高低齿汽封与蜂窝汽封及孑L式阻尼汽封密封性能的比较

使用商用CFD软件Fluent对高低齿汽封、蜂窝汽封及孔式阻尼汽封进行了三维数值模拟,得到三种汽封在不同压比、轴转速和汽封相对间隙时的密封性能,并将高低齿汽封和蜂窝汽封计算值与试验数据进行了对比．结果表明：高低齿汽封流量系数随压比增大而增大,随转速加快而略有减小,随相对间隙的增大而减小;蜂窝汽封与孔式阻尼汽封的流量系数均随压比增大而减小,随转速加快而略有减小,基本呈直线变化规律,随相对间隙的增大而增大;在相同的条件下,蜂窝汽封的漏汽量比高低齿汽封的漏气量减少10％,而孔式阻尼汽封的漏汽量比蜂窝汽封漏汽量减少6％．     

链条炉排的侧密封

以常用的鳞片式链条炉排为例,阐述了炉排侧密封的重要性,揭示了迷宫式密封存在的问题和采用接触式密封和饱合式密封的必要性,并对轻型链带式炉排的侧密封进行探讨。     

迷宫密封转子动特性三维CFD数值的研究

1引言旋转机械转子系统中的非接触密封在阻止流体泄漏的同时,还会产生重要的流体激振力,影响转子振动稳定性。与动压滑动轴承的油膜类似,密封中流体膜(汽膜、水膜或油膜)动力特性中的交叉刚度k是促使转子做非同步低频涡动的激振力来源,直接阻尼C可以生成对这种低频涡动的抑制力     

汽轮机叶顶汽封间隙内的流动损失分析

为了揭示叶顶汽封结构变化对泄漏损失的影响,提高汽轮机运行效率,数值研究了平齿汽封、高低齿汽封和侧齿汽封3种不同叶顶汽封结构下汽轮机高压转子间隙泄漏的流动形态、间隙涡系的形成机理和发展规律,研究表明:在叶顶汽封腔室复杂的周向螺旋状的涡动中,泄漏流体的周向速度是影响漩涡耗散的一个重要因素;高低齿及侧齿的汽封结构可以增强漩涡之间的相互作用,降低泄漏流体的周向速度,使漩涡在腔室内的耗散更加充分;由于掺混损失降低,高低齿及侧齿汽封的泄漏总损失较平齿汽封相比分别下降7.1%和9.8%。     

高速齿轮箱迷宫密封流场和泄漏特性的数值研究

以某型大功率机车传动齿轮箱轴端迷宫密封为研究对象,建立错齿式迷宫密封的数值仿真模型。通过分析迷宫密封的密封机理和对泄漏量的影响因素,确定了数值模拟的边界条件。应用Fluent软件,求解N-5方程和能量方程,模拟迷宫密封腔内流场分布及泄漏特性,研究转速、压比和密封齿隙对泄漏特性的影响规律。研究结果表明：随着进出口压比的增加,泄漏系数先快速增加后趋于平缓;转速对泄漏系数影响很小;泄漏系数与齿隙呈分段线性关系。     

低压隔板低直径汽封和对齿式汽封的数值分析

在汽轮机低压末几级隔板中,有两种比较典型的汽封结构形式——低直径汽封和对齿迷宫式汽封。在某600MW机组改造末三级长叶片优选过程中,针对两种类型的隔板汽封,在末三级环境中,开展全三维CFD分析,对比两者的密封效果,及对整个级效率的影响。数值结果表明,两种汽封结构均有较好的密封效果,对齿迷宫式汽封配合新型设计的末三级叶片,具有较高的气动效率,有助于改善600MW机组低压缸整体经济性。     

防旋板高度对迷宫密封泄漏流动和转子动力特性的影响

采用基于转子多频椭圆涡动模型的Unsteady Reynolds-Averaged Navier-Stokes (URANS)方程求解方法,研究了防旋板高度与第1个迷宫齿前缘高度相同时,防旋板高度对迷宫密封泄漏流动和转子动力特性系数的影响.计算分析了典型中等进口预旋条件下,无防旋板结构以及防旋板高度为1.85,3.7和...     

