| Helicopters are world-widely used for its flight flexibility,but they also suffer from high vibration,severe noise and structural fatigue because of a highly unsteady aerodynamic environment and vibratory loads of the main rotor.At present,vibration and noise reduction is still one of the key objectives pursued by helicopter scientists.Meanwhile,low vibration levels and low noise have been one of the most important criteria for distinguishing between successful and less successful engineering design.In this paper,the rotorcraft multi-disciplinary design optimization methodology was developed by intergrating appropriate disciplines and accounting for important interactions among the disciplines,which aimed at eliminating the isolated descriptions between disciplines in rotorcraft preliminary design.The rotorcraft multi-disciplinary design optimization methodology for vibration reduction,noise supression and maximum fatigue life established in this research has important significance in scientific theory and engineering practice.Rotor system design is a complex task involving multiple disciplines,and it is a typical multidisciplinary comprehensive optimization design problem.For this reason,this paper focuses on the development of a multi-disciplinary theoretical model of rotors with reliable accuracy and reasonable matching,and effectively integrates multi-disciplinary modules of rotor aerodynamics,structural dynamics,aeroacoustics,fatigue strength and flight mechanics.Finally,multidisciplinary design optimization(MDO)technology is used to solve the comprehensive optimization problems of multiple disciplines and systems.This paper focuses on multi-disciplinary comprehensive analysis models,calculation methods,and verification studies of rotors,and establishes multi-disciplinary comprehensive analysis methods of rotors under the aeroelastic framework:(1)In the blade structure model part,developed a full-coupling 19-degree-of-freedom finite element folding beam model based on the moderate deformation beam theory and taking into account shear degrees of freedom and advanced geometries(forward / backward sweep,down-reverse),which improves the accurate description of dynamics such as blade displacement,strain energy,and kinetic energy of advanced geometry.In order to further improve the calculation efficiency,a Gauss based beam element is used to reduce the degree of freedom of the structural model.(2)In the aerodynamic model of the blade,a blade aerodynamic model using the LB dynamic stall model and Johnson free wake was established;and the inner and outer two-layer circulation was constructed to realize the rotor aerodynamic / structural dynamics /flight mechanics balancing For the solution,the inner-layer aeroelastic periodic response calculation uses the three-node fifth-order Emmet format time-limited method,and the outer trimming iteration uses the Newton-Raphson method.(3)In the aerodynamic noise model part,the rotor far-field noise is calculated using the harmonic method based on the aeroelastic load information obtained from the aeroelastic coupling analysis.(4)In the strength evaluation part,according to the blade section dynamic load and motion information,the section stress is calculated by using the theory of medium deformation beam to realize the assessment of the blade’s safe fatigue life.Finally,the SA349/2helicopter was used as an example for medium speed forward flight to verify the dynamics module;The UH-1 helicopter rotor is used as an example to verify the noise calculation module;The results are in good agreement,indicating the correctness of the multidisciplinary analysis method in this paper.This study improves the ability of multi-disciplinary comprehensive analysis of rotors.In order to further improve the key issue of aerodynamic calculation accuracy in multidisciplinary analysis of rotors,this paper adopts a loose coupling strategy to develop the CFD /CSD coupling analysis method,and uses the delta method to introduce the rotor aerodynamic load calculated by CFD into the aeroelastic comprehensive analysis.The CFD module uses the balancing solution output from the dynamic comprehensive analysis code,drives and updates the rotor grid,and constructs the CFD aerodynamics in incremental form to pass to the comprehensive analysis module;the sign of the coupling calculation convergence is the characteristic profile aerodynamic coefficient Increment.In order to further improve the key issue of aerodynamic calculation accuracy in multidisciplinary analysis of rotors,this paper adopts a loose coupling strategy to develop the CFD /CSD coupling analysis method,and uses the delta method to introduce the rotor aerodynamic load calculated by CFD into the aeroelastic comprehensive analysis.The CFD module uses the balancing solution and response information output by the dynamic comprehensive analysis code to drive and update the rotor grid,and constructs the CFD aerodynamics in incremental form to pass to the comprehensive analysis module.The sign of convergence in the coupling calculation is the aerodynamic coefficient increment of the characteristic profile.Based on the converged CFD flow field and load information,Lighthill acoustic analog method was used to recalculate the rotor noise,and the aerodynamic load/structure load/noise calculation result was compared with the calculation result of the comprehensive analysis code,which deepened understanding of rotor load/aero/noise issues.Through the analysis of the SA349 / 2 helicopter at low speed and medium speed,the effectiveness of the CFD / CSD coupling strategy and the stability of the coupling algorithm are verified.In the subsequent multidisciplinary optimization design research,based on the rotor multidisciplinary comprehensive analysis model and the CFD predetermined aerodynamic load,the rotor multidisciplinary optimization design research was carried out,and a multilevel strategy for solving the rotor multidisciplinary optimization problem was proposed.(1)Established a high-precision parametric model of the blade surface for engineering design,realized the definition of effective design space,accurately described the engineering design constraints,and improved the engineering feasibility of the optimized design scheme.(2)A multidisciplinary optimization design method and implementation process for helicopter rotors were proposed and constructed,and the structural design parameters and aerodynamic shape design parameters(forward/backward sweep angle,upside down/downside reverse angle,Chord length configuration,etc.)are optimization design variables;rotor optimization of vibration reduction,noise reduction,fatigue stress reduction,and weight reduction are the optimization goals;optimization process with rotor performance,natural frequency configuration and aeroelastic stability as constraints;multi-population genetic algorithm is used to achieve global optimization of rotor multi-disciplinary design.(3)Using the multi-disciplinary optimization design method proposed in this article,the vibration reduction/noise reduction/weight reduction/fatigue life optimization of a certain type of engineering rotor was completed.The problems in the blade design are solved,and the validity of the method in this paper is also verified.At last,this paper also aimed at a new type of rotor without automatic tilter to achieve rotor attitude control through speed modulation and the introduction of lag-pitch coupling.The basic dynamics theory was researched and a comprehensive nonlinear dynamics analysis model was established.Modal analysis,modal damping identification,hovering response / stability analysis,forward flight trim/stability analysis were performed,and its dynamic coupling mechanism,basic dynamic characteristics and aeroelastic stability characteristics were revealed.It provides the basic theory for the design of this new configuration rotor. |
PDF Full Text Request