COMPUTATIONAL FLUID DYNAMICS ANALYSIS OF HELICOPTER DOWNWASH/SHIP AIRWAKE INTERACTION FLOWFIELD

Abstract

There are problems specific to the helicopter/ship dynamic interface that limit helicopter operations and cause difficulty associated with landing on a moving platform. Significant factors affecting such operations include visibility, ship motion and aerodynamic interactions of the helicopter with the turbulent airflow near the ship. Associated large velocity gradients and areas of turbulence are limiting operations of helicopter flight onto and from the decks of frigate type air capable ships. For this reason, overcoming the problems that the helicopter encounters as it lands and takes off requires the airflow around the ship and through the helicopter rotors to be well-understood. Ship dynamics, the ship induced airwake, and the aircraft/ship interaction strongly affect the processes such as helicopter takeoff from and landing on shipboards (Bridges et al., 2007). Helicopter shipboard operations impose flight envelope restrictions on the rotorcraft due to a harsher environment. This environment also includes ship airwake caused by ship motion, superstructure, and a respectively smaller landing area. A detailed knowledge of the airflow around the ship and the vicinity of the helicopter rotors are necessary to understand the problems associated with helicopter takeoff and landing. The airwake of the ship includes the region of separated flow on the lee side of the ship’s superstructure and hangar door. This region contains steep spatial gradients in flow speed and direction and also contains significant unsteadiness over the bandwidth of concern with respect to handling qualities 0.2-2 Hz (Lee et al., 2013). These characteristics typically have a negative impact on helicopter handling qualities. The time-averaged and unsteady flow phenomena can influence the rotor generated loads and lead to increased pilot workload (Zan et al., 1994).