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％．     

Thermal Performance Prediction in the Air Gap of a Rotor-Stator Configuration: Effects of Numerical Models

This study is dedicated to a numerical investigation of convective heat transfer on the rotor surfaces of a rotor-stator configuration that is typically found in large hydro-generators.The computational fluid dynamics calculations with two turbulence modelling approaches are used to predict the flow structure and heat transfer in the air gap of the rotor-stator configuration.The steady state mixing plane approach is employed at the interface to couple the rotor and stator components.Results show that the location of mixing plane interface in the air gap plays an important role in the prediction of heat transfer on the pole face.Also,it is indicated that the prediction of temperature distribution on the pole face is greatly affected by the turbulence models used.Furthermore,through a comparison between the pure convective and conjugate heat transfer methodologies,it is shown that the inclusion of solid domain into the numerical model significantly improves the thermal prediction of the solid components of the machine.     

Numerical and Experimental Modelling of Gas Flow and Heat Transfer in the Air Gap of an Electric Machine. Part Ⅱ： Grooved Surfaces

The study deals with the cooling of a high-speed electric machine through an air gap with numerical and experimental methods. The rotation speed of the test machine is between 5000-40000 r/min and the machine is cooled by a forced gas flow through the air gap. In the previous part of the research the friction coefficient was measured for smooth and grooved stator cases with a smooth rotor. The heat transfer coefficient was recently calculated by a numerical method and measured for a smooth stator-rotor combination. In this report the cases with axial groove slots at the stator and/or rotor surfaces are studied. Numerical flow simulations and measurements have been done for the test machine dimensions at a large velocity range. At constant mass flow rate the heat transfer coefficients by the numerical method attain bigger values with groove slots on the stator or rotor surfaces. The results by the numerical method have been confirmed with measurements. The RdF-sensor was glued to the stator and rotor surfaces to measure the heat flux through the surface, as well as the temperature.     

Heat transfer in a mechanical face seal

This paper presents a numerical analysis of heat transfer in an experimental inner pressurized mechanical face seal, using CFD. The configuration is similar to the laminar flow between a static and a rotating disc bounded by a co-rotating sidewall. A series of simulations allow the authors to propose a correlation for the global Nusselt number for the rotating ring and the static disc. The Nusselt number is a function of the Reynolds number of the flow and the Prandtl number, as well as of the ratio of the fluid and material thermal conductivities. This last conclusion arises from the fact that the heat source is located in the contact between the rotor and the stator and depends on the temperature distribution in the solids. The cooling oil flow appears not to affect the Nusselt number. The numerical results were validated by comparison with measurements carried out on the experimental seal by means of an infrared camera.     

迷宫密封转子动力学特性的数值模拟

采用数值求解三维Reynolds-Averaged Navier-Stokes(RANS)方程,研究了具有16个齿的迷宫密封转子动力学特性,分析了在两种转速条件下进口预旋对迷宫密封转子动力特性系数的影响,计算了无进口预旋时,在两种压比条件下,迷宫密封系统的交叉刚度和直接阻尼系数随转速的变化关系,并将计算结果与实验值和两控制容积BF(Bulk Flow)方法计算值进行了比较.研究结果表明:所采用的数值方法能较好地预测迷宫密封的转子动力特性,且计算结果优于两控制容积BF方法.对于迷宫密封,交叉刚度与进口预旋近似成正比关系,且随着转速的增大而增大;直接阻尼对转速和进口预旋均不敏感,但随压比的增大而显著增大.过大的进口预旋和转速均会使转子的稳定性降低;工作在较大转速下的迷宫密封系统可以通过施加合理的进口预旋来增强转子的稳定性.     

Numerical analysis of erosion of the rotor labyrinth seal in a geothermal turbine

Excessive erosion of the labyrinth seal of a 110 MW geothermal turbine has been investigated. This study used computational fluid dynamics (CFD) and aims to identify one cause of erosion and a possible solution for substantially reducing it. The predictions were based upon a numerical calculation using a CFD model of the labyrinth seal with a water/steam flow containing hard solid particles and solved with a commercial CFD code: Fluent V5.0. The results confirmed the existence of flow conditions that play a major role in the rotor labyrinth seal erosion. Afterwards, the flow path was simulated with changes of rotor labyrinth seal geometry, which are indeed feasible of being implemented. The results confirmed that it is possible to reduce the erosion process by approximately 80% by incorporating a steam flow deflector in the fourth stage diaphragm, which changes the steam flow direction in the inlet zone to the rotor labyrinth seal channel, resulting in a reduction in steam volumetric mass flow and hard particle velocity by about 44%.     

