Investigation On The Blade-Vortex Interaction Aerodynamic Noise Of Helicopter Rotors

The research on the rotor blade-vortex interaction (BVI) noise is a very important aspect and a very challenging subject in the rotorcraft aeroacoustics field. In this thesis, both the analytical investigation, based upon the rotor free-wake vortex theory and the aeroacoustic methodology in time domain, and the experimental investigation, simulated in an aeroacoustic laboratory and at outdoors, on the BVI noise have been performed. The major contributions of the author's research work are as follows:As the background of the work, the classification of helicopter rotor noise sources is introduced briefly, and the important and difficult aspects in the BVI noise research are pointed out.In Chapter 2, a simplified analytical model is presented for the analysis of the BVI mechanism, adopting the Beddoes' prescribed wake model. By this model, the azimuthal location and miss-distance of the BVI and the radiation directivity of the BVI noise are calculated and discussed, and some conclusions are obtained.In Chapter 3, based upon the blade second-order lifting-line model and rotor free-wake model, an analytical method is developed for predicting the rotor wake structure and BVI airload.Based upon the rotor free-wake analysis and the Farassat Formulation 1A in time domain, an analytical model, which can be used to predict the BVI noise in hover and in forward flight, has been developed in Chapter 4.In Chapter 5, the UH-1 model rotor, the model rotor measured in the present work and the helicopter Z-8 rotor are taken as numerical examples, the calculations on rotor noise under different flight conditions are carried out for validation purposes.In Chapter 6, a new idea for simulating rotor BVI noise experiment is presented using a scissors rotor configuration with the vertical separation between a pair of rotors, based upon the fact that the important aerodynamic feature of this scissors rotor configuration is its close blade-vortex encounter. And the models and facilities designed for the BVI noise experiment are given.Finally, the experiments on the rotor BVI noise are conducted both in an aeroacoustic laboratory and at outdoors, and the noise characteristics at different locations are measured on different blade-tip Mach numbers, collective pitch angles and rotor configurations. Based on the experimental results, some new conclusions are presented.