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

Rayleigh-Taylor instability of electrically conducting Oldroydian viscoelastic fluid in porous medium is considered in the presence of a variable horizontal magnetic field. The cases of two uniform fluids separated by a horizontal boundary and exponentially varying density, viscosity and magnetic field are considered. In each case, the magnetic field succeeds in stabilizing certain wavenumber range which were unstable in the absence of magnetic field whereas the system is found to be stable 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 on the orientation and magnitude of the magnetic field. The growth rates both increase (for certain wavenumbers) and decrease (for different wavenumbers) with the increase in kinematic viscosity, medium permeability, stress relaxation time and strain retardation time.