Abstract
*An experiment was conducted to understand the flow field surrounding a slotted helicopter rotor blade that directs a part of its incident flow along the spanwise direction. Flow visualization and 3-component LDV measurements were made on tip vortices trailing from the slotted blade for four different slot configurations to quantify the swirl and axial velocity components, mean kinetic energy, core development and its turbulent properties at a fixed wake age of 145 degrees. The presence of the slots created a flow velocity in the spanwise direction that resulted in much diffused vortex structure at very early wake ages. An increase in number of slots was shown to increase the diffusion of the tip vortices. However, the slot optimization study indicated that the slotted blade with two slots showed sufficient vortex diffusion, and as much as the blade with four slots. The axial velocity of tip vortices generated by the slotted blade was found to increase with more slots, which is different to the baseline case. Also, the convection swirl of the slipstream about the hub axis was found to be higher for the slotted blade case. This results in an increased mean kinetic energy of the tip vortices explaining the increased power requirement of the slotted blade rotor.
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