THE DYNAMICS OF 2-DIMENSIONAL LOCAL AND FINITE PERTURBATIONS IN ENVELOPES OF ROTATING WHITE-DWARFS .1.

This is a first paper in a series in which we investigate the behavior of two-dimensional local and finite perturbations in envelopes of sta rs. In this paper we explore the dynamics of local and finite perturba tions in an accreted envelope placed on a white dwarf. Viscosity and r otation 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 p ropagation of perturbation in the envelope of a white dwarf. Our most important result is that a local perturbation develops in two basic ph ases: In phase A, which lasts about one dynamics timescale, the pertur bation 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 calculation s were carried out with a Reynolds number of 10(3) and 10(5) and we fi nd that for these Reynolds numbers the viscosity (shear or turbulent) has a minor effect on the development of the local perturbation into a global one.