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A novel high-order scheme for numerical simulation of wake flow over helicopter rotors in hover

Chinese Journal of Aeronautics 2022年第5期35卷 260-274页

作者： Shaoqiang HAN Wenping SONG Zhonghua HAN Institute of Aerodynamic and Multidisciplinary Design Optimization National Key Laboratory of Science and Technology on Aerodynamic Design and ResearchSchool of AeronauticsNorthwestern Polytechnical UniversityXi’an 710072China

Accurate prediction of tip vortices is crucial for predicting the hovering performance of a helicopter rotor.A new high-order scheme(we call it WENO-K)proposed by our research group is employed to minimize numerical dissipation and extended to numerical simulation of unsteady compressible viscous flows dominated by tip vortices over hovering ***-K is referred to as an adaptively optimized WENO scheme with Gauss-Kriging reconstruction,and its advantage is to reduce dissipation in smooth regions of flow while preserving high-resolution around *** WENO-K scheme is adopted to reconstruct left and right state values within the Roe Riemann solver updating the inviscid fluxes on a structured dynamic overset *** minimize the accuracy loss for high-order reconstruction on artificial boundaries of overset grid,a method of multilayer fringes is proposed to carry out interpolation between background grid and blade *** parallel computing considering automatic load balance on averagely partitioned overset grid is developed to reduce the wall-clock time of an unsteady *** results for Caradonna-Tung(C-T)rotor in hover at the conditions of subsonic and transonic tip Mach numbers show that the thrust coefficient error for the result of WENO-K scheme is no more than 3%.Compared with WENO-JS scheme,WENO-K scheme achieves about 40%improvement on accuracy of predicting rotor thrust with only 4.1%extra computational *** importantly,WENO-K scheme can capture more sophisticated unsteady flow structures and resolve tip vortices to a larger wake age with an increment of about 270°compared to WENO-JS scheme.

关键词： Dynamic overset grid helicopter rotors High-order scheme Unsteady flow Vortex flow WENO scheme

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Investigation of rotor control system loads

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Chinese Journal of Aeronautics 2013年第5期26卷 1114-1124页

作者： Sun Tao Tan Jianfeng Wang Haowen School of Aerospace Tsinghua University School of Mechanical and Power Engineering Nanjing University of Technology

This paper concentrates on the aeroelasticity analysis of rotor blade and rotor control systems. A new multi-body dynamics model is established to predict both rotor pitch link loads and swashplate servo loads. Two helicopter rotors of UH-60A and SA349/2, both operating in two critical flight conditions, high-speed flight and high-thrust flight, are studied. The analysis shows good agreements with the flight test data and the calculation results using CAMRAD II. The mechanisms of rotor control loads are then analyzed in details based on the present predictions and the flight test data. In high-speed conditions, the pitch link loads are dominated by the integral of blade pitching moments, which are generated by cyclic pitch control. In high-thrust conditions, the positive pitching loads in the advancing side are caused by high collective pitch angle, and dynamic stall in the retreating side excites high-frequency responses. The swashplate servo loads are predominated by the rotor pitch link loads, and the inertia of the swashplate has significant effects on high-frequency harmonics of the servo loads.

关键词： Comprehensive aeroelasticity analysis Control systems helicopter rotors Loads Multi-body dynamic model

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Structurally coupled characteristics of rotor blade geometrically exact formulation

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Chinese Journal of Aeronautics 2022年第6期35卷 186-197页

作者： Jie WU Yijiang MA Zhidong WANG Zhihao YU School of Naval Architecture & Ocean Engineering Jiangsu University of Science and TechnologyZhenjiang 212100China College of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016China

In rotor dynamics,blades are normally modelled as a slender beam,in which elastic deformations are coupled with each *** identify these coupling effects,new rigid-flexible structural model for helicopter rotor system is proposed in this *** rotations of the whole blade(on flapwise,lagwise,and torsional)are described as three global rigid degrees of *** nonlinear deformation geometrics of the beam is built on geometrically exact beam *** expressions for blade strain energy,kinetic energy,and virtual work of various kinds of external forces are derived as functions of finite rotations and elastic *** quantify the coupling characteristics,following the definition of coupling factor in electromagnetics,a new coupling factor between two modal components on each mode is introduced in modal *** show that the new structural model is highly capable of solving static and dynamic problems in rotor system and the maximum deformation that moderate deformation beam theory can predict might be 15%of beam *** the new coupling factor is applied to study structurally coupled characteristics of rotor blade,it can be concluded that closeness of natural frequencies likely indicates considerable coupling between corresponding DOFs in structure.

