Aerodynamics of an aircraft propeller model with passive tip jet

The feasibility of employing a passive tip jet for enhancing the diffusion of the concentrated vorticity of blade-tip vortices is studied on a small-scale two-bladed propeller. The rotor employs hollow blades with slots for flow suction at the root and ejection at the tip. The centrifugal acceleration of the fluid created inside the blade by the rotational motion of the propeller is used to displace a considerable amount of flow momentum from the most inboard part of the blade to the tip. The particular technology is quite attractive because it does not require additional external power sources to drive the fluid. Test are performed in a low-speed wind tunnel with the propeller mounted at zero angle of attack. Oil-flow visualizations are used to characterize the change of the flow on the blade surface, whereas particle image velocimetry measurements are carried out to quantify the diffusion of the vorticity field obtained for three propeller advance ratios. Results show that the application of tip blowing considerably reduces the blade-tip vortex peak swirl velocity (33% for 0.24 propeller advance ratio) with a considerable increase in the vortex core radius (64% for 0.24 propeller advance ratio) and vortex diffusion. Although the fluid inside the propeller blade experiences viscous losses, no significant change of the blade performance is measured.