AST 4-CT-2005-012238 FAR-Wake Fundamental Research on Aircraft Wake Phenomena _ _ _ Specific Targeted Research Project Start : 01 February 2005 Duration : 40 months Experiments on vortex / pulsed jet Interaction

Experiments were conducted in order to understand the effect of pulsed jets on a variety of aircraft trailing vortex arrangements in the near-field. Cross-flow velocity measurements were performed to assess how a pulsed main engine jet affected a single vortex, an equal strength co-rotating vortex pair and an equal strength counter-rotating vortex pair. Pulsing was conducted at realistically small amplitudes and at forcing frequencies around the optimum Strouhal number based on the jet exit velocity and diameter. Pulsing or steady blowing at the same momentum coefficient produced practically identical results which indicates that pulsing does not have a significant effect on any of the wake configurations tested. A reason for this could be that any additional turbulence generated close to the jet exit because of pulsing, may decay by the time it interacts with the wake vortices. An additional configuration tested studied the effect of a small control jet on a single trailing vortex. In this case, pulsed jets with large amplitude oscillations (but still small momentum coefficients) were used for flow control purposes. A reduction in cross-flow velocity magnitude and a diffusion of the vortex was observed when the jet was located just outside the vortex core. However, this effect deteriorated on positioning the jet inside the core. It is believed that the relatively small size of the jet in comparison to the vortex allowed the dispersion buffer to damp any perturbations generated within the core. FAR-Wake D 2.1.1 7 – Final 14 January 2008 3/66 Table of