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Direct simulations (ILES) of turbulent, separated flow over the wall-mounted hump configuration is conducted to investigate the physics of separated flows. A chord-based Reynolds number of Rec = 47,500 is set up, with a turbulent inflow of Re θ = 1,400 (θ/c = 3%). FDL3DI, a code that solves the compressible Navier-Stokes equations using highorder compact-difference scheme and filter, with the standard recycling/rescaling method of turbulence generation, is used. Two different configurations of the upper-wall are analyzed, and results are compared with both a higher Rec (= 936,000, Re θ = 7,200, θ/c = 0.77%) experiment for major flow features, and RANS (k-ω SST) results. A lower Rec allows for DNS-like mesh resolution, and an adequately wide span. Both ILES and RANS show earlier separation and delayed reattachment compared to experiment, and significantly higher skin friction in the forebody of the hump, as expected. The upper-wall shape only influences the pressure distribution over the hump. Results from this study are being used to setup higher Rec (lower θ/c) ILES.

A set of direct simulations of zero-pressure gradient, turbulent boundary layer flows are conducted using various span widths (62 − 630 wall units), to document their influence on the generated turbulence. The FDL3DI code that solves compressible Navier-Stokes equations using high-order compact-difference scheme and filter, with the standard recycling/rescaling method of turbulence generation, is used. Results are analyzed at two different Re θ values (500 and 1, 400), and compared with spectral DNS data. They show that a minimum span width is required for the mere initiation of numerical turbulence. Narrower domains (< 100 w.u.) result in relaminarization. Wider spans (> 600 w.u.) are required for the turbulent statistics to match reference DNS. The upper-wall boundary condition for this setup spawns marginal deviations in the mean velocity and Reynolds stress profiles, particularly in the buffer region.

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