静水条件下垂直圆管负浮力射流的数值模拟

建立了静水条件下垂直圆管负浮力射流的三维水动力数学模型和物理模型，两者的无量纲垂向速度吻合较好；对静水条件下垂直圆管负浮力射流的水动力特性进行了研究。结果表明：随着射流初始速度的增加，射流初始密度和喷口直径的减小，射流最大上升高度和稳态高度均增加。射流初始速度和射流初始密度对最大上升高度时刻中轴线垂向速度衰减早晚和衰减率的影响不大；随着射流初始密度的增加，稳态高度时刻的射流中轴线上垂向速度衰减较晚，衰减率增加；射流量一定时，随着喷口直径的增加，最大上升高度时刻和稳态高度时刻射流中轴线上垂向流速衰减较早，衰减率减小。分别建立了密度弗劳德数表达的无量纲最大上升高度和稳态高度线性关系式；本研究中射流最大上升高度和稳态高度比值趋近于常数1.52,与密度弗劳德数基本无关。研究结果可以为静水条件下垂直圆管负浮力射流的设计和工程应用提供一定的参考依据。

Numerical simulation of the vertical jet in circular pipe with negative buoyant effect in still water

A three-dimensional hydrodynamic mathematical model and physical experiment of the vertical jet in circular pipe with negative buoyant effect was conducted in still water, and the calculated non-dimensional vertical velocity of the model was in good agreement with that of the experiment. Then, the hydrodynamic characteristics of the negative buoyant jet was analyzed accordingly. The results showed that with the increase of the initial jet velocity and the decrease of the initial jet density and the nozzle exit diameter, the maximum rising height and the steady height increased; however, the initial jet velocity and initial jet density had insignificant influence on the time and rate of the vertical velocity decay at the central line. With the increase of the initial jet density, the vertical velocity decay at the central line tended to arrive late and the decay rate increased; whereas it happened early and the rate decreased at the moment of both maximum rising height and steady height with the increase of the nozzle exit diameter for the scenario of steady height. Based on the findings, the density Froude number was used to obtain the dimensionless linear relationship formulas for predicting the maximum rising height and the steady height respectively. The ratio of the maximum rising height to the steady height was close to the constant of 1.52, which was roughly independent of the density Froude number. The research aims to shed some light on the design and engineering application of the vertical jet with negative buoyant effect in still water.