Effect of vertical rotation and salt on the stability of a couple stress fluid layer

• Combined effects of heat, salt, rotation and couple stresses on convection are analyzed. • Normal mode and energy analysis are employed for examining the system. • Critical Rayleigh numbers and wave numbers are obtained for characterizing the onset of convection. • For large rotation rate, stress free system becomes more stable than rigid-rigid system. The study investigates the stability characteristics of the effect of rotation and salt on convection in a couple stress fluid subject to different conducting boundary conditions. The stability analysis, conducted through linear stability theory and energy theory, confirms that the critical conditions for the onset of instability remain identical for both approaches. The results indicate that couple stresses significantly hinder fluid flow, reducing heat transfer through convection. Furthermore, increased rotation and salt concentration exhibit stabilizing effects, delaying the onset of convection. Among the boundary conditions examined, the free-free (FF) system exhibits an earlier onset of convection, while the rigid-rigid (RR) system demonstrates enhanced stability at lower Taylor numbers. However, beyond a certain threshold of the Taylor number, the FF system becomes more stable than the RR system. These findings underscore the crucial role of boundary conditions and physical parameters in modulating convection in a rotating couple stress fluid layer.