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The features of unsteady flow such as pressure variation and fluctuation in a large hydraulic turbine usually lead to the instability of operation.This article reports the recent in site investigation concerning the characteristic frequencies in pressure fluctuation,shaft torsional oscillation and structural vibration of a prototype 700 MW Francis turbine unit.The investigation was carried out for a wide load range of 200 MW-700 MW in the condition of water head 57 m-90 m.An extensive analysis of both time-history and frequency data of these unsteady hydraulic behaviours was conducted.It was observed that the pressure fluctuation in a draft tube is stronger than that in upstream flow passage.The low frequency with about one third of rotation frequency is dominative for the pressure fluctuation in part load range.Also the unsteady features of vibration of head cover and torsional oscillation of shaft exhibited the similar features.Numerical analysis showed that the vibration and oscillation are caused by vortex rope in the draft tube.In addition,a strong vibration with special characteristic frequency was observed for the head cover in middle load range.The pressure fluctuation in the draft tube with the same frequency was also recorded.Because this special vibration has appeared in the designed normal running condition,it should be avoided by carefully allocating power load in the future operation.  相似文献
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通过实验研究了自激振荡脉冲射流重要参数相互之间的影响关系。实验结果表明:泵压升高,射流频率增加;腔长增大,射流频率降低;而且存在一个最佳腔长使脉冲射流压力峰值达到最大。实验结果与理论分析一致。  相似文献
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基于雷诺时均方程和RNG k-ε湍流模型,应用SIMPLE算法,对混流泵内部流场进行非定常数值模拟,分析不同工况监测点上压力脉动的时域特性和频域特性。取定常计算的外特性与实验值对比,对比结果为不同工况的扬程偏差均小于5%,证明该数值模型能准确地描述泵内流场特征。结果表明:叶片进口处水流冲击产生的回流和漩涡是引起叶轮内压力脉动的主要动力源,叶轮与蜗壳间的动静相干作用是产生蜗壳内压力脉动的主要动力,并且在向下游传播过程中,压力脉动逐渐减弱,叶频占主导地位,在小流量工况运行时,主频有向叶轮转频迁移的趋势,大流量工况下最大压力脉动发生在转轮中间位置;叶轮内的压力脉动要远远高于蜗壳,这是引起机组振动和噪声的主要来源。  相似文献
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为了能在大尺度范围内获得岩溶塌陷典型调查区覆盖层的厚度,采用微动法对柳州市柳城县东泉公社幅岩溶塌陷重点调查区进行了野外观测,并对调查区内已知的56处钻孔进行微动观测,提取特征频率,结合钻孔资料得出覆盖层厚度与特征频率的函数关系满足h =62.5/f。利用此函数关系,结合岩溶塌陷调查区野外微动实测数据提取的特征频率反演出覆盖层厚度。结果表明:该方法的尝试初步见效,经济快捷、适应性强、值得推广,特别适用于大尺度范围内调查岩溶塌陷区域覆盖层厚度分布,结合研究区的地质信息,可以在区域内对岩溶塌陷易发区做一个简单的评价。  相似文献
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