S弯进气道流动控制技术的试验研究

在低速风洞中采用微型叶片作为涡流发生器对某S弯进气道进行流动控制,通过风洞试验研究了微型叶片的不同参数(包括叶片高度、轴向位置、安装组数)对进气道气动特性的影响。试验测量了来流风速V=60m/s、模型攻角α=8°的条件下有/无微型导流叶片时进气道出口截面的总压和静压分布,并由此计算得到进气道出口截面的总压恢复系数和畸变指数。试验结果表明:微型叶片的不同参数(包括叶片高度、轴向位置、安装组数)对进气道流动有明显影响;通过在进气道第一弯道处安装合适高度和组数的微型叶片涡发生器,可以明显改善进气道出口流动;在现有的试验条件下,叶片高度h/Ri=0.02、轴向位置Xvg/Ri=1、组数Nvg=8是相对较优的流动控制方案,主要表现为:与未安装微型叶片相比,进气道流量系数φ=0.8时出口畸变指数降低了0.051,总压恢复系数提高了0.007。     

激波风洞内超燃冲压发动机三面压缩进气道流场实验观测

主要进行了超燃冲压发动机三面压缩进气道的实验观测。利用来流马赫数4.5的直通式激波风洞,考察了三组具有不同压缩角度的进气道模型内部的流场情况。实验观测手段为油流法、丝线法和高速纹影,同时,辅以数值模拟以有助于流场细节分析。纹影照片展示了进气道内部以激波边界层相互作用为主要影响因素的流场复杂结构,数值模拟也显示了相近的结果。油流技术与丝线法显示了近壁面处的流动图像,照片中可见激波、分离线、再附线等分界线位置。根据实验结果,可以推测唇口激波与进气道内边界层的相互作用及其引起的壁面分离是影响进气道内流动的主要因素。同时,尝试了利用抽吸方法减弱激波与边界层相互作用诱发的壁面流动分离,并取得一定结果。     

高超声速三维内收缩式进气道/乘波前体一体化设计研究评述

论述了国内外在高超声速三维内收缩式进气道研究方面的最新研究动态,重点阐述了三维变截面内乘波式进气道的研究进展.介绍了常规矩形进口进气道与乘波体外形一体化相关研究,并对三维内收缩式进气道与前体的一体化问题提出了关注. 最后,对高超声速进气道与前体一体化设计的研究趋势进行了展望,提出三维内收缩式进气道与乘波前体的``双乘波'一体化设计可能为高超声速研究带来新的变革.      

进气道等离子体/磁流体流动控制研究进展

为实现高速飞行器的宽速域飞行,如何保证进气道在非设计状态下的性能至关重要。相比于传统被动控制方式,等离子体/磁流体流动控制技术作为新概念主动流动控制技术,由于其具有结构简单,快速响应,并可根据实际飞行条件进行反馈控制等优势,在国内外上得到了广泛关注。本文介绍了等离子体/磁流体在高超/超声速进气道的主要应用方式与等离子体/磁流体建模方法。当进气道处于超临界状态时,等离子体/磁流体流动控制主要通过热阻塞效应产生虚拟型面,从而将激波系推回至唇口,该技术有望在需要短时间流动控制的高马赫数导弹上走向工程应用;由于等离子体/磁流体激励器与壁面平齐安装,对于高超声速飞行条件,相比于粗糙元其对热防护的要求较低,并且通过超声速风洞实验初步证明了通过高频激励对边界层施加扰动的可行性,需要从稳定性理论的角度对其物理机制进行研究。在后续发展中需要进一步创新等离子体产生技术及激励方式,发展等离子体与流的全耦合计算模型等离子体与流的全耦合计算模型与高效算法 ,为指导工程应用提供依据.      

二维超声速混压式进气道的数值模拟

本文采用TVD格式求解二维可压非定常Euler方程组,对二维超声速混压式进气道进行了数值计算,首先模拟了后部压力对进气道的影响过程,当进气道的后部压力与入口压力的比值逐渐增加时,进气道内的正激波逐渐往前移动,当比值达到一个临界值,进气道将不起动.其次.通过对R52.1和R54.5两种进气道模型进行计算,对它们的总压恢复进行了对比.通过计算得到了喉道处曲线弧的曲率越大,进气道的总压损失越大,进气道也越难起动.     

