The dynamics of two-dimensional local and finite perturbations in envelopes of rotating white dwarfs.
This is a first paper in a series in which we investigate the behavior of two-dimensional local and finite perturbations in envelopes of stars. In this paper we explore the dynamics of local and finite perturbations in an accreted envelope placed on a white dwarf. Viscosity and rotation are included in a full two-dimensional Navier-Stokes system of equations. A time-dependent Chebyshev method of collocation has been developed and implemented for solving numerically the problem of the propagation of perturbation in the white dwarf. Our most important result is that a local perturbation develops in two basic phases: In phase A, which lasts about one dynamics timescale, the perturbation remains local. In phase B the perturbation expands all over the star by means of pressure waves. Thus, a local perturbation becomes a global one after about one dynamic timescale. The present calculations were carried out with a Reynolds number of 10(Power of three) and 10 (power of five) and we find that for these Reynolds numbers the viscosity (shear or turbulent) has a minor effect of the development of the local perturbation into a global one.
|Main Author:||Godon, Patrick.|
|Other Authors:||Shaviv, Giora.|