基于FLUENT的某型燃气轮机迷宫密封机理研究

针对影响透平机械中旋转迷宫密封泄漏特性的3个因素:密封间隙、压比、转速,以某型燃气轮机的隔板迷宫密封为研究对象,数值研究了各个因素对迷宫密封泄漏特性的影响规律,计算分析了该迷宫密封在不同工况下的泄漏特性。研究结果表明:随着转子转速的增加,迷宫密封泄漏量减小;相同密封间隙下,泄漏系数随着压比的提高而近似线性增加;相同转速下,泄漏量随着密封间隙的减小而减小,且泄漏量减小的速度越来越慢。     

MS9001E燃气轮机透平密封改造

浙江镇海的300MW燃气—蒸汽联合联合循环电站由两台100MW的MS9001E燃气轮发电机组、一台100MW蒸汽轮发电机组及两台无补燃余热锅炉组成。燃气轮机由美国GE公司提供,机组起停机时用0#柴油,正常运行时燃用180cSt重油。其中#8燃气轮机(到性能改造前总运行时间37 290·5小时、启动8     

变工况下高低齿迷宫密封泄漏特性及结构优化

高低齿迷宫密封是透平机械中抑制流体泄漏的关键部件。以某机组隔板密封为对象建立高低齿迷宫的计算流体力学(CFD)模型,研究由变工况引起的转子轴向偏移对密封泄漏特性的影响,并通过调整转子凸台宽度和密封腔高度对密封结构进行优化。结果表明:原始结构设计下,转子轴向偏移±3 mm内,泄漏量并未发生大幅度的上升;在-2~1.5 mm范围内泄漏量有所下降,说明在工况变动不大时,密封性能有所提高,但超出±3 mm的范围,泄漏量呈突增趋势;泄漏量分别随转子凸台宽度和密封腔高度呈二次非线性变化,存在一个最佳值使泄漏量达到最小,最佳凸台宽度和密封腔高度分别为5.13和7.5 mm;结构优化后密封泄漏量在正常工况及变工况下均小于原始结构,密封性能得到提高。     

超微燃气透平非接触式密封的三维CFD数值分析

提出将螺旋密封应用于超微燃气透平气体介质密封.采用三维CFD数值计算方法分析了微尺度下无密封齿、迷宫密封和螺旋密封的泄漏规律及流场规律.结果表明:微尺度下迷宫密封最优齿数的存在与进、出口压比和密封间隙有关,而齿形对密封性能的影响没有宏观尺度下明显.在小压比下,密封轴转速对螺旋密封性能的提高明显,其泄漏减少量最高可达19.3%,因此螺旋密封显然优于迷宫密封和无密封齿;在大压比下,螺旋密封与迷宫密封的效果相当,均优于无密封齿.当压比为2时,迷宫密封的泄漏率比无密封齿降低27.1%.     

Model-oriented cast ceramic tape seals for planar solid oxide fuel cells

A straight capillary model is developed to estimate the mass leak rate of the cast ceramic tape seals for planar solid oxide fuel cells (SOFCs), which is further rectified with consideration of microstructure complexity including the tortuosity, cross-section variation and cross-link of leak paths. The size distribution of the leak path, effective porosity and the microstructure complexity are the main factors that influence the leak rate of the cast tape seals. According to the model, Al₂O₃ powders are selected for preparation of the seals by tape casting, and the leak rate is evaluated under various compressive stresses and gauge pressures. The results indicate that Al₂O₃ powder with D₅₀ value about 2 μm and specific surface area near 5 m² g⁻¹ can be used for the cast tape seals; and the obtained leak rate can satisfy the allowable leak limit.     