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%。     

Numerical study of film cooled rotor leading edge with tip clearance in 1-1/2 turbine stage

Numerical simulations were performed to predict the film cooling effectiveness and the associated heat transfer coefficient in a 1-1/2 turbine stage. The leading edge of the rotor blade is film cooled with three rows of film cooling holes. The rotor tip leakage has been investigated for a clearance of 0.8% of blade span. Sliding grid is used for the rotor domain, and interface technique is employed to exchange information between stator and rotor domains. Simulations were carried out for both design and off-design conditions to investigate the effects of the stator–rotor interaction on the film cooling characteristics. The commercial code FLUENT with Reynolds stress model is used in the prediction. It is found that the tilted stagnation line on the rotor leading edge moves from the pressure side to the suction side, and the instantaneous coolant streamlines shift from the suction side to the pressure side with the increasing rotating speed. For the fixed inlet/outlet pressure ratio of turbine stage, the high rpm reduces the heat transfer coefficient on the rotor due to the low rotor relative velocity, and increases the “sweet spot” on the rotor tip. These trends are well supported by the experimental results.     

蜂窝汽封流场及泄漏特性的数值模拟研究

建立了蜂窝汽封三维流场数值模型,系统地分析了蜂窝孔径尺寸、蜂窝高度、入口压力等结构与运行参数对汽封流场及泄漏特性的影响.计算结果与分析表明,在运行参数不变的情况下,降低蜂窝孔径大小或增加蜂窝高度都有利于降低汽封泄漏量,提高密封效果.而在结构参数不变的情况下,汽封泄漏量随入口压力增大而增加,而随旋转速度增大出现减小的趋势.     

汽封力作用下的转子-轴承系统稳定性研究

通过分析汽封力对轴承静态平衡点的影响,表明汽封力能够改变轴承的静、动特性。计算了滑动轴承油膜力和汽封力共同作用下的系统一阶临界转速和一阶对数衰减率,并用实验进行了验证。研究表明,汽封力对系统稳定性的影响是复杂的,其影响因素包括进出口压力、进口预选速度、密封参数等。     

Heat transfer analysis of stratified flow in rotating heat pipes with cylindrical and stepped walls

This paper deals with the flow behavior and the related heat transfer characteristics of stratified flow in axially rotating heat pipes with cylindrical and stepped wall configurations. Flow patterns are presented with existing experimental data of heat transfer in cylindrical and stepped wall rotating heat pipes. Theoretical and semi-empirical models for calculation of the condensation and evaporation heat transfer coefficients are developed. Key dimensionless numbers such as Froude, Galileo, G and ξ-number are identified. Existing experimental data from a rotating cylindrical heat pipe are analyzed and used for regression based on semi-empirical models. Good agreement between the predicted results and experimental data was obtained. Comparison between the present heat transfer models rotating cylindrical wall heat pipes and experimental data from a stepped wall heat pipe shows that the present models can be used to predict the condensation and evaporation heat transfer coefficients in a rotating stepped wall heat pipe.     

Analysis of internal cooling geometry variations in gas turbine blades

The present investigation analyzes the effects of major geometrical modifications to the interior of a convection cooled gas turbine rotor blade. The main focus lies on the flow of the leading edge channels and the impact on the heat transfer. An experimental approach is performed with flow visualization via paint injection into water. Also numerical calculations are carried out in two sets, on the one hand water calculations accompanying the experiments and on the other hand conjugate heat transfer calculations under realistic engine conditions. The latter calculations are still ongoing delivering preliminary results. Five geometry configurations are investigated, three of them with differing turbulator arrangements in the leading edge channels. The operating point of the base configuration is set to Re = 50,000 at the inlet while for the modified geometries the pressure ratio is held constant compared to the base.     

