中文摘要：

孔前流动引起的阻力损失是孔流机械能损失的重要组成部分。本文提出了孔前流动影响区的概念,首先通过悬浮颗粒示踪实验,考察了水通过垂直锐边孔口自由出流的孔前流动影响区的范围和主要影响因素,然后用计算流体力学软件Fluent 6.2对孔流进行了模拟,孔前区范围的模拟结果与实验结果基本吻合。此外,还将孔流系数的模拟值与前期实验值进行了对比,两者基本吻合,说明了模拟的可靠性。藉此讨论了孔前流动影响区的范围、速度分布、压力分布和流动状态随操作条件、孔结构条件的变化,并对“大孔机理”和“小孔机理”的孔前能量损失进行了对比分析。

英文摘要：

The energy dissipation in the flow region in front of the orifice is one of the important components which contribute to total energy loss in orifice discharge.The concept of the contributing flow region in front of the orifice is proposed in this paper,which may help to explain the flow mechanism for orifice discharge.The range and main affecting factors of the contributing flow region in front of the vertical sharp-edged orifice were investigated experimentally by using the suspended tracer particles method.The orifice flow was simulated with computational fluid dynamics（CFD） software Fluent 6.2.The calculated ranges of the contributing flow region in front of the orifice were basically in agreement with the experimental data.Moreover,the simulated orifice discharge coefficients were compared with the initial experimental data,which verified the reliability of simulation for their consistency.Correspondingly,velocity distribution,pressure distribution,flow pattern,and the range of the contributing flow region in front of the orifice were discussed under different operating conditions and orifice configurations.The characteristics of the energy dissipation in front of the orifice was compared between ＂small orifice＂ and ＂large orifice＂.