Mist film cooling simulation at gas turbine operating conditions

Air film cooling has been successfully used to cool gas turbine hot sections for the last half century. A promising technology is proposed to enhance air film cooling with water mist injection. Numerical simulations have shown that injecting a small amount of water droplets into the cooling air improves film-cooling performance significantly. However, previous studies were conducted at conditions of low Reynolds number, temperature, and pressure to allow comparisons with experimental data. As a continuous effort to develop a realistic mist film cooling scheme, this paper focuses on simulating mist film cooling under typical gas turbine operating conditions of high temperature and pressure. The mainstream flow is at 15 atm with a temperature of 1561 K. Both 2D and 3D cases are considered with different hole geometries on a flat surface, including a 2D slot, a simple round hole, a compound-angle hole, and fan-shaped holes. The results show that 10–20% mist (based on the coolant mass flow rate) achieves 5–10% cooling enhancement and provides an additional 30–68 K adiabatic wall temperature reduction. Uniform droplets of 5–20 μm are used. The droplet trajectories indicate the droplets tend to move away from the wall, which results in a lower cooling enhancement than under low pressure and temperature conditions. The commercial software Fluent is adopted in this study, and the standard k–ε model with enhanced wall treatment is adopted as the turbulence model.     

Numerical Simulation on Turbine Blade Leading-Edge High-Efficiency Film Cooling by the Application of Water Mist

Numerical simulation is performed to explore leading film cooling enhancement by the application of injecting water mist into the air. The accuracy of numerical simulation program for conjugate heat transfer methodology is verified with the C3X gas turbine vanes cooled with leading edge films. The effect of various parameters including mist concentration, mist diameter, different particle wall interactions conditions, and different forces on the improvement of cooling performance is investigated in this paper. It indicates that mist film cooling can decrease the temperature of boundary layer without impact on the temperature of the mainstream and the thickness of boundary layer.     

Mist/steam cooling by a row of impinging jets

Mist/steam cooling has been studied to augment internal steam-only cooling for advanced turbine systems. Water droplets generally less than 10 μm are added to 1.3 bar steam and injected through a row of four round jets onto a heated surface. The Reynolds number is varied from 7500 to 22,500 and the heat flux varied from 3.3 to 13.4 kW/m². The mist enhances the heat transfer along the stagnation line and downstream wanes in about 3 jet diameters. The heat transfer coefficient improves by 50-700% at the stagnation line for mist concentrations 0.75-3.5% by weight. Off-axis maximum cooling occurs in most of the mist/steam flow but not in the steam-only flow. CFD simulation indicates that this off-axis cooling peak is caused by droplets’ interaction with the target walls.     

工况不确定性对汽轮机末两级气动性能的影响研究

汽轮机运行条件存在随机波动性,对汽轮机的稳定运行造成一定影响。以往的研究多将汽轮机的工作环境条件作为确定因素,未考虑其随机变化的影响。本文将汽轮机背压、径向气流角和进口流量作为服从一定概率分布的随机变量,采用多项式混沌方法结合计算流体力学（CFD）模拟仿真,研究了以上参数的随机波动对某汽轮机末两级叶片气动性能的影响。结果表明：计算进口边界条件的设置方法对汽轮机末两级总体性能的计算结果影响不大,当给定进口流量边界条件时,末两级效率的计算结果最高;在接近堵塞工况时,进出口条件的随机变化对通流流量的影响不大,但效率存在明显的波动,进口气流角对总体性能的影响相对较小;当背压和进口流量存在随机波动时,末级动叶中激波位置小范围波动,激波位置对径向气流角的波动不敏感。     

双层壁叶片的模型化方法与冷却设计流程研究

提出了一种适用于双层壁叶片的冷却设计流程。沿叶片的叶高和流向抽象提取出简单冷却单元,对其建立一维管网模型并进行多次管网计算,得出各个单元最优的冷却结构方案。将设计好的冷却单元映射回实际叶片中,并对叶片建立一维管网模型,经过多次冷却结构调整与计算迭代,得到叶片初步的冷却结构。对该叶片进行三维气热耦合计算,只需要局部冷却结构微调和少量的CFD计算,就可以得出最终的冷却设计方案。最终设计的叶片CFD计算得到的平均温度为1 049 K,总冷气量为0.288 kg/s,与管网计算结果1 059 K和0.337 kg/s相近。该设计流程方法简便,准确性高,人工工作量和仿真计算量小,优于传统的涡轮冷却设计流程。     

