The effects of double-diffusion and viscous dissipation on the oscillatory convection in a viscoelastic fluid saturated porous layer

The effects of the double-diffusion and viscous dissipation on the convective instability in a horizontal porous layer are investigated. The porous medium is saturated with a binary viscoelastic fluid. The Oldroyd-B model of viscoelastic fluid is considered. Constant temperature and concentration differences are maintained between the boundaries. A basic flow is present in the horizontal direction. The governing parameters are the thermal Rayleigh number (Ra-T), solutal Rayleigh number (Ra-S), Gebhart number (Ge), Lewis number (Le), Peclet number (Pe), dimensionless relaxation time (lambda (1)), and dimensionless retardation time (lambda (2)). A small perturbation to the basic flow is assumed, and a linear stability analysis is performed. A detailed discussion is carried out considering Ra-T as the eigenvalue. The critical wave number and frequency are also derived for a wide range of Lewis numbers and solutal Rayleigh numbers. The oscillatory modes are analyzed. It is found that transverse rolls are the preferred mode for the onset of oscillatory convection, except for some special cases. Moreover, a negative solutal Rayleigh number stabilizes the flow. An opposite effect is seen in the presence of a positive solutal Rayleigh number.