  We study the evolution of viscous, isothermal, rotating, thin, axisymmetric
accretion disks around a compact object using Smoothed Particle Hydrodynamics.
We emphasize the effects of different choices of viscosity prescriptions on the
evolution of angular momentum as well as other physical quantities of the disk.
We show that a flow with the Shakura-Sunyaev viscosity prescription may produce
only {\it shear} shock, where the angular momentum changes significantly across
the shock. We present and study the effects of other prescriptions of viscosity
which render the angular momentum continuous across the shock waves. In
general, it is observed that for flows with a small viscosity, the shocks are
weaker, form farther away and are wider as compared to the shocks in inviscid
flows. If the viscosity is high, shocks do not form at all. The flow remains
subsonic and Keplerian throughout the disk and becomes supersonic only very
close to the horizon.
