基于CFD-DEM的旋流式固液两相流泵数值模拟与试验研究

CFD-DEM Simulation and Experimental Study of Two-phase Flow in Vortex Pump

【目的】探究旋流式固液两相流泵内流动特征。【方法】基于CFD-DEM(Computational Fluid Dynamics-Discrete Element Method)耦合模型,选用油菜籽颗粒,在不同流量工况和颗粒体积分数下对旋流泵固液两相流场进行数值模拟和试验研究,研究旋流式固液两相流泵的内部流动规律及颗粒分布特征。【结果】小流量工况下循环流漩涡特征较明显,进口旋转回流长度较长,对进口来流扰动较大,随着流量增大,循环流影响范围减小;泵内颗粒受到贯通流和循环流的共同作用。管壁中心颗粒受贯通流的影响较大,颗粒穿过无叶腔直接进入叶轮,而靠近管壁的颗粒受循环流的影响较大;叶轮内沿着轴向3个截面处颗粒分布有着较为明显的差异,从叶轮前端面到后盖板,颗粒数量逐渐增多;蜗室内存在一对旋转方向相反的漩涡,在第Ⅴ断面之后前侧涡束逐渐消散,后侧涡束一直旋转至第Ⅷ断面处;在贯通流和循环流的作用下,油菜籽颗粒被旋转回流沿着管壁面带入到进口区域。【结论】循环流的存在导致旋流泵效率较低,但在输送颗粒时循环流起到较大的作用,使得泵输送性能较强;模型泵数值模拟与试验结果基本一致,验证了模拟的可靠性。

【Objective】Vortex pumps are widely used in many hydraulic engineering projects and water flow in them often involves sediments.The aim of this paper is to propose and validate a numeral model to simulate two-phase flow in the pumps.【Method】The numerical model is based on a combination of computational fluid dynamics(CFD)and discrete element method(DEM).Rapeseeds are used as a proxy of the sediment particles in the experiment.Water flow and sediment transport under different flow conditions and sediment concentrations in the pump were simulated.【Results】At low flow rate,the vortex characteristics of the circulating flow in the lateral cavity are more noticeable,the length of the inlet rotation and return flow are both longer,and the disturbance to the inlet flow is large.As the flow rate increases,the radius of the circulating flow and the range of influence decrease.The particles in the pump are subject to a combined effect of the through-flow and the circulating-flow,while particles in the central tube wall are greatly affected by the through-flow.The particles pass through the lateral cavity priori to directly entering the impeller.The particles near the pipe wall are greatly affected by the circulating flow,and distribution of the particles in the three sections along the axial direction in the impeller differ noticeably,with the number of particles gradually increasing from the front end of the impeller to its rear cover.For the vortices with opposite rotation directions,the front vortex beam gradually dissipates after the V section,and the rear vortex beam rotates all the way to the eighth section.Influenced by both the through-flow and the circulating flow,the particles are brought into the inlet area along the pipe wall by the rotating backflow.【Conclusion】The existence of the circulating flow reduces the efficiency of the vortex pump,despite the great role it plays in conveying particles,which increases the conveying performance of the pump.Numerical simulation results are consistent with the experimental data,indicating that the model correctly captures water flow and sediment transport in the pump.