\times \nu_{\rm fund}$), $9.3$ Hz ($\sim 3 \times \nu_{\rm fund}$) and $15$ Hz ($\sim 5 \times \nu_{\rm fund}$). In both the cases, the obtained power density spectra (PDS) of emitted radiation has significant similarity with number of observational results [@rm06; @ndmc12].

![[*Top panel*]{}: Variation of shock location with time. [*Middle panel*]{}: Variation of the bremsstrahlung emission in arbitrary units with time. [*Bottom panel*]{}: Variation of mass outflow rate with time. Here, $\alpha = 0.011$ and $M_B = 10 M_\odot$. Other parameters are same as Figure 3. ](fig4.eps){width="45.00000%"}

The quasi-periodicity that we observed in the power spectra of simulated results seems to be generic in nature. Several Galactic black hole sources exhibit QPO in the X-ray power spectra along with the harmonics. In Figure 7, we plotted one such observed X-ray power spectra of black hole source GX 339-4 of the 2010-11 outburst, which clearly shows the presence of [*fundamental*]{} QPO ($\sim$ 2.42 Hz) and harmonics at $\sim 4.88$ Hz and $\sim 7.20$ Hz [@ndmc12]. This observational finding directly supports our simulation results and perhaps establishes the fact that the origin of such photon flux variation seems to be due to the hydrodynamic modulation of the inner part of the disc 