NUMERICAL SIMULATIONS OF 2-DIMENSIONAL AND 3-DIMENSIONAL ACCRETION FLOWS

Numerical simulations of 2D and 3D accretion flows past a gravitating compact object from a uniform flow at a large distance upstream are performed by solving the Eulerian equations. We find that 2D flows exhibit a 'flip-flop instability' if the central accreting body is small. If the central body is enlarged at some instance in the oscillating flow, then the accretion shock shows a rather periodic oscillation similar to the von Karman vortex street. In the case of 3D flows, it is found that the shock cone is much more robust than in 2D, and the flip-flop instability takes a different, probably less violent form. The causes for the instabilities are discussed.