汽轮机相变区湿蒸汽异质凝结机理及非定常流动特性研究

The wet steam problem occurs within the steam turbine. Water droplets from the steam can erode turbine blades and cylinders, and 1% humidity can reduce stage efficiency by 1%, seriously affecting turbine safety and economy. In fact, in the steam turbine there are a large number of condensation cores and strong chemical reactions, which lead to heterogeneous condensation of impure steam. In addition, unsteady effects caused by complex flow phenomena in steam turbine such as dynamic and static interference and condensation shock wave will also affect heterogeneous condensation flow of wet steam. However, there is a lack of systematic research on the heterogeneous condensation mechanism and unsteady flow characteristics of wet steam in steam turbine. In this project, based on the condensation dynamics, both the heterogeneous dynamic condensation process and droplet growth process models of wet steam by considering the vaporization behavior of the liquid phase are modified by the means of theoretical analysis and visualization experiment, and the heterogeneous condensation phase transformation mechanism is further investigated under different impurity properties, different impurity concentrations, different steam expansion rates, etc. Combined with computational fluid dynamics, the characteristics of heterogeneous condensation flow of wet steam in the phase change area of steam turbine affected by the unsteady flow environment are analyzed, and the relationship between heterogeneous condensation flow and homogeneous condensation flow is established. The aim of this project is to reveal the heterogeneous condensation mechanism of wet steam and the unsteady movement law between steam and liquid in the phase transition zone of steam turbine. The research results are expected to provide theoretical guiding for reducing steam loss of steam turbine and inhibiting water erosion of blade.

湿蒸汽问题和汽轮机同时诞生，蒸汽中的水滴会侵蚀汽轮机叶片和汽缸并且1%的湿度会使级效率降低1%，严重影响汽轮机安全性及经济性。实际汽轮机蒸汽中有大量的凝结核心和强烈的化学作用，导致不纯蒸汽发生异质凝结，并且汽轮机动静干涉、蒸汽内部作用引起的非定常效应会导致不稳定异质凝结流动。然而，对汽轮机湿蒸汽异质凝结机理及非定常流动特性还缺乏系统研究。本项目基于凝结动力学，采用理论研究并辅以可视化实验手段，修正考虑液相蒸发行为的湿蒸汽异质动态凝结过程及水滴生长过程模型，研究不同杂质性质、不同杂质浓度、不同蒸汽膨胀速率等条件下的异质凝结相变机制；结合计算流体动力学分析汽轮机相变区非定常流动环境下的湿蒸汽异质凝结流动特征，建立湿蒸汽异质凝结流动与均质凝结流动之间的相互关系。旨在揭示汽轮机相变区湿蒸汽异质凝结过程机理和蒸汽与液相非定常运动规律，研究结果为减小汽轮机湿汽损失及抑制叶片水蚀奠定坚实的理论基础。

蒸汽发生非平衡相变凝结会侵蚀汽轮机叶片和汽缸，严重影响汽轮机安全性及经济性。为了研究汽轮机相变区湿蒸汽异质凝结机理及非定常流动特性，本项目首先在经典成核增长理论的基础上，对成核模型和液滴增长模型进行了修正并验证了其准确性；在均质凝结流动方程的基础上推导了异质凝结流动控制方程，建立了异质凝结流动数学模型，研究发现修正模型的模拟结果与实验结果吻合较好。之后基于修正后的数学模型，得到了影响Moses-Stein喷管、二维Dykas叶栅及真实汽轮机末级叶栅凝结动态过程和水滴生长过程的影响因素和规律，探究了湿蒸汽异质凝结过程的机理和凝结现象的本质，研究发现提高进口蒸汽过热度和降低膨胀速率可以降低非平衡凝结流动损失，膨胀速率、成核速率、液滴数和湿度随叶片高度的增加而减小。此外，由于凝结激波与湿蒸汽两相流动之间的相互作用可以使流场呈现出多种非定常流动特性，本项目还建立了考虑凝结激波影响的湿蒸汽凝结相变模型，得到了气动激波与凝结激波引起湿蒸汽凝结非定常效应的激波特性，揭示了考虑激波效应时汽轮机级内湿蒸汽凝结流动的非定常特性，研究结果表明进口温度降低和进口压力增加会使凝结激波强度提高，背压的增大降低激波干涉，使流场湿度降低。最后，本项目还研究了汽轮机低压级异质-均质凝结耦合流动，得到了异质凝结和均质凝结在有盐粒子存在时相互影响的凝结变化规律。分析了不同粒子初始浓度和粒径时汽轮机叶栅内异质凝结流动特点，得出了减少非平衡凝结热力学损失的方法。研究发现与均质凝结相比，异质凝结可以有效地改善湿蒸汽的流动状况，减缓非平衡凝结流动的程度。研究结果为减小汽轮机湿汽损失及抑制叶片水蚀奠定坚实的理论基础。项目资助共发表学术论文10篇，其中SCI收录6篇，EI收录3篇，会议论文1篇。项目执行期间共培养硕士研究生4名。