Coriolis-induced modifications to thermosolutal instability in Navier–Stokes–Voigt fluids

The competing influences of rotation-induced Coriolis force and solutal buoyancy on thermal convection in a Navier–Stokes–Voigt fluid layer are investigated. Analytical expressions are derived for the thresholds of both stationary and oscillatory instabilities. A notable outcome is the emergence of closed oscillatory neutral curves, detached from the stationary branches under certain parameter regimes. Unlike the conventional single-threshold criterion, these curves necessitate three distinct thermal Rayleigh numbers to fully delineate the stability boundary. The analysis further reveals instability behaviors not previously reported in either thermosolutal convection or rotating thermal convection of Kelvin–Voigt fluids. Interestingly, under specific parametric conditions, rotation and a stabilizing solute gradient—each suppressing convection in isolation—can together hasten the onset of oscillatory instability, thereby uncovering a counterintuitive destabilizing interaction. The Kelvin–Voigt elasticity parameter exerts an additional decisive influence, alternately amplifying or mitigating instability depending on the regime. The established results for thermosolutal convection and rotating thermal convection are recovered in the appropriate limiting cases.