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1.
Effects of hysteretic and aerodynamic damping on supersonic panel flutter of composite plates 总被引:1,自引:0,他引:1
The governing equation for the finite element analysis of the panel flutter of composite plates including structural damping is derived from Hamilton's principle. The first order shear deformable plate theory has been applied to structural modelling so as to obtain the finite element eigenvalue equation. The unsteady aerodynamic load in a supersonic flow is computed by using the linear piston theory. The critical dynamic pressures for composite plates have been calculated to investigate the effects of structural damping on flutter boundaries. The effects are dependent on fiber orientation because flutter mode can be weak or strong in the fiber orientation of composite plates. Structural damping plays an important role in flutter stability with low aerodynamic damping but would not affect the flutter boundary with high aerodynamic damping. 相似文献
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Experiments have been conducted in a wind tunnel on a parallel triangular tube array with a pitch ratio of 1·375. The aerodynamic component of damping was determined as a function of flow velocity. This damping was found to increase linearly with flow to about 50% of the stability threshold and then to decrease. Additionally, six different sets of tubes were tested to examine the effect of mass ratio on fluid-elastic stability. The results were compared with similar experiments in which damping alone was varied. It is seen that damping and mass ratio do not appear to be linearly dependent parameters which is contrary to the assumption used commonly in the stability analysis of tube banks. More importantly, however, the stability threshold is substantially less dependent on both damping and mass ratio than indicated by conventional theory. 相似文献
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Tarnopolsky AZ Fletcher NH Lai JC 《The Journal of the Acoustical Society of America》2000,108(1):400-406
The results of experiments on the threshold behavior and large-amplitude oscillation of "outward-swinging door" vibrating flap valves in an air environment are reported and compared with the predictions of a simple nonlinear theory that parametrizes aerodynamic effects by means of a simple damping coefficient together with a contraction coefficient for the flow. The agreement is acceptably good for the threshold blowing pressure for valve oscillation, the large-signal vibration amplitude, the pressure jump in the transition from threshold to large-signal behavior, and the variation in vibration frequency, all as functions of reservoir volume. The calculated pressure waveform in the reservoir has the observed phase and magnitude but fails to reproduce finer details. It is concluded that the simple theory provides an adequate account of the behavior of such valves. There are just two parameters in the theory, describing jet contraction and aerodynamic damping, respectively. Since these may depend significantly upon the detailed geometry, valves with different shapes may behave in quantitatively different ways. 相似文献
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E. DE LANGRE 《Journal of sound and vibration》2002,256(2):299-317
The effect of inviscid plug flow on the stability of several hydroelastic systems is investigated by determining the absolute or convective nature of the instability from the linear dispersion relation. The fluid-structure systems consist of plates and membranes with bounded and unbounded flow. A method is proposed to derive systematically in parameter space the boundary between convective and absolute instability, based on the particular symmetries of the dispersion relation as originally noted by Crighton and Oswell. This method is then applied to the case of plates with superimposed tension, thick plates with rotary inertia and walls made of plates or membranes bounding channel flow, oscillating in a sinuous or varicose mode of deformation. A relation is drawn with solutions by previous authors for plates, for pipes and for the Kelvin-Helmholtz instability with surface tension. To illustrate these results some temporal evolutions are calculated by using an integration in the wavenumber space. Based on the large set of new cases solved in the paper some general trends are discussed as to the influence of flow velocity, confinement and structural stiffness on the existence of absolutely unstable waves in inviscid hydroelastic systems. 相似文献
