| Ice accretion on rotors may result in the change of rotor flowfield,serious damage of the aerodynamic performance,reduction of the maneuverability and stability of helicopter and a threat to the safety of helicopter flight.In order to achieve the goal of safe flight in nearly all-weather conditions,research about the mechanism of the ice accretion on rotors and the relevant issues about anti/de-icing technology is carried out,and it is significant in both theory and practice.For this reason,aiming at the problems of ice accretion numerical simulation and anti/de-icing technology,the CFD method for predicting flowfield of the iced rotor,the calculation method for the droplet impingement property and the three-dimensional icing model for rotors are developed in this thesis,and a numerical method and code(CLORNS-ICE)for predicting ice accretion on helicopter rotor are established.On this basis,the analysis of the mechanism and characteristics for the ice accretion on rotors are conducted,the influence law of aerodynamic characteristics and noise characteristics is obtained.Then,the anti/de-icing issues on rotors are investigated,distribution characteristics of anti/de-icing heat power on rotors is obtained,an ice detection method based on the acoustic characteristics for rotors and an active flow control based on the synthetic jet for iced rotors are proposed.The major constructions of the investigated thesis are as follows:In Chapter 1,the research background of ice accretion issue on helicopter rotor are explained.The research progresses of helicopter CFD method,the numerical simulation method for ice accretion on rotors and the anti/de-icing issues on rotors are described.Also,the problems in present research and corresponding methods which will be used in this thesis are briefly introduced.In Chapter 2,considering the complexity and particularity of rotor movement and the shape variation of the iced rotor,a moving-embedded grid method suitable for iced rotors is established by combining the background grid and blade grids firstly.A node-reconstruction method considering the curvature of ice shape(large deformation value)and a grid deforming method based on a spring net(small deformation value)are presented respectively,and they can effectively describe the shape variation of rotors caused by ice and meet the requirements of the flowfield calculation.Then,a CFD method for predicting flowfield of the iced rotor is developed.To simulate the unsteady characteristics of iced rotor flowfield,the dual-time method is adopted and the implicit LU-SGS method is used.To improve the calculation accuracy of the flow separation caused by ice,the Roe-MUSCL type scheme is employed to calculate the convective flux,and the S-A and SST turbulence models are used to simulate the viscosity of airflow.In Chapter 3,the calculation method for the water collection efficiency on rotors is investigated.Firstly,a Lagrangian method for calculating the droplet trace around the rotor is developed.In order to improve the computational efficiency,the droplet search method combined with the displacement vector and a dynamic start-point distribution method are proposed.Then,an Eulerian method for calculating the water collection efficiency on blades in the unsteady vortex flowfield of the rotor is developed.To increase the stability and efficiency of the Eulerian method,the shadow zone dispersion model is proposed.At last,the water impingement property on rotors in hover and forward flight are calculated respectively.The “dry” region in the water droplet flowfield due to the blade-tip vortex is found,and the influence of the blade-tip vortex on the droplet impingement property is analyzed.In Chapter 4,the three-dimensional(3-D)icing model for the rotor is investigated,and a numerical simulation method and code(CLORNS-ICE)for ice accretion on rotors are established.Firstly,considering the limitation of traditional two-dimensional(2-D)rotor ice accretion simulation method and the effect of centrifugal force on ice accretion,the influence of the centrifugal force and water film movement are introduced in the icing model,and the 3-D icing model for rotor is established.Then,combined the CFD method of iced rotors and the calculation method of water collection property,a high-accuracy 3-D numerical simulation method for ice accretion on rotors and a rapid calculation method are established respectively.At last,the ice accretion on rotors is calculated,and some meaningful conclusions are obtained.In Chapter 5,the ice accretion characteristics on rotors and the parameter influence are investigated and analyzed,including the Median Volume Diameter(MVD)and temperature.In the forward flight,the influence of advance ratio on ice accretion is investigated,and the influence of centrifugal force in the ice accretion process on rotors is analyzed.Then,based on the numerical simulation method,the influence of ice on the aerodynamic characteristics of rotor is investigated under the different flight state.Additionally,the influence of the icing position on the aerodynamic characteristics of rotors in the early stage of ice accretion(small ice amount)is mainly studied.At last,on the basis of the icing characteristics and the main distribution methods of the heating elements in the blade,the distribution property of the heat power on the blade surface is calculated and analyzed,and some theoretical guidance for anti/de-icing issues are provided.In Chapter 6,the influence of ice on the acoustic characteristics of rotors and a new ice detection method for rotor are studied.Firstly,the acoustic calculation method based on the acoustic analog method is established.Then,combined the presented numerical simulation method of ice accretion on rotors,the influence of icing parameters on acoustic characteristics is calculated and analyzed,such as the ice accretion time and the icing position on rotors.The result shows the potential of acoustic characteristics of rotors for detecting ice accretion on rotors.At last,the ice detection method based on the acoustic characteristics of rotors is proposed.Through some monitor locations compromising between sensitivity and enablement,the relationship between the ice accretion and the acoustic characteristics of rotors is established,and some new conclusions are obtained.In Chapter 7,the synthetic jet technology is introduced into the anti/de-icing issues for rotors,and the active flow control of iced airfoil/rotor is studied,and a new technique is provided for solving the reduction of rotor aerodynamic force in the ice accretion process.Combined the flow characteristics and common icing area of the airfoil,the blow/suction boundary conditions over the orifice of the synthetic jet actuator and the governing equations are established.Then,the control effect of synthetic jet on aerodynamic characteristics of iced airfoil is calculated,and the parameter influence is analyzed.Additionally,a particular blade with a frame-covering structure is designed and processed,and an experimental platform for the active flow control of rotors is established.The experimental results indicate that the synthetic jet has the capability to delay flow separation over the blade and to improve aerodynamic characteristics of the rotor.Finally,flow control effects of synthetic jets on rotor's aerodynamic characteristics were experimentally investigated with different jet parameters,such as jet locations,jet angles,and excitation voltages. |
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