零压力梯度平板边界层转捩的数值模拟

对平板边界层转捩试验T3A和T3B进行了数值模拟,计算值与实验值吻合的较好。通过对零压力梯度的平板转捩现象的研究得出以下的结论:转捩流动的复杂性对流场边界层的影响不容忽视;M-L转捩模型能比较准确地预测转捩的发生和发展过程,在高湍流度下使用全湍流模型来模拟转捩流动的误差较小。     

考虑转捩的风力机翼型动态失速数值模拟

以风力机专用翼型的动态失速为对象,采用一种基于流场当地变量的Gamma-Theta转捩模型配合SSTk-ω湍流模型进行数值模拟,研究转捩对动态失速性能的影响和动态失速下的转捩规律。结果表明,使用考虑转捩效应,能够使动态失速过程中上仰段大迎角状态下失速和下俯段气流再附的模拟得到改善。在动态失速上仰段,上表面转捩由后缘分离泡向前缘分离泡的转变过程较快,导致转捩点迅速前移;而在下俯段,前缘分离泡向后缘分离泡的转变过程中经过了自然转捩和再层流化的过渡,因此转捩点的移动较上仰段平滑。     

考虑转捩影响的压气机叶型流动特性数值模拟北大核心

通过采用在SST湍流模型基础上发展形成的γ-Reθt转捩模型对某型可控扩散叶型进行了变冲角的数值模拟研究,并与试验结果和LES计算结果进行了比对。结果表明,SSTγ-Reθt转捩模型对叶型型面静压分布的模拟较为准确;在负冲角流动状态下对叶型的气动性能模拟比LES的结果更为贴近试验实际所得,但在正冲角流动状态下的模拟结果仍有提高的空间。     

转捩模型在静叶栅三维粘性流数值模拟中的应用研究

边界层转捩流动的特征参数明显不同于层流或湍流，转捩流动的这些特征直接影响着流体的动力、传热特性。而通过有效地控制转捩起点、转捩区长度就可以有效改善流动效率。作者将修正的转捩模型应用到实际流场计算中，对计算结果进行了比较，从中得到了一些有意义的分析结果。     

转捩对S809翼型气动特性影响的数值模拟

以S809翼型为例分析了转捩对水平轴风力机翼型气动特性的影响.首先采用多种湍流模型对S809翼型开展了全湍流数值模拟,观察了忽略转捩条件下的翼型升阻力特性,然后开展了考虑转捩的数值模拟,分析了转捩对翼型升阻力特性和尾缘分离的影响.结果表明,在附着流动状态下,数值模拟中忽略转捩会导致翼型升力系数被低估约10％,阻力系数则被成倍高估;转捩对翼型尾缘分离也有一定影响,转捩点越靠近前缘,尾缘附近附面层速度型的饱满程度降低,抵抗逆压梯度的能力减弱,尾缘分离越容易发生.     

湍流_转捩模型对气冷涡轮气热耦合计算影响的对比研究

开发了基于三维非结构网格的导热求解程序,将数值解与解析解对比验证了加权最小二乘法相对于格林函数法在求解梯度时具有更高的精度,将基于加权最小二乘法的三阶精度的导热程序与叶栅流场计算程序HIT-3D耦合,实现了气热耦合计算,对MARKII叶片5411实验工况进行了数值模拟,并借助于HIT-3D程序具备的湍流模型研究了转捩对传热计算的影响。结果表明:BL模型预测的温度与实验值相差最大,在转捩点相差10%,BL+AGS转捩模型、SST-Gama模型、q-ω模型由于具备模拟转捩的能力,因此在转捩区计算的温度误差较小,约5%,可见考虑转捩的湍流模型能更好地预测涡轮叶片的温度。     

低雷诺数下NACA64-418翼型的流动分离研究

通过粒子图像测速（PIV）技术，在低速风洞中研究了0°~15°攻角和雷诺数分别为1.54×105、2.57×105和3.59×105下NACA64-418翼型的压力性能，并基于γ-Reθ转捩模型分析了翼型表面的流动分离及涡脱落情况。 研究表明:NACA64-418翼型具有较大的失速攻角,PIV结果的时均流场和瞬时流场表明，NACA64-418翼型具有较大的失速攻角，随着雷诺数的增加，失速攻角变小;从翼型壁面回流区可以看出γ－Reθ转捩模型可以准确评估翼型表面从层流到湍流流动的变化;数值结果与实验结果进行比较，验证了γ－Reθ转捩模型的预测是准确的。     

转捩对风力机翼型优化设计结果的影响研究

采用基于Kriging模型的优化设计方法开展了风力机专用翼型的优化设计工作.除了在全湍流条件下进行设计之外,同时还在气动优化设计中耦合层流湍流转捩预测,将翼型上下表面的转捩点作为约束条件,采用基于Kriging模型的优化设计方法实现了考虑转捩影响的风力机翼型优化设计.风力机翼型最大升阻比优化结果表明:在两种条件下,优化得到的翼型气动性能均得到较大提高,均具有较好的粗糙度不敏感性,但相比而言,考虑转捩影响的风力机翼型优化设计能在更加真实的环境下获得气动性能更好的优化设计结果.     

前加载和后加载叶片转捩特性的数值研究

基于Abu-Ghannam&Shaw转捩模型,定常求解雷诺平均N—S方程组,文章采用商用计算流体动力学软件NU-MECA,数值研究了不同雷诺数工况下,入口湍流强度(Tu)变化对某高负荷前加载和后加载叶片转捩特性的影响,揭示了前加载和后加载叶片吸力面转捩特性的雷诺数和湍流强度效应.文章还对不同湍流强度和雷诺数工况下前加载叶片的流动情况进行分析和比较,研究了该叶片表面极限流线图谱的差异.分析表明,不同雷诺数工况下极限流线图谱存在显著差异,低雷诺数条件下二次流损失明显增大;不同湍流强度的极限流线图谱差异较小,并随湍流强度增大其吸力面下端部的分离线向前缘移动.     

