Modification of dynamic stall using broadcast mode analysis*

The modification of dynamic stall on a pitching airfoil is studied using network analysis in conjunction with discrete vortex method that models the massively separated flow. This allows the discrete vortices to act as the nodes of the network and their interactions as the edges. Aiming to identify effective pathways for vortical perturbations to amplify, this study quantifies the vortical interactions using the Jacobian of the nonlinear function of induced velocity, instead of the induced velocity itself that is commonly used in previous studies. For the time-varying vortical network, we perform broadcast mode analysis to identify important stages during the process of dynamic stall that are receptive to perturbations and the vortices to seed effective perturbations. The analysis shows that the onset of dynamic stall, where the discrete vortices form a vortex sheet emanating from the leading edge, is the most important stage for perturbations to amplify for modifying the vortex dynamics. The vortex sheet remains as the most effective nodes to seed perturbations during the dynamic stall, but limited modification can be achieved when the discrete vortices are populated over the airfoil to form a large leading edge vortex. The present network analysis demonstrates potential for physics-based mitigation of dynamic stall.