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Subsonic impulsively starting flow at a high angle of attack with shock wave and vortex interaction

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Chinese Journal of Aeronautics 2018年第9期31卷 1822-1828页

作者： Chenyuan BAI Juan LI Ziniu WU School of Aerospace Engineering Tsinghua University Institute of Aeroengine Tsinghua University

Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.

关键词： Advance of stall Compressible vortex high angle of attack Subsonic starting flow Unsteady shock waves

Bifurcation analysis of polynomial models for longitudinal motion at high angle of attack

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Chinese Journal of Aeronautics 2013年第1期26卷 151-160页

作者： Shi Zhongke Fan Li School of Automation Northwestern Polytechnical University

To investigate the longitudinal motion stability of aircraft maneuvers conveniently, a new stability analysis approach is presented in this paper. Based on describing longitudinal aerodynamics at high angle-of-attack （a ＆lt; 50 ） motion by polynomials, a union structure of two-order differential equation is suggested. By means of nonlinear theory and method, analytical and global bifurcation analyses of the polynomial differential systems are provided for the study of the nonlinear phenomena of high angle-of-attack flight. Applying the theories of bifurcations, many kinds of bifurcations, such as equilibrium, Hopf, homoclinic （heteroclinic） orbit and double limit cycle bifurcations are discussed and the existence conditions for these bifurcations as well as formulas for calculating bifurcation curves are derived. The bifurcation curves divide the parameter plane into several regions; moreover, the complete bifurcation diagrams and phase portraits in different regions are obtained. Finally, our conclusions are applied to analyzing the stability and bifurcations of a practical example of a high angle-of-attack flight as well as the effects of elevator deflection on the asymptotic stability regions of equilibrium. The model and analytical methods presented in this paper can be used to study the nonlinear flight dynamic of longitudinal stall at high angle of attack.

关键词： Bifurcation high angle of attack Longitudinal motion Polynomials Stability

A source term model of perturbation in a numerical study on flows around a slender body of revolution at a high angle of attack

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Progress in Natural Science:Materials International 2009年第12期19卷 1831-1835页

作者： Yang Liu,Dongjun Ma,Dejun Sun~*,Xieyuan Yin Department of Modern Mechanics,University of Science and Technology of China,Hefei 230027,China [a]Department of Modern Mechanics University of Science and Technology of China Hefei 230027 China

A numerical study on flows around a slender body of revolution at a high angle of attack is conducted to investigate the influence of strength and circumferential angle of perturbation on flow asymmetry.A source term model is applied to simulate a real geometrical perturbation near the tip of the slender *** can greatly facilitate the adjustment of perturbation *** results show that the bistable phenomenon does not appear any more at a small perturbation *** different perturbation strengths,the energy of the asymmetric perturbation flow experiences a similar spatial exponential growth regime with the same growth *** appearance of the bistable phenomenon is closely related to nonlinear saturation of the perturbation flow as perturbation strength increases.

关键词： Slender body high angle of attack Asymmetric vortex Source term model

Control of Asymmetric Flow Fields of Slender Bodies at high angle of attack

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Chinese Journal of Aeronautics 2006年第2期19卷 168-174页

作者：明晓顾蕴松 Department of Aerodynamics Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack. The bi-stable situation of the side forces is observed, which could be easily switched by a tiny disturbances either from coming flow or from artificial disturbances at nose tip （including manufacturing defect）. In turbulent flows the side forces switched randomly between positive and negative. There exists a hysteresis loop of side force with the rolling angle. A rod in front of the slender body is used to change the vortex pattern, which could be kept even the rod is moved out from the stream. A miniature strake attached to the nose tip of the model can be moved to different circumferential position. When the strake is stationary, the hysteresis loop disappears and the side force does not change with the turbulent fluctuation of coming flow. The results from dynamic measurements of section side force indicates that when the strake swung at lower frequency the side force can follow the cadence of the swinging strake. With increasing frequency, the magnitude of the side force decreases. At still high frequency, the side force diminishes to zero. If the strake is swinging, while the middle position can be changed to different circumferential angle Фs on either left or right side, the side forces can be changed proportionally with the angle Фs. On the basis of the experimental results, the mechanism of the asymmetry is discussed.

关键词： high angle of attack asymmetric vortex pattern flow control

Miu-Synthesis Controller Design of the Transverse and Lateral Channels for high angle of attack Air-to-Air Missile

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Miu-Synthesis Controller Design of the Transverse and Latera...

Unsteady aerodynamic modeling at high angles of attack using support vector machines

第30届中国控制与决策会议

作者： Liao Huannian Zhong Kewei Ye Saixian Chen Guangshan Xia Bin Shanghai Aerospace Control Technology Institute

The new generation air-to-air missile is supposed to provide high manoeuvrability. For this demand, the high angle of attack to flight is needed. Aiming at the problem of strong cross-couplings caused by high angle of attack, it’s difficult to satisfy the requirements of the robust stability and robust performance for the ordinary controller design of single channel. The paper takes advantage of multivariable design by Miu-Synthesis control. The method of transverse and lateral double channel design was adopted. And the Miu-Synthesis controller was computed. The effectiveness is validated by simulation comparison between the new method and the single channel classical control design method.