Flowfield and heat transfer past an unshrouded gas turbine blade tip with different shapes

This paper describes the numerical investigations of flow and heat transfer in an unshrouded turbine rotor blade of a heavy duty gas turbine with four tip configurations. By comparing the calculated contours of heat transfer coefficients on the flat tip of the HP turbine rotor blade in the GE-E³ aircraft engine with the corresponding experimental data, the κ-ω turbulence model was chosen for the present numerical simulations. The inlet and outlet boundary conditions for the turbine rotor blade are specified as the real gas turbine, which were obtained from the 3D full stage simulations. The rotor blade and the hub endwall are rotary and the casing is stationary. The influences of tip configurations on the tip leakage flow and blade tip heat transfer were discussed. It’s showed that the different tip configurations changed the leakage flow patterns and the pressure distributions on the suction surface near the blade tip. Compared with the flat tip, the total pressure loss caused by the leakage flow was decreased for the full squealer tip and pressure side squealer tip, while increased for the suction side squealer tip. The suction side squealer tip results in the lowest averaged heat transfer coefficient on the blade tip compared to the other tip configurations.     

Experimental Study of Parameters Affecting the Nusselt Number of Generator Rotor and Stator

In this research, the parameters affecting the Nusselt number of a generator rotor and stator under varying heat transfer rate are experimentally studied. In spite of the stator having no grooves, the rotor has four large triangular grooves. The temperature and then heat transfer rate of the rotor and stator are experimentally measured in three longitudinal and two angular positions. First, the effect of axial Reynolds number and rotor rotational speed on the rotor and stator Nusselt number with constant heat transfer rate ratio is studied. The range of the axial Reynolds number and rotational speed used is from 4000 to 30,000 and from 300 to 1500 rpm, respectively. Next, the effect of stator to rotor heat transfer rate ratio on the Nusselt number at constant axial Reynolds number and rotational speed is investigated. Three experiments were conducted at three heat transfer rate ratios (3, 5, and 8), defined as the ratio of heat transfer rate of the stator to the rotor. The results show that the higher the heat transfer rate ratio, the lower is the stator mean Nusselt number and the higher the rotor mean Nusselt number.     

Numerical modeling of heat transfer and fluid flow in rotor–stator cavities with throughflow

The present study considers the numerical modeling of the turbulent flow in a rotor–stator cavity subjected to a superimposed throughflow with heat transfer. Numerical predictions based on one-point statistical modeling using a low Reynolds number second-order full stress transport closure are compared with experimental data available in the literature [E.M. Sparrow, J.L. Goldstein, Effect of rotation and coolant throughflow on the heat transfer and temperature field in an enclosure, J. Heat Transfer 98 (1976) 387–394; M. Djaoui, A. Dyment, R. Debuchy, Heat transfer in a rotor–stator system with a radial inflow, Eur. J. Mech. B – Fluids 20 (2001) 371–398; S. Poncet, M.P. Chauve, R. Schiestel, Batchelor versus Stewartson flow structures in a rotor–stator cavity with throughflow, Phys. Fluids, 17(7) (2005).]. Considering small temperature differences, density variations can be here neglected which leads to dissociate the dynamical effects from the heat transfer process. The fluid flow in an enclosed disk system with axial throughflow is well predicted compared to the velocity measurements performed at IRPHE [S. Poncet, M.P. Chauve, R. Schiestel, Batchelor versus Stewartson flow structures in a rotor–stator cavity with throughflow, Phys. Fluids, 17(7) (2005)] under isothermal conditions. When the shroud is heated, the effects of rotation and coolant outward throughflow on the heat transfer have been investigated and the numerical results are found to be in good agreement with the data of Sparrow and Goldstein [E.M. Sparrow, J.L. Goldstein, Effect of rotation and coolant throughflow on the heat transfer and temperature field in an enclosure, J. Heat Transfer 98 (1976) 387–394]. Their results have been extended for a wide range of the Prandtl number. We have also considered the case of an open rotor–stator cavity with a radial inward throughflow with heat transfer along the stator, which corresponds to the experiment of Djaoui et al. [M. Djaoui, A. Dyment, R. Debuchy, Heat transfer in a rotor–stator system with a radial inflow, Eur. J. Mech. B – Fluids 20 (2001) 371–398]. Our results have been compared to both their temperature measurements and their asymptotic model with a close agreement between the different approaches, showing the efficiency of the second order modeling. An empirical correlation law is given to predict the averaged Nusselt number depending on the Reynolds and Prandtl numbers and on the coolant flowrate.     

