压气机悬臂静叶流场非定常数值模拟

以现代高压压气机一排悬臂静叶与一排转叶组成的典型级为研究对象,采用非定常数值模拟方法,分析了非定常与定常数值模拟计算得出的级特性线以及峰值效率点气动参数在展向分布的差异,并对悬臂静叶内部流场结构进行了详细分析,结果表明:当悬臂静叶的轮毂设计间隙为2.5%叶高时,非定常计算的综合喘振裕度比定常大5.85%;在峰值效率点工况下,悬臂静叶总压损失和转子效率的非定常影响范围在10%以内,转叶进口相对气流角沿展向分布的影响在0.5°以内。悬臂静叶根部10%叶高以下区域出现了明显的泄漏流动,3.4%叶高压力系数变化最大,轮毂泄漏流起始于20%弦长附近,发展到70%弦长位置时泄漏损失最大,随后逐渐减弱.     

Error estimates for space–time discontinuous Galerkin formulation based on proper orthogonal decomposition

In this study, proper orthogonal decomposition (POD) method is applied to diffusion–convection–reaction equation, which is discretized using space–time discontinuous Galerkin (dG) method. We provide estimates for POD truncation error in dG-energy norm, dG-elliptic projection, and space–time projection. Using these new estimates, we analyze the error between the dG and the POD solution, and the error between the exact and the POD solution. Numerical results, which are consistent with theoretical convergence rates, are presented.     

FINITE ELEMENTAN ALYSIS FOR THE UNSTEADY NEARSHORECIR CULATION DUE TO WAVE－CURRENT INTER－ACTION（I）──NUMERICAL MODEL

ＦＩＮＩＴＥＥＬＥＭＥＮＴＡＮＡＬＹＳＩＳＦＯＲＴＨＥＵＮＳＴＥＡＤＹＮＥＡＲＳＨＯＲＥＣＩＲＣＵＬＡＴＩＯＮＤＵＥＴＯＷＡＶＥ－ＣＵＲＲＥＮＴＩＮＴＥＲ－ＡＣＴＩＯＮ（Ｉ）——ＮＵＭＥＲＩＣＡＬＭＯＤＥＬＷｕＷｅｉ－ｘｉｏｎｇ（吴伟雄）（Ｔｏｎｇｊ...     

俯仰振荡三角翼前缘涡破碎的流动显示

前缘后掠角为６５°和７０°的两个平板三角翼作俯仰振荡运动，前缘涡破碎的流动显示实验研究在南京航空航天大学１米低速风洞中进行。俯仰振荡运动的攻角范围为０°～６０°，折合频率为０．０３和０．０６。采用四氯化钛发烟技术显示前缘涡核轨迹及涡破碎位置。流动显示图形采用相位锁定照相记录。实验结果表明大幅俯仰振荡三角翼的动态涡破碎的弦向位置明显滞后于相应攻角下的静态位置，此滞后量随折合频率增加而增大。本文也根据测得的涡破碎位置随攻角变化曲线讨论了涡破碎位置的传播速度     

Sudden Blocking of a Supercritical Open‐Channel Flow

This paper reports results of experiments in which a steadystate nonuniform supercritical openchannel flow was suddenly blocked by a rapidly falling gate at a downstream distance of about one hundred critical depths. This results in a hydraulic jump propagating upstream. Experimental data on the shape, height, and propagation speed of its leading front are given. It is shown that the parameters of the jump differ significantly from the values found using a quasistationary approach.     

Towards a new partially integrated transport model for coarse grid and unsteady turbulent flow simulations

A new two-equation model is proposed for large eddy simulations (LESs) using coarse grids. The modeled transport equations are obtained from a direct transposition of well-known statistical models by using multiscale spectrum splitting given by the filtering operation applied to the Navier–Stokes equations. The model formulation is compatible with the two extreme limits that are on one hand a direct numerical simulation and on the other hand a full statistical modeling. The characteristic length scale of subgrid turbulence is no longer given by the spatial discretization step size, but by the use of a dissipation equation. The proposed method is applied to a transposition of the well-known k- statistical model, but the same method can be developed for more advanced closures. This approach is intended to contribute to non-zonal hybrid models that bridge Reynolds-averaged Navier–Stokes (RANS) and LES, by using a continuous change rather than matching zones. The main novelty in the model is the derivation of a new equation for LES that is formally consistent with RANS when the filter width is very large. This approach is dedicated to applications to non-equilibrium turbulence and coarse grid simulations. An illustration is made of large eddy simulations of turbulence submitted to periodic forcing. The model is also an alternative approach to hybrid models. PACS 47.27.Eq     

Regime diagram of the development of long-wave near-wall disturbances in a hypersonic boundary layer

A regime diagram of the development of slow near-wall disturbances induced by an unsteady self-induced pressure perturbation in a hypersonic boundary layer is constructed for a disturbance wavelength greater than the boundary layer thickness. It is shown that the main factors shaping the perturbed flow are the gas enthalpy near the body surface, the intensity of the viscous-inviscid interaction, and the nature (sub- or supersonic) of the main part of the boundary layer. Nonlinear boundary-value problems are formulated for regimes in which the near-wall boundary layer region plays a decisive role. Numerical and analytical solutions are obtained in the linear approximation. It is shown that intensification of the viscous-inviscid interaction or an increase in the role of the supersonic main region of the boundary layer impart generally supersonic properties to the main part of the boundary layer, i.e. the upstream propagation of the disturbances is damped and the disturbance growth downstream becomes more intense. Damping of the viscous-inviscid interaction and an increase in the role of the subsonic main part of the boundary layer have the opposite effect. Surface cooling increases the effect of the main part of the boundary layer on the formation of pressure disturbances and surface heating leads to an increase in the effect of the near-wall boundary layer region. It is also shown that for the regimes considered disturbances propagate in a direction opposite to that of the free stream from the turbulent flow region located downstream of the local disturbance development region.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 59–71. Original Russian Text Copyright © 2004 by Bogolepov and Neiland.     

Finite element analysis for the unsteady nearshore circulation due to wave-current interaction (I)—numerical model

In this paper, a numerical model for predicting the unsteady nearshore circulation due to wave-current interaction was proposed. In addition to the traditional continuity, momentum and energy equations, the dispersion and refraction relations were included in the governing equations. Moreover, the effects of lateral shears, wind, radiation and bottom stresses were analysed in the governing equations. Therefore, we expect that this model may more completely and exactly reflect the law of wave-current interaction. In part (II) we will adopt the selective lumping two-step explicit finite element method to solve the model, and some examples will be presented.     

广义Maxwell黏弹性流体在两平板间的非定常流动

将分数阶微积分运算引入Maxwell黏弹性流体的本构方程，研究了黏弹性流体在两平板问的非定常流动．对于广义Maxwell黏弹性流体的分数阶导数模型，导出了对时间具有分数阶导数的特殊运动方程，利用分数阶微积分的Laplace变换理论，得到了流动的解析解．     

一种新的运动激波--非定常边界层相互干扰现象

本文探讨了一种新的激波－非定常边界层相互干扰现象，这种激波－边界层干扰现象既不同于定常激波－边界层干扰现象，又不同于激波在端面反射后与该激波所诱导的边界层之间的干扰现象，而是运动激波与稀疏波和第一激波所诱导的非这常边界层之间的干扰现象，本文对这种现象用微波动力学理论进行分析，并把这种干扰现象看成激波的绕射现象，同时在稀疏波破膜的双驱动激波管中进行实验观察，最后把理论分析与实验观察进行了比较。