Experimental evaluation of a passive flow-control device for a tiltrotor aircraft

This work presents a preliminary investigation into tiltrotor propeller/nacelle/wing flows, and the flow breakdowns that can lead to the phenomenon of whirl flutter. Static blade measurements were performed, results suggesting that tubercles have the potential to provide an increase in performance for the baseline blade design. A small-scale propeller rig (0.7 m swept diameter) has been designed, manufactured, and commissioned at Cranfield’s 8x6 Wind Tunnel. This new rig operates well under static and up to wind speeds of at least 30 m/s. The effect of blade pitch angle (0 to 10◦ ) and propeller rotational speed (0 to 3000 rpm) have been investigated successfully. Forces measured on the wing set at angles of attack within the range 0 to 22◦ indicate the well-established effects due to propeller slipstream. Overall, the propeller wake flow slightly decreases the lift generated by the wing model, whilst also delaying stall. Pressure taps and accelerometers mounted on the wing and propeller nacelle effectively captured the slipstream effects, blade passing frequency, and flow separation regions. Finally, blades containing tubercle-shaped vortex generators were mounted to the propeller rig. Preliminary test results for the tubercle blades are reported in the paper. Overall, effects due to the propeller slipstream are dominant on forces, pressure distribution and vibration of the wing model. At the current stage of this ongoing investigation, it is not possible to conclude whether the tubercles provide any benefit to either the propeller or wing aerodynamic efficiencies. The rig is being equipped to measure propeller thrust and torque. Flow field investigation will also be carried out in future campaigns.