带有冷气掺混的三级透平气动性能数值研究

借助NUMECA数值仿真软件,以某型燃气轮机的三级透平作为计算模型,对其在冷却气体掺混前后的流场进行了数值模拟。考虑到工质物性的影响,采用了变比热高温燃气作为计算工质。同时,针对燃气轮机透平进口的变工况问题,选取不同的透平进口总压值进行数值计算。结果表明,冷却气体的加入使得级损失增大,每列叶片流道出口速度或相对速度减小,下游叶片进口气流角减小;在三级透平冷气掺混时改变进口总压值,每列叶片流道的进口气流角几乎不变,除第三级动叶的激波损失与尾迹损失增大外,其余叶片流道的能量损失变化不明显。     

Numerical modeling of gland seal erosion in a geothermal turbine

Excessive erosion of the low-pressure rotor end gland seal of a 25 MWe geothermal turbine produced a partial loss of turbine vacuum that degraded cycle efficiency. This study used computational fluid dynamics (CFD) to identify the causes of erosion and the optimal steam seal system flow conditions for reducing the erosion problem. The predictions were based upon a numerical calculation using a commercial CFD code (Adapco Star-CD) to model the rotor end gland seal with a steam flow containing hard solid particles. The results confirmed that flow conditions play a major role in rotor gland seal erosion. By changing steam seal flow pressures to vary flow, it was confirmed that there is a threshold seal flow condition below which erosion does not occur, or is minimized. Optimizing the rotor end gland seal supply pressure and intercondenser pressure reduced the turbulent flow kinetic energy by 49%, with a corresponding decrease in the erosion rate of the rotor gland seal surface. The erosion rate is related directly to the particle velocity and turbulent flow kinetic energy. Recommendations are provided for adjusting the rotor end gland seal system to avoid erosion.     

Effect of aspect ratio on the flow and heat transfer characteristics of mist/steam in rectangular ribbed channels

The effects of Reynolds number from 10,000 to 80,000, mist mass ratios from 1 to 6%, and droplet sizes from 5 to 20?µm on flow and heat transfer behaviors of mist/steam in rectangular channels with various aspect ratios of 1/4, 1/2, 1/1, 2/1, and the rib angle of 60° are numerically studied in this paper. Additionally, secondary flow distribution in the four ribbed channels and its effect on heat transfer are analyzed in detail. The 3D steady Reynolds-averaged Navier–Stokes equations with a SST k-ω turbulent model are solved by using ANSYS CFX. The CFD model has been verified by the experimental data for steam-only case with a good agreement. The results indicate that similar secondary flow pattern can be observed in the four ribbed channel except for the size of main secondary flow; the heat transfer augmentation of mist/steam raises as Reynolds number and mist mass ratio increase; a peak value of average Nu is obtained in the case of 15?µm mist among all the sizes of droplets. The friction coefficient decays with increase of Reynolds number and mist mass ratio but is insensitive to droplet sizes. The case of AR?=?1/2 obtains the best thermal performance in mist/steam cooling channels.     

PG6551(B)燃气轮机进气冷却系统的研制

开发了一种可全年利用烟气余热的联合循环双工况燃气轮机进气冷却系统。在气温高、进气冷却系统投用的情况下，能有效增加燃气轮机出力；在气温低、低压加热器投用的情况下，通过回收烟气余热，增加余热锅炉出力，提高蒸汽轮机负荷。介绍了进气冷却系统的工作原理，分析了进气冷却运行方式的初步运行结果。     

Two-phase flow simulation of mist film cooling with deposition for various boundary conditions

