Backward Facing Step (BFS) flows are prevalent in aerial vehicles and most of the applications involve modifications to the conventional step geometry. The present study is concerned with the use of BFS geometry around the ramp-isolator junction of supersonic mixed-compression intakes. The dynamics of laminar supersonic flows around a conventional BFS and a modified Backward Facing Step configuration (BFN) are studied at a Mach number of 2 using a novel Navier-Stokes based Mean Flow Perturbation (NS-MFP) method. The BFN was also studied with an isentropic compression ramp placed upstream, which is relevant to supersonic intakes. Three sets of incoming boundary layers (thin, medium and thick) of the order of step height are considered for analysis. The mean flow over a modified BFS, referred to as a Backward Facing Notch (BFN) configuration has smaller reattachment lengths. The shear layer mode was found to be weak or insignificant for all the boundary layers. Medium to high frequency oscillations exist near the step edge (St_H = 0.5 - 1.3), while the medium frequency dynamics dominate the separated shear layer and post-reattachment zone (St_H = 0.25 - 0.8). The spectra showed a shift of major dynamics to lower frequencies with increase in boundary layer thickness. The BFN flow exhibits complex dynamics and stronger oscillations as compared to the BFS. The presence of compression ramp upstream to the BFN strongly affects its dynamics. The NS-MFP predictions are compared with Large Eddy Simulations (LES) and a good match is observed at low frequencies (St_H = 0.003 - 0.013).
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