On low-frequency unsteadiness in three-dimensional shock/boundary layer interactions*

We carry out DNS of shock/boundary layer interactions (SBLI) in the presence of cross flow, as a surrogate of genuine three-dimensional SBLI. Use of spanwise wide computational domains suggests the presence of organized, large-scale rippling of the instantaneous flow separation line, on a typical length scale proportional to the mean separation extent. We present evidence that In the presence of cross flow these ripples are advected at a fraction of the mean spanwise velocity. Based on the observed data we obtain a predictive formula for the typical frequency of the large-scale unsteadiness, which very well conforms with the computed frequency spectra. In agreement with what observed in experiments and DNS of three-dimensional SBLI, the typical frequency is predicted to increase with the flow skew angle.