大型混流式水轮机模型内部流动稳定性研究

发布时间：2018-07-12 16:59

本文选题：混流式水轮机 + PIV　；参考：《哈尔滨工业大学》2014年博士论文

【摘要】：随着电力需求的不断增长，混流式水轮机逐渐向高转速、大容量以及高水头方向发展。单机容量的增大、转速的提高，导致机组的水力设计呈现高比转速的发展趋势，空化引起的两相流流动稳定性问题逐渐得到重视。本文针对高水头大容量混流式水轮机中普遍存在的空化两相流流动稳定性问题，采用内部流场实验测试、能量特性测试以及数值模拟相结合的手段展开研究。为了实现对混流式水轮机内部流场的粒子成像测速仪（PIV）测量，，建立了局部部件透明的模型混流式实验台，设计了可以观察转轮内部流场并且满足强度要求的透明转轮，加工了便于测量无叶区流场的带有透明有机玻璃视窗的蜗壳、固定导叶和活动导叶等部件，最后基于实验台循环回路建立了PIV实验台测控系统，监测机组的流量、转速、压力以及输出功率等参数，并建立了PIV相位锁定方法以详细分析内部流场的演化规律。通过对无叶区附近流场、叶道涡、叶片表面脱流空化以及尾水管涡带的实验研究，发现：实验测试工况下，活动导叶吸力面流场的变化周期与叶片通过频率有关，其周期性变化是造成无叶区压力脉动的主要原因；尾水管涡带的旋转周期呈现低频特征；转轮内部的叶道涡流动演化的主频为叶片通过频率；叶片进口边背面脱流空化具有高频演化特征，其主频为导叶通过频率。为了详细分析混流式水轮机机组内部的叶道涡、尾水管涡带的流动特征，采用了大涡模拟（LES）方法和基于蒸发/凝结空化模型的计算方法，对模型混流式水轮机的外特性、内流场等进行了数值预测。在任意活动导叶开度下，采用空化两相流计算的外特性结果与实验对比吻合度高，而单相流计算结果与实验值误差较大；在额定工作开度下，转轮出口不存在强旋流流动形态，可以有效地改善尾水管入口流动，降低尾水管的压力脉动；开度较小时，尾水管涡带存在复杂的双涡带现象。为了研究混流式水轮机机组内部流场的流动稳定性，基于数值模拟方法预测了机组内部的压力脉动，捕捉了压力脉动的频谱特征及演化规律，同时基于曲线坐标系下的湍动能输运方程对混流式水轮机无叶区流场的流动稳定性进行了研究。结果表明：不同开度不同工况下，混流式水轮机无叶区的压力脉动主频均为叶片通过频率，次频均为叶片通过频率的两倍频；随着开度增加，尾水管入口处的压力脉动高频分量越来越明显。通过对湍动能在无叶区分布的研究，发现影响流动稳定的主要因素是正应力生成项和切应力生成项；导叶开度较小时，无叶区压力脉动的提高主要是由于活动导叶尾迹流造成的，当活动导叶开度较大时，无叶区压力脉动的提高主要由于活动导叶尾迹流受转轮的干涉作用造成。另外，活动导叶开度较小时，活动导叶的尾迹流动直接影响湍动能正应力生成项大小，而活动导叶开度较大时，转轮叶片的干涉作用造成接近转轮处的湍动能正应力生成项变化较大；故湍动能生成项中影响流动稳定的主要因素是正应力生成项和切应力生成项，弯曲应力生成项以及三维生成项在湍动能生成项中的比例较小。本文研究结果阐明了混流式水轮机无叶区、转轮内部以及尾水管中的流动稳定性问题，对水轮机工程设计具有重要的指导意义。
[Abstract]:With the increasing demand for electric power, the mixed flow turbine is gradually developing towards high speed, large capacity and high head. The increase of the capacity of the single machine and the increase of the speed result in the development trend of the hydraulic design of the unit, and the stability of the two phase flow caused by cavitation is gradually paid attention to. This paper is aimed at the large capacity of high water head. The problem of the stability of the cavitation two phase flow in a mixed flow turbine is studied. The experimental test, the energy characteristic test and the numerical simulation are used to study the flow stability of the cavitation two phase flow.
In order to realize the particle imaging velocimeter (PIV) measurement for the internal flow field in a mixed flow turbine, a transparent model mixed flow test bench with transparent local components is established. A transparent wheel can be designed to observe the internal flow field and meet the requirements of the strength. In the end, the measurement and control system of PIV test bed was established based on the loop loop of the experimental platform. The parameters of the flow, speed, pressure and output power of the unit were monitored, and the PIV phase locking method was established to analyze the evolution of the internal flow field. The experimental study of cavitation and the tail pipe vortex belt shows that the change period of the flow field of the active guide blade is related to the frequency of the blade through the experimental test. The periodic change is the main cause of the pressure pulsation in the vaneless zone; the rotation period of the tailpipe vortex belt presents low frequency characteristics and the evolution of the blade vortex flow inside the runner. The main frequency is the blade passing frequency, and the cavitation at the back edge of the blade inlet has the characteristics of high frequency evolution, and its main frequency is the guide blade passing frequency.
In order to analyze the flow characteristics of the Ye Daowo and the tailpipe vortex belt in a mixed flow turbine unit, the large eddy simulation (LES) method and the calculation method based on the evaporation / condensation cavitation model are used to predict the external and internal flow fields of the model mixed flow turbine. The cavitation two phases are adopted under the arbitrary guide leaf opening. The external characteristic results of the flow calculation are in good agreement with the experimental comparison, but the calculation results of the single-phase flow are in great error with the experimental values. Under the rated working degree, there is no strong swirling flow in the outlet of the runner, which can effectively improve the inlet flow of the tail pipe and reduce the pressure pulsation of the tail pipe. Vortex band phenomenon.
In order to study the flow stability of the flow field in a mixed flow turbine unit, the pressure pulsation in the unit is predicted based on the numerical simulation method, and the spectrum characteristics and the evolution law of the pressure fluctuation are captured, and the flow stability of the flow field in the mixed flow turbine is carried out based on the turbulent kinetic energy transport equation in the curvilinear coordinate system. The results show that under different operating conditions, the main frequency of pressure pulsation in the non leaf area of the mixed flow turbine is the passing frequency of the blade, and the secondary frequency is two frequency doubling of the blade passing frequency. With the increase of the opening, the high frequency component of the pressure pulsation at the entrance of the draft tube becomes more and more obvious. The main factors that affect the stability of the flow are the generation of positive stress and the generation of shear stress. The increase of the pressure fluctuation in the non leaf area is mainly due to the wake of the active guide leaf. When the opening of the guide leaf is large, the increase of the pressure fluctuation in the non leaf area is mainly due to the interference of the wake of the moving guide blade. In addition, the motion guide leaf's wake flow directly affects the magnitude of the positive stress generation of the turbulent kinetic energy, and the interference effect of the rotor blade leads to a larger change in the positive stress generation of the turbulent kinetic energy near the wheel, so the main factors affecting the stability of the turbulent kinetic energy generation are the main factors. The normal stress generation term and the shear stress generation term, the bending stress generation term and the three-dimensional generation term are smaller than those in the turbulent kinetic energy generation term.
The results of this study illustrate the flow stability in the vaneless area of the Francis turbine, the inner of the runner and the tail pipe, which are of great guiding significance to the engineering design of the turbine.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TK733.1

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