| The dynamic stall characteristics of rotor have significant influences on the forward flight speed,sound pressure level,v ibration level of helicopter,aerodynamic performances,as a result,the researches of dynamic stall characteristics of rotor and airfoil would be benefit for exploring the mechanism of dynamic stall of airfoil and improving the aerodynamic perfo rmance of helicopter rotor.Therefore,the dynamic stall is hot and frontier issue in the researches on unsteady aerodynamic characteristics of helicopter rotor.Therefore,the unsteady aerodynamic characteristics of rotor and airfoil are analyzed by emp loying the high-efficient,high-accurate numerical method and the PIV flo wfield measured technology.Meanwhile,the dynamic stall characteristics of rotor and airfo il under variational freestream velocity conditions are analyzed in this work,and the effects of spanwise flow on the aerodynamic characteristics of finite-wing and rotor under dynamic stall conditions are researched respectively.Based on the understanding of dynamic stall,a new semi-empirical model of trailing-edge vortex is established based on the classical Leishman-Beddoes(L-B)dynamic stall model in this work,as a result,the accuracy of the new L-B model simulat ion under reattached process is improved.Based on these researches,the researches of aerodynamic configurat ion optimization under steady-unsteady aerodynamic characteristics are performed respectively.As a result,new rotor and airfoil shapes with better aerodynamic characteristics are obtained in this research.The main researches in this work include:In Chapter 1,the researches background of unsteady aerodynamic characteristics on helicopter rotor are exp lained,the research progresses of helicopter CFD methods are described,and the dynamic stall and aerodynamic configuration optimizat ion of rotor and airfo il at ho me and abroad are discussed.Then aiming at the insufficient of these researches,the research contents and methods of this work are proposed.Considering the co mplexity and particularity of rotor movement,the t wo-dimensional airfo il grid with C-topology is generated by solving the Poisson equations in Chapter 2.Based on the airfoil grid,the blade grid with C-O topology is generated.Then,an efficient moving-embedded grid method suitable for predicting the unsteady flowfield of rotor/airfo il is established by combining the Cartesian background grid,in this method,the donor elements are searched by using the Inverse-Map method,the hole boundary elements are searched by using ―disturbance diffract ion‖ method.Furth more,a high-efficient,high-accuracy unsteady numerical method for rotor and airfoil is established in this work.In o rder to improve the computational accuracy and efficiency of rotor flowfield,the high-efficient LU-SGS imp licit scheme is adopted for temporal discretization.The discretizat ion of convective flu xes is acco mplished by emp loying Roe-W ENO scheme to improve the simulat ion accuracy on separation flow of rotor,and the Spalart-Allmaras turbulence model is used to simulate the viscosity of airflow.Aiming at satisfing the different requests of rotor and airfo il optimization,several optimal methods are established in Chapter 3.Firstly,the genetic algorith m(GA)with high-robustness and global convergence characters is established to satisfy the requstment of rotor airfoil optimaziton under steady condition.Secondly,considering the calculated amount and constrain problems,the sequential quadratic programming(SQP)method suitable for mult i-object ive and multi-constraint problem is established.In order to improve the optimal efficiency,a new linear search strategy based on function fitting method is proposed in this work.Finally,considering the optimization characters of three-dimensional rotor blade,the Kriging surrogate method is established to improve the optimization efficiency.Meanwh ile,to improve the uniform character of sample d istribution,a step sampling LHS method is proposed based on the classical LHS method.In Chapter 4,the effect factors of rotor airfoil,such as average angle of attack,amplitude of angle of attack,freestream velocity,reduced frequency and profile of airfo il,are analy zed by employing the established unsteady numerical method,and some valuable conclusions are obtained.Based on these researches,the unsteady aerodynamic characteristics of rotor airfo il are simu lated under the coupled conditions of variational angle of attack and variational freestream velocity,wh ich explores the mechanis ms of unsteady aerodynamic characteristics of rotor airfo il under variat ional freestream velocity conditions.After that,aerodynamic characteristics of finite wing are researched under the dynamic stall conditions with spanwise flow and without spanwise flow respectively,and the effects of spanwise flo w and wing tip vortex on dynamic stall characteristics are analyzed and exp lored in this work.Then,the unsteady aerodynamic characteristics of rotor are simulated and analyzed under different aerodynamic states,and the effects of rotation and induced downwash on rotor unsteady aerodynamic characteristics are explored in this work.In order to research the dynamic stall characteristics of rotor airfoil deeply,the PIV method is emp loyed to measure the flowfield of rotor airfo ils under dynamic stall conditions,and the characteristics of dynamic stall vortex are measured and analyzed especially.By co mparing the measured results of different rotor airfoils,it is indicated that the influence of airfoil profile on convection velocity of dynamic stall vortex is not obvious.However,the convection velocities of dynamic stall vortex are d ifferent for different relative positions,i.e.the non-dimensional velocity of dynamic stall vortex is 0.39 on airfoil surface,and that is 0.55 in airfoil wake.In Chapter 6,by comparing the numerical results and measurement results of airfoil dynamic stall,a trailing-edge vortex model is proposed based on the analysis of flowfield characteristics of airfo il under dynamic stall conditions,then a new dynamic stall model of rotor airfoil is established by combining the trailing-edge vortex model with classical L-B model,which could be used to simulate the influence of trailing-edge vortex on aerodynamic loads.By co mparing the simulated results of orig inal L-B model with modified dynamic stall model,it is indicated that the modified dynamic stall model could simu late the reattached process of airfoil dynamic stall more accurately.As a result,the simulat ion accuracy of lift coefficient,pitching moment coefficient and drag coefficient is improved.According to the characters of different helicopter,new design states and design objectives of rotor airfoil are proposed in Chapter 7 by considering actual work environ ment of helicopter rotor.Then the optimizations of rotor airfo il under steady conditions are co mpleted by emp loying the present numerical method and optimal method.Aiming at the insufficiency of optimizat ion of rotor airfo il under steady conditions,a new idea of optimizat ion of rotor airfoil under dynamic stall condition is proposed.Therefore,an optimization of rotor airfoil is designed to improve the dynamic stall characteristics of rotor airfo il.Meanwhile,the optimal airfo il has larger lift coefficient,s maller pitching mo ment and larger drag divergence angle under steady conditions.In Chapter 8,based on the airfoil optimization designs and rotor blade dynamic stall analyses,the aerodynamic shape design of rotor blade is conducted by employing the optimizat ion method under hover condition.The blade shape characters of optimizat ion include twist distributions,chord distributions,swept distributions and anhedral angles.As a result,the improvement of rotor aerodynamic performance is obtained,and the Figure of Merit is imp roved significantly.Meanwhile,the lift-drag rat io is also inreased under forward flight condition.Based on this research,the shape design of an unmanned helicopter rotor is performed to improve the aerodynamic performance of rotor under hover conditions,while the aerodynamic characteristics of rotor in forward flight are not deteriorated. |
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