COMBINED EFFECT OF GRAVITY AND MAGNETIC FIELD VARIATIONS ON THE ONSET OF CONVECTION IN A COUPLE STRESS FLUID DRENCHED POROUS MODULE

The combined effect of gravity and magnetic field variations on the onset of convection in an infinite flat porous module drenched with couple stress fluid is investigated subject to an adverse temperature gradient. The modified unsteady Darcy model is used to define the incompressible, laminar flow momentum equation, and the Boussinesq approximation is used in the field of buoyancy-driven flow. Floquet theory is applied to govern the onset condition within the framework of linear stability analysis. The present study investigates how the instability thresholds are getting affected with couple stress behavior subject to the gravity and magnetic field modulations. The results are presented graphically using Mathieu's functions and stability charts. The thermal instabilities of synchronous and subharmonic solutions and the exact changeover point in between them are predicted for the realistic values of control parameters. It is found that the applied magnetic field is more effective in stabilizing the system subject to gravity modulation than the system subject to gravity modulation alone.