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Parametric analyses for synthetic jet control on separation and stall over rotor airfoil

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Chinese Journal of Aeronautics 2014年第5期27卷 1051-1061页

作者： zhao Guoqing zhao qijun National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

Numerical simulations are performed to investigate the effects of synthetic jet control on separation and stall over rotor airfoils. The preconditioned and unsteady Reynolds-averaged Navier–Stokes equations coupled with a k x shear stream transport turbulence model are employed to accomplish the flowfield simulation of rotor airfoils under jet control. Additionally,a velocity boundary condition modeled by a sinusoidal function is developed to fulfill the perturbation effect of periodic jets. The validity of the present CFD procedure is evaluated by the simulated results of an isolated synthetic jet and the jet control case for airfoil NACA0015. Then, parametric analyses are conducted specifically for an OA213 rotor airfoil to investigate the effects of jet parameters（forcing frequency, jet location and momentum coefficient, jet direction, and distribution of jet arrays） on the control effect of the aerodynamic characteristics of a rotor airfoil. Preliminary results indicate that the efficiency of jet control can be improved with specific frequencies（the best lift-drag ratio at F＋= 2.0） and jet angles（40 or 75） when the jets are located near the separation point of the rotor airfoil. Furthermore, as a result of a suitable combination of jet arrays, the lift coefficient of the airfoil can be improved by nearly 100%, and the corresponding drag coefficient decreased by26.5% in comparison with the single point control case.

关键词： Flow control Flow separation Parametric analysis Rotor Synthetic jet

Experiments on unsteady vortex flowfield of typical rotor airfoils under dynamic stall conditions

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Chinese Journal of Aeronautics 2016年第2期29卷 358-374页

作者： Wang Qing zhao qijun National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

A new experiment for airfoil dynamic stall is conducted by employing the advanced par- ticle image velocimetry （PIV） technology in an open-return wind tunnel. The aim of this experimen- tal investigation is to demonstrate the influences of different motion parameters on the convection velocity, position and strength of leading edge vortex （LEV） of airfoil under different dynamic stall conditions. Two different typical rotor airfoils, OA209 and SC1095, are measured at different free stream velocities, oscillation frequencies, and angles of attack. It is demonstrated by the measured data that the airfoil with larger leading edge radius could notably decrease the strength of LEV. The angle of attack （AoA） of airfoil can obviously influence the dynamic stall characteristics of airfoil, and the LEV would be effectively inhibited by decreasing the mean pitch angle. In addition, the con- vection velocity of LEV is estimated in this measurement, and the results demonstrate that the influ- ence of airfoil shape on convection velocity of LEV is limited, but the convection velocity of LEV would be increased by enlarging the oscillation frequency. Meanwhile, the convection velocity of LEV is a time variant value, and this value would increase as the LEV convects to the trailing edge of airfoil.

关键词： Convection velocity Dynamic stall Leading edge vortex PIV Rotor airfoil

Parametric analyses on dynamic stall control of rotor airfoil via synthetic jet

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Chinese Journal of Aeronautics 2017年第6期30卷 1818-1834页

作者： qijun zhao Yiyang MA Guoqing zhao National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

The effects of synthetic jet control on unsteady dynamic stall over rotor airfoil are investigated numerically. A moving-embedded grid method and an Unsteady Reynolds Averaged Navier-Stokes（URANS） solver coupled with k-x Shear Stress Transport（SST） turbulence model are established for predicting the complex flowfields of oscillatory airfoil under jet control. Additionally, a velocity boundary condition modeled by sinusoidal function has been developed to fulfill the perturbation effect of periodic jet. The validity of present CFD method is evaluated by comparisons of the calculated results of baseline dynamic stall case for rotor airfoil and jet control case for VR-7 B airfoil with experimental data. Then, parametric analyses are conducted emphatically for an OA212 rotor airfoil to investigate the effects of jet control parameters（jet location, dimensionless frequency, momentum coefficient, jet angle, jet type and dual-jet） on dynamic stall characteristics of rotor airfoil. It is demonstrated by the calculated results that efficiency of jet control could be improved with specific momentum coefficient and jet angle when the jet is located near separation point of rotor airfoil. Furthermore, the dual-jet could improve control efficiency more obviously on dynamic stall of rotor airfoil with respect to the unique jet, and the influence laws of dual-jet＇s angles and momentum coefficients on control effects are similar to those of the unique jet. Finally,unsteady aerodynamic characteristics of rotor via synthetic jet which is located on the upper surface of rotor blade in forward flight are calculated, and as a result, the aerodynamic characteristics of rotor are improved compared with the baseline. The results indicate that synthetic jet has the capability in improving aerodynamic characteristics of rotor.

