Research On The Aerodynamics Characteristics And Blade Vortex Interaction Noise Of Electrically Controlled Rotor Based On Viscous Vortex Particle Method

Rotor noise is one of the main sources of helicopter noise.Among the different types of rotor noise,blade vortex interaction(BVI)noise is usually generated in the descent or maneuvering flight conditions.Once BVI noise appears,it will extremely annoy people and significantly increase the mid-frequency noise level of the helicopter.Therefore,reducing rotor BVI noise has been one of the most crucial problems in the development of helicopters.Since the trailing edge flap is adopted to replace the swashplate system to implement primary rotor control,electrically controlled rotor(ECR)can theoretically alleviate BVI noise by using active control technology.With the background of the BVI noise alleviation of ECR and a perspective of the BVI noise generating mechanism,a series of topics related to the aerodynamic modeling,aerodynamic characteristics and wake structure analysis,BVI noise characteristics analysis and alleviation of the ECR has been studied in this dissertation.The main research work was listed below:(1)An analytical model based on the viscous vortex particle method and Weissinger-L lifting surface model is established.The unsteady airloads is considered by using Leishman-Beddoes model and Hariharan-Leishman model.The flap deflection induced blade pitch movement is obtained by solving the ECR blade pitch movement equation via the Runge-Kutta fourth-order method.On this basis,to address the low computing efficiency of the viscous vortex wake model,a“relaxation difference”-based trim strategy is developed to reduce the calculation times of the viscous vortex wake model during trim iteration.Furthermore,the established model is verified by a series of conventional rotor example and a control response test of the improved ECR system in hover condition.(2)Aerodynamic characteristics and wake structure of a sample ECR in hovering and forward flight conditions were studied comprehensively.Specifically,the effects of the blade pre-index angle and rotor advance ratio on the flap trim variable,induced inflow,disc load distribution,and wake vorticity were analyzed.The results show that,when the flap deflects significantly,not only the tip vortices with concentrated vorticity but also the intense flap tip vortices at both ends of the flap will trail in the wake flow field of ECR.When the advance ratio is high,not only the tip vortices will form roll-up vortices,but also the flap tip vortices will form roll-up vortices,and the direction of the roll-up vortices is opposite.Furthermore,in the forward flight condition,the ECR flap collective deflection results in cyclic blade pitch movement,while flap cyclic deflection results in a significant portion of the 2/rev harmonic component in the blade pitch movement when the advance ratio is high.Additionally,the “relaxation difference”-based trim strategy developed in this dissertation improves the overall computing efficiency significantly.(3)Based on the aerodynamic calculation model of ECR and the Ffowcs Williams and Hawkings equation,the BVI airloads and noise predicted model of ECR was established.The model was verified by using different examples.On this basis,the aerodynamic and acoustic characteristics of a sample ECR in BVI conditions are analyzed and a study was performed to examine the effect of the pre-index angle on the BVI-induced airloads and noise.The results show that,since the BVI event of the ECR on the advancing side is mainly caused by the interaction between the flap tip vortices and the blades,the blade spanwise range of the ECR BIV occurrence on the advancing side is smaller than that of the conventional rotor.Moreover,instead of miss distance between rotor wake vortex and blade,the different strength of wake vorticity is the main reason for the difference in the BVI-induced airloads and noise among the ECR with different pre-index angle.(4)Simulation and analysis of the non-harmonic flap deflection for the alleviation of BVI noise on the advancing and retreating side of a sample ECR were carried out.According to the generating mechanism of the BVI noise of ECR,the effectiveness of non-harmonic flap deflection in the second-quadrant,intended to reduce the strength of the flap tip vortex as it is generated,and thereby weaken the advancing side interactions was examined.Furthermore,the influence of the input waveform and amplitude on the BVI noise of ECR was analyzed and the BVI noise reduction mechanism was revealed.In addition,the performance of the flap non-harmonic deflection and harmonic deflection to alleviate BVI noise on the advancing side of the sample ECR was compared.On this basis,the control effect of the non-harmonic flap deflection in the third-quadrant on the retreating side BVI noise of the sample ECR was studied.The simulation results show that the non-harmonic flap deflection mainly realizes the BVI noise alleviation by reducing the wake vortex strength on the advancing and retreating sides,but it will lead to the increase of rotor noise in other areas.The harmonic flap deflection not only affects the wake vortex strength,but also has a great impact on the blade vortex miss distance.