桥梁基础局部冲刷CFD模拟的研究进展

局部冲刷是涉水桥梁失效的主要原因之一。合理的桥梁基础局部冲刷估计，对保证桥梁基础的设计、施工和维护具有重要意义。基于CFD开展桥梁基础局部冲刷研究具有现场观测和水槽试验不具备的诸多优点。首先阐述了桥梁基础局部冲刷CFD模拟的控制方程、湍流模型和泥沙输运模型，以及报导的主要CFD模拟软件；介绍了国内外研究进展，总结了现有研究存在的不足，分析了其中的原因，探讨了局部冲刷CFD研究的发展方向。分析表明，现有CFD局部冲刷研究存在流动Re数过小、未考虑来流湍流特性或来流湍流特性估计不足、湍流模型对流动的非定常特性捕捉不足，以及采用经验性的定常流泥沙输运模型等问题，使得局部冲刷坑形态和最大深度估计与试验不符。一种有望解决上述问题的途径是采用大涡模拟数值求解欧拉-欧拉两相流方程，通过求解流体相和泥沙相的质量和动量方程，采用合适的泥沙相和流体相的压格子封闭模型，并合理模拟泥沙相内相互作用和泥沙相与流体相的相互作用，通过组合壁函数实现高效数值求解，以获得桥梁基础局部冲刷的合理估计，从而推动局部冲刷CFD模拟向大尺度模型和高流动Re数发展。

Review on CFD Simulations for Local Scour Around Bridge Foundations

Local scour is blamed as one of the main causes resulting in failure of bridges over water. Reasonable local scour estimation around the bridge foundation is paramount for design, construction and maintain of bridge substructures. The CFD-based local scour study incorporates many advantages over both the field observation and the water flume test. This paper first introduced the governing equations, turbulent model and sediment transportation model related to the CFD modelling on local scour around bridge foundations, as well as the reported CFD modelling software. The up-to-date advances at home and abroad focusing on local scour study around bridge foundation were also presented. Then, issues in some reported CFD scour studies had been discussed, with the related possible reasons. Finally, future trend on CFD-based local scour was presented. It is found that the current CFD-based local scour studies are commonly carried out under low Reynolds number with empirical sediment transportation model for steady flow. They often ignore the incoming flow turbulence or can not provide accurate incoming flow turbulence, and the employed turbulent models often fail to capture flow turbulent properties. Consequently, the estimated local scour hole shape and maximum depth do not agree well with test results. As a newly developed approach, the large eddy simulation coupled with the wall function provides a promising way to deal with those issues through numerically solving the governing equation of Eulerian-Eulerian two-phase flow. Particularly, the mass and momentum equations are solved for the fluid and sediment phases with suitable subgrid turbulence closures for both the fluid and sediment phases. With reasonable models to represent intergranular interactions and inter-phase interactions, acceptable local scour estimation around bridge foundation can be expected based on high-performance computing with well efficiency, which will facilitate CFD-based local sour simulation applicable to large scale models and high Reynolds number.