Wake turbulence of inclined spheroids: influence of Reynolds number and pitch angle

With rapid developments in the technology of aerial vehicle and under-sea exploration, the study of wakes has become crucial for understanding vehicle dynamics. We report results from LES of a 6:1 prolate spheroid placed at pitch angles, α= 0^◦, 10^◦ and 20^◦. Cases at Reynolds number (Re= UL/ν) of 3 × 10⁴, 9 × 10⁴ and 1.8 × 10⁵ are considered. The turbulent kinetic energy budget is diagnosed and modal analysis is performed using Spectral Proper Orthogonal Decomposition (SPOD) to find dominant coherent structures and frequencies in the wake.

The cases with a finite pitch angle show a counter-rotating streamwise vortex pair in the wake. This pair significantly affects the turbulence statistics, altering vertical velocity based components of turbulent production. In contrast, at zero pitch, only the streamwise velocity is important for production. For finite pitch, SPOD of the near wake reveals high-frequency flapping modes and low-frequency oscillating asymmetric modes with different symmetry-breaking characteristics. The low-frequency mode leads to a substantial unsteady force. These modes decay quite rapidly and no dominant frequency is found one body length after separation. In the case of zero pitch, clear vortex shedding is observed which persists for long downstream distance.