关键词： Computational geometry Flexible couplings helicopter rotors Modal analysis Structural dynamics

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EXPERIMENTAL INVESTIGATION OF AERODYNAMICINTERACTION EFFECT OF ROTOR WAKE ONFUSELAGE OF helicopter

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Chinese Journal of Aeronautics 2000年第1期13卷 1-7页

作者：徐锦法高正梅卫胜 National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

The interaction effect of rotor wake on fuselage of helicopter was investigated with experimental method. The results from experiment have proved that for the drag of fuselage the effect of rotor airflow is closely in connection with both the flight speed and the collective pitch of blades, while for the thrust and pitch moment of fuselage the collective pitch angle of blades plays more important role. A simple and effective computing method about aerodynamic interaction can be derived from the measured data. In order to implement the experiment, a fuselage model, a special sensor, the measurement and data acquisition and processing system were designed and manufactured according to the special requirements of this research project, thereby a good base was built up for carrying out experiments successfully with high quality.

关键词： Aerodynamic loads Computational methods Data acquisition Drag Fuselages helicopter rotors Mathematical models Sensors Wakes

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FINITE ELEMENT ANALYSIS OF THE FLOW INDUCED BY ROTATING BLADES IN AN INCOMPRESSIBLE VISCOUS FLUID

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Journal of Hydrodynamics 2002年第2期14卷 36-40页

作者： Wang, Yan-Xing Yang, Guo-Wei Lu, Xi-Yun Zhuang, Li-Xian Dept. of Mech. and Mech. Eng. Univ. of Sci. and Technol. of China Hefei 230026 China

Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data.

关键词： Aerodynamic loads Finite element method helicopter rotors Navier Stokes equations Three dimensional Turbomachine blades Wakes

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Autonomous Landing of Small Unmanned Aerial Rotorcraft Based on Monocular Vision in GPS-denied Area

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IEEE/CAA Journal of Automatica Sinica 2015年第1期2卷 109-114页

作者： Cunxiao Miao Jingjing Li the School of Mechanical Engineering University of Science and Technology Beijing Beijing Aerospace Times Optical-electronic Technology Co. Ltd(ATOT)

Focusing on the low-precision attitude of a current small unmanned aerial rotorcraft at the landing stage, the present paper proposes a new attitude control method for the GPS-denied scenario based on the monocular vision. Primarily, a robust landmark detection technique is developed which leverages the well-documented merits of supporting vector machines (SVMs) to enable landmark detection. Then an algorithm of nonlinear optimization based on Newton iteration method for the attitude and position of camera is put forward to reduce the projection error and get an optimized solution. By introducing the wavelet analysis into the adaptive Kalman filter, the high frequency noise of vision is filtered out successfully. At last, automatic landing tests are performed to verify the method's feasibility and effectiveness. © 2014 Chinese Association of Automation.

关键词： Aircraft Attitude control helicopter rotors Landing Nonlinear programming rotors Vision Wavelet analysis

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Analytical Model of Elastomeric Lag Damper Kinematic Coupling and Its Effect on helicopter Air Resonance in Hover

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Chinese Journal of Aeronautics 2002年第1期15卷 27-32页

作者：胡国才向锦武张晓谷 Institute of Aircraft Design Beijing Univ. of Aero. and Astro. Beijing 100083 China

For an elastomeric lag damper with nonlinear properties and kinematic couplings, its differential equation about equilibrium position was derived in a rotating frame. The equation was then transformed into a non-rotating frame by multi-blade transformation and incorporated into the rotor/airframe differential equations for eigen analysis. The effects of damper steady displacement and kinematic couplings on helicopter air resonance in hover were analyzed. The results demonstrate that the elastomeric damper can increase helicopter dynamic stability; however, its available damping will decrease as its steady displacement increased. For the notional rotor system, the damper steady displacement will decrease when kinematic couplings are introduced, and hence the regressive lag modal damping can be increased.

关键词： Airframes Differential equations helicopter rotors Kinematics Resonance

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