转捩点预测对风力机翼型气动性能分析的影响

分别用带转捩模型的边界层耦合计算方法和基于RANS方程的通用CFD方法对风力机常用翼型S809进行了气动分析.通过自由转捩、强制转捩和全湍流模式的比较,着重阐述边界层转捩点预测对风力机翼型气动性能计算分析的影响.     

阶梯溢流坝过渡台阶体型水力特性研究

鉴于阶梯溢流坝采用台阶消能具有较好的消能效果,且阶梯溢流面与WES曲面的衔接处常采用过渡台阶可改善水流流态,采用数值模拟计算与模型试验相结合的方法,分析了四种不同过渡台阶体型下的阶梯坝面水流流态、流速、掺气起始点位置、掺气浓度和消能率等水力特性。研究结果发现,方案2、3、4在流态方面稳定,流速方面有一定的减小,消能率方面显著提高,但方案2、3在掺气起始位置方面略微下降。为此对方案4内凹型的过渡台阶的设置进行3种工况下的试验研究,证明其具有较好的工程价值和研究意义。     

风沙环境对翼型边界层厚度的影响研究

为研究风沙环境对风力机翼型边界层的影响,采用无黏模型、转捩模型和离散相模型对三维S809翼型的边界层特性进行数值模拟,并对清洁空气和风沙环境中翼型的边界层特性进行对比分析.结果表明:相较于清洁空气,沙尘颗粒的加入使翼型边界层厚度减小.同一弦向位置,随着颗粒直径的增大,翼型边界层厚度呈先减小后增大的趋势;随着颗粒质量浓度...     

Laminar-turbulent transition tripped by step on transonic compressor profile

The shock wave boundary layer interaction on the suction side of transonic compressor blade is one of the main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). The experimental and numerical results for the flow structure investigations are shown for the flow conditions as the existing ones on the suction side of the compressor profile. The two cases are investigated: without and with boundary layer tripping device. In the first case, boundary layer is laminar up to the shock wave, while in the second case the boundary layer is tripped by the step. Numerical results carried out by means of Fine/Turbo Numeca with Explicit Algebraic Reynolds Stress Model including transition modeling are compared with schlieren, Temperature Sensitive Paint and wake measurements. Boundary layer transition location is detected by Temperature Sensitive Paint.     

Large eddy simulation of transition of free convection flow over an inclined upward facing heated plate

Transition of free convection flow of air over an inclined heated surface is investigated numerically by using a large eddy simulation method. In particular, we focus on how inclination angle of an upward-facing heated plate affects flow transition. Special attention is paid to the development of the thermal boundary layer and the transition from the laminar to turbulent stage. Results show that the transition occurs early when the plate is moved from its vertical position due to the rapid growth of both the velocity and thermal boundary layers. As a consequence, the critical Grashof number drops. Effects of the inclination of plate on the turbulent velocity fluctuations are also investigated, and the predicted results are in very good agreement with various experimental data available in the literature.     

汽液相变换热过程唯象系数的计算

基于非平衡热力学理论,导出了汽液相变过程化学势的变化及汽泡临界半径的计算式;在此基础上。提出用唯象系数表征相变换热过程的强度。给出了相变换热过程的唯象系数的计算式并进行了数值计算;讨论了相变过程的推动力和汽泡半径等参数对相变过程唯象系数的影响。     

Shape of “True” transition boiling curve and two‐mode boiling

Two‐mode boiling could occur on the same heating element, which provided information on the criterion separating the stable and metastable boiling regimes. The “equal‐area” criterion based on the complete boiling curve interpreted the criterion of coexistence of the two boiling modes. However, the transition boiling curve could not be constructed by the pool boiling tests. Literature works adopted various correlations of transition boiling curves for analysis, but failed to recognize the possible errors incorporated in such an approximation. This paper demonstrated the relative errors embedded in calculating the equal‐area criterion by assuming various shapes of the transition boiling curve. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(7): 593–601, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10113     

Macrolayer formation and mechanisms of nucleate boiling,critical heat flux,and transition boiling

The drying process of a macrolayer on a 15 mm diameter boiling surface was observed with high speed video in the region of nucleate and of transition boiling close to the critical heat flux (CHF). It was found that the macrolayer rests beneath a large vapor mass. It partially dries in nucleate boiling and completely dries in transition boiling at the detachment of the vapor mass. The macrolayer thickness at CHF and in transition boiling was determined on the basis of the energy balance relation proposed by Katto and Yokoya. The macrolayer thickness at low heat flux was obtained by decreasing CHF with downward-facing heating surfaces and agreed well with the correlation proposed previously by the present authors. The macrolayer thickness in transition boiling with a vertical surface also agrees fairly well with the correlation, when the heat flux at macrolayer formation, given on the nucleate boiling curve, is extrapolated to surface superheat of transition boiling and when the surface temperature at macrolayer formation is equal to a time-averaged value. © 1998 Scripta Technical, Heat Trans Jpn Res, 27(2): 155–168, 1998     

燃烧室过渡段冲击冷却效果计算与分析

论述了单管型重型燃气轮机燃烧室过渡段的冲击冷却形式的作用,通过三维数值模拟,对比计算了E级、F级燃烧室过渡段冷却效果,论证了在F级工况下,过渡段冲击冷却结构能够以一定的压降为代价,大幅降低过渡段表面的温度,使过渡段壁面温度降低到材料许应温度范围内,从而使其能够长期稳定工作,起到保护作用.