Wind Tunnel Investigation of a Rotor Under the Influence of Unsteady Ship Airwakes with Azimuth-Correlated Measurements

The performance and unsteady loads of a rotor operating in shipboard environments are highly sensitive to the influence of unsteady ship airwakes. In extreme cases, this interaction can significantly degrade rotorcraft handling qualities and constrain the safe launch and recovery flight envelope. This study presents wind tunnel measurements of azimuth-correlated rotor hub loads for a 1:100 scale single main rotor, modeled after the NATO Generic Rotorcraft, hovering above and around the landing deck of the NATO Generic Destroyer. These measurements were complemented with Particle Image Velocimetry (PIV) measurements. Unlike time-averaged data, azimuth-resolved measurements reveal detailed insights into the interactional aerodynamics between the rotor and ship airwake at specific rotor azimuth angles. By comparing phase-averaged rotor load responses to a trimmed reference condition measured up-and-away from the ship airwake, this study discovered both beneficial and detrimental load variations across different azimuth angles. These variations were strongly influenced by the hovering location of the rotor relative to the ship deck. While longitudinal shifts along the deck centerline resulted in gradual changes, lateral offsets induced significant changes in azimuthal thrust characteristics. Additionally, the wind-over-deck (WOD) angle had a considerable effect, with quartering wind conditions causing significant detrimental impacts on the upstream blades at certain azimuth angles, locally leading to a substantial loss of thrust. These findings were further supported by horizontal and vertical plane PIV measurements. Both the extracted downwash velocity data and local thrust estimates based on momentum conservation showed notable azimuthal and radial variations in downwash velocities and thrust production across the rotor disk, closely matching direct thrust measurements across different hovering conditions.