电控旋翼气弹动力学建模研究

研究了电控旋翼的气弹动力学建模方法。以有限元旋翼气弹分析程序LORA01为基础,首先给出了一种能计及襟翼移轴补偿影响的时域综合非定常气动力模型,并将伺服襟翼作为额外引入的质量体计入结构动力学模型;之后结合有限元法,根据Hamilton原理导出由广义力表示的带襟翼桨叶非线性运动方程,采用基于Newmark方法的隐式数值积分法对桨叶运动方程进行求解。最后,利用主动控制襟翼旋翼的试验数据对模型进行了比较验证,证明了所建模型的正确性。

无轴承旋翼气弹动力学多目标减振优化

提出了无轴承旋翼柔性梁及扭管处的等效匹配处理方法,建立了无轴承旋翼的优化设计模型,采用混合法的灵敏度分析技术、Kriging的代理模型及改进遗传模拟退火算法的优化策略对某型无轴承旋翼进行了减振的气弹动力学多目标优化。结果表明:其桨毂谐波振动载荷与优化前相比,径向力、横向力、垂直力分别降低了24.2%、19.5%、15.8%;滚转力矩、俯仰力矩、偏航力矩分别降低了21.4%、20.8%、20.9%;3/转变距拉杆拉力、4/转变距拉杆拉力、5/转变距拉杆拉力分别降低了11.6%、18.4%、8.1%。表明本文方法减振效果明显。

直升机旋翼气弹动力学优化策略(Ⅱ)——多目标优化解法研究

在旋翼气弹动力学模型基础上进行了多目标优化问题的描述和分类,定义了多目标优化问题及其解,讨论了多目标优化问题的解法,提出了直升机旋翼气弹动力学多目标优化问题的解法。使用改进的遗传模拟退火算法、加权系数法、全局准则法相结合的混合式解法进行旋翼气弹动力学多目标优化问题的求解。算例结果表明:使用混合法的多目标优化解法设计变量变化平缓;同时设计目标函数的3次/转、4次/转、5次/转谐波振动载荷和桨叶总质量分别比初始设计减少13.4%、31.5%、20.9%和7.36%,优化效果明显。由本文的研究可知,在直升机旋翼气弹动力学多目标优化问题中,使用混合式多目标优化问题解法能使旋翼气弹动力学多目标优化收敛到Pareto最优解,同时可提高多目标优化问题解质量和结果的鲁棒性。

直升机旋翼气弹动力学优化策略(Ⅰ)——灵敏度分析技术研究

基于旋翼气弹动力学模型以及摄动法的灵敏度分析和直接解析的链式规则灵敏度分析相结合技术,推导了直升机旋翼气弹动力学的气弹稳定性、模态频率、自转惯量、桨叶质量、桨叶动应力等参数的灵敏度计算过程。通过算例计算结果表明:使用灵敏度分析方法与直接优化相比,实现动应力减少1.2%,质量减少0.84%,优化时间缩短2.73倍;该灵敏度分析技术对于直升机旋翼气弹动力学优化设计收敛的速度和优化结果效果明显。

直升机旋翼动力学优化浅析

阐述了直升机旋翼动力学优化在国内外研究发展情况。通过对国内外旋翼动力学模型、优化方法及优化策略等方面的对比研究,得出国内在直升机旋翼动力学优化方面与国外研究的差距,为进一步开展相关优化研究指明了方向。

基于桨叶模态修型的直升机减振优化

基于Hamilton原理推导了模态修型减振优化的有限元动力学模型,通过修改桨叶的剖面刚度和线密度来改变结构的动力学模态。以最小振动载荷为目标函数,以桨叶剖面刚度及质量为设计变量,以桨叶的频率、自转惯量、质量及模态修型参数等为约束条件,进行了减振优化。算例表明:在约束条件都满足的情况下,优化后,3/转的桨根剪力减小了55.4%,4/转的桨根剪力减小了66.5%,5/转的桨根剪力减小了53.4%,优化效果明显。

模态修型减振的旋翼桨毂谐波振动载荷计算

基于模态修型的方法推导了直升机旋翼桨叶根部剪力的计算公式,通过合成桨叶根部载荷推导了旋翼桨毂的谐波振动载荷公式。将本文建立的桨毂谐波载荷计算模型与商用软件CAMRAD计算出的结果进行对比,结果表明:本文所建立模型的旋翼计算频率与CAMRAD计算的频率相比,基阶频率计算误差在2%以内,前十阶频率误差都在8%以内;与已有文献试验测试的桨毂谐波振动载荷相比最大误差在25%以内。说明了本文建立的旋翼桨毂谐波振动载荷计算模型具有可行性和有效性。

