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Title: Analysis of In Situ Ship Air Wake Dynamic Interface Phenomena Using a Small Scale Helicopter

Author(s): Chen Friedman and Murray Snyder

Abstract: The phenomenon of dynamic interface between air wakes of a ship and a helicopter is investigated experimentally in situ on a 32.9 m long ship, using a scaled radio controlled helicopter mounted on a pole at a fixed location. The research ship has a similar design to that of a modern warship, including a hangar structure and a flight deck. Air wakes are surveyed by using up to 6 anemometers to measure air velocity inside the dynamic interface zone at two fixed heights of 1.15 and 1.54 diameters above the deck, and at a radial position of 75% of the rotor radius. For both ß=0° (headwind conditions), and ß=-15° (wind at 15° off the starboard bow), significant downwash velocities are measured by the Port and Starboard anemometers, while the Forward anemometer measures no downwash as the wake is convected towards the stern. A wake skew angle calculation and smoke visualization are used to support this finding. The Aft anemometer measures significant downwash for approximately 50% of the cases, due to complex interaction with the ship air wake. Power spectral density results present a much more pronounced effect of the rotor wake at low frequencies under 0.2 Hz, as it drives the recirculation zone immediately behind the hangar wall. These results may support validation of computational tools for dynamic interface analysis, as well as evaluate modifications to the ship's hangar for the purpose of altering the ship’s air wake.