Characteristic Regimes of Transitional Separation Bubbles in Unsteady Flow

This experimental investigation deals with transition phenomena of a separated boundary layer under unsteady inlet flow conditions. The main purpose of this investigation is to understand the influence of the rotor-stator interaction in turbomachinery on the subsequent, highly loaded boundary layer. The research project is divided into two phases. In the first phase, which has been completed recently, only the variation of mean velocity caused by upstream blades was simulated in the experiments while the free-stream turbulence intensity was retained at a constant low level. The experiments are carried out in an Eifel-type wind tunnel to investigate the laminar separated boundary layer of a flat plate under oscillating inlet conditions. The adverse pressure gradient, similar to that of turbomachines, is generated by the contoured upper wall. The unsteadiness is produced by a rotating flap located downstream of the test section. The reduced frequency, the amplitude and the mean Reynolds number are varied to simulate the conditions prevailing in turbomachines. In addition to the Kelvin–Helmholtz instability of the separated shear layer, a lower frequency instability was observed. This is frequently referred to as `free shear layer flapping' and results in two distinctly different ways of re-attachment, depending primarily on the Reynolds number. For low momentum thickness Reynolds numbers at the separation point, large-scale vortices locked to the frequency of the unsteady main flow are identified. They originate nearly at the top of the separation bubble and are ejected downstream. A fully turbulent boundary layer develops after these vortices mix out. For higher Reynolds numbers, transition is completed within a short length of the free shear layer and there-attachment region. The characteristic momentum thickness Reynolds number separating these two regimes in unsteady flow is about 125. The Strouhal number (reduced frequency) does not appear to have any significant effect. Based on the experimental results, this behaviour is discussed in some detail. This revised version was published online in July 2006 with corrections to the Cover Date.     

An efficient method for solving the mixed direct-inverse problem of the transonic rotational flow in plane casades

The method in [1] has been extended to the case of rotational flow in this paper. A new method for dealing with the shock wave is presented. This method has the advantages of both the shock-fitting and the shock capturing methods. The direct problem and the mixed direct-inverse problem of the rotational flow in a transonic plane cascade at both design and off design conditions are solved, and the results show that the present method has rapid convergence rate and high accuracy even for the flow with moderately strong shocks. The calculations have been carried out on the DPS-8 computer, and for the direct problem, only 50–80 iterations are needed, and 50–80 seconds of CPU time are required.     

Stabilized finite element method for flows with multiple reference frames

We present a space‐time finite element method capable of dealing with flows in multiple co‐rotating reference frames. Since equal order interpolation is used for all degrees of freedom, Galerkin/least‐squares stabilization is applied. We give a detailed derivation of the equations involved, introduce the variational form, present the stabilization parameters, and also discuss implementation issues. Numerical examples in 2D and 3D show generality and efficiency of the method, if steady‐state behavior of rotating components is sufficient for the CFD analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

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。     

论基础数学工具的创新运用

在建立叶轮机三元流面理论时,吴仲华巧妙地、创造性地提出了全导数型的沿流面方向偏导数的概念和表达式,导出了两类流面气动力学数学模型,不但数学形式简洁,而且具有明晰的物理意义,有利于分析和求解。在吴氏流面理论的启示下,作者不断致力于基础数学工具和概念的推广和创新运用,挖掘并发挥其潜在功能。本文将通过流体力学、传热学以及最优控制论方面的一些实例来综合介绍个人的心得和体会。     

叶轮机械复杂流动的PIV应用研究

本文发展了适用于叶轮机械等复杂内流系统使用的ＣＣＤ视场标定技术,以及能够消除视窗大颗粒污染带来的影响的图象处理技术,并在高速压气机实验台上对一小展弦比高负荷跨音风扇转子尖部的非定常瞬态流场进行了成功测量．     

Numerical simulation of the unsteady behaviour of cavitating flows

A 2D numerical model is proposed to simulate unsteady cavitating flows. The Reynolds‐averaged Navier–Stokes equations are solved for the mixture of liquid and vapour, which is considered as a single fluid with variable density. The vapourization and condensation processes are controlled by a barotropic state law that relates the fluid density to the pressure variations. The numerical resolution is a pressure‐correction method derived from the SIMPLE algorithm, with a finite volume discretization. The standard scheme is slightly modified to take into account the cavitation phenomenon. That numerical model is used to calculate unsteady cavitating flows in two Venturi type sections. The choice of the turbulence model is discussed, and the standard RNG k–εmodel is found to lead to non‐physical stable cavities. A modified k–εmodel is proposed to improve the simulation. The influence of numerical and physical parameters is presented, and the numerical results are compared to previous experimental observations and measurements. The proposed model seems to describe the unsteady cavitation behaviour in 2D geometries well. Copyright © 2003 John Wiley & Sons, Ltd.     

叶轮机械中考虑气体粘性的激波关系

叶轮机械中考虑气体粘性的激波关系黄修乾，徐建中（中国科学院工程热物理研究所北京１０００８０）关键词激波关系，叶轮机械，粘性流动，三维流动１引言随着叶轮机械叶尖速度和负荷的提高，其内部空间激波及激波／边界层相互作用对性能的影响更加显著。就激波／边界层相...     

高精度高分辨率迎风格式应用于不同速度范围内粘性流动

提出了一种适合于不同速度范围的高精度高分辨率的迎风有限差分格式，并基于此数植模型发展了适应于速度范围极宽的非定常粘性流动通用软件，不仅适用于超音速下捕捉强间断面，跨音速及高亚音速下捕捉弱间断面和滑移面，还可以精确地模拟低速情况下的粘性流动。此软件可分别用于研究内流和外流的流动特性以及预估其粘性损失。     

缘线匹配对非定常流动影响初探

为深化缘线匹配对叶轮机非定常流动影响的认识,本文以关注尾迹撞击叶表展向轨迹为出发点,围绕缘线匹配对叶轮机非定常流动及性能影响进行了初步数值探索.研究表明:不同缘线匹配时叶片整体性能参数具有不同的脉动水平;给定缘线匹配下,整体性能参数脉动幅值随工况几乎不变或变化很缓;在设计点为达到降低某种脉动目的而实施的缘线匹配在非设计点同样有效;尽管微弱,数值模拟中还发现缘线匹配对上游尾迹随流掺混产生影响;缘线匹配严重影响时均相关项量值水平,尤其在叶尖、叶根和前缘附近.