  We numerically investigate the thermally unstable accretion disks around
black holes. We adopt an evolutionary viscous stress equation to replace the
standard alpha-prescription based on the results of two MHD simulations. We
find a kind of interesting oscillations on some running models in limit-cycle
outburst state. The oscillations arise near the inner boundary and propagate
radially outwards. We deem that they are the trapped $p$-mode oscillations
excited by sonic-point instability. We directly integrate the local radiation
cooling fluxes to construct the mimic bolometric light-curve. We find a series
of overtones beside the fundamental harmonic on the power spectra of mimic
light-curves. The frequency of the fundamental harmonic is very close to the
maximum epicyclic frequency of the disk and the frequency ratio of the
fundamental harmonic and overtones is a regular integer series. We suggest that
the code for ray-tracing calculation must be time-dependent in virtual
observation and point out the robustness of the black hole spin measurement
with high frequency QPOs.
