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Efficient prediction of ground noise from helicopters and parametric studies based on acoustic mapping

Chinese Journal of Aeronautics 2018年第2期31卷 273-284页

作者： Fei WANG Guohua XU yongjie shi National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

Based on the acoustic mapping, a prediction model for the ground noise radiated from an in-flight helicopter is established. For the enhancement of calculation efficiency, a high-efficiency second-level acoustic radiation model capable of taking the influence of atmosphere absorption on noise into account is first developed by the combination of the point-source idea and the rotor noise radiation characteristics. The comparison between the present model and the direct computation method of noise is done and the high efficiency of the model is validated. Rotor free-wake analysis method and Ffowcs Williams-Hawkings（FW-H） equation are applied to the aerodynamics and noise prediction in the present model. Secondly, a database of noise spheres with the characteristic parameters of advance ratio and tip-path-plane angle is established by the helicopter trim model together with a parametric modeling approach. Furthermore, based on acoustic mapping, a method of rapid simulation for the ground noise radiated from an in-flight helicopter is developed. The noise footprint for AH-1 rotor is then calculated and the influence of some parameters including advance ratio and flight path angle on ground noise is deeply analyzed using the developed *** results suggest that with the increase of advance ratio and flight path angle, the peak noise levels on the ground first increase and then decrease, in the meantime, the maximum Sound Exposure Level（SEL） noise on the ground shifts toward the advancing side of rotor. Besides, through the analysis of the effects of longitudinal forces on miss-distance and rotor Blade-Vortex Interaction（BVI） noise in descent flight, some meaningful results for reducing the BVI noise on the ground are obtained.

关键词： Acoustic mapping Helicopter Noise footprint Rotor noise Second-level acoustic radiation model

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High-resolution simulation for rotorcraft aerodynamics in hovering and vertical descending flight using a hybrid method

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Chinese Journal of Aeronautics 2018年第5期31卷 1053-1065页

作者： Liangquan WANG Guohua XU yongjie shi National Key Laboratory of Science and Technology on Rotorcraft Aeromeehanics Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

A high-resolution simulation tool for rotorcraft aerodynamics is developed by coupling CFD with a Vorticity Transport Model（VTM）. An Eulerian-based CFD module is used to model the blade near body flowfield, and a Lagrangian-based VTM module is employed for vortex tracking in the far wake. The coupling procedure is implemented by transmitting vortex sources to the VTM module and feeding boundary conditions back to the CFD module. The presented CFD/VTM hybrid solver is firstly validated by hover cases of three different rotor configurations. Simulation results, including the blade surface pressure distribution, rotor downwash, and hover figure of merit, exhibit favorable correlations with available experimental data. Then, a rotor operated in vertical descending flight with a fixed collective pitch is investigated. It is shown that the CFD/VTM coupling method is suitable for rotor wake simulation. Wake instabilities（far wake breakdown in hover and toroidal wake pattern in the vortex ring state） are successfully demonstrated with a moderate computational cost.

关键词： Descending flight Hybrid method Rotorcraft Vortex ring state Vorticity transport model

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Numerical study of the rotor thickness noise reduction based on the concept of sound field cancellation

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Chinese Journal of Aeronautics 2022年第3期35卷 214-233页

作者： Runze XIA yongjie shi Teng LI Guohua XU National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and AstronauticsNanjing 210016China China Helicopter Research and Development Institute Jingdezhen 333001China

Numerical studies were performed to investigate the mechanism and potential of several active rotors for reducing low-frequency in-plane thickness noise generated by rotating blades.A numerical method coupling the blade element theory,prescribed wake model and Fowcs Williams-Hawkings(FW-H)equation was established for rotor noise *** is indicated that the excitation force on the blade tip can generate anti-noise that to partly cancel the in-plane thickness noise with an appropriate actuation *** from the phase,frequency and amplitude sweeps show that the excitation force direction and actuation law are the crucial factors affecting the noise reduction,which determine the noise reduction area in the elevation and azimuth directions,*** active trailing-flap rotor can generate the in-plane excitation force,but because of large lift-drag ratio the anti-noise is mainly from the vertical lift,which is caused by flap deflection similar to a variable camber *** the harmonic control rotor and active twist rotor,the excitation force is also attributed to the vertical blade *** vertical force can reduce the noise near the rotor plane,it will also cause the noise increase in most other ***,two new active rotors were proposed to generate the in-plane chordwise and spanwise excitation *** the modified actuation law,the noise in most areas around the rotor was reduced,which improved the acoustic characteristics of rotor significantly.

