【作者】 宋慧芳；

【导师】 高学平；

【作者基本信息】 天津大学 ， 水力学及河流动力学， 2007， 博士

【摘要】 扩散流是水工建筑物中常见的水流现象,如抽水蓄能电站上/下水库的进/出水口、有压泄水隧洞的出水口等的水流运动大多属此类流动。在一定边界和较大扩散角条件下,扩散流在边壁处将发生流动分离,一旦扩散水流与边界分离,近边界处将发生漩涡运动;扩散流的主流部分,在漩涡的不稳定位移或其它微小的扰动下,将形成不稳定的横向摆动运动。在恒定流条件下,扩散段内主流部分发生横向摆动运动的现象,我们称之为局部非稳态流动现象。由于局部非稳态流动发生的区域并不局限在边界附近,因此,对水工构造物可能产生的不利影响就较为突出。然而,相对其重要性而言,现今对局部非稳态流动现象的研究,却极为有限。针对扩散段中存在的局部非稳态流动现象,本文通过模型试验、数值模拟以及理论分析,对其形成条件、产生机理、运动规律等问题进行了较为系统的研究。(1)某抽水蓄能电站上水库进/出水口模型试验研究。结合某抽水蓄能电站上水库进/出水口物理模型试验,采用ADV三维流速仪,对抽水工况下进/出水口拦污栅处的流速进行测量,同时采用频谱分析,对数据资料进行分析,探讨各点流速的特征,揭示了该有压扩散流中存在局部非稳态流动现象。(2)有压扩散段局部非稳态流动专门试验研究。对不同平面扩散角的有压扩散段进行试验,研究在一定边界条件下扩散段内产生局部非稳态流动现象的运动特征。应用壁面丝线流动显示技术,对其流动过程进行观测研究;应用ADV三维流速仪记录特征点的流速历时,对测点流速进行分析。探讨局部非稳态流动的运动规律、产生机理及形成条件。(3)有压扩散段局部非稳态流动数值模拟研究。利用大涡模拟技术,系统研究了有压扩散段内整个流场的变化和发展情况,并结合谱分析方法对恒定有压扩散段中的水流流动特性进行分析,并与试验结果进行比较。(4)有压扩散段局部非稳态流动理论分析。对试验结果和数值模拟结果进行理论分析,结果表明,一定边界条件下扩散流主流将与边壁分离,并在壁面附近形成不稳定的漩涡区。在这些不稳定漩涡的影响下,流体的主流部分将随着漩涡主体的不规则运动而发生摆动运动,即出现恒定流中的局部非稳态现象。也就是说在有压扩散流中,不仅存在随机的水流脉动,还存在由大涡运移引起的低频拟序的主流整体摆动运动,一般情况下,主流的摆动运动和水流的随机脉动相比具有较低的主频率和较大的摆动幅值,并遵循一定的规律性。更多还原

【Abstract】 Divergent current is one common flow phenomenon in hydraulic structures, for example the flow movement in intakes/outlets of a pumped-storage power station, outlets of pressure discharge tunnel and so on. Under given boundary condition, flow separation would occur near the boundary. Once the flow separates from the boundary vortex would appear, and under the action of unsteady displacement of the vortex or other little disturbance the major flow would develop to unstable lateral swings. The phenomenon of main flow swinging laterally in divergent segment is called local unsteady-state flow. Due to the region of local unsteady-state flow being not localized near the boundary, the harmful effects of the flow to structures would be evident. However, compared with its importance, the study on the local unsteady-state flow is scarce.The forming condition, forming mechanism and movement rules of the phonomenon of local unstable-state flow in divergent segment are systemically studied in this paper, according to physical test, numerical simulation and theoretical analysis.(1) The model experiment study on intakes/outlets of one pumped-storage power station. In the model test of intakes/outlets of one pumped-storage power station, ADV 3-D velocity metre is used to measure the velocity at the outlets under the pumping condition, and through frequency spectrum analysis of data gained, the velocity characters of each point is discussed, the phenomenon of local unsteady-state flow existing in the pressure divergent flow is revealed.(2) The experimental study on local unsteady-state flow in pressure divergent segment. Based on the pressure divergent segment experiment of different divergent angle, the motion characters of local unsteady-state flow appeared in divergent segment under given boundary condition is studied. The flow pattern is observed by silk thread affixed to the wall, and the velocity duration course of characteristic points recorded by ADV 3-D velocity metre is analysed. The forming condition, forming mechanism and movement rules of the local unsteady-state flow are discussed.(3) The numerical simulation study on local unsteady-state flow in pressure divergent segment. The movement and development of whole flow field in pressure divergent segment are given through large eddy simulation, flow characters are analysed by spectrum analysis, and the results are compared with the experiment result.(4) The theoretical analysis of local unsteady-state flow in pressure divergent segment. The results of theoretical analysis on results of experiment and numerical simulation show the main flow of divergent flow would separate from the boundary, and form the unstable vortex region near the boundary. Under the effect of these unstable vortexes, the main flow would swing with the irregular movement of vortex, the phenomenon is namely local unsteady flow in stable flow. In other words, there are low-frequency and pseodu-order unstable swings of main flow, which is caused by the transport and motion of large eddy, besides stochastic flow fluctuation. In common cases, compared with the flow stochastic fluctuation, the swing of main flow shows the lower-frequency and bigger swing range and follows some regularity.更多还原