关键词： high angle of attack Strong Cross-Couplings Transverse and Lateral Double Channel Design Miu-Synthesis Control

来源： cnki会议评论

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Chinese Journal of Aeronautics 2015年第3期28卷 659-668页

作者： Wang Qing Qian Weiqi He Kaifeng State Key Laboratory of Aerodynamics Computational Aerodynamics Institute China Aerodynamics Research and Development Center

Abstract Accurate aerodynamic models are the basis of flight simulation and control law design. Mathematically modeling unsteady aerodynamics at high angles of attack bears great difficulties in model structure determination and parameter estimation due to little understanding of the flow mechanism. Support vector machines （SVMs） based on statistical learning theory provide a novel tool for nonlinear system modeling. The work presented here examines the feasibility of applying SVMs to high angle.-of-attack unsteady aerodynamic modeling field. Mainly, after a review of SVMs, several issues associated with unsteady aerodynamic modeling by use of SVMs are discussed in detail, such as sele, ction of input variables, selection of output variables and determination of SVM parameters. The least squares SVM （LS-SVM） models are set up from certain dynamic wind tunnel test data of a delta wing and an aircraft configuration, and then used to predict the aerodynamic responses in other tests. The predictions are in good agreement with the test data, which indicates the satisfving learning and generalization performance of LS-SVMs.

关键词： Aerodynamic modeling high angle of attack Support vector machines(SVMs) Unsteady aerodynamics Wind tunnel test

Experimental investigation of influence of strake wings on self-induced roll motion at high angles of attack

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Chinese Journal of Aeronautics 2016年第6期29卷 1591-1601页

作者： Geng Xi Shi Zhiwei Cheng Keming College of Aerospace Engineering Nanjing University of Aeronautics and Astronautics

The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.

关键词： Cruciform fins high angle of attack PIV Roll motion Strake wing

COMPUTATION OF FIELD STRUCTURE AND AERODYNAMIC CHARACTERISTICS OF DELTA WINGS AT high angleS OF attack

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Applied Mathematics and Mechanics(English Edition) 2005年第6期26卷 797-806页

作者：杨立芝高正红 Department of Aircraft Engineering Northwestern Polytechnical University

A numerical investigation of the structure of the vortical flowfield over delta wings at high angles of attack in longitudinal and with small sideslip angle is presented. Three-dimensional Navier-Stokes numerical simulations were carried out to predict the complex leeward-side flowfield characteristics that are dominated by the effect of the breakdown of the leading-edge vortices. The methods that analyze the flowfield structure quantitatively were given by using flowfield data from the computational results. In the region before the vortex breakdown, the vortex axes are approximated as being straight line. As the angle of attack increases, the vortex axes are closer to the root chord, and farther away from the wing surface. Along the vortex axes, as the adverse pressure gradients occur, the axial velocity decreases, that is, A is negativee, so the vortex is unstable, and it is possible to breakdown. The occurrence of the breakdown results in the instability of lateral motion for a delta wing, and the lateral moment diverges after a small perturbation occurs at high angles of attack. However, after a critical angle of attack is reached the vortices breakdown completely at the wing apex, and the instability resulting from the vortex breakdown disappears.

关键词： computational method high angle of attack vortex flow

Influence of artificial tip perturbation on asymmetric vortices flow over a chined fuselage

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Chinese Journal of Aeronautics 2015年第4期28卷 1016-1022页

作者： Shi Wei Deng Xueying Tian Wei Wang Yankui Ministry-of-Education Key Laboratory of Fluid Mechanics Beihang University

An experimental study was conducted with the aim of understanding behavior of asymmetric vortices flow over a chined *** tests were carried out in a wind tunnel at Reynolds number of 1.87 · 105 under the conditions of high angles of attack and zero angle of *** results show that leeward vortices flow becomes asymmetric vortices flow when angle of attack increases over *** asymmetric vortices flow is asymmetry of two forebody vortices owing to the increase of angle of attack but not asymmetry of vortex breakdown which appears when angle of attack is above *** vortices flow is sensitive to tip perturbation and is nondeterministic due to randomly distributed natural minute geometrical irregularities on the nose tip within machining *** asymmetric vortices flow can be obtained by attaching artificial tip perturbation which can trigger asymmetric vortices flow and decide asymmetric vortices flow *** by artificial tip perturbation, the vortex on the same side with perturbation is in a higher position, and the other vortex on the opposite side is in a lower *** suction on the lower vortex side is larger, which corresponds to a side force pointing to the lower vortex side.

关键词： Asymmetric vortices flowChined fuselage Tip perturbation high angle of attack Flow regimes