The effects of unsteady change in wind direction on the airflow over the helicopter platform of a polar icebreaker

Abstract

The effects of the unsteady change of the wind direction on the airwake over the helicopter platform of a Canadian Coast Guard polar icebreaker were studied experimentally. By application of particle image velocimetry on a scaled model of the icebreaker, quantitative flow field data were obtained for several rates of change in the wind direction. This study was conducted in a water channel that featured a simulated atmospheric boundary layer as inflow condition. The rate of change in the incidence angle, α˙, varied in the range −0.25 ≤ α˙L/U ≤ 0.25, where L and U are the characteristic length and velocity, respectively. In addition to the time-averaged velocity fields, the turbulence intensity was evaluated to investigate the unsteadiness of the flow. Increasing the rate of change of the incidence angle of the incoming flow resulted in an increase of the turbulent intensity for all considered nominal incidence angles of the inflow. A notable exception to this trend was observed at α = 60°, where the direction of the inflow change had a pronounced effect on the structure of the flow over the helicopter deck. Thus, negative values of α˙L/U resulted in the wake of the superstructure not affecting the flow over the helicopter platform.