Abstract
This study numerically investigates magnetohydrodynamic Casson nanofluid flow over a curved stretching sheet under the influence of Joule heating, thermal radiation, activation energy, and chemical reaction. The Buongiorno model incorporating Brownian motion and thermophoresis describes nanoscale transport, while gyrotactic motile microorganisms stabilize the nanoparticle suspension through bioconvection. A systematic comparison between Newtonian and non-Newtonian (Casson) fluid models highlights the yield stress effects on transport characteristics. The governing equations of the Casson nanofluid flow are transformed into coupled ordinary differential equations by using similarity variables. The obtained system is solved by using the built-in bvp4c method of MATLAB. Key findings reveal that the Casson nanofluid exhibits lower velocity but higher temperature and concentration profiles than the Newtonian fluid due to enhanced viscous resistance and internal friction. Velocity decreases with increasing magnetic parameter (M) and buoyancy ratio (Nr), while it increases with mixed convection (λ). Temperature rises with higher thermal radiation (Rd), Brownian motion (Nb), thermophoresis (Nt), and thermal Biot number (β₁). Concentration enhances with increasing Brownian motion, mass Biot number (β₂), and activation energy (E). Microorganism density increases with motile Biot number (β₃) and curvature (A), but decreases with Peclet number (Pe) and bioconvection Lewis number (Lb). Skin friction rises with magnetic and Casson parameters, while the Nusselt, Sherwood, and motile density numbers show strong Biot number dependence. Results agree excellently with existing literature. This comparative analysis demonstrates that non-Newtonian behavior significantly alters thermal and transport characteristics, making the Casson model suitable for biomedical and industrial applications involving yield-stress fluids such as blood and polymer solutions.