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The flow-induced instabilities of a fairly general class of compliant coatings are investigated theoretically. The coatings are of finite length and consist of elastic plates or membranes stretched over a fluid substrate having a density which may be different from the main flow. Provision is also made for the plate to be backed by an elastic foundation of arbitrary spring stiffness. Fairly standard aeroelastic methods are followed. The aerodynamic forces generated by the main flow are calculated by using thin aerofoil theory with a correction factor to allow for the presence of a boundary layer. The pressure induced in the substrate fluid is calculated by assuming potential flow and applying the method of images. A single-mode analysis shows that coatings with laminar boundary layers suffer a divergence-type instability in contrast to turbulent boundary layers which always give rise to a flutter-type instability with a higher critical velocity. The order of the most dangerous mode is calculated and found to rise with an increase in equivalent spring stiffness for fixed tension or flexural rigidity. Results are presented for plates and membrane coatings with an air stream over air and water substrates. Taking account of the substrate fluid dynamics reduces the growth rate of the instability by an order of magnitude and completely suppresses flutter with water substrates. Single-, double- and triple-mode analyses are carried out and the results compared. The critical velocity is adequately predicted by single-mode analysis but a coupling of odd and even modes can lead to flutter even with a laminar boundary layer. 相似文献
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The paper presents the results of theoretical and experimental studies of the occurrence and locations of aerodynamic noise sources in air blowers related to air flow around stationary and moving elements inside a machine body. These studies were based on basic research by Lighthill and Curle and used a developed method for measuring pressure pulsations on rotating blades and stationary elements of a machine body. The most significant sources of discrete and broadband components of aerodynamic noise were revealed. The role of blades in an impeller in the emission of discrete noise components was studied. It was established that broadband peaks in the emitted noise are associated with acoustic resonances of the internal volume of the air blower. It was shown that the turbulence and velocity of the incoming flow influence the intensity of aerodynamic sources inside the body. Our studies spurred both deeper research into the nature of aerodynamic noise sources that form in air blowers and recommendations for reducing the noise produced by these sources. 相似文献
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基于介质阻挡与准直流电弧放电的物理过程, 分析了它们的气动激励机理, 建立了各自的气动激励模型, 并分别研究了它们对低速和超声速流动的激励效果. 结果显示: 介质挡板放电等离子体气动激励机理是改变了连续流体中的三种力, 即由牛顿内摩擦引起的剪切应力、由电动力学引起的体积力及由压力突变引起的冲击力, 其中基于电动力学的体积力效应占主导地位; 临近空间环境中体积力的作用效果更强, 诱导速度更大; 超声速来流下准直流电弧放电气动激励机理主要是等离子体的热阻塞效应, 本文所建立的爆炸丝传热模型可以用于仿真其控制激波的过程; 热电弧对于超声速来流而言就像一个具有一定斜坡角度的虚拟突起, 可用于高超声速飞行器前体激波的控制. 相似文献
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颤振是航空发动机、燃气轮机等运行安全的重要威胁,但颤振稳定性与流动结构之间的关系尚不清晰。本文使用行波法和影响系数法,对某宽弦复合掠型高速跨音风扇转子的一阶模态进行了颤振特性研究,计算了在100%转速下从堵塞点到近失速点的颤振表现。使用影响系数法时,分析了不同通道数的计算域对气动阻尼计算的影响,并与行波法得到的结果进行了对比。研究了流动结构与叶片表面气动阻尼之间的关系,旨在提高对流动致颤机理的认识。结果表明影响系数法和行波法均能对叶片的气动阻尼进行较好的预测;流动结构方面,激波、激波附面层分离、叶尖泄漏流以及吸力面前缘叶顶附近的非定常压力波动,对叶片的气动阻尼分布有较大的影响。 相似文献
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采用有效多松弛时间-格子Boltzmann方法(Effective MRT-LBM)数值模拟了微尺度条件下的振荡Couette和Poiseuille流动. 在微流动LBM中引入Knudsen边界层模型,对松弛时间进行修正. 模拟时平板或外力以正弦周期振动,Couette流中考虑了单平板振动、上下板同相振动这两类情况. 研究结果表明,修正后的MRT-LBM模型能有效用于这类非平衡的微尺度流动模拟;对于Couette流,随着Kn数的增大,壁面滑移效应变得越明显. St越大,板间速度剖面的非线性特性越剧烈;两板同相振荡时,若Kn,St均较小,板间流体受到平板拖动剪切的影响很小,板间速度几乎重叠在一起;在振荡Poiseuille流动中,St数增大到一定值时,相位滞后现象减弱;相对于Kn数,St数对振荡Couette 和Poiseuille流中不同位置处速度相位差的产生有较大影响.
