Active attenuation of a trailing vortex
Trailing vortices are generated in aeronautical and maritime applications and produce a variety of adverse effects that remain difficult to control. Often, intuitive control strategies lead to suboptimal control. To design a control strategy for attenuating a trailing vortex, we employ linear stability analysis. We solve the parabolized stability equations (PSE) on a trailing vortex aft of a NACA0012 half-wing at an angle of attack of alpha = 5° and a chord Reynolds number of 1000. For the initial condition of the PSE, we perform a parallel stability analysis at x/c = 0.25, finding numerous unstable modes. As the modes evolve downstream, the principal mode co-rotates with the base flow near the tip vortex region, resulting from the convective nature of the PSE. However, a subdominant mode displays non-monotonic growth rate behavior, becoming unstable as the trailing vortex develops farther downstream, counter-rotating around the tip vortex, which is indicative of a vortex instability. From these results, we hypothesize that the subdominant mode provides a pathway to excite the trailing vortex instability potentially resulting with its attenuation. Hence, we conduct DNS with trailing-edge actuation based on the principal and subdominant mode shape to attenuate the tip vortex. Although both controlled cases achieve trailing vortex attenuation, the subdominant mode exhibits attenuation of the trailing vortex more effectively