关键词： Airfoil Dynamic stall characteristics:Flow control Moving-embedded gridmethodology Navier-Stokes equations Parametric analyses Rotor Synthetic jet

基于CFD/CSD耦合的TEF旋翼气弹特性高精度模拟

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航空学报 2024年第18期45卷 147-162页

作者：王华龙张夏阳赵国庆招启军马砾南京航空航天大学直升机动力学全国重点实验室南京210016

为分析前飞状态带有后缘小翼的旋翼的气弹特性,建立了一套基于计算流体力学/计算结构动力学(CFD/CSD)耦合的高精度分析方法。基于参数化建模发展了一套含动态后缘小翼的旋翼运动嵌套网格方法。在气动分析方面,在传统气动模型的基础上引... 详细信息

为分析前飞状态带有后缘小翼的旋翼的气弹特性,建立了一套基于计算流体力学/计算结构动力学(CFD/CSD)耦合的高精度分析方法。基于参数化建模发展了一套含动态后缘小翼的旋翼运动嵌套网格方法。在气动分析方面,在传统气动模型的基础上引入高精度CFD方法,可以精确模拟旋翼非定常流场和气动特性。在结构方面,建立了刚性后缘小翼动力学模型,以附加质量、阻尼、刚度等矩阵的形式考虑刚性后缘小翼运动对旋翼系统的影响,基于Hamilton原理和Timoshenko梁模型建立了系统的非线性动力学方程。采用基于代数变换的弹性网格变形方法,在此基础上发展流固非定常耦合策略。通过对比模型旋翼和SA349/2旋翼气弹响应的计算结果,验证了CFD/CSD耦合方法的有效性。以带后缘小翼的SMART旋翼为算例,与桨叶剖面等效法向力系数的计算结果进行了对比;着重开展Fulton模型旋翼的计算分析,分别研究悬停状态下桨根扭矩和前飞状态下挥舞弯矩幅值的变化规律,并与文献结果进行对比。结果表明:所建立的CFD/CSD耦合方法可以提高旋翼非定常气弹载荷的分析精度,精确捕捉低速前飞旋翼的桨-涡干扰(BVI)现象,挥舞弯矩平均误差可控制在11.68%;同时计算得到的带后缘小翼的桨叶固有频率误差不超过4.0%,桨根挥舞弯矩幅值平均误差为15.15%,能够有效模拟后缘小翼的气弹特性。在单一后缘小翼操纵规律下,Fulton旋翼的桨毂垂向力Fz能够得到有效控制,载荷幅值的降幅可达80%以上。

关键词：旋翼动力学后缘小翼气动弹性 CFD/CSD方法气弹载荷

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高速直升机推力桨气动干扰特性研究

飞行力学 2024年第4期42卷 13-20页

作者：廖霆汉曹宸恺招启军陈希赵国庆南京航空航天大学直升机动力学全国重点实验室江苏南京210016

针对前飞状态高速直升机全机气动干扰特性开展了研究。首先,基于动量源方法建立共轴刚性旋翼气动分析模型,并通过与试验结果对比,验证了数值模拟方法的可靠性;然后,采用滑移网格方法建立推力桨干扰的数值计算模型,采用非结构网格对机身... 详细信息

针对前飞状态高速直升机全机气动干扰特性开展了研究。首先,基于动量源方法建立共轴刚性旋翼气动分析模型,并通过与试验结果对比,验证了数值模拟方法的可靠性;然后,采用滑移网格方法建立推力桨干扰的数值计算模型,采用非结构网格对机身进行划分;最后,开展了旋翼、机身、平/垂尾等对推力桨气动干扰的模拟,分析了平尾气动布局参数对推力桨气动特性的影响规律。结果表明:相较于孤立推力桨,全机干扰情况下推力桨推力系数降低、巡航效率提高;随着平尾负安装角增大,在相同推力桨总距情况下,推力桨推力系数和功率系数均增大。

关键词：高速直升机推力桨气动布局动量源方法滑移网格

Experimental investigations for parametric effects of dual synthetic jets on delaying stall of a thick airfoil

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Chinese Journal of Aeronautics 2016年第2期29卷 346-357页

作者： zhao Guoqing zhao qijun Gu Yunsong Chen Xi National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronauticsand Astronautics Nanjing 210016 China College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

A promising strategy of synthetic jet arrays （SJA） control for NACA0021 airfoil in preventing flow separation and delaying stall is investigated. Through aerodynamic forces, flowfield and velocity profiles measurements, it indicates that the synthetic jet （S J） could enlarge the mixing of the shear layer and then enhance the stability of boundary layer, resulting in scope reduction of the flow separation zone. Furthermore, the control effects of dual jet arrays positioned at 15%c （Actuator 1） and 40%c （Actuator 2） respectively are systematically investigated with different jet parameters, such as two typical relative phase angles and various incline angles of the jet. The jet closer to the leading edge of airfoil is more advantageous in delaying the stall of airfoil, and overall, the flow control performances of jet arrays are better than those of single actuator. At the angle of attack （AoA） just approaching and larger than the stall AoA, jet array with 180° phase difference could increase the lift coefficient more significantly and prevent flow separation. When momentum coefficient of the jet arrays is small, a larger jet angle of Actuator 2 is more effective in improving the maximum lift coefficient of airfoil. With a larger momentum coefficient of jet array, a smaller jet angle of Actuator 2 is more effective.

