HYDROMAGNETIC RAYLEIGH-TAYLOR INSTABILITY OF OLDROYDIAN VISCOELASTIC FLUIDS IN POROUS-MEDIUM IN PRESENCE OF VARIABLE MAGNETIC-FIELD

Rayleigh-Taylor instability of electrically conducting Oldroydian visc oelastic fluid in porous medium is considered in the presence of a var iable horizontal magnetic field. The cases of two uniform fluids separ ated by a horizontal boundary and exponentially varying density, visco sity and magnetic field are considered. In each case, the magnetic fie ld succeeds in stabilizing certain wavenumber range which were unstabl e in the absence of magnetic field whereas the system is found to be s table for potentially stable configuration/stable stratifications. It is found that the stability criterion is independent of the effects of medium permeability, viscosity and viscoelasticity and is dependent o n the orientation and magnitude of the magnetic field. The growth rate s both increase (for certain wavenumbers) and decrease (for different wavenumbers) with the increase in kinematic viscosity, medium permeabi lity, stress relaxation time and strain retardation time.