冲击式水轮机流动干涉特性及其对比尺效应影响研究

Pelton turbine, applied to high head and small discharge, has promising applications in the western China, in which rich of high head resources. However, the flow character and flow interference after the interaction of jet and impacted body is quite complex. Now it is still lack of scientific description and deeply research of the impact regularity. This application plans to investigate high head Pelton turbine, which aims at revealing hydrodynamic performance for typical unsteady 3D gas-liquid two-phase flow and flow interference in Pelton turbine by theoretical analysis, numerical simulation and experimental investigation. It will explore appropriate numerical models and methods for multi-phase flow such as free jet and free water sheet flow, which may be validated by experimental date. Also this application will investigate the unsteady flow behavior of three typical type of flow interference happened in Pelton turbine, including the interference between the bucket rear-surface and the jet, interference between the bucket rear-surface and the following bucket's outflow, and free surface water sheet flow interference. Internal flow patterns will be revealed and quantitative analysis of the influence of flow interference on unit hydrodynamic performance will be obtained. Thus it will come up with control methods to reduce unsteady flow interference. In addition, in operating regions where the flow interference is easy to happen, it will carry on numerical simulation of flow interference character both in the model and prototype turbine according to the model test and field test data. It will quantitatively analyze the relationship between the flow interference and scale effect and improve the scale effect theory of Pelton turbines. The summing-up of the fundamental problems of free jet and flow interference will offer theoretical basis for performance optimization and safe operation of high head Pelton turbine, which has important significance to efficient and safe utilization of high head water resource.

冲击式水轮机在高水头资源丰富的地区应用前景广泛，其流动干涉现象十分复杂，至今仍缺乏对其规律和比尺效应的科学描述与深入研究，仍是水力机械学科研究的热点和难点。本申请以高水头冲击式水轮机为研究对象，将理论分析、数值计算与试验相结合，旨在揭示机组内典型的三维非定常气液两相流及流动干涉的水动力学特性。探讨适合自由射流、水膜流等多流态的数学模型和数值方法，结合已有试验结果进行评价。探讨机组内典型流动干涉发生时的流动规律，如射流与水斗背面干涉，出流与水斗背面干涉，多喷嘴时水膜流干涉等，定量分析流动干涉对机组水动力特性的影响，进而提出改善流动干涉的方法。在易发流动干涉工况区，结合模型试验和现场实测，分别对模型与真机进行流动干涉特性的数值计算，定量分析流动干涉与比尺效应之间的关系，完善冲击式水轮机的比尺效应换算理论。研究可为冲击式水轮机的性能换算、优化设计与安全稳定运行提供理论基础。

我国水电开发主战场已转向西南高原河流，仅雅江大拐弯一处的可开发水能装机容量就占全国的10%，目前正依托其梯级开发，研制50万千瓦级、1000米以上超高水头大型冲击式水轮发电机组，而冲击式水轮机内部多态、多相流动特性、流动干涉、比尺效应等的准确研究仍不够深入。本项目开展的流动干涉特性及其对比尺效应影响研究具有重要理论意义和工程应用价值。发表论文33篇，其中SCI检索13篇，另EI检索论文16篇。.选取两套冲击式水轮机，基于均质多相流模型、SST k-omega双方程模型描述多相流场，深入探讨了CFL条件和网格收敛因子等对射流/水膜计算精度的影响，指出了精确模拟整体流道多种流态转换过程所需满足的离散关系，发展了包含管内流、喷嘴射流及水斗水膜流多种流态和流态转换的整体流道非定常多相流数值模拟方法，结合试验数据验证了计算的准确，研究成果在ISROMAC 2016国际会议分会场做了特邀报告。.基于该方法，系统分析了冲击式水轮机中的几种典型流动干涉及其对水力性能定量影响规律。水斗切割射流对射流的破坏导致水斗背面与射流接触位置会出现负压，该负压与背面挤压联合作用，引起水斗背面与射流间的干涉。在计算的低水头工况，流动干涉使转轮的水力效率降低约4%。此类干涉随运行水头的降低而加剧，适当减薄水斗缺口厚度可改善。对出流与水斗背面干涉，计算了水斗出流角和水头变化的影响。水斗在出水边出流角过大和高水头工况，更容易发生出流与水斗背面干涉。为避免对水斗背面的破坏，可适当减小水斗出流角或减薄水斗出水边的厚度。若将喷嘴数增至六，运行工况参数都不变，数值分析了水斗内两股水膜流动干涉现象产生机理及其对水力性能的影响。结果显示，喷嘴数增加使相邻射流进入同一水斗的时间间隔缩短，水斗先后接受的两股射流会在水斗表面碰撞，使此工况下机组水力效率降低10.91%，同时水斗内表面压力波动的幅值加剧，也会对水斗的安全性能造成极大威胁。.结合模型试验数据，对模型与真机的非定常流动特性进行了数值计算，比较了三组单位流量工况下，真机与模型机中流动干涉是否发生；根据IEC标准和模型试验结果，对比计算的原型、模型机水力效率，量化的分析了冲击式水轮机中影响比尺效应的主要因素，发现雷诺数的影响相对较大，而弗劳德数和韦伯数的影响也不可忽略。