Noise Reduction Design Of Helicopter Rotor And Noise Characteristics Analysis Of Whole Vehicle

Because of its unique flight mode,the helicopter has a wide range of applications and broad prospects in military and civil fields.However,the problem of noise pollution is a short board of helicopters.Design of the low-noise rotor and prediction of the helicopter's whole vehicle noise also becomes an important subject in the field of Helicopter Aerodynamics.In this paper,a numerical method for unsteady flow field of helicopter rotors(tail rotor)and aerodynamic noise calculation method were established.Based on this,the influence of rotor blade tip on rotor aerodynamic performance and noise level was studied,and low-noise rotor design solution was proposed.Finally,considering the atmospheric absorption of sound waves,the ground acoustic field of the simplified helicopter model was calculated.The research work of this paper includes the following aspects:As a research background,the domestic and foreign researches on helicopter rotor aerodynamic calculation,noise calculation and noise reduction design were reviewed.Problems and difficulties of the current research were pointed out.The research content and research methods in this paper were presented.Aiming at the geometric characteristics of helicopter rotor(tail rotor)blades,an efficient parametric body-fitted blade grid generation method was established.In order to accurately describe the rotor blade motion,a method of moving overset grid with hole cutting and honor cells searching as the core technology was established.On this basis,the calculation method of rotor aerodynamic noise based on FW-H equation was established.Then,a CFD solver for rotor(tail rotor)unsteady flow field and aerodynamic noise calculation program were developed.Comparing the result of the program with the standard case,the validity of the method and the program was verified.A rotor with five rectangular blades,a standard chord length of 0.42 m and an aspect ratio of 17.62 was used as a reference rotor to change the geometric shape of the blade tip through taper,sweepback and anhedral,the influence of rotor blade tip on rotor aerodynamic characteristics and noise characteristics during hovering were analyzed.It is expected that these laws can be instructive and meaningful to the design of blade shape that has good aerodynamic performance and noise performance at the same time.Under the guidance of the influence of blade tip geometric characteristics on the aerodynamic performance and noise level of the rotor,two blade profile combining forward-back-swept and taper were proposed.The aerodynamic performances and noise levels of the two improved rotors and the reference rotor in hovering state,cruising flight state and descending flight state were respectively calculated and compared.Based on the comparison of aerodynamic performance and noise level,the final low noise blade profile was given.Ignoring the helicopter's engine noise and the scattering effect of the fuselage,a simplified helicopter whole vehicle noise calculation model was established.The aerodynamic noise of rotor and tail rotor of isolated rotor,isolated tail rotor and rotor/tail rotor in the interaction flow field were calculated and contrasted on low-speed forward flight state and medium-speed forward flight state.Finally,the atmospheric absorption of the sound waves was introduced,and the ground sound field of helicopter noise was calculated.