明渠完全掺气水流水力特性数值模拟研究北大核心CSCD

明渠自掺气现象常见于水利工程,当水流流速较高时,空气在较大的紊动作用下会扩散至水槽底部形成明渠完全掺气水流,水流掺气对水力特性有较大影响。目前对掺气的研究大多通过模型试验,而模型试验又存在难以忽略的缩尺效应。本文采用混合模型、紊流模型和浓度方程建立了一套水气二相流数值模型,利用有限差分方法进行离散求解。采用明渠自掺气试验对该数值模型进行验证,掺气浓度和水流流速的数值模拟结果与试验数据吻合良好,说明本文建立的数值模型能有效地模拟明渠完全掺气水流水力特性。进一步研究发现,对于明渠完全掺气水流,掺入水体的空气受强烈紊动作用可以到达水槽底部,使得壁面对掺气水流阻力作用减小,造成掺气水流流速明显大于相应非掺气水流流速。

Numerical simulations on hydraulic characteristics of fully aerated water flows in open channel

Self-aeration of open channel flows is common in hydraulic engineering. When flow velocity is high, air bubbles are transported up to the channel bottom under violent turbulences, forming fully aerated water flow. At present, most of the previous studies on water flow aeration are based on the physical model tests, which have a significant scale effect. This paper describes a set of numerical models we have developed recently, including a mixing model, a turbulence model, and a concentration model. These numerical models are discretized and solved using a finite difference method. Then, they are verified through comparing the calculations of air concentration and water velocity in open channel flows with previous self-aeration experiments, achieving a good agreement and showing their applicability to the study of hydraulic characteristics of the fully aerated flows. Further examination of the calculation results reveals that in the fully aerated water flow, entrained air can reach the channel bottom due to violent turbulences, and reduce the wall resistance to the flow, thus resulting in a channel flow velocity higher than that of the corresponding non-aerated flow.