The performance of a Kaplan turbine in partial operation conditions is often limited by cavitation and stability, especially at the large flow rate operation conditions. Many problems such as vibration, efficiency dropping, cavitation, and blade cracks caused by unstable flow in each of the flow passage components of the turbine seriously affect the safe operation of the unit, and because of these problems, many power plants are forced to undergo downtime for repairs or renovation. In this paper, a model Kaplan turbine with a semi-spiral case was taken as the research object and the optimal operating point and a large flow rate operating point was chosen as the operating point for research. In order to reveal the reasons that cause the performance deterioration of the turbine at the large flow rate conditions, the comparative analysis of the Kaplan turbine performance at these two operating points was conducted by using the numerical simulation methods. It was found that the following factors caused the poor performance in the large flow rate conditions:1)In the spiral case, the discharge in the non-snail-shaped part was much more than the snail-shaped part relatively, the inertia of water made most of discharge flow into the guide vane at the non-snail-shaped part of the spiral case directly, this led to the axial symmetry of flow field distribution in the semi-spiral case along the circumferential direction deteriorate significantly, and all these imbalance hydraulic factors were passed to the guide vanes and runner, and could not be eliminated. 2) In the guide vane region, the flow distribution along the height direction of the guide vane was uneven, the flow rate increased from the top to the bottom of the guide vane, there were some vortices between the guide vanes located at the snail-shaped part of the spiral case, and these vortices between the guide vanes formed a circumferential unstable source, which not only can lead to the destruction of the guide vane surface, but also have an serious influence on the runner. 3) The destabilizing hydraulic factors generated in the spiral case and guide vanes could be transmitted to the flow passage components behind, lead to the poor axis of symmetry of the hydraulic elements in the runner, and make the blades located in different positions of the runner suffer different hydrodynamic moments. These produced alternating dynamic stress on the blades during rotating, and led to blade cracks and damage. Therefore, at the large flow rate conditions, all these instability hydraulic factors will cause a serious threat for the stability and strength of the unit. This research provides a reference for the Kaplan turbine hydraulic design and actual operating at the large flow rate conditions.%为了研究大流量工况下，轴流式水轮机机组振动严重、效率锐减、空蚀破坏严重、叶片产生裂纹等问题产生的原因，该文以某不完全蜗壳轴流转浆式水轮机模型为研究对象，对其最优工况及大流量工况进行了全流道数值分析，以揭示引起大流量工况下水轮机运行性能变差的主要原因，结果表明：水流惯性使大部分流量直接由非蜗形区域进入导水机构，蜗形区域过流量偏少，蜗壳内流场沿圆周方向分布的轴对称性变差，并且将这些不均匀性传递向下游；水流沿导叶高度方向分配不均匀，蜗形段的活动导叶叶道内产生叶道涡，形成圆周方向不均匀的非稳定源，并对下游转轮产生影响；蜗壳及导叶内的不均匀水力要素传递向下游，使得转轮内不同位置的叶片所受水力矩产生差异，转轮叶片在旋转过程中受交替动应力作用而容易产生裂纹和破坏。因此在大流量工况下，这些水力不稳定因素不仅限制了水轮机的运行范围，而且对机组的稳定性及强度产生威胁。该研究结果对轴流水轮机的水力设计以及大流量工况下的实际运行具有一定的参考意义。
展开▼
