Research On Optimization Dynamic Design Of Composite Rotor Blade For Helicopter Vibration Reduction

Vibration problems of the helicopters keeps it from being quiet and comfortable flight like a jet, how to reduce the vibration has been the difficulty of helicopter design. Helicopter vibration reduction is one of the hot fields of helicopter technology at home and abroad research. Rotor is the core component of the helicopter rotor, also it is the main source of the helicopter vibration, this paper research on rotor dynamics optimization design method, and exploration the method from the source to reduce vibration load for rotor design, which has important scientific theoretical significance and engineering application value.。Helicopter rotor with slender and soft blade, under the complex environment of pneumatic, produce the strong aeroelastic coupling between degrees of freedom of flap, lag and twist, and the nonlinear structure and load characteristics requires structure model can accurately reflect the geometrically nonlinear deformation and coupling characteristics between each degrees of freedom. Helicopter flight test showed that serious vibration problom when transition or high speed flight, the two state corresponds to the different aerodynamic characteristics. For transition state, rotor aerodynamic model need to be able to description the inflow of rotor vortex interference.In high-speed flight, aerodynamic model the unsteady subsonic air compression effect need considered. Throughout the flight envelope, always need to consider the unsteady aerodynamic load and part of the blade position of dynamic stall, all of these factors is the source of aerodynamic load high frequency harmonic.Establish a highly efficient and reliable comprehensive analysis model of rotor dynamics is the key mechanisms of optimization design and optimized vibration reduction design of rotor blade. Based on the moderate deformation beam theory, this paper developed the explicit nonlinear finite element model of the structure for the balance of the calculation accuracy and efficiency of aerodynamic-aeroelastic analytical model. The analytical model with at least second order of geometrical nonlinear precision in this paper mainly account for the couplings of various DOF of the blade structures, significant improvement of structural response calculation accuracy was invalidated by examples taking nonlinear effects in consideration. The aerodynamic model is a improved one of B-L unsteady dynamic stall model, which showed a better forecasting accuracy of pneumatic phase and peak load compared to the original model when the Mach number of inflow is less than 0.3. The low speed flight rotor vortex interference characteristics were gained by Johnson-free wake model. Based on the integrated aerodynamic-elastic analysis model established in the above, the comparison of example and flight test showed a better accuracy of the aerodynamic force and structural load calculation accuracy than similar foreign software. To optimize computational efficiency and to avoid the long time-consuming problem during solving process introduced by the tight couplings of aerodynamic-aeroelastic, this paper take the aerodynamic force derived from steady aerodynamic load of balanced aerodynamic-aeroelastic model as the applied load of the nonlinear dynamic model. Numerical examples showed that the calculation accuracy of dynamic analysis model based on aerodynamic force was still within the acceptable range, the load harmonic phase and amplitude characteristics were also effectively captured.Unsteady aerodynamic force and the structure of the elastic modeling increased the difficulty in solving complex rotor dynamics equation,this paper based on the wavelet method, established a wavelet time finite element algorithm for slove the second order differential equatio, Daubechies wavelet time element was deduced, wavelet has multi-scale and multi-resolution characteristics, which can improve the solution accuracy of the rotor aerodynamic/elastic dynamics equation and the more efficiency. Through the load analysis results of SA349/2 helicopter examples and flight measured data, show that the established dynamic model of rotor dynamic load calculation are in good agreement with flight load test data accuracy, and more computational efficiency, provides a new method for rotor aerodynamic/elastic dynamic response solution.In view of the rotor blade optimization design demand, a a high-fidelity parameterized model of the typical composite C-type beam blade has bulided, the parameterized model can describe the blade engineering design parameterized, a efficient finite element mesh algorithm based on background grid has establish, and via the finite element method to obtain the distribution of blade section properties, which are input parameters for the aerodynamic/elastic dynamics model. This paper build a "Dolphin" helicopter composite blade parameters model by use the parameterized method, accurate expression of "Dolphin" helicopter blade structure, the section characteristic calculation results verify the reliability of this parametric design model.Eventually on the basis of parametric design model and the background of vibration reduction and optimization in rotor dynamics, the specific design variables of blade optimization are given. Constraint functions are defined according to blade modes and engineering constraints and different objective function are proposed aiming at different dynamics problem. Using uniform experimental design method to preprocess the initial distribution of design parameters, which are distributed more reasonable within the design space, the possibility of obtaining global optimal solution raises. Rotor dynamics analysis model is considered as a core optimization model, which is based on the predefined load and uses the improved multi-population genetic algorithm, and aerodynamic load is fixed with the consideration of pneumatic/elastic coupling model as the outer optimization model. The method improves the computing efficiency of rotor dynamics vibration optimization and the ability of global optimization.Based on the above research, a full set of optimization design method for helicopter rotor dynamics vibration reduction is established, which implements the optimization design of pneumatic/elastic dynamics tailoring for the composite blades of "Dolphin" helicopter rotor. The example shows not only the reasonability of the original "dolphin" helicopter blade design, but the design space of improvement. By optimizing distribution of the concentrated mass and adjusting the blade structure parameters(such as beam shape, thickness of the inside beam and length of the trailing edge strip), the hub load and blade section load are reduced effectively.