A generalized hydrodynamic (GHD) model depicting the behaviour of visco-elastic fluids has often been invoked to explore the behaviour of a strongly coupled dusty plasma medium below their crystallization limit. The model has been successful in describing the collective normal modes of the strongly coupled dusty plasma medium observed experimentally. The paper focuses on the study of nonlinear dynamical characteristic features of this model. Specifically, the evolution of coherent vorticity patches are being investigated here within the framework of this model. A comparison with Newtonian fluids and Molecular Dynamics (MD) simulations treating the dust species interacting through the Yukawa potential has also been presented.
The strongly coupled dusty plasma has often been modelled by the Generalized Hydrodynamic (GHD) model used for representing visco-elastic fluid systems. The incompressible limit of the model which supports transverse shear wave mode is studied in detail. In particular dipole structures are observed to emit transverse shear waves in both the limits of sub and super luminar propagation, where the structures move slower and faster than the phase velocity of the shear waves, respectively. In the sub -luminar limit the dipole gets engulfed within the shear waves emitted by itself, which then backreacts on it and ultimately the identity of the structure is lost.However, in the super -luminar limit the emission appears like a wake from the tail region of the dipole. The dipole, however, keeps propagating forward with little damping but minimal distortion in its form. A Poynting like conservation law with radiative, convective and dissipative terms being responsible for the evolution of W , which is similar to 'enstrophy' like quantity in normal hydrodynamic fluid systems, has also been constructed for the incompressible GHD equations.The conservation law is shown to be satisfied in all the cases of evolution and collision amidst the nonlinear structures to a great accuracy. It is shown that monopole structures which do not move at all but merely radiate shear waves, the radiative term and dissipative losses solely contribute to the evolution of W . The, dipolar structures, on the other hand, propagate in the medium and hence convection also plays an important role in the evolution of W . * amita@ipr.res.in 1 arXiv:1510.07114v1 [physics.plasm-ph]
A visco -elastic fluid is represented frequently by the Generalized Hydrodynamic (GHD) model. Unlike Navier Stokes fluid such a system supports transverse shear waves. Thus, while a sheared flow structure in a Navier Stokes fluid system is marred by the development of the KelvinHelmholtz (KH) instability alone, in the case of visco -elastic GHD fluid, a shear flow pattern can be expected to be effected by both, namely the KH instability and the emission of transverse shear waves. The manuscript explores this feature in detail. For this purpose (a) the modifications on the KH instability mode due to strong correlations in linear as well as nonlinear regime and (b) the conditions under which either the KH mode and/or the transverse shear wave emission dominates have been identified in the manuscript.
The Kelvin-Helmholtz (KH) instability is studied in a two dimensional strongly coupled dusty plasma medium using a fluid approach as well as through a molecular dynamic (MD) simulation. For the fluid description the generalized hydrodynamic (GH) model which treats the strongly coupled dusty plasma as a visco-elastic fluid is adopted. For the MD studies the ensemble of particles are assumed to interact through a Yukawa potential. Both the approaches predict a stabilization of the KH growth rate with an increase in the strong coupling parameter. The present study also delineates the temporal evolution and the interaction of transverse shear waves with the collective dynamics of the dusty plasma medium within the framework of both these approaches.
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