  Accretion flows having low angular momentum and low viscosity can have
standing shock waves. These shocks arise due to the presence of multiple sonic
points in the flow. We study the region of the parameter space in which
multiple sonic points occur in viscous flows in the absence of cooling. We also
separate the parameter space in regions allowing steady shocks and oscillating
shocks. We quantify the nature of two critical viscosities which separate the
flow topologies. A post-shock region being hotter, it emits harder X-rays and
oscillating shocks cause oscillating X-ray intensities giving rise to
quasi-periodic oscillations. We show that with the increase in viscosity
parameter, the shock always moves closer to the black hole. This implies an
enhancement of the quasi-periodic oscillation frequency as viscosity is
increased
