基于三方程VLES模型的进水池吸气涡数值模拟

Numerical Simulation of Air-entrained Vortex in Intake Based on Three-equation VLES Model

摘要:

开敞式进水池在大流量、低水位情况下易出现表面涡，严重时将发展为吸气涡，影响泵站安全稳定运行。为准确模拟吸气涡流动结构，采用S-CLSVOF方法捕捉水气交界面，并基于混合RANS/LES方法中的VLES方法解析湍流场结构，分析了网格与计算时间对计算结果的影响，同时研究了VLES模型的特性。结果表明：VLES模型可以准确地预测吸气涡流场中的速度分布；不同网格数量级对速度分布与相对吸气率的变化规律影响较小，为降低计算资源消耗，网格数量级达到O(106)即可；根据相对吸气率随时间的变化规律可判断吸气涡达到稳定的时刻，在该时刻之后计算10s即满足相关标准的要求，进一步延长计算时间不改变吸气涡位置与相对吸气率的变化规律；在本算例中，VLES模型的解析度主要受湍流积分尺度的影响，在近壁面为RANS模式以降低近壁面网格要求，而在湍流核心区为混合RANS/LES以提高计算精度。

Abstract:

Under the condition of large flow rate and low water level, the free surface vortices vortex is easy to appear in the open intake, which will develop into suction vortices when it is serious, affecting the safe and stable operation of pump station. In order to accurately simulate the flow structure of the vortex, the S-CLSVOF method was adopted for capturing the water-air interface and the VLES, one of the hybrid RANS/LES methods, was used to resolve the turbulence. The effects of mesh and computational time on the results were analyzed in detail, together with the characteristics of the VLES model. The results showed that the VLES model can accurately predict the velocity distributions in the air-entrained vortex flow field. The effect of different grid order of magnitude on the velocity distribution and relative air-entrainment rate was small. To decrease the required computational resources, it was recommended to adopt the mesh with an order of magnitude equals to O(106). According to the variation of relative air-entrainment rate with time, the time when the air-entrained vortex reached stability can be judged. After that, another computation of 10s was necessary to satisfy the corresponding standard for clearly identifying the free surface vortex. Further prolonging the calculation time did not change the variation of the position of the air-entrained vortex and the relative air-entrainment rate. In this case, the resolution of VLES was mainly affected by the turbulent integral length scale. In the near wall region, VLES behaved as RANS to decrease the demand on the mesh resolution near the wall, while in the turbulence core region, it turned to hybrid RANS/LES to increase the accuracy of the simulation. The research results can be used to guide the simulation of the air-entrained vortex in hydraulic intakes.