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Rudraiah N.,Bangalore University | Rudraiah N.,National Research Institute for Applied Mathematics | Shankar B.M.,Bangalore University | Ng C.O.,University of Hong Kong
Special Topics and Reviews in Porous Media

The linear stability of electrohydrodynamic poorly conducting couple stress viscous parallel fluid flow through a porous channel is studied in the presence of a nonuniform transverse electric field using an energy method. Supplemented with a single term Galerkin expansion. The sufficient condition for stability is obtained using the nature of the growth rate as well as sufficiently small values of the Reynolds number, Re. From this condition we show that strengthening or weakening of the stability criterion is dictated by the values of the strength of the electric field, the coefficient of couple stress fluid, and the porous parameter. In particular, it is shown that the interaction of the electric field with couple stress is more effective in stabilizing the poorly conducting couple stress fluid compared with that in an ordinary Newtonian viscous fluid. © 2011 by Begell House Inc. Source

Stasic J.,Vinca Institute of Nuclear Sciences | Gakovic B.,Vinca Institute of Nuclear Sciences | Trtica M.,Vinca Institute of Nuclear Sciences | Desai T.,National Research Institute for Applied Mathematics | Volpe L.,University of Milan Bicocca
Laser and Particle Beams

A comparative study of superficial changes on the superalloy Inconel 600, induced by a picosecond Nd:YAG laser operating at 1064, 532, and 266 nm, is presented. All of the laser wavelengths, as well as the used fluences of 2.5 (1064 nm), 4.3 (532 nm), and 0.6 J/cm 2 (266 nm) were found to be adequate for inducing surface variations. Quite different surface features were produced depending on the laser wavelength used. The measured surface damage thresholds were 0.25, 0.13 and 0.10 J/cm 2 for 1064, 532, and 266 nm, respectively. Drastic differences, in function of the wavelength used, were recorded for the crater depths, as well the appearance of hydrodynamic effects and periodic surface structures. Differences in crater depths were explained via an easier propagation of the first harmonic laser radiation (1064 nm) through the ejected material and plasma compared to a radiation at 532 and 266 nm. Finally, changes in the surface oxygen content caused by ultrashort laser pulses were considered. © 2012 Cambridge University Press. Source

Rudraiah N.,National Research Institute for Applied Mathematics | Rajaprakash B.M.,Bangalore University
Journal of Applied Fluid Mechanics

Nonlinear oberbeck convection in a chiral incompressible Boussinesq fluid flowing through a vertical channel bounded by rigid permeable isothermal boundaries kept at different temperatures is investigated in this paper in the presence of a uniform transverse magnetic field, under the influence of viscous dissipation. The nonlinear-coupled momentum and energy equations are solved analytically using a regular perturbation method valid for small values of buoyancy parameter N. To validate the results obtained from the analytical solutions of the non-linear equations, which are also solved numerically using a finite difference method supplemented with the successive over recreation (SOR) technique. The velocity, temperature, skin friction, mass flow rate and the rate of heat transfer are computed for various values of electromagnetic thermal number Wemt, buoyancy parameter N, and suction Reynolds Number Re. The results obtained are represented graphically and found that an increase in Wemt, increases the velocity and temperature. Physically, we attributes this to setting up of small scale turbulence by magnetic filed. The effect of perturbation parameter N is shown to increases the skin friction, heat transfer and the mass flow rate. Source

Desai T.,University of Milan Bicocca | Desai T.,National Research Institute for Applied Mathematics | Bussoli M.,University of Milan Bicocca | Dezulian R.,University of Milan Bicocca | And 5 more authors.
Physica Scripta T

In this work, we report on the possibility of using laser-generated craters to investigate planetary events such as meteorite impact craters. Experiments using a 0.44 μm/350 ps wavelength laser beam on aluminum foil targets are performed. We obtain simple and complex craters similar in contour to those formed due to meteorite impacts on the terrestrial surface. Our preliminary results show that the central peak of complex craters seems to be higher because of the turbulence beneath the crater floor. Results obtained using a two-dimensional radiation hydrodynamic code, MULTI, show that the laser ablation surface modifies and rises. This could be one of several factors explaining the central peak existence. © 2010 The Royal Swedish Academy of Sciences. Source

Rudraiah N.,Bangalore University | Sujatha N.,National Research Institute for Applied Mathematics | Kumar J.S.,Indian Institute of Technology Bhubaneswar
Journal of Applied Fluid Mechanics

The flow and heat transfer characteristics of Oberbeck convection of a chiral fluid in the presence of the transverse magnetic field, viscous dissipation and variable viscosity are investigated. The coupled non-linear ordinary differential equations governing the flow and heat transfer characteristics of the problem are solved both analytically and numerically. The analytical solutions are obtained using a regular perturbation and numerical solutions obtained using finite difference method. The solution is valid for small values of Buoyancy parameter N and variable viscosity parameter R1. The analytical results are compared with the numerical results and found good agreement. The role of temperature dependent viscosity and viscous dissipation on velocity, temperature, skin friction and the rate of heat transfer are determined. The results are depicted graphically, from these graphs it is noticed that the velocity is parabolic in nature and increases with an increase in magnetochiral number M . Physically this is attributed to the fact that magnetochiral number introduces small scale turbulences. Source

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