Wingtip Vortex Stability and Control Using Mean Flow Perturbation

Wingtip vortices generated by aircraft are the source of induced drag. Therefore, flow control devices such as winglets have been created to reduce the impact of tip vortices and consequently improve the wings performance. To use other flow control devices such as periodic heat-flux sources, the receptivity to the actuator must be fully optimized to be effective. The optimization process includes actuator placement, frequency selection and spatial modulation. The Mean Flow Perturbation (MFP) technique is a linear stability analysis that can be used to understand the receptivity of base flows to small perturbations. Its advantage over other linear stability analyses is that it can be applied fairly easily to complex 3-D flows in a relatively efficient manner, embedded within traditional flow-solver frameworks. This technique can help in gaining a better understanding of the receptivity of a flow control actuator that is used to control a complex 3-D flow. The current study seeks to apply the MFP technique to the author’s previous work on unsteady tip vortices. The aspect-ratio-four, rounded-tip wing has a NACA0012 section and operates at a Reynolds number of Re = 2 × 105 and incidence of α = 12°. The objective is to uncover the least stable mode shapes and frequencies of the structure using MFP in hopes of informing future flow control design techniques. At these conditions, the MFP shows a dominant least stable frequency and mode shape that occurs near the trailing edge of the wingtip. A region near the incipient separation of the vortex also showed with a definitive spatial wavelength that may be susceptible to tailored control.