Theory, Computation and Experiment on Criticality and Stability of Vortices Separating from Edges
Technical Report,15 Apr 2013,15 Apr 2016
Department of Mechanical and Aerospace Engineering, North Carolina State University Raleigh
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The aim of this research effort was to extend earlier work airfoil leading-edge vortex LEV shedding to finite-wing flows. The current research shows that leading-edge suction, which was shown in the earlier work to govern LEV formation in airfoils with rounded leading edges, also governs LEV formation on finite wings. It is shown that when the maximum value of the span wise distribution of leading-edge suction on a finite wing reaches a critical value, LEV initiation takes place. The critical value is the same as that for the corresponding airfoil section, allowing it to be determined from 2D experiments or computations. Further, the critical value is independent of motion kinematics so long as LEV formation is not preceded by significant trailing-edge flow reversal. This insight was used to augment an in viscid unsteady vortex lattice method UVLM to handle LEV shedding from finite wings by using a vortex sheet to model the LEV shedding along the span. By convecting the LEV sheet using local velocity, the UVLM was able to predict vortex-sheet roll up, which agreed well with high-order computations. The current research has brought to light important insights in the initiation of LEV shedding on finite wings, which can be used in low-order modeling and flow control.