MULTI-BODY AEROELASTIC STABILITY ANALYSIS OF TILTROTOR AIRCRAFT IN HELICOPTER MODE

The muhi-body analysis of the aeroelastic stability of the tiltrotor aircraft is presented. Muhi-body dynamic differential equations are combined with the equations of the unsteady dynamic inflow model to establish the complete unsteadily aeroelastic coupling analytical model of the tiltrotor. The stability of the tiltrotor in the helicopter mode is analyzed aiming at a semi span soft-inplane tihrotor model with an elastic wing. Parametric effects of the lag stiffness of blades and the flight speed are analyzed. Numerical simulations demonstrate that the multibody analytical model can analyze the aeroelastic stability of the tiltrotor aircraft in the helicopter mode.

A Comparative Assessment of Aerodynamic Models for Buffeting and Flutter of Long-Span Bridges

Wind-induced vibrations commonly represent the leading criterion in the design of long-span bridges. The aerodynamic forces in bridge aerodynamics are mainly based on the quasi-steady and linear unsteady theory. This paper aims to investigate different formulations of self-excited and buffeting forces in the time domain by comparing the dynamic response of a multi-span cable-stayed bridge during the critical erection condition. The bridge is selected to represent a typical reference object with a bluff con- crete box girder for large river crossings. The models are viewed from a perspective of model complexity, comparing the influence of the aerodynamic properties implied in the aerodynamic models, such as aerodynamic damping and stiffness, fluid memory in the buffeting and self-excited forces, aerodynamic nonlinearity, and aerodynamic coupling on the bridge response. The selected models are studied for a windspeed range that is typical for the construction stage for two levels of turbulence intensity. Furthermore, a simplified method for the computation of buffeting forces including the aerodynamic admittance is presented, in which rational approximation is avoided. The critical flutter velocities are also compared for the selected models under laminar flow.

Fluid-structure interaction of panel in supersonic fluid passage

Fluid-structure interaction of panel in supersonic fluid passage is studied with subcycling and spline interpolation based predict-correct scheme. The passage is formed with two parallel panels, one is rigid and the other is flexible. The interaction between fluid flows and flexible panel is numerically studied, mainly focused on the effect of dynamic pressure and distance between two parallel panels. Subcycling and spline interpolation based predict-correct scheme is utilized to combine the vibration and fluid analysis and to stabilize long-term calculations to get accurate results. It’s demonstrated that the flutter characteristic of flexible panel is more complex with the increase of dynamic pressure and the decrease of distance between two parallel panels. Via analyzing the propagation and reflection of disturbance in passage, it’s determined as a main cause of the variations.

Simulation of aerothermodynamics model on ballistic safety of fusible alloy fuze

In order to ensure the ballistic safety of fusible alloy fuze at reliable delay arming, melting point of fusible alloy needs to be calculated based on projectile velocity at safe time and distance. Taking shrapnel KZVD fuze of Switzerland oerlikon 2ZLa/353 35 mm double barrel self-propelled antiaircraft artillery as an example, based on the aerodynamics heating theory, the calculation of theory model and simulation of projectile head stagnation point temperature were done in initial stage of sim-plified exterior ballistic from engineering viewpoint when the initial projectile velocity was 1 175 m/s and the error was ±15 m/s. The melting point of fusible alloy in the safe distance was obtained by analyzing the temperature of projectile head stagnation point at corresponding projectile velocity. The simulated results indicate that the melting point of fusible alloy de-rived by theoretical calculation is identical with the result of simulation at the velocity range of 1 160 to 1 190 m/s. So the aero- thermodynamics model can be applied to design the fusible alloy fuze of corresponding melting point based on the requirement of safe distance. This method can be taken as the reference in studying the thermodynamic question of projectile flying at high speed.

CFD Investigation of Compressible Low Angles of Attack Flow over the Missile

In modem missile design, the operation of a missile aerodynamics with angles of attack is required to serve a demand on the maneuverability. The key aero-physics is the development of vortices and its interaction to the control surface such as wing and fins. This paper thus presents the investigation of the missile flow field at 4° and 8° degrees of angles of attack. The Mach numbers for both case were varied from 0.6 to 5.5. Here, the Steady Reynolds-Averaged Navier-Stokes （SRANS） equations with standard κ-ε turbulence model were selected. The numerical results of aerodynamics coefficients （both force and moment） were compared against semi-empirical data computed using Missile DatCOM. The results revealed the development of vortices observed and their interaction with fin at the rear part of the missile.

