This communication investigates the effect of permeability variation on the heat transfer and the flow through a highly porous medium bounded by an infinite flat porous plate with constant suction. The permeability of the porous medium varies in space and time both. The problem becomes three dimensional due to the periodic variation of permeability in the transverse direction. The governing equations are solved by adopting complex variable notations and the expressions for the velocity and temperature fields are obtained. The wall shear stress and rate of heat transfer are finally discussed. It is found that the amplitudes |L|, |M|, |H|, respectively, of the skin friction components in the main and transverse directions and the rate of heat transfer, all decrease with the increase of the permeability of the porous medium, K0, or the frequency of the permeability fluctuations, ω.
The stability of the plane interface separating two viscoelastic superposed fluids of uniform densities has been studied. The stability analysis has been carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities. It is found that the system is stable for stable configuration and unstable for unstable configuration. The behaviour of growth rates with respect to stress relaxation time and strain retardation time parameters ate examined analytically.
IntroduetionThe instability of the plane interface between two incompressible and viscous fluids of different densities when the lighter is accelerated into the heavier has been discussed b y CnA~DRAS~KHAR [2]. The influence of viscosity on the stability of the plane interface separating two incompressible superposed fluids of uniform densities, when the whole system is i m m e r s e d in a uniform horizontal magnetic field, is studied b y BHATIA [1]. H e has carried out the stability analysis for two fluids of equal kinematic viscosities and different uniform densities. SHARMA [4] studied the t h e r m a l instability of a layer of viscoelastic (OLDROYD) fluid acted on b y a uniform rotation. The rotation is found to have a destabilizing as well a s a stabilizing effect under certain conditions in contrast to t h a t of a Maxwell fluid where ir always has a destabilizing effect. The stabi-]ity of a layer of Oldroyd fluid heated from below and subject to a magnetic field has been studied b y SHARMA [5].Ir m a y be of some interest to s t u d y the stability of the plane interface separating two incompressible superposed viscoelastic fluids of uniform densities. This aspect forros the subject m a t t e r of the present p a p e r wherein we have carried out the stability analysis for two fluids of equal kinematic viscosities and different uniform densities.
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