  Using a 2.5D time-dependent axisymmetric numerical code we recently
developed, we solve the full compressible Navier-Stokes equations (including an
alpha-viscosity prescription) to determine the structure of the boundary layer
between the white dwarf and the accretion disk in non-magnetic cataclysmic
varia ble systems. In this preliminary work, our numerical approach does not
include radiation. In the energy equation, we either take the dissipation
function (Phi) into account or we assumed that the energy is instantly radiated
away (Phi). For a slowly rotating non magnetized accreting white dwarf, the
accretion disk e xtends all the way to the stellar surface. There, the matter
impacts and spread s towards the poles as new matter continuously piles up
behind it. We carried out numerical simulations for different values of the
alpha viscosity parameter (alpha), corresponding to different mass accretion
rates. In the high viscosity cases (alpha=0.1), the spreading boundary layer
sets off a gravity wave in the s urface matter. The accretion flow moves
supersonically over the cusp making it s usceptible to the rapid development of
gravity wave and/or Kelvin-Helmholtz shea ring instabilities. This BL is
optically thick and extends more than 30 degrees to either side of the disk
plane after only 3/4 of a Keplerian rotation period (19s). In the low viscosity
cases (alpha=0.001), the spreading boundary layer does not set off gravity
waves and it is optically thin.
