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An Examination of a Pumping Rotor Blade Design for Brownout Mitigation

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Trident Scholar Project rept.

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Brownout is a significant concern for Naval rotorcraft operations. It occurs when a rotorcraft operates over an unprepared surface and becomes engulfed in a cloud of sediment. High resolution flow visualization FV and particle image velocimetry PIV measurements were taken to examine the development and evolution of rotor tip vortices. The current work focuses on diffusing tip vortices through the use of pumping rotor blades, as the tip vortices are the primary means of sediment uplift. A baseline non-pumping and four pumping blade designs were tested. All the pumping blade designs used a centrifugal pumping design, but the internal flow exited the blade tips at orientations of 0 deg., 30 deg., 45 deg., and 60 deg. above the horizontal axis. All blade designs were tested in a hovering state in ground effect at a blade loading coefficient of 0.08. Additional measurements were performed on the baseline and 0 deg. pumping blades at a lower blade loading coefficient of 0.053, which was considered the functional equivalent of testing a higher mass flow through the pumping slots. The pumping blades experienced a power penalty in comparison to the baseline, which was a result of profile losses due to the exit slots at the tip. When operating at the higher thrust condition, the pumping blades were found to merely prolong the initial formation of the tip vortices, rather than completely diffusing them. However, the 0 deg. pumping blade was found to generate significantly diffused tip vortices at the lower thrust condition, which greatly reduced upwash velocities near the ground.

Subject Categories:

  • Military Aircraft Operations
  • Helicopters
  • Fluid Mechanics

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