Near-field fluctuations and far-field noise of a three-element airfoil system by a discrete vortex method

A circulation-based discrete vortex method is used on a three-element airfoil system. Kutta conditions and Kelvin’s circulation theorem are additional conditions required for this method to determine the circulation distributions on each element and to determine vortex shedding. Discrete shed vortices are introduced near the four sharp edges to represent the sharp-edge vortex shedding caused by unsteady flow separation. The computational procedure warrants neutrally stable solutions of the self-sustained fluctuating flowfield that can provide broad-band spectral information for far-field noise predictions. The near-field vortex method directly calculates the parameters used in an asymptotic formula for far-field sound computation that attributes the noise sources to vortex interactions among the shed vortices and the surface circulations of the three-element airfoil system. The far-field noise characters are then analyzed and compared to the experimental data in the literature.