Helicopter Rotor Ground Effect and Frigate Interaction Investigated by Particle Image Velocimetry

Helicopter maneuvers on frigates develop an essential role during military operations. However, the complex flow generated by the frigate bluff-body shapes and the interaction with the helicopter downwash during the recovery process must be studied in detail. In addition, the ground effect can also affect helicopter performance during the maneuver. This study aims to use particle image velocimetry in wind tunnel to analyze the airflow generated by a 1:100-scaled helicopter rotor of the Sea King SH-3 navy helicopter isolated and with the presence of a full and a partial ground to consider the ground effect at different heights. Once the rotor has been studied, experimental tests were carried out of the rotor working next to a frigate model during the recovery maneuver. The measured velocity indicates that the flow asymmetry below the rotor can increase with the proximity to a partial ground distance up to 1.39 times. During the study of the rotor for the frigate landing approach, the downwash asymmetry is also important and changes abruptly the tendency during the last phase of the maneuver. It can lead to dangerous instabilities and problems for the helicopter pilot during the hovering over ships.