【作者】 叶飞；

【导师】 高学平；

【作者基本信息】 天津大学 ， 水力学及河流动力学， 2010， 博士

【摘要】 非稳态漩涡是水工建筑物中普遍的水流现象。扩散流动如抽水蓄能电站上下水库出水口，若扩散角度较大，边壁处会产生流动分离并在分离区内产生非稳态漩涡运动，对水工建筑物造成不利影响比较突出。进水非稳态漩涡现象容易在各种水工建筑物如水电站、水泵站、通航船闸、调节流量水位的建筑物及核电站的中央应急冷却系统的集水井等建筑的进水口处产生。当漩涡转变为贯通性吸气漩涡时，对工程结构会产生危害。如减少进流量、降低流量系数；引起机组或结构物的振动；降低机组效率；卷吸漂浮物、堵塞或损坏拦污栅等。由于非稳态漩涡的不确定性，持续时间短，运动规律复杂，对模型试验以及数值模拟研究均造成较大困难。目前针对非稳态漩涡运动规律以及成因分析的研究极为有限。因此，本文通过理论分析、模型试验以及数值模拟对非稳态漩涡运动以及产生机理进行研究。(1)有压扩散段非稳态流动的数值模拟研究。用大涡模拟方法，系统研究了有压扩散段内整个流场的变化以及发展情况，结合谱分析的方法对有压扩散段内水流水力特性进行研究。结果表明，壁面流动分离区产生非稳态漩涡的横向振荡诱发扩散段内产生非稳态现象，即主流在扩散段内做非周期性摆动。(2)进水非稳态漩涡的试验研究。通过水槽试验，考虑来流边界的时均流速分布、紊动强度、水面波动强度以及进水口周边脉动压力等，对进水非稳态漩涡的特征和影响因素进行研究。结果表明：进水口附近水面非稳态吸气漩涡数量的历时过程具有和紊流相似的“拟序结构”特性。(3)进水非稳态漩涡数值模拟研究。采用大涡模拟方法，针对不同工况水槽流体进行计算，分析不同工况下进水口处流场特点，漩涡形态，运动规律，漩涡结构以及进水漩涡影响因素。结果表明，随来流紊动强度的增大，进水口附近漩涡运动活跃，进水口吸气漩涡数量增加。对称边界条件以及进水口胸墙向上游伸出一段距离均可减少吸气漩涡现象发生。(4)非稳态漩涡形成机理的理论分析。讨论了涡管的扭曲变形对涡量的影响，并对实际流体中侧部和底部孔口的漩涡的拉伸原因作了解释，依据紊流复合涡模型和能量级联结构，分析水面漩涡的能量平衡过程以及漩涡的形成演变过程。更多还原

【Abstract】 Unsteady vortexes phenomena are universal in the flow of hydraulic structures.Seperation flow often generates from the wall with unsteady vortexes in the seperation region when the diffusion angle is larger than a certain value in the outlet of a pumped storage station which have harmful effects on hydraulic structures. The vortexes have been observed frequently at intakes of hydraulic structures such as hydroelectric power stations, navigation locks, flow and level regulation and withdrawal from sumps in Emergency Core Cooling Systems (ECCS) of nuclear power stations. The presence of air-core vortexes at an intake can cause discharge reduction, increase the fluctuation of hydraulic structure, reduce pumping efficiency, and in extreme cases, completely disable the intake. Due to its randomicity, short-time persistence and motion complexity which contribute great difficultness to vortex research, At present, few literature about vortex motion and formation mechanism is found. Therefore, an analytical, computational, and experimental study was conducted to describe unsteady vortices and its formation mechanisms. The principal contents and achievements of this dissertation are as follows:(1) The numerical simulation study on local unsteady-state flow in pressure divergent segment. The motion and development of the whole flow field in pressure divergent segment are given. The flow characteristics were studied by large eddy simulation (LES) combined with frequency spectrum analysis. It is indicated that the flow is composed of traverse swing with lower frequency and fluctuation with high frequency, and the swing is caused by the transverse oscillation of eddies in the separation region.(2) The physical model test of flume was made to study the average velocity distributin, turbulence indencity, surface fluctuation and turbulence pressure. The hydraulic characteristics and influencing factor of unsteady vortexes were researched. Model test results shown that the history of near-intake unsteady votexes has the approximate feature with turbulent coherent structures of the flow in the flume.(3) The numerical simulation of the flow with unsteady vortexes near intake in the flume under different conditions was achieved by large eddy simulation. The flow field characteristics, vortex configuration motion rule vortex structure and their influencing factor were researched. Results showed that vortex movement was active near the intake and the number of air-core vortexes increased with the increase of turbulence intensity. Symmetric boundary conditions and forward-tilting breast wall may reduce the generation of air-core vortexes.(4) The theoretical analysis of unsteady vortexes at intakes was completed. The reason for vortex stretching at the bottom and the side intakes was explained. According to Rankine’s combined vortex model and Cascade structure of energy, free surface vortex energy-balance process and the vortex forming, developing and varying were probed.更多还原