Flow Separation and Control

Wall-resolved large-eddy simulations of separated turbulent flows over a flat plate are conducted to explore the effects of spanwise inhomogeneity in turbulent separation bubbles (TSB). Simulations of spanwise homogeneous cases resulting in statistically 2D TSB are also conducted to compare with the spanwise-inhomogeneous 3D TSB and to assess the effect of the spanwise width on the separation characteristics. All simulations consider a friction Reynolds number Reτ ≈ 240 at a reference station upstream of separation and a freestream Mach number M∞ ≈ 0.6. Separation is induced using a suction-blowing boundary condition located eight reference boundary layer thicknesses above the flat plate. The 3D TSB cases consider different spanwise extents of the region of imposed suction and blowing varying between 20, 40, and 60 times the boundary layer thickness at the reference station (δ), resulting in different widths of the separation bubble, for spanwise domain widths of 148δ, 128δ, and 108δ, respectively. Wall-normal profiles of mean velocities and turbulence quantities as well as two-point correlations of velocity fluctuations are examined, revealing the presence of a spanwise region of statistical quasi-homogeneity for the two wider 3D TSB cases, whereas the case with the narrower bubble exhibits substantial differences with increased three-dimensional effects throughout the entire separation bubble. Skin-friction surface patterns on the flat plate are used to characterize the topology of separation and reattachment. Low-frequency characteristics of the separation bubbles are analyzed with wall-pressure power spectral density plots along streamwise and spanwise directions, complemented with the application of modal analysis to study separation bubble dynamics.

Funding acknowledgement

Financial support for this work provided by the PSAAP-III program, DOE/NNSA grant 94435-Z7124202