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335 - Development of low-noise ducted-fan tail rotor for helicopter antitorque system
Chung K., Kang H., Song K., Hwang C., Joo G.
Abstract
A ducted tail rotor antitorque system can reduce the risk of component damage as well as enhance the safety of operators, passenger, and ground personnel. With respect to the performance of the tail rotor of the ducted-fan type, it has great advantage that a blow-out speed is high, and a thrust drop call ¡°a vortex ring state¡± can be prevented. In the tail rotor of the ducted-fan, in order to decrease an axial length of the duct to reduce an head resistance area, it is required to shorten a chord of the rotor blade. Therefore, in order to obtain a required total area of the rotor blades, the number of the rotor blade is necessarily increased. With respect to the noise, high-frequency noises are generated because the noises are composed mainly of a frequency equal to the product of the revolution number and the number of rotor blade. Therefore, on an acoustic detectability standpoint, ducted-fan tail rotor has an advantage with respect to conventional tail rotor with high acoustic energy content at low frequencies. Even if the sound pressure level of this high frequency noise is lower than that of the noise from the main rotor, the noise from the tail rotor is considered as the main source of noise in rotorcraft because the noise from the main rotor is low-frequency one. In this paper, low-noise ducted-fan tail rotor that is designed and tested at KARI(Korea Aerospace Research Institute) will be addressed. Unequal angular spacing method is used for low-noise technique. The optimal angular spacing position is predicted by using an acoustic analogy and detailed performance and noise radiation are calculated by using time-marching free-wake method and Farassat Formulation 1-A. The predicted performance and noise results are compared with those of real scale experiments performed by KARI.
Citation
Chung K.; Kang H.; Song K.; Hwang C.; Joo G.: Development of low-noise ducted-fan tail rotor for helicopter antitorque system, CD-ROM Proceedings of the Thirtheenth International Congress on Sound and Vibration (ICSV13), July 2-6, 2006, Vienna, Austria, Eds.: Eberhardsteiner, J.; Mang, H.A.; Waubke, H., Publisher: Vienna University of Technology, Austria, ISBN: 3-9501554-5-7