Turbulence structure resulting from a perpendicular airfoil-vortex interaction

The perpendicular interaction of a streamwise vortex with an airfoil was studied in incompressible flow to provide useful information regarding the accurate prediction of helicopter rotor noise by analyzing some of the fundamental fluid dynamics associated with the interaction. Three-component velocity and turbulence measurements were made using a sub-miniature four sensor hot-wire probe. The airfoil sheds negative vorticity into its wake due to the angle of attack variation along its span induced by the passing vortex. Instability in the vortex core results from its interaction with this negative vorticity region causing a dramatic magnification of the scale and intensity of the turbulent flowfield as well as a fundamental change in the turbulence structure of the vortex core evidenced by velocity autospectra measured there. (Author)