Rotor Aeroekastic Modeling And Investigation On Blade-vortex Interaction Control With Actively Controlled Flaps

The blade-vortex interaction(BVI)of the helicopter widely exists in most common flight states such as forward flight and descending.When the blade-vortex interaction exists,the BVI fluctuating loads will be generated on the surface of blade due to the wake-induced velocity,and act as a second type of hydrodynamic sound source radiating fluid noise to the environment,which will significantly raise the noise radiation level of the helicopter and weaken its stealth performance.Therefore,the research on the control technology of BVI noise is of great significance for reducing the noise of helicopter and improving its its stealth performance.First of all,the rigid-flexible coupling dynamic model and the free-wake aerodynamic model for rotor system are established in this thesis,then an advanced aeroelastic model for helicopter rotor is developed,which has higher computing accuracy and reliability than traditional ones.The aeroelastic model was used as a research tool to carry out research on the control technology for BVI noise by actively controlled flaps(ACF);the control law of the BVI noise based on ACF technology is analyzed,and its internal mechanism is discussed.The detailed research contents are as follows:1.Based on the geometrically exact beam theory and deduction method of the second Lagrange equation,a rigid-flexible coupling dynamic model for the rotor sysrem is established.Based on the traditional Nitsche variational method,a modified variational method suitable for non-linear structures modeling is established.Combining with the idea of “layer-by-layer” expansion,the kinematic equation of the rotor system is obtained.The generalized-implicit integral numerical method is used to calculate the response of the rotor model,and the accuracy and reliability of the model are verified by comparing with the literature data.2.Based on the free-wake lifting surface method,a free-wake aerodynamic model for rotor system which considerd the the influence of trailing edge flaps was established.In view of the need for the presupposition of initial wake in traditional "time-accurate" wake calculation methods,a "space-time accurate" free-wake numerical calculation method which only based on the boundary information is proposed.The numerical truncation error of the discrete equation for the wake velocity is compensated by numerical analysis,and a free wake difference scheme with third-order accuracy is obtained,which improves the accuracy and reliability of the wake model.And the calculation efficiency of the aerodynamic model was improved by using the velocity interpolation technique.3.Based on the dynamic model and the aerodynamic model of rotor system,an advanced aeroelastic model for helicopter rotor is developed.In the process of modeling,considering the inconsistency of grid nodes between structural dynamics model and aerodynamic model,grid interpolation technology is used to establish the information interaction between structure and aerodynamics.The aeroelastic coupling algorithm of the rotor is established based on the PIPC method.The accuracy and reliability of the model are verified by comparing with experimental data and literature data.4.By using the developed aeroelastic model,we analyzed the impacts of blade-vortex interaction on the aerodynamic loads and inflow for the rotor disc,then proposed the separation method and quantitative index(BVI-P)of the BVI loads.By using BVI-P as an indirect measurement index of BVI noise,the control law of BVI noise based on ACF control technology are obtained,compared with the BVI noise control law obtained from NASA test in the United States,the validity of the research method in this paper is verified.It is found that the control frequency,the relative position of wake&rotor-disc and the blade flexibility have important effects on the control law of BVI noise;the control of BVI noise based on ACF may cause the increase of hub vibration load,and It is difficult to take into account both BVI noise and hub vibration control when using single harmonic frequency signal as control input.5.Based on the control law of BVI noise obtained above,more in-depth research has been carried out.The internal relations among rotor motion,circulation of the rotor disc,wake circulation,inflow of the rotor disc,wake motion and control effect of BVI noise have been further analyzed.Part of mechanisms of control law for BVI noise are revealed.The research on parameter design of trailing edge flaps was carried out,and some practical rules which may guide engineering design are summarized.