High-frequency plate flutter

Earlier, using the global instability method, the stability of a strip plate in a supersonic gas flow was investigated. In addition to the classical (low-frequency) flutter developing upon the interaction between the plate oscillation modes, a novel (high-frequency) flutter type in which the oscillations are unimodal was detected. In the present study, the effect on the high-frequency flutter of the plate width (earlier only an asymptotic analysis for a width tending to infinity was performed), its damping characteristics, and the presence of a gas at rest on the side opposite the flow is investigated.     

径向无叶扩压器的稳定性区域

径向无叶扩压器的稳定性区域窦华书（清华大学水利水电系北京１０００８４）关键词：无叶扩压器，旋转失速，喘振，稳定性区域一、导怕旋转失速和喘振是离心压气机中两种不同的气动不稳定现象。无叶扩压器是可能导致这些不稳定现象的主要通流部件之一。近三十年来，许多作...     

低速轴流压气机单转子旋转失速三维数值模拟和实验比较

本文通过求解三维不可压N-S方程,对三级低速轴流压气机第一级的孤立转子进行数值模拟,在出口加上节流阀进行了非定常计算,得到了失速先兆的特性,并且与压气机失速实验进行了比较。结果表明,计算与实验的特性线符合较好,单转子三维计算与压气机三级实验中第一级转子在失速先兆和失速团的特性一致。并且数值失速过程中动叶通道内部动态压力的变化与实验结果也很接近。     

被动控制装置改进轴流风机失速余度的实验研究

1前言近年来，使用被动控制装置改进风机的失速特性一直引起风机设计和研究人员的重视。例如：在转子前加装可调进口导叶，在转子叶尖区吹气和放气，机匣处理装置（轴向、斜向和周向开缝）等来抑制风机失速的技术已被实际应用。但这些装置仍然存在着一些缺点。例如：降低了风机的最高效率尚2％－4％），改进失速余度的范围小，大约只有20％的流量失速金度的改进．以及装置本身结构复杂，增加了造价。因而一种被称为空气分流器的被动控制技术，首先由NBAHOB；C．K申请了专利川。由于空气分流器在控制轴流风机失速有很好的效果，因而许多…     

一台低速压气机的失速前扰动分析

本文应用小波的方法对一台三级、低速、轴流压气机的动态实验数据进行了分析。所分析的数据点的范围从压气机发生旋转失速前1000转开始,分析结果表明:失速前扰动的出现是间歇性的,即扰动出现、发展、消失、再出现、再发展、再消失。将所有沿圆周方向布置的传感器信号一起分析,失速前扰动形成的团沿圆周方向旋转。而且,越接近失速点,失速前扰动团沿圆周方向传播的距离相对越长。同时,表明结构的不均匀产生在第七传感器和第一传感器之间。     

CFD analysis of an oscillating wing at various reduced frequencies

The effect of various reduced frequencies has been examined for an oscillating aspect ratio 10 NACA 0015 wing. An unsteady, compressible three‐dimensional (3D) Navier–Stokes code based on Beam and Warming algorithm with the Baldwin–Lomax turbulence model has been used. The code is validated for the study against published experimental data. The 3D unsteady flow field is simulated for reduced frequency values of 0.1, 0.2 and 0.3 for a fixed mean angle of attack position and fixed amplitude. The type of motion is sinusoidal harmonic. The force coefficients, pressure distributions and flow visualization show that at the given conditions the flow remains attached to the wing surface even at high angles of attack with no clear separation or typical light‐to‐deep category of dynamic stall. Increased magnitude of hysteresis and higher gradients are seen at higher reduced frequencies. The 3D effects are even found at midspan locations. In addition, the rate of decrease in lift near the wing tips compared with the wing root is not much like in the static cases. Copyright © 2008 John Wiley & Sons, Ltd.     

An analysis of the Circumferential Grooves Casing Treatment for transonic compressor flow

The stall mechanism of the NASA Rotor 37 is investigated through the analysis of the critical flow structures near the stall under the transonic condition. The performance of the rotor with Circumferential Grooves Casing Treatment (CGCT) is also studied based on the Reynolds-Averaging Navier-Stokes approach. The study finds that stall margin improvement can be achieved without significant penalty on the efficiency for the two CGCT configurations applied. The effects of circumferential grooves on the critica...     

Intermittency in a cantilever plate in a randomly fluctuating fluid flow

Fluid–elastic systems nearing dynamic instabilities are known to be sensitive to fluctuations in fluid flow. A cantilever plate in axial flow with random temporal fluctuations, is examined numerically for its dynamical behaviour. The numerical model comprises of a nonlinear structural model for the flexible plate, coupled with unsteady lumped vortex model for the fluid forces. As the mean flow velocity is increased, the system transitions to limit cycle oscillations from a state of rest, through a regime of intermittent oscillations. The conditions for onset and disappearance of intermittency are discussed and are interpreted using stochastic bifurcation theories. While the onset of intermittency is found to be unaffected by the time scales of the flow fluctuations, they are observed to affect the length of the intermittency regime. The effect of plate flexibility on intermittency is also discussed.     

Note on the critical variational state in elasticity theory

Recently Prof. Chien Wei-zang pointed out that in certain cases, by means of ordinary Lagrange multiplier method, some of undetermined Lagrange multipliers may turn out to be zero during variation. This is a critical state of variation. In this critical state, the corresponding variational constraint can not be eliminated by means of simple Lagrange multiplier method. This is indeed the case when one tries to eliminate the constraint condition of strain-stress relation in variational principle of minimum complementary energy by the method of Lagrange multiplier.By means of Lagrange multiplier method, one can only derive, from minimum complementary energy principle, the Hellinger-Reissner Principle, in which only two type of in-dependent variables, stresses and displacements, exist in the new functional. Hence Prof. Chien introduced the high-order Lagrang multiplier method bu adding the quadratic terms.to original functions. The purpose of this paper is to show that by adding to original functionals one     

分析输流曲管临界流速的迁移矩阵法

提出了一种分析输液曲管临界流速的方法。与其它方法相比,该方法不但容易处理带任意多个中间支承和变刚度、变曲率的输液曲管问题,而且由于对各段位移、内力关系导出了一系列显式,故不管离散段数多少,最终都只需解一个三阶矩阵方程,因此计算量小、精度高。