Analysis of fluid–structure interaction by an arbitrary Lagrangian–Eulerian finite element formulation

In this paper, the interaction fluid–rigid body is analysed by a finite element procedure that incorporates the arbitrary Lagrangian–Eulerian (ALE) method into a well‐known two‐step projection scheme. The flow is assumed to be two‐dimensional, incompressible and viscous, with no turbulence models being included. The flow past a circular cylinder at ℛℯ=200 is first analysed, for fixed and oscillating conditions. The dependence of lock‐in upon the shift between the mechanical and the Strouhal frequencies, for a given amplitude of forced vibration, is illustrated. The aerodynamic forces and the wake geometry are compared for locked‐in conditions with different driving frequencies. The behaviour of a rectangular cylinder (B/D=4) at ℛℯ=500 (based on height D) is also analysed. The flutter derivatives associated with aerodynamic damping (H₁* and A₂* in Scanlan's notation) are evaluated by the free oscillation method for several values of reduced flow speed above the Strouhal one (namely for 3≤U*≤8). Torsional flutter was attained at U*≥5, with all the other situations showing stable characteristics. Copyright © 1999 John Wiley & Sons, Ltd.     

两自由度舵-轴系统振动三维效应修正模型

考虑到小展弦比舵所存在的三维效应,利用附加质量系数ε和环量系数δ对经典Theodorsen两自由度运动方程进行修正,并与经典颤振实验结果进行比较,验证了修正后两自由度运动方程的适用性.质量比μ的不同会引起两自由度舵-轴系统振动V-g曲线形态的差异,故根据V-g曲线形状的不同将系统的振动分为第一类振动和第二类振动,其对应情况下可能发生的颤振为第一类颤振和第二类颤振.利用修正后的两自由度颤振理论模型分析了支撑刚度k_h、扭转刚度k_α、舵弦向重心位置x_α和初始攻角AOA对舵-轴系统颤振特性的影响规律,并通过开展相关实验对理论计算值进行验证,实验结果与计算值吻合良好.计算结果表明,k_h,k_α,x_α和AOA对颤振速度V_F存在显著影响,它们可以分别在一定的取值范围内导致系统发生第二类颤振.并且,V_F随k_h的增大单调增大,随k_α和x_α的增大先增大再减小,随AOA的增大则逐渐减小.其中,令V_F存在非零值的x_α取值范围狭小,反映了系统振动形态对x_α的敏感性.因此,在设计阶段避免将x_α设置在这个狭小的范围内可以降低颤振的发生几率.另一方面,由于V_F对k_h和k_α的反应缓慢,一旦颤振发生就可以通过将刚性轴锁紧来消除颤振效应.     

Response of skin panels to combined self- and boundary layer-induced fluctuating pressure

Fluctuating pressures are a critical consideration in the life-prediction of thin-gauge hot-structures operating in high-speed flow. Sources include both boundary layer turbulence and self-induced components, where the latter arises from panel vibrations. While a considerable body of research is available for the structural response of thin-gauge panels to self-induced pressure fluctuations, the response to boundary layer turbulence is not well-understood due to the complexity in modeling the loads. Important open issues are the degree of coupling between the boundary layer induced fluctuating loads and the thermo-structural response, and also the potential for interactions between a turbulent boundary layer and structural response to result in structural instabilities. This study seeks to address these issues by incorporating a phenomenological model for turbulent boundary layer loads into an aerothermoelastic framework. The enhanced aerothermoelastic model is then used to study the combined effect of self- and boundary layer-induced fluctuating pressures on responses of simple panels, and to characterize features in the turbulent boundary layer loads that can lead to large amplitude structural vibrations. The developed phenomenological model predicts that the magnitude of the boundary layer induced fluctuating pressure increases with increasing panel inclination, and decreases with increasing temperature. Furthermore, it is found that both RMS magnitude and phase angle of the boundary layer induced pressure loads play key roles in panel response. Certain combinations of these features, coupled with the self-induced pressure fluctuations, are found to cause onset of fluid–structural instabilities earlier than observed when pressure fluctuations from the turbulent boundary layer are either neglected or decoupled from the panel response.     

Nonlinear LCO “amplitude–frequency” characteristics for plates fluttering at supersonic speeds

The nonlinear aeroelastic behavior of isotropic rectangular plates in supersonic gas flow is examined. Quadratic and cubic aerodynamic nonlinearities as well as cubic geometrical nonlinearities are considered in this study. While the aerodynamic nonlinearities are the results of the expansion of the nonlinear piston-theory aerodynamics loading up to the third-order, the geometrical nonlinearities are due to stiffening effects from the panel out-of-plane deformation consistent with the von Karman’s nonlinear plate theory. While in vacuum the typical nonlinear hardening frequency vs. oscillation amplitude, one characterized by monotonically increasing amplitudes at increasing frequencies, exists, in the presence of a high-speed flow, qualitative and quantitative changes of the nonlinear relationship are expected. This paper shows how the thin-plate behavior is influenced by the high-speed flows providing the “amplitude–frequency” dependency, which describes the nonlinear oscillations of the considered aeroelastic system.     

