气冷涡轮叶片气热耦合数值模拟研究

采用气热耦合计算方法进行气冷涡轮气动性能-传热分析,这种方法无需指定对流换热系数和热流密度等经验参数,只须要给出气流与固体之间的流动换热物理条件.利用该方法对某三维涡轮导叶进行数值模拟,计算结果表明,气热耦合计算的叶片温度场更接近真实情况,针对该叶片尾缘烧蚀问题,利用气热耦合计算方法,研究了叶片尾缘冷却设计方案,通过对在尾缘开缝冷却方案的分析计算,结果表明,该设计方案可以使得尾缘最高温度下降了130K.     

跨音速涡轮叶栅数值计算方法研究与试验验证

以某跨音速涡轮叶栅为对象,研究计算流体动力学数值计算方法,应用CFD软件ANSYS CFX,分析不同网格量和不同湍流模型对数值计算结果的影响,得到最理想且最吻合试验结果的数值计算方法,并与试验结果进行对比分析。结果表明,考虑权衡数值计算结果与试验值吻合度和所耗时间的均衡性,三维网格的S1流面网格量为1万最为合适,SST湍流模型的模拟结果最为理想。     

高压涡轮动叶气膜冷却的数值模拟

为研究旋转造成的非稳定性对高压涡轮动叶气膜冷却的影响,建立了3维涡轮叶栅通道模型,应用周期性边界条件数值模拟了不同转速下涡轮动叶表面气膜冷却效率和换热系数的分布,冷气进口与涡轮前总压比为1.07,温度比为0.5。转速增加,叶片前缘滞止线从压力面移向吸力面,气膜出流从吸力面移向压力面;压力面气膜冷却效率上升,换热系数下降;吸力面冷却效率先上升后降低;换热系数下降。与静止相比,旋转不稳定性增大了叶片表面气膜覆盖面积。     

高压涡轮导叶传热数值计算与分析

以NASA C3X线性叶栅为研究对象,采用非耦合和耦合方法分析叶片表面外换热系数分布.结果表明:离前缘越远,外换热系数越容易受到壁温的影响,带转捩的k-ωSST湍流模型能很好地预测耦合换热.运用牛顿冷却定律对其进行修正和可行性分析,对比外换热系数分布,表明非线性方法简单有效.     

不同前缘气膜冷气流下某涡轮叶栅流场分析

针对引入前缘气膜冷却的某高压涡轮转子叶片，运用NUMECA进行建模，对引入气膜冷却后的涡轮叶栅流场进行分析，得到了加入前缘气冷后温度、速度、总压等参数的变化。再改变前缘气膜冷气流量，得到了不同流量工况下涡轮叶栅流场的变化情况。通过计算得到结论，冷气流量增大，气膜与叶片壁面分离位置提前，整体流速更快到达最大值且沿着壁面下降更快。冷气流量减小，冷却效率降低；吹风比越大，不同冷气流下冷却效率的变化更为集中；但随着冷气流的改变，总压恢复系数没有发生本质变化。     

不同湍流模型对叶片表面换热系数结果的影响

为了比较湍流模型对涡轮叶片外换热计算结果的影响,采用的三种湍流模型对NASA-C3X导向叶片进行了表面换热计算并与实验数据进行了对比,结果表明:边界层流态的转变对换热的影响很显著,缺乏对湍动能发展的控制是影响换热计算结果主要原因;标准的k-ε模型换热计算效果较差,Reynolds Stress模型体现了边界层流动状态的转变对换热影响;研究在不同计算域采用不同湍流模型的计算技术,是一种较好的可行的方案.     

基于气热固耦合的涡轮模态分析

主要研究了气热固耦合场对涡轮模态参数的影响.采用基于k-ε湍流模型理论建立了涡轮的流场模型,进行网格划分和边界条件的加载.通过气热固耦合分析计算获得了流场内部温度和压力的分布,把气动力及温度载荷映射到涡轮结构上,并在此基础上进行了涡轮模态的计算.计算结果表明,气热固耦合场主要影响涡轮结构的模态固有频率,对模态振型的影响较小.     

