Computation Of Rotational Noise And Research Of Blade-Vortex Interaction Noise For Rotors Based Upon Wake Analysis

Rotor noise is a challenging subject in the field of helicopter aerodynamics. Based on wake analysis, on one hand, the computational method for rotor rotational noise in hover and forward flight and the effect of parameters are investigated in this thesis. On the other hand, the detective method on blade-vortex interaction and directionality of its noise in the near/far field and radiation intensity are deeply analyzed. Also, the radiation characteristics about BVI noise of modern rotors with new blade tips and parameter influences are investigated. The major contributions of the author's research work are as follows:As the background of present work, the objectives of the research are firstly described. The research and development in the field of the helicopter rotor rotational noise, blade-vortex interaction sources detection, directionality and radiation characteristic of BVI noise, as well as wake analysis are briefly introduced. The difficulties in the current research on the BVI noise are pointed out. In addition, the methods used in the present research are briefly introduced. In order to provide an accurate airfoil aerodynamic model for computation of the rotor aerodynamic loading and noise, Chapter 2 establishes a method of computing airfoil unsteady aerodynamic forces at the attached flow, separated flow and stalled flow, based upon the Leishman-Beddoes model. The comparisons with the available experimental data are also made to show the capability of the method.Aiming at rotational noise computation and BVI detection, a free-wake model for hover and forward flight rotor is presented. By using this model, the free-wake geometry, induced inflow and loading distribution of the rotor at different advance ratios are calculated for validation purposes. By employing Farassat Acoustic Formula 1A in the time domain and combining the free-wake model, a numerical method of rotational noise computation for hover and forward flight has been developed. By the method developed, both rotor thickness and loading noise are computed. The influence of different design parameters on the rotational noise, such as rotor speed, blade number and rotor diameter, are also investigated. On the basis of the investigation, some meaningful results are obtained.Then, a new model for studying BVI noise directionality and radiation characteristics at the advancing side and retreating side of a rotor is developed with the help of the Beddoes modified wake model. The distribution features of BVI noise at the rotor advancing side and retreating side are studied, and the effect of different parameters such as blade number, advance ratio and tip Mach number, are also analyzed. Some conclusions have been drawn from analyzing the BVI noise radiation characteristics. Furthermore, a novel method of analyzing BVI noise radiation characteristics for the rotor with new blade tips such as backward-swept tip, forward-swept tip and sawtooth tip, is derived and established in this thesis. The features of the rotor BVI noise radiation with these modern blade-tips are investigated by using the method, and the influences of these modern tips on rotor BVI noise directionality and radiation characteristics are also discussed. Based on the research, some results which are helpful for the rotor design of reducing BVI noise are obtained.Finally, applying the free wake model, a plane detection method for rotor BVI miss-distance detection is developed. From this method, the miss-distance of BVI at the different conditions is computed, and the influences of the blade number, advance ratio and attack angle of tip-path-plane on the miss-distance and blade-vortex angle are emphatically analyzed.