Transactions of Nanjing University of Aeronautics & Astronautics
Aerodynamic Interference and Performance Changes in “2-lead” Multi-lift System with Helicopters
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Abstract:
As the helicopters in a multi-lift system fly in a close formation， there is severe aerodynamic interference between the wake of the rotors， bringing complex aeromechanics coupling. So it is necessary to investigate interference and resulting performance changes before studying performance optimization and advanced formation control. A baseline configuration of four tandem helicopters carrying a load cooperatively in a “2-lead” formation is performed to explore the interference and performance. A vortex-panel approach based on the viscous vortex particle method is employed to investigate the performances and flow fields in a steady-flight state. The steady-flight state is obtained by a hierarchical trimming method， and the vortex-panel approach is validated by wind tunnel experiments. On this basis， aerodynamic interferences and performances at different flight speeds and variant relative positions are investigated. Computational results indicate that for the baseline configuration， there exists serious interference between helicopters in the front-and-rear arrangement， especially at forward flight. At the advance ratio of 0.1， there exists a 20% thrust loss and a 15% power increase for the front rotor of the tandem helicopter behind the formation. The aerodynamic interference will be reduced significantly if the distance between the front and the rear helicopter meets any of the three conditions below： more than 3.5D（D represents the rotor diameter） in the longitudinal direction， more than 0.75D in the lateral direction， or more than 0.5D in the vertical direction.
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V211
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