In Situ Velocity Measurements in the Near-Wake of a Ship Superstructure

Velocity measurements in a ship airwake are obtained in situ aboard a 108 ft naval training vessel. The measurements and analyses aremotivated by the need for validation data for airwake computational fluid dynamics simulations. Three-component anemometers are placed above the bow of the ship and at numerous locations above a flight deck at the stern of the ship. Data are presented for a direct headwind (nominally 0 deg wind-over-deck). The mean velocity field shows a clear structure to the flow, dominated by a recirculation region in the near-wake of a hangar-like backward-facing step. The location of this primary vortex and the reattachment point on the flight deck are estimated. Reynolds stresses are presented to quantify the turbulent fluctuations, which are required for the prediction of unsteady loading on rotorcraft operating in this environment. Significant anisotropy is measured in the wake, both within the primary vortex and in the far field. The peak Reynolds shear stress is located in the recirculation region, while the streamwise normal stress is found to increase with height throughout the measurement domain. Finally, autoand two-point velocity correlations from the flight deck provide an estimate of flow scales, showing the potential influence of turbulence on piloted helicopter operations.