Abstract:

The behavior of the fluid flowing through vertical sharp-edged orifices with the same cross-section area but different geometry was investigated experimentally on typical “large orifice” and “small orifice”.The profiles of orifice discharge coefficient curves of circular, elliptical, square, rectangular and triangular orifices were similar, and the profile of the circular one is the highest and that of the triangular one is the lowest.It can be concluded that the orifice’s geometry has some effect on orifice discharge, but it is not the key parameter, because it doesn’t change the orifice’s flow mechanism essentially.The effects of the orifice’s geometry on energy losses were evaluated based on the analysis of the hydraulic radius of orifice, interfacial tension in acute angle, and penetrating phenomenon of jet flow through non-circular orifices, which might complement the flow mechanism of the circular orifice the authors studied before.Afterwards, the orifice flow was simulated with CFD software Fluent 6.2 in order to investigate the effect of orifice’s geometry on velocity distribution and energy losses of orifice discharge.It can be seen from the simulated flow field that the geometry of orifice had little effect on the overall range and velocity distribution of the contributing flow region in front of the orifice, and the energy dissipation in front of the orifice still could be calculated by the hemisphere model.It may help to understand that the difference of mechanical energy losses in orifice flow appears after flowing into the orifice.

Key words:

孔流系数, 孔几何形状, 计算流体力学

摘要： 通过实验，分别考察了相同流通截面积下，圆形、椭圆形、正方形、矩形和三角形等不同几何形状的垂直锐边典型“大孔”和“小孔”的自由出流特性。所得孔流系数曲线形态基本相同，孔流系数值略有差异，圆孔最高，三角形最低，说明孔几何形状对孔流能量损失有一定影响，但不是关键结构参数，不会从根本上改变孔流机理。其能量损失差异可根据孔口的水力半径、锐角界面张力以及非圆形孔射流的穿透现象加以解释，藉此对前期的圆孔流动机理进行了补充。此后，为了详细考察孔形状对孔流速度分布和能量损失的影响，采用计算流体力学软件Fluent 6.2对其进行了模拟，模拟流场说明孔形状对孔前流动影响区的主体范围和速度分布基本没有影响，孔前流动的机械能损失仍可采用半球形模型研究，进一步说明不同孔形状的孔流机械能损失差异是入孔以后造成的。

关键词:

孔流系数, 孔几何形状, 计算流体力学