Computational Analysis For Aerodynamics And Acoustics Of Helicopter Tail Rotor And Noise Reduction Research

The research of tail rotor's aerodynamics and noise is an important subject in the field of Helicopter Aerodynamics. In this thesis, combining Navier-Stokes equations with FW-H equations, a computational method and a model are established for the aerodynamics and noise of helicopter main rotor(tail rotor). By the method, the aerodynamics and noise of conventional tail rotor and scissors tail rotor are calculated and analyzed respectively, and the noise reduction method of scissors tail rotor is studied, in the meantime, the characteristics of tail rotor noise with/without the interaction of main rotor are calculated and compared. The main work is as follows:As the background of the work, the objectives of the thesis and the current research of the domestic and overseas are firstly described, and then the difficulties in the current research are pointed out. The methods and the contents in this thesis are introduced.In the second chapter, according to the outlines and motions of main rotor(tail rotor), based on embedded grid, a computational method suited for the flowfield of helicopter rotor(tail rotor) is established based on Navier-Stokes equations. In this method, the Roe scheme is used to discretize the space, and the implicit LU-SGS scheme is applied to the pseudo-time step of the dual time method. The Spalart-Allmaras one-equation model is also used to solve the flowfield, then by this method, the Caradonna-Tung rotor hover test and Helishape 7A rotor forward-flight test are calculated to validate the method. Based on this, the 1/7 UH–1H rotor mode is taken as the noise calculation example which shows the accuracy of noise calculation.Applying the method, in the third chapter, the aerodynamics and noise of scissors tail rotor are firstly calculated in hover and forward flight, and the results are compared with conventional tail rotor. Then, the influences of motion parameters and blade-tip shape parameters of scissors tail rotor to the noise are analyzed. Some practical and meaningful conclusions are obtained.Based on the analysis of the blade-tip shape parameters' influence to the noise in the third chapter, in the fourth chapter, the noise reduced methods of scissors tail rotor are studied by changing the blade-tip shape and the airfoil thickness of blade-tip section. Based on this, the influences of the blade-tip shape and the airfoil thickness of blade-tip section to the noise are understood.For studying the influence of helicopter rotor's aerodynamics interaction to tail rotor noise, in fifth chapter, a geometry model of main rotor/tail rotor is given out, and then the characteristics of tail rotor aerodynamics and noise with the interaction of main rotor are calculated and analyzed. By comparing with isolated tail rotor, the interaction of main rotor to tail rotor is given out. The influence of forward flight ratio to tail rotor's aerodynamics and noise is calculated.In the sixth chapter, the main work and obtained conclusions in the thesis are summarized, and some aspects needed to be more completed are pointed out. Some suggestions are putted forward for the latter research.