关键词： Active flow control Airfoil Dual synthetic jet arraysFlow separation Stall

An adaptive integration surface for predicting transonic rotor noise in hovering and forward flights

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Chinese Journal of Aeronautics 2019年第9期32卷 2047-2058页

作者： Siyu CHEN qijun zhao Yiyang MA National Key Laboratory of Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

In this paper, a new permeable adaptive integration surface is developed in order to evaluate transonic rotor noise in accordance with FW-H_pds equations(Ffowcs Williams-Hawkings equations with penetrable data surface). Firstly, a nonlinear near-field solution is computed on the basis of Navier-Stokes equations, which is developed on moving-embedded grid *** solution calculated through the present CFD method is used as the input for acoustic calculations by FW-H_pds equations. Then, two criteria for constructing integration surfaces are established based on the analysis of the quadrupole source strength and the nonlinear characteristic.A new surface is determined adaptively by the pressure gradient or density in a given flowfield,eschewing the uncertainties associated with determining cylinder-shaped integration surfaces. For varying hover cases, transonic noises are simulated with new integration surfaces for a UH-1 model rotor. Furthermore, numerical results of the new integration surface derived from the density perturbation value conform better to experimental data than results derived from the pressure ***, the integration surface given by jrqj being 0.1, which is an applicable criterion obtained from hover cases, is used to predict transonic rotor noise in forward flight. The computational accuracy of the new integration surface method has been validated in predicting transonic rotor noise of an AH-1 model rotor at different advance ratios.

关键词： FW-H_pds equations Integration surface Navier–Stokes equations Rotor Transonic rotor noise

CFD calculations on the unsteady aerodynamic characteristics of a tilt-rotor in a conversion mode

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Chinese Journal of Aeronautics 2015年第6期28卷 1593-1605页

作者： Li Peng zhao qijun Zhu Qiuxian National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conver- sion mode, a virtual blade model （VBM） and an real blade model （RBM） are established respec- tively. A new multi-layer moving-embedded grid technique is proposed to reduce the numerical dissipation of the tilt-rotor wake in a conversion mode. In this method, a grid system generated abound the rotor accounts for rigid blade motions, and a new searching scheme named adaptive inverse map （AIM） is established to search corresponding donor elements in the present moving- embedded grid system to translate information among the different computational zones. A dual-time method is employed to fulfill unsteady calculations on the flowfield of the tilt-rotor, and a second-order centered difference scheme considering artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the single program multiple data （SPMD） model parallel acceleration technology is adopted, according to the characteristic of the current grid system. The lift and drag coefficients of an NACA0012 airfoil, the dynamic pressure distributions below a typical rotor plane, and the sectional pressure distributions on a three-bladed Branum- Tung tilt-rotor in hover flight are calculated respectively, and the present VBM and RBM are val- idated by comparing the calculated results with available experimental data. Then, unsteady aero- dynamic forces and flowfields of an XV-15 tilt-rotor in different modes, such as a fixed conversion mode at different tilt angles （15°, 30°, 60°） and a whole conversion mode which converses from 0° to 90°, are numerically simulated by the VBM and RBM respectively. By analyses and comparisons on the simulated results of unsteady aerodynamic forces of the tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in a conversion mode are obtained, and these investigation

关键词： CFD Conversion mode Multi-layer moving-embedded grid Tilt-rotor Unsteady flowfield

Integrated optimization analyses of aerodynamic/stealth characteristics of helicopter rotor based on surrogate model

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Chinese Journal of Aeronautics 2015年第3期28卷 737-748页

作者： Jiang Xiangwen zhao qijun zhao Guoqing Li Peng National Key Laboratory of Science and Technology on Rotorcraft Aeromechanics Nanjing University of Aeronautics and Astronautics

Abstract Based on computational fluid dynamics （CFD） method, electromagnetic high-frequency method and surrogate model optimization techniques, an integration design method about aerody- namic/stealth has been established for helicopter rotor. The developed integration design method is composed of three modules： integrated grids generation （the moving-embedded grids for CFD sol- ver and the blade grids for radar cross section （RCS） solver are generated by solving Poisson equa- tions and folding approach）, aerodynamic/stealth solver （the aerodynamic characteristics are simulated by CFD method based upon NavieStokes equations and Spalart-Allmaras （S-A） tur- bulence model）, and the stealth characteristics are calculated by using a panel edge method combining the method of physical optics （PO）, equivalent currents （MEC） and quasi-stationary （MQS）, and integrated optimization analysis （based upon the surrogate model optimization technique with full factorial design （FFD） and radial basis function （RBF）, an integrated optimization analyses on aerodynamic/stealth characteristics of rotor are conducted. Firstly, the scattering characteristics of the rotor with different blade-tip swept and twist angles have been carried out, then timfrequency domain grayscale with strong scattering regions of rotor have been given. Meanwhile, the effects of swept-tip and twist angles on the aerodynamic characteristic of rotor have been performed. Furthermore, by choosing suitable object function and constraint condition, the compromised design about swept and twist combinations of rotor with high aerodynamic performances and low scattering characteristics has been given at last.

关键词： Aerodynamic characteristicsEquivalent currents Physical optics Quasi stationary Rotor Radar cross section Stealth characteristics Surrogate model