关键词:
格子Boltzmann方法
有效MRT模型
Knudsen层
振荡流 相似文献
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S. M. Dmitriev A. A. Dobrov D. V. Doronkov A. N. Pronin D. N. Solntsev V. D. Sorokin A. E. Khrobostov 《Thermophysics and Aeromechanics》2018,25(5):695-703
The article presents the results of experimental studies of the influence of different designs of mixing spacer grids on the coolant flow in FA-KVADRAT PWR. The investigations were carried out by simulating the coolant flow in the core on the experimental air stand being an aerodynamic open loop through which air is pumped. To measure the local hydrodynamic characteristics of the coolant flow, special pneumometric sensors were used for measuring the total velocity vector and the flow rate value. During the investigations of the local hydrodynamics of the coolant, transverse flow velocity, as well as the coolant flow rates in the cells of the experimental model FA-KVADRAT, was measured. The analysis of spatial distribution of projections of absolute flow velocity allowed studying and detailing the coolant flow pattern behind the mixing spacer grids with different designs of deflectors as well as selecting the optimal design of the deflector. The accumulated database on the coolant flow in FA-KVADRAT has formed the basis for engineering assessment of active zones’ structures of PWR. The results of experimental studies are used to verify CFD codes (in both foreign and domestic development) as well as programs for detailed cell-by-cell calculation of active zones in order to reduce conservatism when assessing heat engineering reliability. 相似文献
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挤压气膜阻尼作用研究 总被引:2,自引:0,他引:2
本文通过薄板弯曲驻波模型,在一定假设条件下,对空气挤压膜的阻尼作用作了理论分析,导出了包括五种参量(气膜厚度、振动频率、板的结构量、气体的粘滞性和气压)的损失因数的新公式。这些公式较全面地反映了气膜阻尼的特性。以其计算两种结构的损失因数的预测值和参考文献所报道的实测值相当接近。 相似文献
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Cantilevered flexible plates in axial flow lose stability through flutter. Using the inextensibility condition for the cantilevered nonlinear plate equation of motion and the unsteady lumped-vortex model to calculate the fluid loads, a flutter boundary has been obtained. In the time-domain analysis performed to this end, the wake behind the oscillating cantilevered plate is assumed to issue tangentially from the free trailing edge and extend downstream with an undulating form. The influence of the wake on system stability may be characterized in terms of the non-dimensional mass ratio, reduced flow velocity and flutter frequency. For large values of the mass ratio, the plate vibrates with high frequency and high-order mode content. It is shown that the wake has less influence on system stability for long plates than it does for short ones. 相似文献
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旋转飞行器具有独特的周期性非定常气动现象,其动态特性更加复杂,气流与旋转高度非定常关联,俯仰阻尼导数和Magnus力矩导数同等重要.文章从飞行器气动力建模的理论基础出发,考虑飞行器自转角速度非零的事实,将其作为基态影响参数,重新构建了旋转飞行器气动力数学表达式,并借鉴成熟的常规动导数强迫振动法,采用Fourier级数表征旋转影响,沿用旋转飞行器周期气动等效概念,建立了基于基态旋转流场的周期气动等效平均俯仰动稳定导数、纵向洗流时差导数和滚转动稳定导数获取的原理表达式,并设计了相应的运动模式,可供数值计算和风洞实验使用. 相似文献
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《理论物理通讯》2017,(7)
In this paper, a smooth repetitive oscillating wave traveling down the elastic walls of a non-uniform twodimensional channels is considered. It is assumed that the fluid is electrically conducting and a uniform magnetic field is perpendicular to flow. The Sisko fluid is grease thick non-Newtonian fluid can be considered equivalent to blood. Taking long wavelength and low Reynolds number, the equations are reduced. The analytical solution of the emerging non-linear differential equation is obtained by employing Homotopy Perturbation Method(HPM). The outcomes for dimensionless flow rate and dimensionless pressure rise have been computed numerically with respect to sundry concerning parameters amplitude ratio ?, Hartmann number M, and Sisko fluid parameter b1. The behaviors for pressure rise and average friction have been discussed in details and displayed graphically. Numerical and graphical comparison of Newtonian and non-Newtonian has also been evaluated for velocity and pressure rise. It is observed that the magnitude of pressure rise is maximum in the middle of the channel whereas for higher values of fluid parameter it increases. Further, it is also found that the velocity profile shows converse behavior along the walls of the channel against multiple values of fluid parameter. 相似文献
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Arguillat B Ricot D Bailly C Robert G 《The Journal of the Acoustical Society of America》2010,128(4):1647-1655
Direct measurements of the wavenumber-frequency spectrum of wall pressure fluctuations beneath a turbulent plane channel flow have been performed in an anechoic wind tunnel. A rotative array has been designed that allows the measurement of a complete map, 63×63 measuring points, of cross-power spectral densities over a large area. An original post-processing has been developed to separate the acoustic and the aerodynamic exciting loadings by transforming space-frequency data into wavenumber-frequency spectra. The acoustic part has also been estimated from a simple Corcos-like model including the contribution of a diffuse sound field. The measured acoustic contribution to the surface pressure fluctuations is 5% of the measured aerodynamic surface pressure fluctuations for a velocity and boundary layer thickness relevant for automotive interior noise applications. This shows that for aerodynamically induced car interior noise, both contributions to the surface pressure fluctuations on car windows have to be taken into account. 相似文献