歼击机进气道结构强度设计方法研究

重点介绍了基于几何非线性和总体-局部(GLOBAL-LOCAL)求解策略的进气道结构强度仿真分析技术,以此技术建立先进的进气道结构强度设计方法。该方法精度高,工程实用性强。该方法对现代歼击机进气道结构设计能够大幅度提高进气道结构强度品质,降低设计成本,提高设计一次成功率。给出了应用实例。     

磁流体动力学在航空工程中的应用与展望

介绍了磁流体动力学在航空工程中的主要应用方式,主要包括:磁流体冲压组合发动机、磁流体涡轮组合发动机、燃烧室后磁流体发电、表面磁流体发电、磁流体加速风洞、磁流体推力矢量、进气道大尺寸磁流体流动控制、边界层分离流动控制、边界层转捩控制、飞行器头部热流控制等;探讨了磁流体技术在应用中存在的关键科学与技术问题,对导电流体的产生、磁流体实验设备与实验技术、多场耦合机理及数值模拟方法等进行了分析;最后对磁流体技术在航空工程上的应用与发展进行了总结与展望.     

基于离散等收缩比的前体/进气道流向双乘波一体化设计

前体/进气道一体化设计是高超声速飞行的关键技术,一体化设计的核心是前体与进气道在基准流场上的气动融合.针对腹部进气布局中前体压缩后的非均匀流影响进气道性能的问题,文章基于局部收缩比处处一致的思想,提出了离散等收缩比设计方法,实现了乘波前体/内转式进气道流向气动融合与遵循气动规律的变截面流道设计.将进气道的三维流场分解成一簇具有相同收缩比的三维流管,视每根流管侧壁为轴对称流场;以锥导乘波前体压缩后的非均匀流作为来流条件,以总压恢复为目标对每根流管进行优化设计;通过匹配激波反射位置将流管重新组合起来,流管的对应边界组成内转式变截面进气道.该设计方法适配任何已知的非均匀来流,可灵活控制唇口位置,且适用于任意形状之间的变截面转换.数值研究表明,依托该方法设计的一体化构型性能符合预期,出口流场均匀,具有优越的抗反压能力,且非设计点流场波系结构良好.离散等收缩比设计方法为腹部进气布局中前体/进气道一体化气动融合设计提供了新思路.     

脉冲爆震发动机进气道气动性能的数值研究

采用有限体积法计算了脉冲爆震发动机某轴对称超音速进气道在3种 不同出口条件(单个正弦扰动压力、某脉冲爆震发动机爆震室头部表压和进气道出口堵塞) 下的进气道内结尾正激波的运动情况，得出了进气道内结尾正激波运动特性和不同出口条件 的关系. 在计算中，采用了多块结构化网格，控制体积的界面无黏通量采用三阶迎风格 式插值获得，同时采用了minmod通量限制器以确保在激波处的解的物理特性；扩散通量采 用二阶中心差分格式插值获得. 定常计算采用当地时间步法，非定常计算采用双时间步法. 离散的代数方程采用交替方向迭代法求解。     

前体涡发生器对轴对称高超声速进气道激波振荡流动的影响实验

激波振荡是高超声速进气道不起动过程中常见的流动现象,会显著降低进气道气流捕获与压缩效率、产生剧烈的非定常气动力载荷而危害飞行器安全. 从激波振荡的控制出发,实验研究了前体转捩带位置的涡发生器对轴对称高超声速进气道激波振荡流动的影响. 分别在起动和激波振荡两种进气道流态下,选择无、0.5 mm与1 mm高度涡发生器工况进行对比研究. 并采用高速纹影与壁面动态测压同步记录非定常流动特征. 结果表明,1 mm高度内的涡发生器对起动状态的进气道主流流场结构、壁面压强分布影响不显著. 但对于激波振荡流动,涡发生器会明显缩小外压缩面分离区运动范围,缩短振荡周期,提升振荡周期内壁面压强的时均值. 涡发生器的影响程度随其高度的增大而增强,其中振荡周期从无涡发生器的4 ms缩短到1 mm高度涡发生器的3.13 ms. 此外,0.5 mm高度涡发生器会使得进气道内部测点的压强振荡幅值整体下降,相比无涡发生器工况的下降幅度可达23%. 流场结构与壁面压强信号的分析表明,涡流发生器主要通过其产生的流向涡影响激波振荡流动,包含流向涡对下游边界层的扰动以及流向涡与分离区的相互干扰.      

