Turbulence Structure Resulting from a Vortex/Wing‐Tip Encounter

Measurements are presented of the flow produced by the perpendicular encounter between a streamwise vortex and a wing tip. The resulting flow field, which contains two interacting tip vortices, models the lurbulence found in the near tip region on the advancing side of a helicopter rotor. This region is a significant source of blade‐wake interaction (BWI) noise at level flight and mild climb conditions. Both single and two‐point turbulence measurements are presented. The single‐point measurements reveal the form of the turbulence structure generated by the interaction of the tip vortices. The two‐point measurements reveal, in terms of wavenumber‐frequency spectra, the turbulence length scales that would be encountered by a noise‐generating blade cutting this flow. It is concluded that the interaction between the vortices not only winds up the wakes to which they are attached but is also a source of new organized turbulence. It is also found that wavenumber‐frequency spectra measured in this flow are dominated by the large‐eddies present in the turbulence and are not well modeled by asuming a homogeneous isotropic spectrum.