The air flow induced by a water jet freely falling inside a vertical pipe with its top and bottom both open to the atmosphere was investigated experimentally and numerically. In the experiments, the radial air velocity distribution and the air pressure variation along the vertical pipe were measured. The air drag of the falling water jet was related to the jet surface disturbance and analyzed by introducing the equivalent friction factor. A predictive model was developed for the air flow inside a 3-m-high pipe based on the momentum equation and its results compared well with the experimental measurements. Numerical simulations were also conducted by approximating the free-falling water jet as a continuous moving solid with diameter and velocity varying in the direction of motion. The effects of pipe size on the air velocity profile and the induced air flow rate were examined. The simulation results showed that the streamwise air velocity profiles inside pipes of different sizes approached the same after a certain traveling distance. The maximum induced air flow rate was found at the pipe diameter of about 20 times of initial water jet diameter.

通过实验和数值研究了由水射流自由落入顶部和底部均向大气开放的垂直管道内引起的气流。在实验中，测量了沿垂直管道的径向空气速度分布和气压变化。下落水射流的空气阻力与射流表面扰动有关，并通过引入等效摩擦系数进行分析。基于动量方程开发了一个 3 米高管道内的气流预测模型，其结果与实验测量结果进行了很好的比较。数值模拟也通过将自由落体的水射流近似为直径和速度在运动方向上变化的连续移动固体来进行。检查了管道尺寸对空气速度分布和诱导空气流量的影响。仿真结果表明，不同尺寸管道内流向风速分布在一定距离后趋于一致。在管道直径约为初始水射流直径的 20 倍时发现最大诱导空气流量。