Experimental Correlation of Ship Airwake and Rotorcraft Unsteady Loads under Longitudinal Gusts with PIV and Gust Generator

Abstract:
This paper presents an experimental investigation of ship airwake-rotor interaction under cruise-only and longitudinal gust conditions (cruise + gust). A model-scale NATO Generic Destroyer and rotorcraft were tested using time-resolved stereoscopic particle image velocimetry, a six-axis force/torque load cell, and flush pressure sensors. Flow structures, pressure distributions, and spectral energy within the pilot workload-relevant frequency bands were analyzed. High-pressure regions on the ship deck surface show the interactions between the ship recirculation region and rotor ground effects from downwash. The reduced forward velocity within the airwake leads to decreased thrust and a nose-down pitching moment across the ship deck. For high-disk-loading rotorcraft, the rotor ground effects are less important than the ship airwake effects. The power spectral densities of CT, CMx, and CMy decrease toward higher frequencies, while the PSDs of CFx and CFy retain comparatively higher energy at the upper end of the full-scale pilot workload frequency band. A maximum increase of 54.3% in the CMy pilot workload factor in the cruise + gust conditions is observed at Ldeck, which denotes a significant rise in the demand of pilot inputs near the ship stern. The overall pilot workload factor in the cruise + gust case increased by 35.6% compared to cruise-only at 1.5Ldeck, and decreases into the deck. Overall, gust-driven airwake dynamics intensify rotor loading and increase pilot workload demands during shipboard helicopter operations.

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