燃气涡轮静叶表面气膜冷却效率实验研究

采用放大的燃气涡轮静叶模型,利用大尺度叶栅风洞进行实验,测量了涡轮静叶表面完全气膜覆盖下气膜冷却特性。风洞实验段由三个叶片组成,中间叶片为实验叶片,由有机玻璃制成。对叶片前腔和后腔表面换热情况分别进行实验,主要研究了不同主流雷诺数及不同质流比对气膜冷却效率影响。研究结果表明:气膜对前腔壁面冷却效果总体上优于后腔壁面,在叶片不同区域气膜冷却效率变化规律有所不同。     

基于湍流SST模型电解加工温度场数值仿真研究

针对电解加工过程中电解液温度难以准确预测的问题,采用湍流SST模型求解电解液流速及Euler双流体模型求解气泡率分布,建立多场耦合仿真模型求解极间间隙中电解液的温度分布。对比湍流k-ε、SST模型以及SST耦合Euler模型计算温度分布的结果,分析了不同流量和出口压力对电解液温度分布的影响。结果表明:采用湍流SST模型计算得到的电解液温度分布比k-ε模型更接近试验结果;考虑气泡率对温度的影响,采用SST耦合Euler模型计算得到温度分布的结果更精确;出口处电解液温度随流量的增加而降低;在相同流量下,极间电解液温度随出口压力的增加而小幅上升。     

CFD在涡轮钻具机械性能预测分析中的应用

文中采用实体建模、CFD前置处理器等工具真实、准确地建立涡轮定、转子单周期跨叶片流道计算模型,应用CFD(计算流体动力学)技术研究分析了其在不同转速下的内流场。对模拟出的涡轮叶栅内流场,重点分析了转子叶片表面压力场的分布情况,并将模拟结果与十级涡轮台架的实验数据进行了对比,证明了应用CFD技术对涡轮钻具叶栅内流场模拟分析的有效性,为涡轮钻具机械性能预测分析提供了一种有力的技术手段。     

风冷冰箱冷冻室的数值模拟与试验研究

对一台家用风冷冰箱的冷冻室建立了三维综合热流体模型。采用稳态可实现k-ε紊流模型进行数值模拟和分析,并进行了试验验证。结果表明,模拟温度稍高于试验温度。测点的模拟温度值与实验温度相对误差最小的是1.03%,最大的是5.26%,表明模拟结果可靠。分析模拟结果发现,在远离出风口的位置气流基本停滞,不利于内部气流的换热,可以适当提高入风口的气流速度、在抽屉的底部开孔来增加上下的气流流动可以提高腔室的温度分布均匀性。     

Performance analysis of air-cooled microchannel absorber in absorptionbased miniature electronics cooling system

Theoretical analysis and simulation of performance of an air-cooled microchannel absorber is reported in this study. It is shown that the air-cooled microchannel absorber can be integrated into an absorption-based miniature electronics cooling system by which the chip junction temperature can be maintained near room temperature, while removing 100 W of heat load. Water/LiBr pair is used as the working fluid and refrigerant vapor is intended to counter-currently flow against aqueous LiBr solution flow. Parametric study is carried out to determine the effects of several operating parameters, including inlet temperature and mass flow rate of the coolant, and inlet temperature of LiBr solution. To facilitate the air-cooling of microchannel absorber, an offset-strip-fin array is adopted, by which enhanced air-side heat transfer coefficient and large heat transfer area are obtained. The performance of the air-cooled absorber is compared to liquid-cooled absorber.     

Performance test and component characteristics evaluation of a micro gas turbine

This study aims to analyze engine performance and component characteristics of a micro gas turbine based on detailed measurement of various parameters. A test facility to measure performance of a micro gas turbine was set up and performance parameters such as turbine exit temperature, exhaust gas temperature, engine inlet temperature, compressor discharge pressure and temperature, and fuel and air flow rates were measured. The net gas turbine performance (power and efficiency based on the gas turbine shaft end) was isolated and analyzed. With the aid of measurement based simulation, component characteristic parameters such as turbine inlet temperature, compressor efficiency, turbine efficiency and recuperator effectiveness were estimated. Behaviors of the estimated characteristic parameters with operating condition change were examined and sensitivities of estimated parameters to the measured parameters were analyzed.     

闭式冷却塔空冷传热性能的试验研究及优化运行

搭建了扭曲管闭式冷却塔的换热实验平台,在空冷模式下通过测试在不同风机频率以及风机频率固定时不同的管内流体进口温度、空气干球温度情况下闭塔的传热性能、流动阻力和能耗,得到了风机频率、管程体积流量以及管程进口温度、环境温度对综合传热性能和空冷传热量的影响,进而得出优化闭塔空冷换热的方式,并推导出在不同的季节温度下最合理的运行方式。同时本试验拟合了风机频率和风机功率等与迎面风速的试验关联式以及空冷管外空气的传热系数试验关联式,对扭曲管式闭式冷却塔的优化设计有一定的指导作用。     

合成氨厂氮氢气压缩机级间废热利用技术研究

提出了一种利用多级压缩机级间的废热,采用溴化锂吸收式制冷,来降低压缩机一级入口气体的温度的方法,达到了增加压缩机排气量的目的。并对系统进行了建模与模拟,当采用三段废热时,可将压缩机入口气体温度由35℃降到15℃。提高产能10%左右。     

