Conditional analysis of unsteadiness in shock boundary layer interactions

Abstract

The features of the interaction between an oblique shock wave and a Mach 2.3 turbulent boundary layer are examined in an effort to differentiate the dynamics of bubble dilation (upstream shock motions) from bubble collapse (downstream shock motions). A dataset obtained from Large Eddy Simulations, which has been validated against experiments is used for the analysis. A relatively new technique, Empirical Mode Decomposition (EMD), is used for low-pass filtering to facilitate separation of upstream shock motions from downstream shock motions. To examine the dynamics of bubble dilation versus collapse, three Dynamic Mode Decomposition (DMD) analyses are carried out: considering the full dataset, considering strictly upstream motions, and considering only downstream motions. For each case, results of DMD are shown for the pressure field to accentuate different aspects of the physics. The results highlight differences in the dynamics of dilation and collapse, which aid in the understanding of unsteadiness in these interactions. A comparison of the speeds at which either process occurs is also shown to yield similar conclusions as the DMD analyses.