Air film cooling is a conventional cooling technique that has been successfully used for gas turbine hot-section components, such as combustor liners, combustor transition pieces, and turbine vanes and blades. However, the increased benefit seems to approach a limit. This paper investigates the film cooling effectiveness considering mist injection. All the studies for various boundary conditions are conducted numerically, including the effects of droplet size, the flow rates of droplet injection, and the coolant air. Film cooling is also affected by the interaction between deposition and mist injection. A deposition configuration is located near the film hole with an inclination angle of 35°. Results show that the combined effect of injection and deposition is to weaken the film cooling effectiveness, especially upstream of x/d?=?19. For the coolant air at a low speed, the mist injection cannot provide better cooling protection than without the mist injection.     

Numerical simulation of a hydrogen fuelled gas turbine combustor

The interest for hydrogen-fuelled combustors is recently growing thanks to the development of gas turbines fed by high content hydrogen syngas. The diffusion flame combustion is a well-known and consolidated technology in the field of industrial gas turbine applications. However, few CFD analyses on commercial medium size heavy duty gas turbine fuelled with pure hydrogen are available in the literature. This paper presents a CFD simulation of the air-hydrogen reacting flow inside a diffusion flame combustor of a single shaft gas turbine. The 3D geometrical model extends from the compressor discharge to the gas turbine inlet (both liner and air plenum are included). A coarse grid and a very simplified reaction scheme are adopted to evaluate the capability of a rather basic model to predict the temperature field inside the combustor. The interest is focused on the liner wall temperatures and the turbine inlet temperature profile since they could affect the reliability of components designed for natural gas operation. Data of a full-scale experimental test are employed to validate the numerical results. The calculated thermal field is useful to explain the non-uniform distribution of the temperature measured at the turbine inlet.     

船用核汽轮机装置仿真研究

建立了适合船用核汽轮机装置实时仿真分析计算的两相流仿真模型。利用该仿真模型对快速变负荷工况下船用核汽轮机装置的动态特性进行了计算分析。结果表明,该模型能准确模拟核汽轮机装置的变负荷运行特性,满足核动力二回路系统实时仿真分析要求。模型已经成功应用于两型船用核动力训练模拟器的开发,对操纵人员的培训及操作规程的验证具有重要意义。     

长短叶片水轮机转轮气液两相流的数值模拟

为降低水轮机运行过程中的空化现象并提高经济效率,以长短叶片混流式水轮机HLA351 LJ 170原型机为研究对象,采用完整的空化流模型和商用CFD软件FLUENT中的Mixture多相流无滑移模型,在大流量工况下对长短叶片混流式水轮机进行了气液两相流数值模拟。计算结果表明,该工况下长短叶片水轮机转轮流速、压力分布合理,水力性能较好。由此预测了长短叶片水轮机空化发生的部位和程度,对水轮机优化设计或改型等具有重要的指导意义。     

500MW汽轮机蒸汽冷却改造的数值分析

为了降低转子由高温蠕变导致的永久弯曲变形速率,以俄制500 MW汽轮机对称进汽结构中压转子的冷却装置为研究对象,利用Fluent软件分析了不同冷却蒸汽流量对再热蒸汽流场的干扰程度以及对机组热效率的影响.在不同冷却蒸汽温度下,对转子前两级的表面温度分布以及转子的高温蠕变速率进行了计算.结果表明:当冷却蒸汽流量在20 t/h以下时,其对再热蒸汽流场的影响很小;冷却蒸汽的最小流量应该大于0.65 t/h,否则在第一级叶轮根部会发生蒸汽逆向流动;当冷却蒸汽流量在允许范围内变化时,流量对转子的冷却效果影响不大,影响转子温度场的主要因素是冷却蒸汽温度;当冷却蒸汽温度分别为470℃、480℃和490℃时,可以分别使转子的安全运行时间延长至19.0年、14.3年和11.0年.     

