高水头混流式水轮机转轮泥沙磨损特性模拟研究

Numerical study of hydro-abrasive erosion in high-head Francis turbine runner

泥沙磨损是导致混流式水轮机组失效的主要原因之一,特别在水头相对较高时,由于内部流速相对也较高,其磨损问题会更为严重。为研究混流式机组转轮磨损的形成机理,本文根据电站泥沙实测数据统计得到汛期的泥沙平均浓度和粒径,对高水头混流式水轮机在最优开度和小开度两种工况下的固液两相流特性进行数值计算,基于拉格朗日方法模拟颗粒的运动轨迹,选取Oka模型对转轮的磨损特性进行了预测。通过分析转轮内的流动特性、颗粒的运动轨迹和壁面冲击特性,对混流式机组转轮磨损形态的形成原因进行了探讨,并将计算结果与文献中的实际磨损情况进行对比分析。预测的结果表明:采用欧拉-拉格朗日方法可较好地对混流式水轮机转轮的主要磨损区域进行定性的预测;在小导叶开度的偏工况时,转轮内部的涡旋流特性会导致颗粒产生局部富集等现象,从而引起对应区域磨损速率的增加。

Sediment wear is one of the main causes of Francis turbine failure.For a high-head turbine unit,its sediment erosion rate can be greatly enhanced due to relatively high velocities of its internal flow.To study the sediment erosion mechanism of Francis turbines,in this paper we first obtain the average concentration data and particle size data for the sediment flows in a high-head turbine at a hydropower station based on field measurements,and simulate its characteristics of two-phase flows in the conditions of optimal openings and small openings of its guide vanes.Then,we calculate the trajectories of sediment particles using a Lagrangian method and numerically predict the runner erosion patterns using the Oka model.The erosion mechanism is explored through an analysis on flow characteristics,particle trajectories,and wall impact characteristics;simulation results are verified by comparing with previous studies in the literature.Results show the Eulerian-Lagrangian method gives satisfactory qualitative predictions of the erosion patterns.Under the condition of small guide vane openings,the vortex core developed in the runner passage leads to sediment particles conglomerating,thus intensifying the erosion around the corresponding locations.