Model Order Reduction of Complex Airframes Using Component Mode Synthesis for Dynamic Aeroelasticity Load Analysis

Airframe structural optimization at different design stages results in new mass and stiffness distributions which modify the critical design loads envelop. Determination of aircraft critical loads is an extensive analysis procedure which involves simulating the aircraft at thousands of load cases as defmed in the certification requirements. It is computationally prohibitive to use a GFEM （Global Finite Element Model） for the load analysis, hence reduced order structural models are required which closely represent the dynamic characteristics of the GFEM. This paper presents the implementation of CMS （Component Mode Synthesis） method for the generation of high fidelity ROM （Reduced Order Model） of complex airframes. Here, sub-structuring technique is used to divide the complex higher order airframe dynamical system into a set of subsystems. Each subsystem is reduced to fewer degrees of freedom using matrix projection onto a carefully chosen reduced order basis subspace. The reduced structural matrices are assembled for all the subsystems through interface coupling and the dynamic response of the total system is solved. The CMS method is employed to develop the ROM of a Bombardier Aerospace business jet which is coupled with aerodynamic model for dynamic aeroelasticity loads analysis under gust turbulence. Another set of dynamic aeroelastic loads is also generated employing a stick model of same aircraft. Stick model is the reduced order modelling methodology commonly used in the aerospace industry based on stiffness generation by unitary loading application. The extracted aeroelastic loads from both models are compared against those generated employing the GFEM. Critical loads modal participation factors and modal characteristics of the different ROMs are investigated and compared against those of the GFEM. Results obtained show that the ROM generated using Craig Bampton CMS reduction process has a superior dynamic characteristics compared to the stick model.

Numerical study on the correlation of transonic single-degree-of-freedom flutter and buffet

Transonic single-degree-of-freedom(SDOF) flutter and transonic buffet are the typical and complex aeroelastic phenomena in the transonic flow. In this study, transonic aeroelastic issues of an elastic airfoil are investigated using Unsteady Reynolds-Averaged Navier-Stokes(URANS) equations. The airfoil is free to vibrate in SDOF of pitching. It is found that, the coupling system may be unstable and SDOF self-excited pitching oscillations occur in pre-buffet flow condition, where the free-stream angle of attack(AOA) is lower than the buffet onset of a stationary airfoil. In the theory of classical aeroelasticity, this unstable phenomenon is defined as flutter. However, this transonic SDOF flutter is closely related to transonic buffet(unstable aerodynamic models) due to the following reasons. Firstly, the SDOF flutter occurs only when the free-stream AOA of the spring suspended airfoil is slightly lower than that of buffet onset, and the ratio of the structural characteristic frequency to the buffet frequency is within a limited range. Secondly, the response characteristics show a high correlation between the SDOF flutter and buffet. A similar "lock-in" phenomenon exists, when the coupling frequency follows the structural characteristic frequency. Finally, there is no sudden change of the response characteristics in the vicinity of buffet onset, that is, the curve of response amplitude with the free-stream AOA is nearly smooth. Therefore, transonic SDOF flutter is often interwoven with transonic buffet and shows some complex characteristics of response, which is different from the traditional flutter.

Theoretic analysis and experiment on aeroelasticity of very flexible wing

A high-altitude long-endurance aircraft with high-aspect-ratio wing usually generates large deformation,which brings the geometric nonlinear aeroelastic problems.In recent decades,it has become a key focus of the international researchers of aeroelasticity.But some critical technologies are not developed systematically,such as aerodynamic calculation methods of the curved wing with deformation,moreover,there are few experimental validations of these technologies.In this paper,we established the steady aerodynamic calculating method of the curved wing with quite large deformation based on the extended lifting line method,and calculated the unsteady aerodynamics using the strip theory considering curved surface effects.Combining the structure geometrical nonlinear finite element method,we constructed a systematic analytic approach for the static aeroelasticity and flutter of very flexible wing,and further designed the ground vibration and wind tunnel test to verify this approach.Through the test and the theoretic results comparison,we concluded that the extended lifting line method has adaptable precision for the static aeroealsticity and the strip theory considering curved surface effects for flutter analysis can give exact critical speed and flutter mode when the dynamic stall does not happen.The work in this paper shows that the geometric nonlinear aeroelastic analytic approach for very flexible wing has very high efficiency and adaptable precision.It can be used in the engineering applications,especially the iterated design in preliminary stage.

