Flow Separation and Control

We examine the effects of wing sweep from Λ = 0° to 45° on the wake dynamics of a NACA0012 finite wing of semi aspect-ratio sAR = 2 at an angle of attack of 14°, across Reynolds numbers from Re = 600 to 10000. By analyzing this parameter space, we aim to bridge the knowledge gap between existing studies on separated flows over swept finite wings at low Reynolds numbers (Re~10²) and the behavior of turbulent flows at higher Reynolds numbers (Re~10⁴). Our results show that the progressive weakening and eventual disappearance of the tip vortex, when increasing the wing sweep, is accompanied by the emergence of a dominant inboard vortical structure near the root. At higher Reynolds numbers and sweep angles, the inboard vortical structure merges with the main wake, significantly altering the lift characteristics. Specifically, while increasing the sweep angle reduces the lift coefficient at low Reynolds numbers, it enhances lift at higher Reynolds numbers due to the formation of the ram’s horn vortex near the root. The flow changes that lead to the formation of the ram’s horn vortex are analyzed in terms of the streamwise vorticity, revealing two key effects: (i) a change in the sign of streamwise vorticity with increasing sweep angle, due to the increasing spanwise velocity component, and (ii) the concentration of negative streamwise vorticity near the mid-span at Λ = 45°, associated with the ram’s horn vortex. Our results contribute to a deeper understanding of the aerodynamic mechanisms governing swept-wing wakes, which is crucial for applications in aerospace vehicle design.

Funding acknowledgement

This work was supported by the U.S. Army Research Office (Grant Number W911NF-21-1-0060) and the U.S. Air Force Office of Scientific Research (Grant Number FA9550-21-1-0174)