Experimental study of effects of discrete jets on tip vortex attenuation

An experimental study of the effects of destabilizing the tip vortices from a model wing and a model rotor using perturbations introduced by discrete jets located at the tips was conducted. A study on a fixed wing was conducted in a water tunnel using hydrogen bubble flow visualization for qualitative observations. Results of steady spanwise blowing indicated increased flow unsteadiness, as well as decreased tangential velocities and a displaced vortex core. Pulsed injection at selected frequencies increased the unsteadiness in the flow, resulting in a wake flow with no observable vortex core. This preliminary study offers the potential for continued work in optimizing pulsing and jet configurations for maximum tip vortex instability and dispersion. Preliminary testing was also conducted on a static rotor test stand to study the potential use of discrete jets on rotor blades to reduce the effects of blade vortex interactions - a common problem in rotor aerodynamics. Hot-film measurements in the wake of a 'hovering' rotor were used to quantitatively compare velocities associated with tip vortices between a baseline and an experimental blade. Results for baseline tests (no blowing) were consistent with previous studies. Results from the experimental blade showed dramatic reductions in maximum velocities. Typical reductions were observed from 0.475V_tip (baseline) to 0.25V_tip with blowing at C_μ = 0.0033. Also, increased unsteadiness in the region of the vortex with the blowing blade was observed. A basis for future research has been established by showing potential reductions in blade vortex interaction effects using this technique.