汽封结构内部流动现象的数值研究

本文采用作者发展的叶轮机械通用计算程序ＧＡＰ１０对带围带汽封和隔板汽封结构的动 叶片排流场进行了三维数值模拟,并着重对汽封结构内部流动结构进行了分析。     

不同部分进汽度及不同堵塞方式情况下的动叶片性能

本文对不同部分进汽度及不同堵塞方式情况下的调节级动叶片效率、流量和叶片升力等总体性能作了分析和总结,这些结果将对调节级动叶片的设计提供极为宝贵的参考。     

汽封泄漏流动对透平叶片级通道

本文采用作者发展的叶轮机械通用计算程序GAP10程序对带汽封结构反动式透平叶片级流场进行三维数值模拟,分析了汽封泄漏流动进入叶栅通道后动叶片通道的流场结构,并讨论了泄漏流动对通道二次流动发展方式的影响.     

汽轮机调节级静叶栅中采用多分流叶栅的研究

l引言调节级效率的高低，对整个汽轮机的效率有很大的影响，调节组的效率比中间级的效率低得多。所以，许多汽轮机厂和研究所一直把改善和提高调节级效率作为研究的课题之一。由于相对叶高对叶栅的端部损失影响很大，因而调节级叶片不能太短，只能采用部分进汽度结构，造成了部分进汽损失，这一损失占据调节级的比重很大。例如上海汽轮机厂的125MW机组的调节级叶栅中，叶型损失为6％其中型面损失为1％，端部损失为5凡而部分进汽损失，按照上海汽轮机厂应用的公式计算，部分进汽损失在设计工况时达到8．49％。因此决定调节级效率高低的主要…     

某向心式蒸汽透平的气动设计与数值研究

本文针对太阳能热发电过程中蒸汽流量小、焓降高的特点设计了一种部分进汽的向心式蒸汽透平。所设计的蒸汽透平在流量仅为2.33 kg/s、压比为3.36的工况下仍有较高的效率。通过三维数值模拟的方法分析了导叶和叶轮内部流动特性,探讨了部分进汽对通道流通能力及总效率的影响。     

对旋风机叶片造型优化对气动特性的影响

以一台已有对旋风机为原型进行三维数值计算,通过计算结果分析风机内部流动。在对数值结果和速度三角形分析的基础上,通过调整叶片的叶型弯角和扭转角改变叶片气流攻角及其内部流动进行了叶片的三维造型优化。对优化结果计算分析表明优化后对旋风机的内部流场更为合理,通道涡得到了抑制。计算结果和试验数据表明优化后对旋风机比优化前最大流量提高1 m~3/s、最大全压升提高1300 Pa,效率和功率在大流量下有所改善。     

涡轮叶栅气热耦合数值模拟

本文建立了透平机械叶栅流场与叶片温度场的气热耦合计算模型,编制了三维非正交曲线坐标系下的温度场求解程序,计算了实心及空心叶片的温度场分布。介绍了区域分解方法在耦合计算及并行计算中的应用,以矩形区域温度场求解程序为例研究了程序的并行化,最后进仃了叶栅流场计算与叶片导热计算程序的分区耦合计算。     

叶轮机械转动叶片上三维可压边界层微分方程的求解方法

本文应用非正交曲线坐标,在叶轮机械转动叶片上建立了三维边界层的微分方程及其求解方法。对一个压气机转子叶片的压力面和吸力面上的三维边界层进行了计算,结果表明,与实验结果比较符合。     

边界层转捩对风力机气动性能模拟结果的影响

本文采用CFD软件包FINETM/Turbo,选用结合AGS转捩模型的S-A湍流模型,研究边界层转捩对NORD-TANK 500/41型风力机LM19.1叶片三维流场的影响,并与采用-方程S-A和两方程k-ω(SST)模型获得的全湍流计算结果比较.在计算结果与实验数据进行对比的基础上,分析了三维粘性流场的流动细节,探讨了边界层转捩对风力机叶片气动性能和载荷预估的影响,获得了叶片转捩线随风速和沿展向的变化趋势.结果显示边界层转捩使数值计算的叶片性能和载荷增大、边界层分离推迟,为风力机叶片的优化设计提供参考.     

端壁边界层抽吸技术在汽轮机调节级静叶栅中的应用

提出一种在调节级静叶栅叶片吸力面侧端壁处抽吸低能流体至轴封漏汽腔室,以降低静叶栅二次流损失的方法。采用三维稳态时均Ｎ－Ｓ方程组的有限容积差分法数值求解技术,对不考虑栅后漏汽工况、存在吸力面侧端壁抽吸工况及存在栅后蒸汽泄漏工况下的二次流的发展进行了模拟。计算结果表明,所提出的方法可以有效地提高静叶栅效率。     

动态冰浆流动特性分析

阐述了动态冰浆流变性质的Bingham模型,并利用该模型计算了冰浆在层流和湍流状态下的摩擦因子,得到了冰浆在水平直管内流动的压降曲线,分别就层流和湍流情形分析了各种参数对流动压降的影响。     

侧风条件下短舱流动分离等离子体流动控制研究

利用数值仿真开展了侧风条件下短舱流动分离等离子体流动控制研究,首先研究了不同侧风条件下短舱流动分离特性,揭示了侧风角度以及速度大小对流动分离的影响规律.随着侧风角度的增加,进气唇口处分离区域不断扩大且进气截面的总压损失更加严重;随着侧风速度的变大,分离区域变化并不明显,进气截面总压损失系数降低.进一步将等离子体激励布置...     

