Nonlinear development of vortex instabilities over HyTRV lifting body

Streamwise vortices are ubiquitous structures on the surfaces of three-dimensional aircrafts and are prone to Z- and Y-mode instabilities. We systematically investigate the nonlinear development of vortex-mode instabilities and resonant interactions employing plane marching nonlinear parabolised stability equations (NPSE3D) and quasi-direct numerical simulation (QDNS). The results suggest the moderately strong subharmonic resonance, and that the detuned interaction between a high-frequency Y-mode and a low-frequency Z-mode may precipitate the transition process. Albeit without any sign of the fundamental resonance, the self-interaction of a Y-mode generates mean flow distortion (MFD) that, in turn, yields the amplitude saturation and causes the hairpin vortex formed by the Y-mode to cascade into smaller scale vortices via vortex reconnection. Sensitivity analysis reveals that MFD exerts a destabilising direct effect on modal instability, but this is offset by its stabilising indirect effect through weakened base-flow shear, ultimately resulting in net stabilisation. Higher-frequency modes display heightened sensitivity to MFD. Moreover, QDNS exhibits a late-stage surface skin friction overshoot, accompanied by an amplification of subharmonic frequencies.