  We investigate the dynamical structure of advective accretion flow around
stationary as well as rotating black holes. For a suitable choice of input
parameters, such as, accretion rate ($\dot {\cal M}$) and angular momentum
($\lambda$), global accretion solution may include a shock wave. The post shock
flow is located at few tens of Schwarzchild radius and it is generally very hot
and dense. This successfully mimics the so called Compton cloud which is
believed to be responsible for emitting hard radiations. Due to the radiative
loss, a significant energy from the accreting matter is removed and the shock
moves forward towards the black hole in order to maintain the pressure balance
across it. We identify the effective area of the parameter space ($\dot {\cal
M} - \lambda$) which allows accretion flows to have some energy dissipation at
the shock $(\Delta {\cal E})$. As the dissipation is increased, the parameter
space is reduced and finally disappears when the dissipation is reached its
critical value. The dissipation has a profound effect on the dynamics of
post-shock flow. By moving forward, an unstable shock whose oscillation causes
Quasi-Periodic Oscillations (QPOs) in the emitted radiation, will produce
oscillations of high frequency. Such an evolution of QPOs has been observed in
several black hole candidates during their outbursts.
