低比转速水泵水轮机驼峰稳定性及其影响因素研究

发布时间：2018-04-15 23:16

本文选题：低比转速水泵水轮机 + 驼峰特性　；参考：《清华大学》2016年博士论文

【摘要】：高水头水泵水轮机的稳定运行是极其重要的,在水泵工况中的运行不稳定主要表现为驼峰特性。本文采用模型试验、数值模拟和理论分析相结合的手段对水泵水轮机的驼峰特性及其影响因素进行了研究,模型试验主要采用等比例缩尺的模型水泵水轮机为研究对象,利用叶轮进口的高速摄像观测空化形态及演变规律;数值计算采用2?-f湍流模型对不同工况点进行模拟以分析驼峰发生前后的内部流场,并基于二维简化模型的模拟总结旋转失速产生的原因并总结了旋转失速频率与导叶开度的经验公式;理论分析基于湍动能产生项的展开形式,对活动导叶内不同湍动能产生项的分布进行分析,总结驼峰发生时流动的主要不稳定特点。通过试验和计算分析可以发现,当驼峰发生时,主要观测到的现象为导叶区域出现的旋转失速,其特征为较低的旋转频率,在大开度下,此频率约为0.32倍的转频,随着开度的降低,该频率逐渐降低,在最小开度下,该频率降为0.066倍的转频;失速核在圆周上的个数随着导叶开度降低而减少。通过二维计算结果发现,旋转失速发生的原因是由于当前流道内的横向速度造成下一个流道内的压力降低,当导叶开度降低时,“旋转”所需要的横向速度增大,因此旋转失速频率降低,该频率与导叶开度的正弦值成正比关系。通过数值计算,还分析了压力脉动在机组内不同位置的分布规律。试验和计算结果表明,空化对驼峰特性的影响随着导叶开度的变化而变化,在大开度下,叶轮进口压力面的空化主要对驼峰起到削弱作用;在中等开度下,进口吸力面的片状空化对驼峰特性基本没有影响;而在小开度下,进口吸力面的脱流空化主要使驼峰特性提前发生,空化对外特性的影响主要取决于空化发生的区域和形态。通过分析不同湍动能生成项的分布规律,总结了驼峰发生时旋转失速对流动产生的影响,主要是造成反向速度也即回流,其次是造成较大速度梯度,再次是使局部速度增加,当驼峰发生时,导叶区流动的三维特性也明显提升。综上所述,本文对水泵水轮机的驼峰特性产生和发展过程中的稳定性进行了研究,并对其影响因素进行了分析,为运行过程中减小驼峰对机组的影响提供了参考依据。
[Abstract]:The stable operation of high head pump turbine is very important.In this paper, the hump characteristics of pump turbine and its influencing factors are studied by means of model test, numerical simulation and theoretical analysis.The cavitation morphology and evolution law were observed by using high-speed camera at the inlet of impeller, and the internal flow field before and after hump was analyzed by numerical simulation using 2ka-f turbulence model to simulate different working conditions.Based on the simulation of two-dimensional simplified model, the causes of rotating stall are summarized, and the empirical formulas of rotational stall frequency and guide blade opening are summarized, the theoretical analysis is based on the expansion form of turbulent kinetic energy production term.The distribution of turbulent kinetic energy in the active guide vane is analyzed, and the main unstable characteristics of the flow during the hump are summarized.Through test and calculation analysis, it can be found that when the hump occurs, the main phenomenon observed is the rotating stall in the guide vane area, which is characterized by a lower rotation frequency, which is about 0.32 times of the rotation frequency at large opening.With the decrease of opening, the frequency decreases gradually, at the minimum opening, the frequency decreases by 0.066 times, and the number of stall nuclei on the circumference decreases with the decrease of the opening of the guide vane.The results of two-dimensional calculation show that the reason for the stall is that the pressure in the next channel is reduced due to the transverse velocity in the current channel, and the lateral velocity required for "rotation" increases when the opening of the guide vane decreases.Therefore, the rotational stall frequency is decreased, and the frequency is proportional to the sinusoidal value of the guide vane.The distribution of pressure pulsation in different positions of the unit is also analyzed by numerical calculation.The experimental and calculated results show that the effect of cavitation on hump characteristics changes with the change of guide vane opening, and the cavitation of impeller inlet pressure surface mainly weakens the hump at wide opening, and at medium opening,The flake cavitation of the inlet suction surface has no effect on the hump characteristics basically, but the deswelling cavitation of the inlet suction surface mainly causes the hump characteristics to occur ahead of time, and the external characteristics of cavitation mainly depend on the region and form of cavitation.By analyzing the distribution of different turbulent kinetic energy generation terms, the effect of rotational stall on the flow during hump is summarized, which mainly results in reverse velocity, that is, reflux, followed by large velocity gradient, and local velocity increase.When the hump occurs, the three-dimensional characteristics of the flow in the guide vane area are obviously improved.To sum up, this paper studies the stability of hump characteristics and development of pump turbine, and analyzes the influencing factors, which provides a reference for reducing the hump effect on the unit during operation.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TV743;TV734

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