Using a 2.5D time-dependent axisymmetric numerical code we recentlydeveloped, we solve the full compressible Navier-Stokes equations (including analpha-viscosity prescription) to determine the structure of the boundary layerbetween the white dwarf and the accretion disk in non-magnetic cataclysmicvaria ble systems. In this preliminary work, our numerical approach does notinclude radiation. In the energy equation, we either take the dissipationfunction (Phi) into account or we assumed that the energy is instantly radiatedaway (Phi). For a slowly rotating non magnetized accreting white dwarf, theaccretion disk e xtends all the way to the stellar surface. There, the matterimpacts and spread s towards the poles as new matter continuously piles upbehind it. We carried out numerical simulations for different values of thealpha viscosity parameter (alpha), corresponding to different mass accretionrates. In the high viscosity cases (alpha=0.1), the spreading boundary layersets off a gravity wave in the s urface matter. The accretion flow movessupersonically over the cusp making it s usceptible to the rapid development ofgravity wave and/or Kelvin-Helmholtz shea ring instabilities. This BL isoptically thick and extends more than 30 degrees to either side of the diskplane after only 3/4 of a Keplerian rotation period (19s). In the low viscositycases (alpha=0.001), the spreading boundary layer does not set off gravitywaves and it is optically thin.
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