# Complex Turbulent Flows

**Shock Boundary Layer Interaction (SBLI)**

The adverse pressure gradient across a shock can produce boundary layer separation and significant flow unsteadiness across a wide range of frequencies. The TFCL investigates both 2D and 3D SBLIs in collaboration with the Computational Fluid Dynamics Laboratories at the University of Arizona (Prof. Hermann Fasel) and New Mexico State (Prof. Andreas Gross).

**Figure: ** Left: Schematic diagram showing pertinent features in a simplified inviscid environment. Right: Instantaneous tomographic PIV field. Contours of u (m/s) plotted at spanwise limits of domain (contour levels at Δu/u_{∞} = 0.1). SBLI bubble region visualized using isosurface of streamwise velocity at u/u_{∞} = 0.5, surface colored by difference to mean field between (u-ū)/u_{∞} = -0.15 (blue, enlarged bubble) and (u-ū)/u_{∞} = +0.15 (red, diminished bubble), with increments of Δu/u_{∞} = 0.05. Separation shock and incident shock visualized using isosurface of wall-normal velocity at u/u_{∞} = 0.1, surface colored by difference to mean field between (v-v̄)/u_{∞} = -0.04 (brown, downsteam shock) and (v-v̄)/u_{∞} = +0.04 (green, upstream shock), with increments of Δv/u_{∞} = 0.02.

**Boundary Layer Separation under the of Influence Structural Motion**** **

New advances in composite manufacturing are enabling the implementation of more aerodynamically efficient high aspect ratio wings. These wings are inherently more flexible than traditional structures and the aerodynamic effects of this motion must be considered especially near stall where separation control is of interest. The TFCL investigates the effects of structural motion on boundary layer separation and its control in collaboration with the Computational Fluid Dynamics Laboratories at the University of Arizona (Prof. Hermann Fasel) and New Mexico State (Prof. Andreas Gross).

**Figure:** Surface pressure distribution for plunging motion at k = 0.7 (8 Hz), h = 3.2% (left) and 4.8% (right) (0.38 in and 0.57 in respectively), for Re = 200,000. Nominal angle of attack is 10° case and the lift variation is sinusoidal. At 12°, the laminar separation bubble burst on the down stroke. The shedding of the laminar separation bubble generates moment stall shortly followed by lift stall.

Mark Agate, Jesse C. Little, Andreas Gross, and Hermann F. Fasel. "Oscillatory Plunging Motion Applied to an Airfoil Near Stall", 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-0998). https://doi.org/10.2514/6.2017-0998.

**Figure:** Contours of swirling strength calculated from phase-averaged PIV at select instances of the plunging cycle. Active flow control is provided by ac-DBD plasma actuation over 75% of the cycle. The forcing frequency is commensurate with the shear layer instability of the time-averaged bubble (F^{+}=fc/U (1.6 kHz) with C_{μ} = 0.0007%). This generates coherent 2D (laminar) roller-like structures near the leading edge that entrain freestream momentum and prevents the formation and burst of the laminar separation bubble at Re = 200,000.

Mark Agate, Arth Pande, Jesse C. Little, Andreas Gross, and Hermann F. Fasel. "Active Flow Control of the Laminar Separation Bubble on an Oscillating Airfoil Near Stall", 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-2049). https://doi.org/10.2514/6.2018-2049.