Longitudinal Gust Effects on Ship Airwake Characteristics for Helicopter Landing Operations with Correlations to Pilot Workload Factor

An experimental study was conducted to characterize the unsteady flow field above the ship deck of a model NATO Generic Destroyer (NATO-GD) under both constant-wind and longitudinal-gust conditions. Time-resolved stereoscopic particle image velocimetry (PIV) was used to measure the velocity field along a 5° helicopter stern-approach landing path, enabling quantification of mean-flow features, turbulence levels, and gust-induced unsteadiness. Velocity-fluctuation metrics were obtained through turbulent kinetic energy, proper orthogonal decomposition (POD), and power spectral density analysis, including integration of pilot workload factor (PWF) over the 0.2–2 Hz full-scale conditions. The results show that the longitudinal gust cycle substantially amplifies streamwise and spanwise velocity fluctuations, increases turbulent kinetic energy, and strengthens coherent structures within the airwake. The POD analysis reveals that the dominant coherent flow structures are shifted towards the stern in longitudinal gusts. Band-limited spectral energy was consistently higher during the gust at all downstream locations, indicating a more demanding aerodynamic disturbance environment for shipboard rotorcraft recovery.