The flow noise level at microphones in flow ducts

When sound measurements are made in flow ducts one has to insure that the signal-to-noise ratio of the sound signal to the flow noise, which is produced by the turbulent flow at the microphone, is sufficiently high. To accomplish this, knowledge of the flow noise level under the specific given flow conditions is required. In this paper two procedures for determining the flow noise level are described. For the first method, the mean flow velocity and the turbulence level have to be known to estimate the flow noise level as a function of duct diameter and frequency. For the second method knowledge of only the mean flow velocity is required. The procedure involves two measurements: one with a microphone fitted with a conventional nose cone and one with a microphone fitted with a slit-tube. The slit-tube is a special device for reducing the flow noise level. Finally, guidelines are given for sound measurements in the presence of flow and for the use of a microphone with a slit-tube under unusual temperature conditions or in gases other than air.     

Phase-field lattice-Boltzmann investigation of dendritic evolution under different flow modes

ABSTRACT

Numerical modelling offers an effective method to investigate the effect of convection on dendritic growth; however, the current numerical approach to modelling convection behaviour is simplified, e.g. only simulating a shear flow by setting a constant inlet velocity and a zero-velocity-gradient outlet boundary condition. In this work, based on a phase-field lattice-Boltzmann approach, the effect of various flow modes on dendritic growth is investigated by introducing an external force term to induce flow. Numerical tests (2-D and 3-D) validate that the results according to the force-induced flow agree well with those by the velocity-imposed flow. Intricate convection effects under complex boundary conditions are discussed in detail. Furthermore, this force-induced flow mode allows additional freedom by eliminating the restriction on the initial position of the nuclei, which provides new ways to the microstructure modelling under complex convection.     

Phase-field simulation of a Fe-Mn alloy under forced flow conditions

In this work a study through numerical simulation of dendritic growth for the system Fe-Mn under the influence of a forced flow field is presented. The investigations are based on an extension of the quantitative phase-field approach developed by Echebarria et. al. Phy. Rev. E 061604 (2004), to simulate the solidification of Fe-Mn under the influence of a forced flow field. The simulations are performed for isothermal conditions and the investigation concentrates on the effects of forced flow on the dendrite morphology during the growth dynamics. The effects of forced flow on microsegregation are also discussed.     

A Stochastic Description of Transition Between Granular Flow States

Two-dimensional granular flow in a channel with small exit is studied by molecular dyhamics simulations. We firstly define a key area near the exit, which is considered to be the choke area of the system. Then we observe the time variation of the local packing fraction and flow rate in this area for several fixed inflow rate, and find that these quantities change abruptly when the transition from dilute flow state to dense flow state happens. A relationship between the local flow rate and the local packing fraction in the key area is also given. The relationship is a continuous function under the fixed particle number condition, and has the characteristic that the flow rate has a maximum at a moderate packing fraction and the packing fraction is terminated at a high value with negative slope. By use of the relationship, the properties of the flow states under the fixed inflow rate condition are discussed in detail, and the discontinuities and the complex time variation behavior observed＇in the preexisting works are naturally explained by a stochastic process.     

Growth of patterned and aligned carbon nanotube bundles on micro-structured substrate

Microstructures are used as inducement for growth of patterned and aligned carbon nanotube (CNT) bundles by pyrolysis of iron phthalocyanine (FePc) under H₂/Ar. The flow of mixture gas can be influenced by geometry profile of microstructure, and the distribution density of catalyst will be different related to the different microstructure. Many types of substrates with different microstructures are used in this study, and several different profiles of CNT bundles are achieved under different process conditions, especially an apical dominance like plant growth is observed under specific H₂/Ar flow rate. Through using appropriate microstructures and controlling the flow rate, the density of CNT bundles can be adjusted, which is very important for weakening electric field shielding effect.     

转/静干扰效应纳入设计体系的途径探索

1前言近年来,叶轮机非定常流动时间精确模拟获得十足发展。虽然如此,关于时间精确解仍然存在很多问题。因而就目前而言,将叶轮机非定常干扰时间平均效应纳入设计体系,实现准四维设计体系是缩短我国和发达国家叶轮机气动设计水平差异的关键工作,其中叶轮机非定常流动时均流动模拟方法是首要解决的问题。叶轮机时均流动模拟工作,国外主要有Adamczyk［llRhie［‘］国内作者和孟庆国博士也开展了研究［‘－’］,其中文献问详细阐述了时均流动模拟理论和方法,并对时均流动模拟基本方式进行分类（图1）。2反映转／静干扰效应的时均N－S…     

微重力条件下不同截面形状管中毛细流动的实验研究

利用落塔设施创造的短时间微重力条件, 研究了不同尺寸的正方形和三角形截面的毛细管中的流体在微重力条件下的流动行为, 并与圆形毛细管中的毛细流动进行了对比, 总结出了毛细管尺寸和截面形状对界面张力主导的毛细流动行为的影响规律. 结果显示, 对于同样形状的毛细管, 其尺寸对于毛细流动的影响规律基本相同; 而对于不同的截面形状, 方形管和三角形管都与截面积小得多的圆形管有一定的类似性. 相关结果对于深入理解不同条件下的界面张力主导的毛细流动特性, 以及在空间微重力条件下通过改变毛细管的形状来实现流速和流量的独 立控制等方面都具有明显的现实意义. 关键词： 微重力 毛细流动 毛细管形状     

Multi-value cellular automata model for mixed bicycle flow

In this paper, we investigate mixed bicycle flow using the multi-value cellular automata (CA) model. Two types of bicycles with different maximum speed are considered in the system. The system of mixed bicycles is investigated under both deterministic and stochastic regimes. It is shown under the deterministic case that there appear multiple states both in congested flow and free flow regions. Analytical analysis is carried out and is in good agreement with the simulation results. Under the stochastic case, the multiple states effect disappears only when both slow and fast bicycles are randomized. Spacetime plots are presented to show the evolution of mixed bicycle flow.