直接空冷凝汽器换热性能影响因素研究

以内蒙古某电厂为研究对象,采用理论计算和数值模拟相结合的方法,研究了环境温度、风速、湿度及风机转速对直接空冷凝汽器换热特性的影响。研究表明:来流风速为(13~15)m/s时,总换热量较设计工况降低了(3.2~7.5)%;环境温度对总换热量影响很大,但当环境温度大于15℃时,总换热量下降趋势逐渐变的缓慢;环境湿度对总换热量的影响较小;随着环境风速的增加,各空冷单元风机进口流量整体呈下降趋势,其中迎风侧的第一个风机进口流量降幅最大。     

Heat/mass transfer characteristics in the near-tip region on a turbine blade surface under combustor-level high inlet turbulence

Heat/mass transfer characteristics on the near-tip blade surface under combustor-level high inlet turbulence have been investigated within a high-turning turbine rotor passage by using the naphthalene sublimation technique. The inlet turbulence intensity and length scale are 14.7% and 80 mm, respectively. The tip gap-to-chord ratio is changed to beh/c = 0.74, 1.47, and 2.94 percents. Increasingh/c results not only in higher heat/mass transfer in the pressure-side tip region but also in more convective transport on the pressure surface even far away from the tip edge. Severe heat/mass transfer is always observed in the suction-side tip-leakage flow region which can be divided into two distinct high transport regions. There is a local maximum of heat/mass transfer along the trailing-edge centerline. This arises from the interaction of a tip-leakage vortex with a trailing-edge vortex shedding. Comparisons of the present data forh/c = 2.94 percents with the previous low turbulence one show that there is a large discrepancy of heat/mass transfer in the pressure-side near-tip area, which diminishes with departing from the tip edge. The suction-side heat/mass transfer in the tip-leakage flow region is less influenced by the high inlet turbulence than that at the mid-span. The leading-edge heat/mass transfer under the high inlet turbulence is always higher than that in the low turbulence case, while there is no big difference in the trailing-edge heat/mass transfer between the two cases.     

The effect of cooling conditions on convective heat transfer and flow in a steam-cooled ribbed duct

This work presents a numerical and experimental investigation on the heat transfer and turbulent flow of cooling steam in a rectangular duct with 90° ribs and studies the effect of cooling conditions on the heat transfer augmentation of steam. In the calculation, the variation range of Reynolds is from 10,000 to 190,000, the inlet temperature varies from 300°C to 500°C and the outlet pressure is from 0.5MPa to 6MPa. The aforementioned wide ranges of flow parameters cover the actual operating condition of coolant used in the gas turbine blades. The computations are carried with four turbulence models (the standard k-?, the renormalized group (RNG) k-?, the Launder-Reece-Rodi (LRR) and the Speziale-Sarkar-Gatski (SSG) turbulence models). The comparison of numerical and experimental results reveals that the SSG turbulence model is suitable for steam flow in the ribbed duct. Therefore, adopting the conjugate calculation technique, further study on the steam heat transfer and flow characteristics is performed with SSG turbulence model. The results show that the variation of cooling condition strongly impacts the forced convection heat transfer of steam in the ribbed duct. The cooling supply condition of a relative low temperature and medium pressure could bring a considerable advantage on steam thermal enhancement. In addition, comparing the heat transfer level between steam flow and air flow, the performance advantage of using steam is also influenced by the cooling supply condition. Changing Reynolds number has little effect on the performance superiority of steam cooling. Increasing pressure would strengthen the advantage, but increasing temperature gives an opposite result.     

Flow visualization of microscale effusion cooling within mainstream boundary layer on a flat plate

Effusion cooling can be one of the attractive methods of cooling in a current high-efficiency gas turbine which has a very hot gas temperature above 1600 °C. For higher effectiveness of the air cooling for a gas turbine vane and blade, the air-cooled flow through effusionholes should not overshoot into the mainstream flow but still remain within the mainstream boundary layer. The present study is intended to examine flow structure of a microscale effusion cooling for gas turbine applications through flow visualization which is highly effective to obtain better understanding of the flow physics. The air flow through effusion-holes can be visualized with an oil atomized droplets, a laser-sheet and a high-speed CCD imaging system. The qualitatively visualized results show their flow patterns and characteristics with different effusion hole size and blowing ratio for effusion cooling. A series of vortical structure can be observed within the boundary layer along the microscale effusion flat plate which provided that the effusion cooling can be a plausible candidate up to the effusion-hole size of 0.7 mm.