基于FLOW-3D的台阶式溢流堰掺气水流数值模拟

Numerical Simulation of the Aerated Flow on Stepped Spillway Using FLOW-3D

数值模拟是研究掺气水流的一种不可或缺的手段。但受限于对水气微观耦合机理和多相流模拟方法的认知,考虑掺气作用的数学模型在水利水电工程领域的应用仍不多见。为了探究FLOW-3D软件中亚格子掺气模型的准确性,以某台阶式溢流堰上掺气水流的试验数据为参考,对自掺气水流进行了数值模拟。研究发现所采用的模型可以较好的模拟非掺气区的边界层发展以及掺气的初生位置,且算得的气泡大小在合理的区间之内,但模拟得到的流速和掺气浓度分布与试验值相比仍有一定偏差;拖曳系数和Richardson-Zaki系数乘数对掺气浓度的计算结果影响并不显著;受FLOW-3D中FAVOR技术的影响,湍流参数的计算结果对网格解析度比较敏感。基于上述结果,对此亚格子掺气模型的可靠性进行了综合评价,并对其后期的修正和完善提出了若干建议。研究成果可供相关数值模型的研发完善及类似工程问题的模拟参考。

Numerical simulation is an indispensable method for the investigation of aerated flow.However,limited by the cognition of microcosmic air-water coupling mechanism and multiphase flow simulation techniques,the application of mathematical models that are able to include the aeration effect remains rare in the field of water conservancy and hydropower engineering.In order to explore the accuracy of the sub-grid air entrainment model in FLOW-3D,the air-water two-phase flow on a stepped spillway is simulated as a benchmark.The simulation results are compared with the experimental data.It is found that the air entrainment model in FLOW-3D is able to correctly reproduce the turbulence development in the non-aerated region and the inception location of the surface air entrainment.Moreover,the computed bubble diameter is reasonable.However,the model still has to be improved since the calculated velocity and air concentration profiles remain unsatisfactory.The drag coefficient and Richardson-Zaki coefficient multiplier have an insignificant effect on the air concentration results.Affected by the FAVOR technique,the turbulence parameters are very sensitive to grid resolution.Based on the above results,the reliability of the sub-grid air entrainment model is comprehensively evaluated,and thus several suggestions are put forward for its future improvement.This paper can be used as a reference for the development of related numerical models and simulations of similar engineering problems.