  The mechanisms governing the low-frequency unsteadiness in the shock
wave/turbulent boundary layer interaction at Mach 2 are considered. The
investigation is conducted based on the numerical database issued from
large-eddy simulations covering approximately 300 cycles of the low-frequency
shock fluctuations. The evaluation of the spectrum in the interaction zone
indicates that the broadband low-frequency unsteadiness is predominantly
two-dimensional, and can be isolated via spanwise averaging. Empirically
derived transfer functions are computed using the averaged flow field, and
indicate the occurrence of a feedback mechanism between downstream flow regions
and shock fluctuations. The transfer functions are also used as an estimation
tool to predict the shock motion accurately; for the largest streamwise
separation between input and output signals, correlations above 0.6 are
observed between predicted and LES data. Computation of spectral proper
orthogonal decomposition (SPOD) modes confirms the existence of upstream
traveling waves in the leading spectral mode. Finally, the spectral modes
obtained using selected flow regions downstream of the shock enable the
reconstruction of a significant portion of the energy in the interaction zone.
The current results shed further light on the physical mechanisms driving the
shock motion, pointing towards a causal behavior between downstream areas and
the characteristic unsteady fluctuations at the approximate shock position.