Numerical Investigation on Aeroelastic Behavior of Composite Material Plate Excited by Pulsed Air Jet

Nowadays, carbon fiber composite material is becoming more and more popular in aero engine industry due to its high specific strength and stiffness. Laminate carbon fiber composite material is widely used to manufacture the high load wide chord fan blade, containment casing, etc. The aeroelastic behavior of composite product is critical for the optimization of the product design and manufacturing. In order to explore its aeroelastic property, this paper discusses the coupled simulation of aerodynamic excitation applied on laminate composite material plate. Mechanical behavior of composite material plate is different from that of isotropic material plate such as metal plate, because it is anisotropy and has relative high mechanical damping due to resin between plies. These plates to be studied are designed using 4 different layup configurations which follow the design methods for composite fan blade. The numerical simulation of force response analysis mainly uses single frequency mechanical force input to simulate the electromagnetic shakers or other actuators, which could transmit mechanical force to the test parts. Meanwhile, pulsed air excitation is another way to "shake" the test parts. This excitation method induces aero damping into the test part and simulates the unsteady flow in aero engine, which could cause aeroelastic problems, such as flutter, forced response and non-synchronous vibration(NSV). In this study, numerical simulation using coupled method is conducted to explore the characteristics of laminate composite plates and the property of aerodynamic excitation force generated by pulsed air jet device. Modal analysis of composite plate shows that different ply stacking sequences have a significant impact on the plate vibration characteristics. Air pulse frequency and amplitude in flow field analysis are calibrated by hot wire anemometer results. As the air pulse frequency and amplitude are varied, incident angle of flow and layup configurations of plate can be analyzed in details by the simulations. Through the comparisons of all these factors, air pulse excitation property and the aeroelastic behavior of composite material plate are estimated. It would provide a possible way to guide the next-step experimental work with the pulsed air rig. The new composite fan blade design can be evaluated through the process.

Dynamic Response of Warship Structure under Air Non-contact Explosion

The ship hull is simplified as a free beam with varying sections. Based on hydroelasticity and explosion mechanics theory,mechanical model and kinetic equation for hull girder vibration under non-contact explosion are established. The equation is solved by Wilson-θ algorithm. On the basis of the above principles,a structure kinetics analysis program is compiled. The dynamic response of supposed warship under air explosion is calculated conveniently and quickly. Under the explosion condition designed in the paper,the positive pressure period of non-contact explosion wave is much less than the natural periods of the first four modes of hull girder and the resonance of ship girder overall vibration can be avoided. The ratio of midship maximum moment to ultimate bearing strength under non-contact explosion accelerates with the increment of impact factor.

The aeroelastic effects on the scatter phenomenon of wind-tunnel data

The unsteady Reynolds-averaged Navier-Stokes equations coupled with the k-co SST turbulence model are solved to obtain the steady and unsteady aerodynamic forces for airfoils and wings. The effects of vibration types and amplitudes on aerody- namic forces of airfoils and wings are studied. The deformation characteristics of a swept wing induced by steady aerodynamic load are presented. It is found that for a vibrating elastic wing at small and medium incidences, its mean aerodynamic loads are almost the same as those obtained from the static one. On the contrary, at high incidences especially around the stall incidence, the vibration may change the mean values. In addition, the larger amplitude is, the larger discrepancy will be. For a swept wing, the steady aerodynamic loads usually lead to the ＂pitching down＂ effect on the wing tip which delays the stall compared with a rigid one; But this phenomenon dose not occur on a aeroelastic wing which can induce the separation ahead and trigger the stall. The above conclusions are in good agreement with the scatter characteristics of wind-tunnel data. The reason why the data obtained from wind tunnel and CFD are different is also analyzed. Meanwhile, it can be an explanation for scatter phe- nomenon of wind-tunnel data, especially for high incidence cases, which remains a puzzle so far.

Studies on aeroservoelasticity semi-physical simulation test for missiles

Missiles may be damaged when aeroservoelastic problem occurs,which is caused by the interaction of structure flexibility and flight control system.Because of the limit of wind tunnel test condition,numerical methods are mostly used in previous aeroservoelastic studies.However,series of assumptions and simplification on structures,aerodynamics and flight control systems are unavoidably introduced,and various nonlinear factors are also ignored,therefore,they result in considerable errors.A novel method called aeroservoelasticity semi-physical simulation test is proposed in this paper,which takes the flexible missile with control system as the test object.Vibration signals at several locations of the missile are measured by accelerometers,then corresponding unsteady aerodynamics is computed based on the fact that airflow at high Mach is nearly quasi-steady,and finally unsteady aerodynamics is exerted simultaneously by shakers at certain locations of the missile.The aeroservoelasticity semi-physical simulation test system can be constructed after the control system is closed.Open loop transfer function test and closed loop stability test are carried out in sequence.The test principle and method proposed in this paper are verified by the concordance between the results of numerical simulation and experiment.