流经挡水壁上孔口的水流。 常见的孔口形状为矩形和圆形。
岩溶泉域地下水具有集中排泄的特点，它类似于流体力学中的非恒定孔口出流。
The groundwater in Karst spring basin has a characteristic of concentration drain, it is similar to unsteady orifice outflow in fluid mechanics.
运用孔口出流公式、伯努力方程、沿途泄流公式及损失规律，建立了泄流管路的通用方程组。
By means of formula of orifice come out, Bernoulli equation, formula of discharge along way and law of lose, general group of equation of discharge flow was established.
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