  This work investigates the self-excited shock wave oscillations in a
three-dimensional planar over-expanded nozzle turbulent flow by means of
Detached Eddy Simulations. Time resolved wall pressure measurements are used as
primary diagnostics. The statistical analysis reveals that the shock
unsteadiness has common features in terms of the root mean square of the
pressure fluctuations with other classical shock wave/boundary layer
interactions, like compression ramps and incident shocks on a flat plate. The
Fourier transform and the continuous wavelet transform are used to conduct the
spectral analysis. The results of the former indicate that the pressure in the
shock region is characterized by a broad low-frequency content, without any
resonant tone. The wavelet analysis, which is well suited to study non
stationary process, reveals that the pressure signal is characterized by an
amplitude and a frequency modulation in time.
