Unsteady Shear Layer Dynamics in an Asymmetric Wake

This study investigates the flapping behavior of the shear layer within an unsteady separated wake generated by a slender body at a high angle of attack (alpha). The flow physics are evaluated using high-fidelity Implicit Large Eddy Simulations (I-LES) performed at a freestream Mach number, M = 1.1 and a freestream Reynolds number, Re = 600,000, past a 8-degree nose angle cone at alpha = 30-degrees. The crossflow boundary layer develops around the curvature of the cone and eventually separates into a pair of asymmetric counter-rotating primary vortices. Near the leading edge, two separation bubbles form along the primary separation regions. The shear layers which bounds these separation bubbles exhibit an oscillatory motion within the separation and reattachment points. The port side shear layer has a more pronounced flapping motion compared to starboard side shear layer, although the starboard side separation bubble is larger than the port side separation bubble. As a result of the flapping motion and shear layer instabilities, large-scale and fine-scale coherent structures form and shed from the reattachment points. These structures exert a pressure imbalance along the primary separation regions which contributes to the asymmetric aerodynamic loading experienced by slender bodies at high angles of attack. The major shear layer unsteadiness is characterized by a frequency analysis which identifies low and high frequency shear layer instabilities. Spatial support of these shear layer instabilities are extracted using modal analysis.