Direct numerical simulation of turbulent flow over a backward-facing step

h = 9000. The discretisation is performed using a spanwise periodic spectral/hp element method. The inlet flow has turbulent velocity and pressure fields that are formed by a regenerating channel segment upstream of the inlet. Time and spanwise averages show secondary and tertiary corner eddies in addition to the primary recirculation bubble, while streamlines show a small eddy forming at the downstream tip of the secondary corner eddy. This eddy has the same circulation direction as the secondary vortex. Analysis of three-dimensional time-averages shows a wavy spanwise structure that leads to spanwise variations of the mean reattachment location. The visualisation of spanwise averaged pressure fluctuations and streamwise velocity shows that the interaction of vortices with the recirculation bubble is responsible for the flapping of the reattachment position, which has a characteristic frequency of St = 0.078.