Helical Jet in moving air was used to simulate the flow downstream of a helicopter blade tip or a wing tip. The jet was generated by means of an opened pipe supplied tangentially (tangential nozzle), and placed in a wind tunnel. Flow properties were investigated in several cross-sections downstream of the nozzle. The flow direction and the total pressure were measured in function of the azimuthal angle and the distance from the axis of the system. The flow was visualized using the planar laser scattering technique. The decay of swirl intensity was measured by means of a probe with a rotating plate fixed to a miniature voltage generator.

A helicopter blade tip vortex generates impulsive noise of high intensity when it impinges upon the following blade. In the present work, the vortex is attenuated by coaxial swirling jet rotating in the opposite direction. The jet issues from a nozzle located at the blade tip. The nozzle was supplied with compressed air transported in the blade channel. The decrement of vortex strength is measured as a function of the compressed air pressure related to the dynamic pressure of the flow in the wind tunnel. It was found that the jet, even of relatively low intensity, considerably effects the blade tip vortex formation.