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.     

Panel flutter prediction in two dimensional flow with enhanced piston theory

Piston theory may be used in the high Mach number supersonic flow region and/or in very high frequency subsonic or supersonic flow. In this flow model, the pressure at a point on the fluid-solid interface only depends on the downwash at the same point. However the classical piston theory may not be sufficient for some phenomena in aeroelasticity and aeroacoustics (far field prediction). Dowell and Bliss have created an extension of piston theory that allows for higher order effects that take into account the effect the distribution of downwash on pressure at any point. For simple harmonic motion, expansions in reduced frequency, inverse reduced frequency and/or inverse (square of) Mach number have all been created; The effects of higher order terms in these several expansion in creating an enhanced piston theory was illustrated for plunge and pitch motion of an airfoil (discrete system) by Ganji and Dowell. In the present paper, flutter prediction for a flexible panel in two –dimensional flow is investigated using enhanced piston theory. The goal of the present paper is to demonstrate that an enhance version of piston theory can analyze single degree of freedom flutter of a panel as compared to the classical piston theory and quasi-steady aerodynamic models which can only treat coupled mode flutter.     

PIV EXPERIMENTS ON FLOWFIELD CHARACTERISTICS OF ROTOR AIRFOIL DYNAMIC STALL AND MODIFICATIONS OF L-B MODEL

为测量翼型动态失速的非定常涡流场特性,采用3D-PIV 技术,对典型直升机旋翼翼型SC1095 的动态失速流场特性进行测量,发现涡在不同位置处的输运速度不同：位于翼型表面的涡的无量纲速度为0.39,位于尾迹区的涡的无量纲速度为0.55. 利用前缘涡输运速度变化这一特征,改进了经典的翼型动态失速利什曼-贝多斯（Leishman-Beddoes,L-B）模型,将该模型中固定的涡时间常数修正为可以随涡位置变化的时变函数,修正后的模型计算得到翼型法向力峰值相对原L-B 模型提升5%,力矩系数负峰值相对原L-B 模型提升13%,与试验值相比更加吻合,表明修正后的翼型动态失速模型更好地体现了翼型前缘涡的物理特征.     

Computational aeroelastic investigation of a transonic limit-cycle-oscillation experiment at a transport aircraft wing model

Aeroelastic measurements of a three-dimensional wing model, the so-called Aerostabil wing, were conducted in the Transonic Windtunnel Göttingen. This clean, backward-swept wing allowed the experimental investigation of limit cycle oscillations in a certain transonic parameter range. In this paper, a detailed insight into the observed physical phenomena, especially the measured limit cycle oscillations, is presented by means of CFD–CSM coupled simulations. These simulations on the basis of a detailed structural finite element model reveal the specific properties of the Aerostabil wing and furthermore allow investigating the unstable behavior of this windtunnel model for transonic flow settings. The aerodynamic characteristics include a two-shock system and large flow separation areas, further increasing the complexity of the aeroelastic problem. A structural single degree-of-freedom system is used for the prediction of the experimental stability range and the limit cycle oscillation investigations. Due to the good agreement of simulation and experiment the limit cycle oscillations can be explained by means of nonlinear aerodynamic effects.     

基于前失速先兆检测机理的叶顶喷气扩稳实验研究

拓宽轴流压气机稳定工作裕度及探索其流动失稳控制途径一直是内部流动研究的焦点。本文从前失速先兆检测机理入手,对前失速先兆与叶顶间隙泄漏流非定常性进行了关联性研究,发现了前失速先兆与叶顶间隙泄漏流非定常性有一定的关联性。在认识这类关联性的基础上,提出了基于前失速先兆捕捉的失稳控制途径,并结合DSP控制器构建扩稳控制方案,在低速轴流压气机上进行了实验验证。实验结果表明:采用叶顶喷气扩稳控制措施后,简化了原来复杂的控制机构,并为控制措施的实施预留了反馈控制时间,与原来的定常喷气控制措施相比有变工况自适应的优势。     

Parametric studies on relationships between flutter derivatives of slender bridge (Ⅱ)

Based on curve fitting of coefficients of three component forces of the Messina Straits Bridge, and the previously proposed semi-analytical expressions of flutter deriva-tives of flexible structure, the change of flutter derivatives of slender bridge cross-section with respect to its aerodynamic center, rotational speed and angle variation is studied using a parametric method. The calculated results are compared with the measured ones, and expressions of flutter derivatives of the Messina Straits Bridge are derived. The in-trinsic relationships existing in flutter derivatives are validated again. It is shown that the influence of the rotational speed on flutter derivatives is not negligible. Therefore, it provides an additional semi-analytical approach for analyzing flutter derivatives of the bridge with streamlined cross-section to get its aerodynamic information.     

Monte-Carlo Simulation of Multiple-Molecular-Motor Transport

Multimotor transport is studied by Monte-Carlo simulation with consideration of motor detachment from the filament. Our work shows, in the case of low load, the velocity of multi-motor system can decrease or increase with increasing motor numbers depending on the single motor force-velocity curve.The stall force and run-length reduced greatly compared to other models.Especially in the case of low ATP concentrations, the stall force of multi motortransport even smaller than the single motor's stall force.     

壁板颤振的分析模型、数值求解方法和研究进展

研究壁板颤振问题需要计及大挠度变形下结构的几何非线性效应,不仅涉及气动弹性稳定性,而且关心结构的非线性颤振响应.该文回顾了飞行器壁板颤振问题的国内外研究情况,评述了在壁板颤振研究中采用的分析模型、数值求解方法以及在理论分析和试验方面的研究成果,并提出了今后壁板颤振问题的4个研究方向.