Analysis of Rotor Start-Up and Shutdown on a Sea-Based Oil Rig

A combined rotor transient responses and analysis tools/computational fluid dynamics effort was completed to assess the rotor response in a complex flowfield. A generic helicopter on an oil-rig platform was chosen because the bluff nature of the rig presents unique challenges to rotorcraft operations. The rotor start-up and shutdown simulation model was validated with the test data. Comprehensive studies of rotor transient responses under various wind directions and wind speeds were conducted to establish the safe-operation envelope. The study found that horizontal wind velocities may be accelerated by the oil-rig building corner, and cause significant rotor flap motions. The upwash and downwash flow due to the blockage of the helicopter fuselage to the crosswind had great impact on rotor transient responses, and the peak blade flap responses can be 2.5 times higher than the simulation results when the effect of airframe on air wake was ignored. The influence of unsteady air wake on rotor transient responses was also investigated, and the results showed that it could increase the blade tip deflections by 70% if the unsteady-flow components were included. The sensitivity of the rotor-blade initial azimuth positions for rotor start-up operations was also examined.