三角翼上分离及涡流的数值模拟

综述了三角翼(包括双三角翼,边条-三角翼,近距耦合鸭翼)上分离及涡流问题的数值模拟进展,介绍了用Euler方程、N-S方程的数值方法模拟不同三角翼,在不同攻角、不同来流M数等多种条件下的复杂涡流形态和流动结构,研究了控制方程、网格、湍流模型和计算方法等对计算结果的影响。      

A turbulence model for inclined, bubbly flows

A new turbulence model for the flow of a two phase (liquid-liquid) flow in an inclined pipe is presented. An eddy viscosity is used to model the effects of shear induced turbulence and bubble induced turbulence. The cross-pipe momentum transport arising from the buoyant rise of bubbles across the axial flow is also modelled. Numerical simulations have been carried out in both one and two dimensions. One and two dimensional numerical simulations are presented.On leave from the University of Leeds, Leeds LS2 9JT, U.K.     

Multi-scale numerical simulation of fluidized beds: Model applicability assessment

In the past few decades, multi-scale numerical methods have been developed to model dense gas-solid flow in fluidized beds with different resolutions, accuracies, and efficiencies. However, ambiguity needs to be clarified in the multi-scale numerical simulation of fluidized beds: (i) the selection of the sub-models, parameters, and numerical resolution; (ii) the multivariate coupling of operating conditions, bed configurations, polydispersity, and additional forces. Accordingly, a state-of-the-art review is performed to assess the applicability of multi-scale numerical methods in predicting dense gas-solid flow in fluidized beds at specific fluidization regimes (e.g., bubbling fluidization region, fast fluidization regime), with a focus on the inter-particle collision models, inter-phase interaction models, collision parameters, and polydispersity effect. A mutual restriction exists between resolution and efficiency. Higher-resolution methods need more computational resources and thus are suitable for smaller-scale simulations to provide a database for closure development. Lower-resolution methods require fewer computational resources and thus underpin large-scale simulations to explore macro-scale phenomena. Model validations need to be further conducted under multiple flow conditions and comprehensive metrics (e.g., velocity profiles at different heights, bubbles, or cluster characteristics) for further improvement of the applicability of each numerical method.     

Report on Turbulence and Mixing in Geophysical Flows II

We describe the presentations at the international meeting/workshop on Mixing in Geophysical Flows that took place at Vilanova i la Geltru, near Barcelona during the 20, 21 and 22nd of March 1997. There were more than 100 participants from 20 countries with 66 oral and poster presentations covering experimental and theoretical aspects of rotating and stratified fluids as well as field observations. The main topics discussed at the workshop were stratified flows, rotating stratified flows, gravity waves, instabilities and mixing, convection, experiments and numerical simulations of Geophysical flows and turbulent mixing. The papers are summarised in this report giving a state-of-the-art overview of present research in geophysical turbulent mixing.     

Fluid Dynamical Analysis of Atmospheric Reacting and Isothermal Swirling Flows

A series of unconfined swirling premixed natural gas/air flames was investigated. Reynolds-numbers spanned from 10,000 to 42,300. Respective isothermal flows were studied additionally to gain insight into changes of fluid dynamical features caused by combustion. Statistical moments, Reynolds-stresses, temporal time scales, spatial length scales, and power spectral densities were deduced from one- and two-point laser Doppler velocimetry (LDV) data. Properties of the turbulent flows and dependencies on Reynolds-number, swirl number, and chemical reactions are discussed. Most distinct differences between combusting and isothermal flows were precessing vortex cores (PVC) occurring only for the latter cases. The study is aimed to serve as a database of a generic flame geometry featuring important characteristics of industrial applications for validation of numerical simulations. Therefore, nozzle exit profiles as important inlet conditions to numerical simulations are thoroughly documented.     

