  We derive the conditions for shock formation in a quasi-spherical, slightly
rotating flows. We verify the results of semi-analytical, stationary
calculations with the time evolution studied by numerical hydro-simulations,
and we study the oscillations of the shock position. We also study the
behaviour of flows with varying specific angular momentum, where the
'hysteresis' type of loop is found when passing through the multiple sonic
points region. Our results are in agreement with the timescales and shapes of
the luminosity flares observed in Sgr A*. These models may also be applicable
for the Galactic stellar mass black holes, like GX 339-4 or GRS 1915+105, where
periodic oscillations of X-ray luminosity are detected.