关键词： Active rotor Helicopter Noise reduction Sound field cancellation Thickness noise

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A New Single-blade Based Hybrid CFD Method for Hovering and Forward-flight Rotor Computation

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Chinese Journal of Aeronautics 2011年第2期24卷 127-135页

作者： shi yongjie ZHAO Qijun FAN Feng XU Guohua National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

A hybrid Euler/full potential/Lagrangian wake method,based on single-blade simulation,for predicting unsteady aerodynamic flow around helicopter rotors in hover and forward flight has been *** this method,an Euler solver is used to model the near wake evolution and transonic flow phenomena in the vicinity of the blade,and a full potential equation（FPE） is used to model the isentropic potential flow region far away from the rotor,while the wake effects of other blades and the far wake are incorporated into the flow solution as an induced inflow distribution using a Lagrangian based wake *** further reduce the execution time,the computational fluid dynamics（CFD） solution and rotor wake analysis（including induced velocity up-date） are conducted parallelly,and a load balancing strategy is employed to account for the information exchange between two *** the developed method,several hover and forward-flight cases on Caradonna-Tung and Helishape 7A rotors are *** agreements of the loadings on blade surface with available measured data demonstrate the validation of the ***,the CPU time required for different computation runs is compared in the paper,and the results show that the pre-sent hybrid method is superior to conventional CFD method in time cost,and will be more efficient with the number of blades increasing.

关键词： hybrid CFD method Euler equations full potential equations wake model rotor helicopters

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Rotor Airload and Acoustics Prediction Based on CFD/CSD Coupling Method

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Transactions of Nanjing University of Aeronautics and Astronautics 2018年第2期35卷 343-352页

作者： Wang Liangquan Xu Guohua shi yongjie National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

An advanced airload and noise prediction method based on computational fluid dynamics/computational structural dynamics(CFD/CSD)coupling for helicopter rotor has been developed in this *** the present method,Navier-Stokes equation is applied as the governing equation,and a moving overset grid system is generated in order to account for the blade motions in rotation,flapping and *** blade structural analysis is based on 14-DOF Euler beam model,and the finite element discretization is conducted on Hamilton′s variational principle and moderate deflection *** noise is calculated by Farassat 1 Aformula derived from FW-H *** the developed method,numerical example of UH-60 Ais performed for aeroelastic loads calculation in a low-speed forward flight,and the calculated results are compared with both those from isolated CFD method and available experimental ***,rotor noise is emphatically calculated by CFD/CSD coupling method and compared with the isolated CFD *** results show that the aerodynamic loads calculated from CFD/CSD method are more satisfactory than those from isolated CFD method,and the exclusion of blade structural deformation in rotor noise calculation may cause inaccurate results in low-speed forward flight state.

关键词： helicopter rotor airload aerodynamic noise computational fluid dynamics (CFD) computational structural dynamics (CSD)

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New Progress in Helicopter Rotor Wake Research

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Transactions of Nanjing University of Aeronautics and Astronautics 2019年第1期36卷 36-56页

作者： XU Guohua shi yongjie ZHAO Qijun National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

Rotor wake analysis,a fundamental research of helicopter technology,has been widely applied for rotor aerodynamic analysis. This paper summarizes the research of different rotor wake models at home and abroad and reviews the development process of rotor wake methods as well as the research achievement obtained in each ***,the new progress of helicopter rotor wake methods is described in detail. It includes constant circulation contours modeling method of rotor wake,pseudo-implicit relaxation iteration and time-accurate solution method,research on aerodynamic interaction characteristics of helicopter rotor/fuselage by wake method,research on the rotor blade-vortex interaction noise and interaction of coaxial rigid rotor aerodynamics by viscous vortex particle method,and application of free wake method to helicopter flight dynamics modeling. In the end,some prospects for the research of helicopter rotor wake method are put forward,which clarifies the ideas for the future development of rotor wake method.

关键词： helicopter rotor free wake viscous vortex particles aerodynamic characteristics flight dynamics wake progress

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A coupling VWM/CFD/CSD method for rotor airload prediction

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Chinese Journal of Aeronautics 2017年第1期30卷 204-215页

作者： shi yongjie Xu Yi Xu Guohua Wei Peng National Laboratory of Science and Technology on Rotorcraft Aerodynamics Nanjing University of Aeronautics and Astronautics Pre-noncommissioned Officers Training Base Army Aviation Institute

A coupling fluid-structure method with a combination of viscous wake model（VWM）,computational fluid dynamics（CFD） and comprehensive structural dynamics（CSD） modules is developed in this paper for rotor unsteady airload prediction. The hybrid VWM/CFD solver is employed to model the nonlinear aerodynamic phenomena and complicated rotor wake dynamics;the moderate deflection beam theory is implemented to predict the blade structural deformation; the loose coupling strategy based on the ‘delt method＇ is used to couple the fluid and structure *** cases of Helishape 7A rotor are performed first to investigate the effect of elastic deformation on airloads. Then, two challenging forward flight conditions of UH-60 A helicopter rotor are investigated, and the simulated results of wake geometry, chordwise pressure distribution and sectional normal force show excellent agreement with available test data; a comparison with traditional CFD/CSD method is also presented to illustrate the efficiency of the developed method.

