2D continuity, momentum and energy equations are formulated in terms of stream function, vorticity and temperature. The vorticity equation contains the buoyancy and Lorentz force terms due to their appearance in the ‐momentum equation. Time discretization is performed using implicit backward Euler method, while space derivatives are approximated by the radial basis functions (RBFs). Three different magnetic field functions are considered, namely, a uniform magnetic field , an increasing magnetic field , and a decaying magnetic field . The effects of the Hartmann number on flow structure, vorticity distribution, and heat transfer characteristics are analyzed for a fixed Rayleigh number (). The results show that the overall flow suppression and heat transfer reduction are governed by the effective Hartmann number (). The time‐increasing magnetic field leads to the most pronounced flow damping with reductions of 99.90% in maximum stream function, 97.54% in vorticity, and 46.18% in the average Nusselt number for due to the continuous growth of during the transient process. Conversely, the rapidly decaying field exhibits minimal long‐term suppression as vanishes before steady state is achieved.