Research On Predict Methods Of Helicopter Rotor Noise

For a conventional helicopter, the tail rotor is one of primary sources for helicopter noise. It is important to obtain the physical understanding of this noise and develop a tail rotor with low noise level. In this thesis, the major contributions of the author's research work are as follows:At first, the classification of helicopter tail rotor noise sources and the existent method of helicopter noise research is introduced briefly.In Chapter 2, the fluctuate equation of monopoly sound field and dipole sound field is deduced detailedly, the root of this equation is given. Analytical models is developed to investigate the noise of helicopter tail rotor, that is to say: the thickness noise and the loading noise is determined by a monopole source and a dipole source respectively.The theoretical deduction in Chapter 3 shows that the shape of load distribution used in the arithmetic is a decisive fact of the error margin size, the more the adoptive shape looks like the actual case, the smaller the error margin will be, therefore the tilt parabola shape can instead of the actual shape of load distribution in the permissible error margin when we predicting constant loading noise caused by the tail rotor of helicopter. In addition, the error comes from the arithmetic discussed above is analyzed and an error criterion which made this arithmetic suitable for forecasting the loading noise in engineering is given based on the calculational results.Chapter 4 presents the mechanism of helicopter tail rotor noise, developed a new analytical model to investigate the noise of tail rotor when helicopter fly forward.In Chapter 5, the helicopter AS350B2 rotor are taken as numerical examples in order to validate the model developed in chapter 4.Finally, Chapter 6 summarizes the current research, some advices for future research on this subject is given.This thesis provides an approach for the prediction of the tail rotor noise and the design of a tail rotor with low noise level.