三维透平叶片扭转颤振问题的流固耦合数值研究

颤振,尤其是失速颤振是引起叶轮机械安全事故的重要原因之一。由于叶片颤振的复杂性,过去人们一直采用半经验的方法研究叶片的颤振。本文发展了一套更精确的流固耦合计算方法,并用这种算法研究了三维透平叶片的扭转颤振。在模拟大负攻角下的颤振时发现,传播失速响应频率向固有频率靠近是振动发散的一个重要判据。通过计算得出了压比和攻角对颤振影响的特性曲线,它不但可用于判断流体激振的稳定性,而且可以研究颤振的强度。     

叶轮机械叶片颤振研究的进展与评述

颤振一类气动弹性稳定性问题是叶轮机械设计者关心的主要问题之一. 本文对叶轮机械叶片颤振模型研究的进展进行了回顾, 包括非定常气动模型、结构模型以及颤振的预测方法等内容. 通过对颤振模型研究的介绍, 讨论了不同方法处理颤振这类气动弹性稳定性问题的优缺点. 提出了关于颤振研究目前的不足和部分难点, 认为流固耦合模型的研究值得进一步重点关注.      

一种高效的叶轮机叶片气动阻尼计算方法

运用叠加原理, 发展了一种可以运用于小振幅运动的叶轮机叶片非定常气动力降阶模型, 并将该模型与传统的能量法相结合, 提出了一种叶轮机叶片气动阻尼的高效求解方法. 运用该方法求解叶轮机叶片的气动阻尼系数, 对某个频率、某个模态只需要进行一次非定常计算, 就可以求出所有叶间振动相角下的气动阻尼系数, 提高了气动阻尼的求解效率. 在STCF4和NASA Rotor67两个算例上运用非定常雷诺平均N-S(RANS)方程和提出的降阶模型进行了对比计算.算例表明, 在小振幅下该方法的计算结果与RANS方程计算得到的气动阻尼系数能很好地吻合, 而计算效率相比多通道非定常RANS方程计算提升了近一个数量级, 并且该方法还可以运用于有失谐情况的颤振分析, 在工程上有较高的应用价值.      

两种湍流模型时域颤振计算方法研究

采用时域计算分析方法进行了机翼跨音速颤振特性研究。在结构运动网格的基础上,采用格点格式有限体积方法进行空间离散和双时间全隐式方法进行时间推进求解雷诺平均N-S方程。针对流动粘性分别应用了SST湍流模型和SSG雷诺应力模型,通过对跨音速标模算例AGARD445.6机翼的计算结果与实验值的对比分析,其中应用SST湍流模型得到的颤振速度与实验值最为接近,特别是在跨音速段平均相对误差在3%以内;并且计算结果整体上反映了跨音速颤振"凹坑"物理特性,验证了方法的有效性。     

FLUTTER INSTABILITY OF SUPPORTED PIPES CONVEYING FLUID SUBJECTED TO DISTRIBUTED FOLLOWER FORCES

In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes ...     

Limit cycle oscillation behavior of transonic control surface buzz considering free-play nonlinearity

The limit cycle oscillation (LCO) behaviors of control surface buzz in transonic flow are studied. Euler equations are employed to obtain the unsteady aerodynamic forces for Type B and Type C buzz analyses, and an all-movable control surface model, a wing/control surface model and a three-dimensional wing with a full-span control surface are adopted in the study. Aerodynamic and structural describing functions are used to deal with aerodynamic and structural nonlinearities, respectively. Then the buzz speed and buzz frequency are obtained by V-g method. The LCO behavior of the transonic control surface buzz system with linear structure exhibits subcritical or supercritical bifurcation at different Mach numbers. For nonlinear structural model with a free-play nonlinearity in the control surface deflection stiffness, the double LCO phenomenon is observed in certain range of flutter speed. The free-play nonlinearity changes the stability of LCOs at small amplitudes and turns the unstable LCO into a stable one. The LCO behavior is dominated by the aerodynamic nonlinearity for the case with large control surface oscillation amplitude but by the structural nonlinearity for the case with small amplitude. Good agreements between LCO behaviors obtained by the present method and available experimental data show that our study may help to explain the experimental observation in wind tunnel tests and to understand the physical mechanism of transonic control surface buzz.