Three-dimensional convective flow adjacent to backward-facing step - effects of step height

Three-dimensional simulations are presented for incompressible laminar forced convection flow adjacent to backward-facing step in rectangular duct and the effects of step height on the flow and heat transfer characteristics are investigated. Reynolds number, duct's width, and duct's height downstream from the step are kept constant at Re=343, W=0.08 m, and H=0.02 m, respectively. The selection of the values for these parameters is motivated by the fact that measurements are available for this geometry and they can be used to validate the flow simulation code. Uniform and constant heat flux is specified at the stepped wall downstream from the step, while other walls are treated as adiabatic. The size of the primary recirculation region and the maximum that develops in the Nusselt number distribution increase as the step height increases. The “jet-like” flow that develops near the sidewall within the separating shear layer impinges on the stepped wall causing a minimum to develop in the reattachment length and a maximum to develop in the Nusselt number near the sidewall. The maximum Nusselt number, in the spanwise distribution, develops generally in the same region where the reattachment length is minimum. The maximum in the friction coefficient distribution on the stepped wall increases with increasing step height inside the primary recirculation flow region, but that trend is reversed downstream from reattachment. The three-dimensional behavior and sidewall effects increase with increasing step height.     

150 MW汽轮机高压缸级内流场的数值模拟

采用Numeca软件对带隔板汽封和叶顶间隙汽封的高压缸二、三级叶栅流动进行了数值模拟,并与不带汽封的二、三级叶栅流场进行了比较.结果表明,汽封泄漏损失使级效率显著下降,汽封出口处的低能流体使端壁的附面层变厚,端壁摩擦损失增大;隔板汽封出口处的气体周向速度较小,导致了较大的负攻角流动,它与下排叶栅的横向流动相结合大大促进了下通道涡的发展.     

Low Reynolds number forced convection in three-dimensional wavy-plate-fin compact channels: fin density effects

Steady forced convection in periodically developed low Reynolds number (10 ? Re ? 1000) air (Pr = 0.7) flows in three-dimensional wavy-plate-fin cores is considered. Constant property computational solutions are obtained using finite-volume techniques for a non-orthogonal non-staggered grid. Results highlight the effects of wavy-fin density on the velocity and temperature fields, isothermal Fanning friction factor f, and Colburn factor j. The fin waviness is seen to induce the steady and spatially periodic growth and disruption of symmetric pairs of counter-rotating helical vortices in the wall-trough regions of the flow cross-section. The thermal boundary layers on the fin surface are thereby periodically interrupted, resulting in high local heat transfer near the recirculation zones. Increasing fin density, however, tends to dampen the recirculation and confine it. The extent of swirl increases with flow rate, when multiple pairs of helical vortices are formed. This significantly enhances the overall heat transfer coefficient as well as the pressure drop penalty, when compared to that in a straight channel of the same cross-section. The relative surface area compactness as measured by the (j/f) performance or the area goodness factor nevertheless increases with fin density.     

错齿式迷宫密封齿形对泄漏量的影响

以某型大功率机车传动齿轮箱轴端迷宫密封为研究对象,采用GAMBIT软件建立错齿式迷宫通道的二维结构化网格模型,应用FLUENT软件计算3种不同齿形及其夹角的变化对流场和泄漏量的影响。研究结果表明：直角梯形齿的背风齿比迎风齿具有更好的密封效果,而且存在最佳的齿顶角度30。使泄漏量最小;三角齿和等腰梯形齿具有相似的结论,即泄漏量与齿顶角度呈线性关系。     

动静态下汽封间隙对汽封性能的影响研究

应用Fluent软件,采用SIMPLE算法、RNG k-ε双方程紊流模型和有限体积法离散N-S方程,对动静状态下汽封内的三维流场进行了数值模拟。结果表明:在汽封间隙内部的泄漏流动中,黏性作用是不占主导地位的。间隙值越大,漏泄现象就越严重。转子旋转效应的影响存在于近壁区内,但汽封间隙变化对漏汽量的影响要远大于旋转效应所产生的影响。不同间隙下转速对间隙内流场的流线存在一定的影响,汽封间隙较小时漏汽平均速度受转子转速的影响要大一些。     

Investigations of the conjugate heat transfer and windage effect in stepped labyrinth seals