透平叶片的气动优化设计系统

发展了一个叶轮机械叶片全三维粘性杂交问题的气动优化设计系统。该系统包括分析技术与组合优化技术的耦合：前者基于高精度、鲁棒型的数值分析方法，已成功地用于蒸汽透平叶片的流动分析．并经详细考核已将其纳入到了实际的叶片气动设计体系；后者基于优秀的iSIGHT商用优化平台．通过对多种优化方法的集成从而发展了组合的叶片全三维气动优化策略。数值结果与试验数据的比较表明了这一气动优化设计系统真正纳入到工业设计体系是完全可能的。     

基于图形组态的汽轮机振动与故障设置仿真建模

针对汽轮机振动的全工况仿真，讨论了一种基于图形组态的汽轮机振动与故障设置的数学模型，提出了一种可扩充的故障设置方法，并就油膜振荡故障和大轴弯曲故障的设置给出了适用于培训用汽轮机振动仿真建模的数学模型。     

汽轮机转子蒸汽冷却计算模型构建研究

提高初参数是火力发电实现节能与环保两项国策的重要措施。在蒸汽初温提高的条件下,为确保汽轮机部件的强度与寿命,需要在提高材料耐热性的同时采取蒸汽冷却技术,降低转子的温度与热应力。针对工程要求计算方法快捷、精确的特点,本文构造了转子根部冷却的一维参数计算模型,该模型综合考虑了冷却蒸汽对叶片表面的射流冲击冷却以及冷却蒸汽流过转子根部时的热传导冷却。应用该模型计算了超临界机组中压缸第一级转子经冷却后的温度场,并与三维计算结果比较,证明该模型能满足工程要求。     

船舶饱和蒸汽轮机动态特性仿真

介绍了船舶饱和蒸汽轮机功率、转速全工况实时仿真模型。该模型基于各守恒定律和水蒸汽物性,考虑了蒸汽的可压缩性、机内实际膨胀过程和调节级变工况特性的影响。仿真结果表明该模型稳态精度高、动态趋势合理,适用于核动力装置全工况范围正常运行和异常事故运行,此模型已在一台船舶核动力装置模拟器上得到了成功的应用。     

基于CFD的水电站厂房水力振源模拟研究

传统的水力振源特性研究主要依赖于模型试验,计算方法亦过于简化。通过建立水轮机全流道模型,基于CFD计算软件,对正常工况下的厂房进行了流体计算,总结了蜗壳壁面压力脉动的变化、分布规律及数值大小,进而根据CFD计算结果拟定了5种水力振源施加方案,并利用谐响应算法计算了厂房楼板、机墩、风罩等薄弱部位的振动响应情况,认为可根据流体计算结果在蜗壳内壁不同部位施加相应简谐荷载;且在流体计算结果中提取厂房蜗壳壁面各点的压力脉动数值,采用时程分析法施加于蜗壳对应节点,观察厂房结构振动响应情况,给出了水电站厂房水力振源更加精确、合理的模拟与施加方式。     

Performance prediction of an improved air-cooled steam condenser with deflector under strong wind

For an air-cooled steam condenser (ACSC), environmental wind can cause a large flow rate reduction in the axial fans mainly near the windward side of the air-cooled platform due to cross-flow effects, resulting in a heat transfer reduction. This leads to an increase of turbine back pressure, and occasional turbine trips occur under extremely gusty conditions. A new method is proposed in this paper to remove the strong wind effect by adding deflecting plates under the air-cooled platform, which contributes to forming a uniform air mass flow rate in the axial fans by leading enough cooling air to the fans in the upwind region. Numerical simulation is made of the thermal-flow characteristics and heat transfer performance of the improved ACSC with deflectors. A heat exchanger model is used for simulating the flow and heat transfer in the ACSC, in which the heat exchanger is simplified to a porous medium and all flow losses are taken into account by a viscous and an inertial loss coefficient. A fan model is used for reaching the flow condition at the heat exchanger inlet with the actual performance curves of the fan. It is found that the improved ACSC with deflector shows a significant enhancement in both the cooling air mass flow rate and the heat rejection rate compared with the conventional ACSC. The higher the wind speed is, the larger the heat transfer enhancement of the improved ACSC is. The effect of the plate inclination is also investigated, and the inclination angle of 45° is found to be the optimum value for the arrangement of the deflector.