Nonlinear Rosseland Radiation Effects on Unsteady MHD Mixed Convection of Casson Cu-CMC Nanofluid over an Inclined Stretching Sheet with Gravity Modulation

Abstract

A numerical investigation is conducted to analyze the unsteady mixed convective thermal behavior of a magnetized, radiatively active Casson-type Cu-CMC nanofluid moving over an angled stretching surface subjected to oscillatory gravitational effects. The study incorporates transverse magnetic forcing, Rosseland radiative diffusion, Joule dissipation, and viscous heating within the non-Newtonian nanofluid transport equations. Through appropriate similarity transformations, the governing partial differential system is reduced to a coupled set of nonlinear ordinary differential equations, which are subsequently solved using the implicit Keller-box finite-difference scheme. The nonlinear treatment of the Rosseland radiative flux, which retains the full temperature dependence of the absorption characteristics, modifies the effective thermal diffusion coefficient and consequently the radiation-modified Nusselt number. Systematic comparison with the published benchmark solutions for appropriate limiting cases confirms the fidelity of the numerical implementation. Parametric investigation examines the sensitivity of the velocity and temperature fields, wall friction, and heat transfer rates to variations in the Casson rheological parameter, magnetic interaction coefficient, radiation parameter, Eckert number, surface inclination, nanoparticle loading, and gravity modulation characteristics. The results indicate that magnetic damping reduces the momentum boundary-layer thickness, copper nanoparticle addition enhances thermal penetration, and the combination of radiative transport with irreversible heating mechanisms substantially alters the thermal boundary-layer structure. These findings offer practical insights for the design and optimization of thermal management systems that depend on electrically conducting non-Newtonian nanofluids.