Fluid flow over a horizontal circular cylinder is encountered in industrial and practical engineering processes, such as electronics cooling, hyperthermia treatment, aerospace industries, thermal power plant, chemical reactors, solar and power system. The main aim of the present study is to investigate the magnetohydrodynamic boundary layer flow and heat transfer behavior of a Williamson ternary hybrid nanofluid \(\left( {Al_{2} O_{3} + Cu + TiO_{2} /H_{2} O} \right)\) over a horizontal circular cylinder, by incorporating the effects of viscoelasticity, magnetic effects, thermal radiation, heat generation, porous media and slip boundary conditions. The governing nonlinear equations are transformed into a non-dimensional form using appropriate non-similarity transformations and are numerically solved using the Keller box method an implicit finite difference scheme with second order accuracy. The numerical implementation is validated by comparing the results with existing published studies. The influence of key dimensionless parameters on velocity and temperature profiles, as well as on the local Nusselt number and skin friction coefficient, are systematically analysed and presented through graphical and tabular representations. The results show that increasing nanoparticle complexity reduces peak velocity, with hybrid and ternary hybrid nanofluids exhibiting 8.73% and 14.86% lower velocities respectively, compared to conventional nanofluids. This reduction is due to increased effective viscosity, which enhances the internal fluid friction and also stabilizes the boundary layer. Conversely, quantitative analysis reveals that the ternary hybrid nanofluid enhances heat transfer rates by 4.85% and 2.42% relative to the hybrid nanofluid and conventional nanofluids, highlighting its superior thermal performance.