Conjugated heat transfer investigation with racetrack-shaped jet hole and double swirling chamber in rotating jet impingement

A numerical study is performed to investigate the effects of jet hole shape and channel geometry on impingement cooling for both stationary and rotating condition. Two hole shapes and two channel geometries are introduced to counteract the adverse effects of centrifugal force and Coriolis force which are induced by rotation. Both the fluid and solid part are considered for realizing the conjugate heat transfer simulation. The unsteady k-ω SST turbulence model was employed to obtain the time-averaged Nusselt number distributions, time-averaged temperature and temperature gradient fields and the turbulent flow structure. The results show that the cooling jet from the racetrack-shaped hole can effectively withstand the intensive streamwise crossflow to enhance the heat transfer. The double swirling chamber (DSC) channel significantly improves the heat transfer characteristics on the cambered surface and diminishes the adverse effects of the Coriolis force. The high Nu number region is expanded while the temperature uniformity is improved. The combination of the racetrack-shaped hole and DSC channel provides the highest heat transfer among the four cases. The averaged Nu numbers on both the leading and trailing sides for all tested cases show obvious downtrend as rotation number increases, especially at high Reynolds number.     

燃气轮机叶片内部扰流肋冷却方式研究进展

随着燃气透平转子进口温度的不断提高,燃气轮机叶片冷却日益重要。带有扰流肋的内部通道冷却是叶片冷却的一个重要部分。综述了内部扰流肋冷却的研究历程与研究现状,详细论述了静止状态下带肋内部通道的换热研究、旋转对带肋通道内换热的影响研究以及扰流肋与其他方式相结合的复合冷却研究。结论指出,在国内外静止状态下带肋通道内的换热研究已经很成熟,旋转对通道内流动与换热的影响是最近几年来的研究热点,而关于旋转状态下复合冷却方式的研究相对较少。优化旋转状态下内部肋结构和将内部扰流肋与其他冷却方式相结合的研究是今后的发展方向。     

Conjugate heat transfer characterization in cooling channels

Cooling technology of gas turbine blades,primarily ensured via internal forced convection,is aimed towards withdrawing thermal energy from the airfoil.To promote heat exchange,the walls of internal cooling passages are lined with repeated geometrical flow disturbance elements and surface non-uniformities.Raising the heat transfer at the expense of increased pressure loss;the goal is to obtain the highest possible cooling effectiveness at the lowest possible pressure drop penalty.The cooling channel heat transfer problem involves convection in the fluid domain and conduction in the solid.This coupled behavior is known as conjugate heat transfer.This experimental study models the effects of conduction coupling on convective heat transfer by applying iso-heat-flux boundary condition at the external side of a scaled serpentine passage.Investigations involve local temperature measurements performed by Infrared Thermography over flat and ribbed slab configurations.Nusselt number distributions along the wetted surface are obtained by means of heat flux distributions,computed from an energy balance within the metal domain.For the flat plate experiments,the effect of conjugate boundary condition on heat transfer is estimated to be in the order of 3%.In the ribbed channel case,the normalized Nusselt number distributions are compared with the basic flow features.Contrasting the findings with other conjugate and convective iso-heat-flux literature,a high degree of overall correlation is evident.     

Average temperature of the rotor of high-speed rotating heat exchanger during the period of thermal start-up

The paper presents results of the calculations of the average temperature variations of model rotor of a high-speed rotating heat exchanger in the course of thermal start up. A model rotor adopted for the calculations has a porous structure formed by radially oriented ducts of a constant circular cross-section. The scope of this paper covers numerical calculations of temperature distribution in the material of the rotor versus its rotational speed, temperature difference of the gases at the inlet, and types of the rotor material. With the use of these results, graphs are elaborated representing the dependence of the rotor’s dimensionless temperature on the Fourier number, with the Biot number used as a parameter.     

Temperature Distribution and Heat Saturating Time of Regenerative Heat Transfer

In this paper, heat transfer of the ceramic honeycomb regenerator was numerically simulated based on the computational fluid dynamics numerical analysis software CFX5. The longitudinal temperature distribution of regenerator and gas were obtained. The variation of temperature with time was discussed. In addition, the effects of some parameters such as switching time, gas temperature at the inlet of regenerator, height of regenerator and specific heat of the regenerative materials on heat saturating time were discussed. It provided primarily theoretic basis for further study of regenerative heat transfer mechanism.