Wing sweep effects on laminar separated flows

We reveal the effects of sweep on the wake dynamics around NACA 0015 wings at high angles of attack using direct numerical simulations and resolvent analysis. The influence of sweep on the wake dynamics is considered for sweep angles from 0 degrees to 45 degrees and angles of attack from 16 degrees to 30 degrees for a spanwise periodic wing at a chord-based Reynolds number of 400 and a Mach number of 0.1. Wing sweep affects the wake dynamics, especially in terms of stability and spanwise fluctuations with implications on the development of three-dimensional (3-D) wakes. We observe that wing sweep attenuates spanwise fluctuations. Even as the sweep angle influences the wake, force and pressure coefficients can be collapsed for low angles of attack when examined in wall-normal and wingspan-normal independent flow components. Some small deviations at high sweep and incidence angles are attributed to vortical wake structures that impose secondary aerodynamic loads, revealed through the force element analysis. Furthermore, we conduct global resolvent analysis to uncover oblique modes with high disturbance amplification. The resolvent analysis also reveals the presence of wavemakers in the shear-dominated region associated with the emergence of 3-D wakes at high angles of attack. For flows at high sweep angles, the optimal convection speed of the response modes is shown to be faster than the optimal wavemakers speed suggesting a mechanism for the attenuation of perturbations. The present findings serve as a fundamental stepping stone to understanding separated flows at higher Reynolds numbers.

Automated summary

The study reveals that wing sweep attenuates spanwise fluctuations and influences wake dynamics in terms of stability and spanwise fluctuations, especially in the development of three-dimensional wakes. Global resolvent analysis uncovers oblique modes with high disturbance amplification and shows that for flows at high sweep angles, the optimal convection speed of the response modes is faster than the optimal wavemakers speed, providing insights into the mechanism for the attenuation of perturbations in separated flows at higher Reynolds numbers.