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Two-phase numerical study of the flow field formed in water pump sump: influence of air entrainment

机译:水泵集水池中形成的流场的两相数值研究:夹带空气的影响

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摘要

In a pump sump it is imperative that the amount of non-homogenous flow and entrained air be kept to a minimum. Free air-core vortex occurring at a water-intake pipe is an important problem encountered in hydraulic engineering. These vortices reduce pump performances, may have large effects on the operating conditions and lead to increase plant operating costs.This work is an extended study starting from 2006 in LML and published by ISSA and al. in 2008, 2009 and 2010. Several cases of sump configuration have been numerically investigated using two specific commercial codes and based on the initial geometry proposed by Constantinescu and Patel. Fluent and Star CCM+ codes are used in the previous studies. The results, obtained with a structured mesh, were strongly dependant on main geometrical sump configuration such as the suction pipe position, the submergence of the suction pipe on one hand and the turbulence model on the other hand. Part of the results showed a good agreement with experimental investigations already published. Experiments, conducted in order to select best positions of the suction pipe of a water-intake sump, gave qualitative results concerning flow disturbances in the pump-intake related to sump geometries and position of the pump intake. The purpose of this paper is to reproduce the flow pattern of experiments and to confirm the geometrical parameter that influences the flow structure in such a pump. The numerical model solves the Reynolds averaged Navier-Stokes (RANS) equations and VOF multiphase model. STAR CCM+ with an adapted mesh configuration using hexahedral mesh with prism layer near walls was used. Attempts have been made to calculate two phase unsteady flow for stronger mass flow rates and stronger submergence with low water level in order to be able to capture air entrainment. The results allow the knowledge of some limits of numerical models, of mass flow rates and of submergences for air entrainment. In the validation of this numerical model, emphasis was placed on the prediction of the number, location, size and strength of the various types of vortices coming from the free surface. Contours of vorticity at free surface, air cores, isoline of pressure surface were particularly examined for some cases. Streamlines issued from the free surface and the volume of fraction of air allows visualizing the air entrainment.
机译:在泵油槽中,必须将非均匀流量和夹带的空气量保持在最低水平。进水管处出现的空芯涡流是水利工程中遇到的重要问题。这些涡流会降低泵的性能,可能会对运行条件产生重大影响,并导致工厂运行成本增加。这项工作是2006年在LML上进行的一项扩展研究,由ISSA等人发表。分别在2008年,2009年和2010年进行了研究。使用了两个特定的商业代码,并根据Constantinescu和Patel提出的初始几何形状,对几种油槽配置案例进行了数值研究。先前的研究中使用了Fluent和Star CCM +代码。使用结构化网格获得的结果在很大程度上取决于主要的几何形状集水槽配置,例如吸管位置,一方面是吸管的浸没,另一方面是湍流模型。部分结果显示与已经发表的实验研究有很好的一致性。为了选择一个水箱的吸入管的最佳位置而进行的实验给出了与水箱的几何形状和水泵的位置有关的水泵进水流扰动的定性结果。本文的目的是重现实验的流型并确定影响此类泵中流结构的几何参数。数值模型解决了雷诺平均Navier-Stokes(RANS)方程和VOF多相模型。使用具有六面体网格的自适应网格配置的STAR CCM +,该网格具有靠近壁的棱镜层。为了能够捕获空气夹带,已经进行了计算两相非稳态流动的尝试,以获得更高的质量流量和更强的低水位浸没。结果允许了解数值模型的一些限制,质量流率和空气夹带的浸没。在此数值模型的验证中,重点放在对来自自由表面的各种类型涡旋的数量,位置,大小和强度的预测上。在某些情况下,特别检查了自由表面,空气核心,压力表面等值线的涡流轮廓。从自由表面发出的流线和空气的体积允许可视化空气夹带。

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