关键词： Airload CFD/CSD coupling Navier-Stokes equations Rotor Viscous wake model

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Numerical study on flow control of ship airwake and rotor airload during helicopter shipboard landing

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Chinese Journal of Aeronautics 2019年第2期32卷 324-336页

作者： yongjie shi Xiang HE Yi XU Guohua XU National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics Shanghai Institute of Electro-Mechanical Engineering

A numerical study on flow control of ship airwake during shipboard landing is carried out to address the effect of flow control devices on helicopter rotor airload. The in-house Reynolds Averaged Navier-Stokes(RANS) based solver Rotorcraft AeroDynamics and Aeroacoustics Solver(RADAS), with combination of momentum source approach is employed to conduct the helicopter shipboard landing simulation. The control effects of three aerodynamic modifications of ship superstructure, i.e. ramp, notch and flap, in different Wind-Over-Deck(WOD) conditions are *** the steady simulation results, the effect of spatial variation of ship airwake on rotor airloads is concluded. The aerodynamic modifications reduce the strength of shedding vortex and increase rotor normal force through delaying and relieving flow separation, and therefore are beneficial to alleviate the limitation of control inputs. By contrast, the perturbation of unsteady ship airwake can cause the serious oscillation of rotor forces during shipboard landing. The unsteady simulations show that the turbulence intensity of ship airwake and oscillatory rotor airloading, represented by Root-Mean-Square(RMS) loading, can be remarkably reduced by the ramp and notch modifications, while the flap modification has adverse effect. It means that flow control devices have large potential benefits to alleviate the pilot's workload and improve the shipboard landing safety, but they should be well designed to avoid the introduction of more vortex, which leads to increase in disturbance of flow field.

关键词： Flow control Helicopter Rotor airload ship airwake shipboard landing

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Simulation on Helicopter Scissors Tail-Rotor Noise Based on N-S Equations and F1A Formulas

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Transactions of Nanjing University of Aeronautics and Astronautics 2017年第6期34卷 710-719页

作者： Meng Xiaowei Xu Guohua shi yongjie Wang Liangquan National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China

Aiming at the noise of helicopter scissors tail-rotor,an advanced numerical method is established by combining computational fluid dynamics(CFD)model with Farassat 1 A(F1 A)*** this method,Navier-tokes(N-S)equations are used as governing equations,and the flow field is solved at quasi-steady and unsteady states in hover and forward fight,respectively,based on two different types of embedded grid systems.A simple and effective solution approach is provided for the generation difficulty of donor cells caused by the close gap among scissors tail-rotor *** the CFD calculation results as input,the thickness noise,loading noise and total noise of tail-rotor are calculated by F1 *** the method,numerical examples on rotor flowfield and noise are performed and the results are compared with available ***,aerodynamic and acoustic characteristics of scissors tail-rotor are emphatically calculated in both hover and forward ***,the research on the effects of blade-tip shape parameters on scissors tail-rotor noise is carried ***,the scissors tail-rotor is compared with the conventional tail-rotor,and the results show that in hover,the noise of a scissors tail-rotor is not always the smaller one.

关键词： FW-H equation scissors tail rotor thickness noise loading noise helicopter computational fluid dynamics(CFD)

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Robust Navier-Stokes method for predicting unsteady flowfield and aerodynamic characteristics of helicopter rotor

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Chinese Journal of Aeronautics 2018年第2期31卷 214-224页

作者： Qijun ZHAO Guoqing ZHAO Bo WANG Qing WANG yongjie shi Guohua XU National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

A robust unsteady rotor flowfield solver CLORNS code is established to predict the complex unsteady aerodynamic characteristics of rotor flowfield. In order to handle the difficult problem about grid generation around rotor with complex aerodynamic shape in this CFD code,a parameterized grid generated method is established, and the moving-embedded grids are constructed by several proposed universal methods. In this work, the unsteady Reynolds-Averaged Navier-Stokes（RANS） equations with Spalart-Allmaras are selected as the governing equations to predict the unsteady flowfield of helicopter rotor. The discretization of convective fluxes is accomplished by employing the second-order central difference scheme, third-order MUSCL-Roe scheme, and fifth-order WENO-Roe scheme. Aimed at simulating the unsteady aerodynamic characteristics of helicopter rotor, the dual-time scheme with implicit LU-SGS scheme is employed to accomplish the temporal discretization. In order to improve the computational efficiency of holecells and donor elements searching of the moving-embedded grid technology, the ‘‘disturbance diffraction method＂ and ‘‘minimum distance scheme of donor elements method＂ are established in this work. To improve the computational efficiency, Message Passing Interface（MPI） parallel method based on subdivision of grid, local preconditioning method and Full Approximation Storage（FAS） multi-grid method are combined in this code. By comparison of the numerical results simulated by CLORNS code with test data, it is illustrated that the present code could simulate the aerodynamic loads and aerodynamic noise characteristics of helicopter rotor accurately.

关键词： Aerodynamic characteristicsHelicopter rotor Moving-embedded grid Navier-Stokes equations Upwind schemes

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