  This work is a numerical study of a transitional shock wave boundary layer
interaction (SWBLI). The main goal is to improve our understanding of the well
known low-frequency SWBLI unsteadiness and especially the suspected role of
triadic interactions in the underlying physical mechanism. To this end, a
Direct Numerical Simulation (DNS) is performed using high-order finite volume
scheme equipped with a suitable shock capture procedure. The resulting database
is then extensively post-processed in order to extract the main dynamical
features of the interaction zone (involved characteristic frequencies,
characteristics of the vortical structures, etc.). The dynamical organisation
and space-time evolution of the flow at dominant frequencies are then further
characterised by mean of a Spectral Proper Orthogonal Decomposition (SPOD)
analysis. In order to study the role of triadic interactions occurring in the
interaction region, a BiSpectral Mode Decomposition (BSMD) analysis is applied
to the data base. It allows us to extract the significant triadic interactions,
their location and the resulting physical spatial modes. Strong triadic
interactions are detected in the downstream part of the separation bubble whose
role on the low-frequency unsteadiness is characterised. All the results of the
various analyses are then discussed and integrated to formulate a possible
mechanism fuelling low-frequency SWBLI unsteadiness.