In the current paper, conjugate heat transfer and windage heating in the stepped labyrinth seals with smooth and honeycomb lands are numerically investigated by using the commercial software ANSYS CFX11.0. Firstly, the utilized numerical approaches, such as the turbulence model and grid independence analysis, are determined to ensure a suitable numerical method for the present study. Based on the obtained measurement data, the computed heat transfer coefficients on the rotor and stator surfaces are carefully validated. To reveal the influence of the solid domain on the heat transfer computations, the comparisons between the results with and without solid domain are performed. It shows that the predicted heat transfer coefficient distributions with the presented conjugate heat transfer methods (with solid domain) agree well with the experimental data. Difference between the numerical results with and without solid domain only exists in the high temperature gradient region. Compared to the smooth labyrinth seal, the presence of honeycomb cells increases the temperature gradient in the labyrinth fin (solid domain) and significantly decreases the temperature gradient in the stator (solid domain). Secondly, in order to assess the influence of the rotating effect on the windage heating for the stepped labyrinth seal, total temperature difference between the seal inlet and outlet are computed under different effective pressure ratios for both the smooth and honeycomb configurations. Based on the energy conservation law, the windage loss for the high speed rotating seal is also obtained by taking the heat transfer between the fluid and solid into consideration. Finally, the influences of the effective pressure ratio and inlet preswirl ratio on the heat transfer coefficient distributions of rotor and stator for both the smooth and honeycomb configurations are discussed in detail.     

Heat transfer improvement by arranging detached ribs on suction surfaces of rotating internal coolant passages

Heat transfer coefficient, flow field, and wall static pressure distributions were measured in a rotating two-pass square duct with detachment of 90° ribs from the first pass leading wall and second pass trailing wall as well as attachment of 90° ribs onto the other two opposite walls. Laser-Doppler velocimetry was used to measure the local flow velocity. The ribs were square in cross-section and their detached-distance/height ratio was 0.38. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. Duct Reynolds number was fixed at 1 × 10⁴ and rotating number ranged from 0 to 0.2. Results are documented in terms of the main flow development, cross-stream secondary flow structure, the distributions of the pressure coefficient, the variation of friction factor with Ro, and passage averaged Nusselt number ratios under constant flow rate and constant pumping power conditions. For CFD reference, the periodic fully developed rotating flow condition is attained after the 6th rib pair in the first pass. In addition, the relationships between the regional averaged Nusselt number, transverse and streamwise mean velocity components, and turbulent kinetic energy are addressed. Using these relationships the general superiority of heat transfer enhancement of the attached–detached 90° ribs arrangement over the attached–attached one can be reasonably illustrated. Simple expressions are obtained to correlate the friction factor with Ro, which are lacking in the published literature. The respective contributions of the ribs and passage rotation on the passage friction loss are identified.     

Turbulent separated convection flow adjacent to backward-facing step—effects of step height

Simulations of turbulent convection flow adjacent to a two-dimensional backward-facing step are presented to explore the effects of step height on turbulent separated flow and heat transfer. Reynolds number and duct’s height downstream from the step are kept constant at Re₀ = 28,000 and H = 0.19 m, respectively. Uniform and constant heat flux of q_w = 270 W/m² is specified at the stepped wall downstream from the step, while other walls are treated as adiabatic. The selection of the values for these parameters is motivated by the fact that measurements are available for this geometry and they can be used to validate the flow and heat transfer simulation code. Two-equation low-Reynolds-number model is employed to achieve the turbulent Prandtl number. The primary and secondary recirculation regions increase in size as the step height increases. The bulk temperature increases more rapidly as the step height increases. Increasing the step height causes the magnitude of the maximum turbulent kinetic energy to increase. Near the step and below the step height, the turbulent kinetic energy becomes smaller as the step height increases. Inside the recirculation region, magnitude of the peak friction coefficient does not significantly change with the increase of step height. The friction coefficient becomes smaller in magnitude with the increase of the step height. The peak Stanton number becomes smaller as the step height increases.