A third-order compact nonlinear scheme for compressible flow simulations

Reynolds-averaged Navier-Stokes simulations based on second-order numerical methods are widely used by commercial codes and work as dominating tools for most industrial applications. They, however, suffer from limitations in accurate and reliable predictions of skin-friction drag and aerodynamic heating, as well as in simulations of complex flows such as large-scale separation and transition. A remedy for this is the development of high-order schemes, by which numerically induced dissipation and dispersion errors of low-order schemes can be effectively reduced. Weighted compact nonlinear schemes (WCNSs) are a family of high-resolution nonlinear shock-capturing methods. A stencil-selection procedure is introduced in the proposed work with an aim to improve the nonlinear weight of the third-order WCNS. By using the approximate dispersion relation analysis, it is demonstrated that the new scheme has reduced dissipation and dispersion errors, compared with WCNSs using two typical nonlinear weights. Improvements are also achieved by the new scheme in numerical tests such as the double Mach reflection problem and the Rayleigh-Taylor instability simulation, which are characterized by strong shock discontinuities and rich small scales, respectively. The new scheme is therefore highly favored in the simulation of flow problems involving strong discontinuities and multiscales phenomena.     

Properties and Averaged Equations for Flows of Bubbly Liquids

Averaged properties of bubbly liquids in the limit of large Reynolds and small Weber numbers are determined as functions of the volume fraction, mean relative velocity, and velocity variance of the bubbles using numerical simulations and a pair interaction theory. The results of simulations are combined with those obtained recently for sheared bubbly liquids [19] and the mixture momentum and continuity equations to propose a complete set of averaged equations and closure relations for the flows of bubbly liquids at large Reynolds and small Weber numbers.     

Direct numerical simulation of driven cavity flows

Direct numerical simulations of 2D driven cavity flows have been performed. The simulations exhibit that the flow converges to a periodically oscillating state at Re=11,000, and reveal that the dynamics is chaotic at Re=22,000. The dimension of the attractor and the Kolmogorov entropy have been computed. Explicit time-integration techniques are discussed.     

基于非结构网格的TTGC有限元格式的实现及在超声速流动中的应用

基于非结构网格系统,实现了时空三阶精度的TTGC有限元格式,并在三阶TTGC格式上发展了基于人工粘性的激波捕捉技术。在非结构网格下,采用这种方法对若干典型的超声速流动问题(SOD激波管、马赫数为3的前台阶流动以及马赫数为8的高超声速圆柱流动)进行了验证计算。结果表明,TTGC格式分辨率高,在粗糙网格下能够准确的模拟超声速流场中的激波、接触间断等复杂流动现象,并且能有效的控制间断附近的数值色散现象。与传统的有限体积方法相比,本文实现的TTGC有限元格式在模拟超声速流动问题方面具有格式精度高、数值耗散小等优点。     

An accurate pressure–velocity decoupling technique for semi‐implicit rotational projection methods

In this paper, an accurate semi‐implicit rotational projection method is introduced to solve the Navier–Stokes equations for incompressible flow simulations. The accuracy of the fractional step procedure is investigated for the standard finite‐difference method, and the discrete forms are presented with arbitrary orders or accuracy. In contrast to the previous semi‐implicit projection methods, herein, an alternative way is proposed to decouple pressure from the momentum equation by employing the principle form of the pressure Poisson equation. This equation is based on the divergence of the convective terms and incorporates the actual pressure in the simulations. As a result, the accuracy of the method is not affected by the common choice of the pseudo‐pressure in the previous methods. Also, the velocity correction step is redefined, and boundary conditions are introduced accordingly. Several numerical tests are conducted to assess the robustness of the method for second and fourth orders of accuracy. The results are compared with the solutions obtained from a typical high‐resolution fully explicit method and available benchmark reports. Herein, the numerical tests are consisting of simulations for the Taylor–Green vortex, lid‐driven square cavity, and vortex–wall interaction. It is shown that the present method can preserve the order of accuracy for both velocity and pressure fields in second‐order and high‐order simulations. Furthermore, a very good agreement is observed between the results of the present method and benchmark simulations. Copyright © 2016 John Wiley & Sons, Ltd.