Large Eddy Simulation Of The Internal Flow Characteristics For The Stator And Rotor Cascades In Centrifugal Pump

Interfering of dynamic and static cascade with each other is one of important causes of vibration, noise and reduced efficiency of hydraulic machinery. The running instability of pump is increased due to the flowing of liquid in dynamic and static cascade at off-design conditions. In this paper, the centrifugal pump with radical diffusers, which flow is45m3/h, is analyzed using large eddy simulation numerical method. Based it, the pump external characteristic curve at five different flow conditions which are0.6Q,0.8Q,1.0Q,1.2Q and1.4Q, respectively, radical and axial forces vector distribution are analyzed. Meanwhile, the static pressure, speed, trace and vorticity distribution in the middle section of the impeller, vane and volute in Z-axis are also analyzed. The main contents and conclusions of the paper are as follows:1. The efficiency of hydraulic design of radical vane and volute is improved by programming its calculation process using MATLAB. And the three-dimensional solid model with various components of the whole flow passage is also obtained using Pro/E software. By using ICEM CFD, the structured mesh operation is made aimed at various components of the whole flow passage, where the periodically structured mesh of the impeller and vane also is implemented.2. The whole flow-field internal unsteady flow characteristics of model pump are summarized by using the standard k-s turbulence model, and the results show that:(1) With the increase of flow, the radial forces of impeller and volute gradually decrease, the radial force of the guide vane gradually increases, and the axial force of the impeller, whose direction is opposite to the velocity direction of the impeller inlet, gradually increases.(2) From the inlet to outlet for the impeller, the static pressure of the middle section, perpendicular to Z axis, for the impeller approximately showed an increasing trend in the radial direction of the impeller. The static pressure distribution on the middle section, perpendicular to Z axis, for the guide vanes and volute is similar under different flow conditions.(3) It appears significant reflux in the impeller under small flow conditions. As the flow increases, the relative velocity distribution tends to be uniform. The flow state of the fluid in the model pump is worse under small conditions. And guide vanes can improve the flow state for the impeller under large flow conditions. (4) The maximum and minimum for the vorticity vary greatly, and most of the vorticity magnitude does not exceed25001/s. With the flow increasing, the contour range of the lowest vorticity interval of the middle section, perpendicular to Z axis, for the impeller is reduced, and vorticity distribution tends to be uniform.3. The calculation methods of large eddy simulation of hydraulic machinery are studied. The unsteady flow characteristics of model pump in five different flow conditions are obtained when using five different flow conditions of the unsteady calculations as the initial condition of Smagilly large eddy simulation numerical calculation. The results indicate that:(1) The lift, efficiency, torque and shaft power all change one cycle when the impeller rotates a flow range. And the period number of approximately sinusoidal variation for the lift, efficiency, torque and shaft power in a rotation period is equal to the number of the blades of the impeller.(2) Under small flow conditions, the radial forces for the impeller approximately appear elliptical distribution. On the whole, as the flow increases, the degree of distortion of the radius vector ellipse increases, and the radius vector ellipse gradually decreases.(3) The static pressure distribution of the middle section, perpendicular to Z axis, for the impeller has no significant correlation with the impeller rotation phase, but has relations with the relative position between the impeller and the volute.(4)With the flow increasing, the thickness of the flow disorder region on the blade pressure surface side is reduced, and the internal vortex is weakened, and the start position where the separation of flow is generated on the blade suction surface gradually move along the twist direction of the blade.(5)Under a certain flow condition,the vorticity distribution of the middle section,perpendicular to Z axis, for the impeller does’t significantly change with time, and the vorticity distribution appears obvious coherent structures. At the same time, the coherent vortex structures have some orderly changes with the flow change. With the flow increasing, the large vorticity region of the middle section, perpendicular to Z axis, for the impeller gradually decreases. The large vorticity region of the middle section, perpendicular to Z axis, for the impeller is mainly concentrated on the suction surface side at the blade outlet. Under large flow conditions, the large vorticity region on the blade suction surface near the blade outlet appears zonal distribution. As the flow increases, the large vorticity distribution of the middle section, perpendicular to Z axis, for the guide vanes is uneven, and the local large vorticity distribute region at the diffusing section, the prolonged segment of the guide vanes and the tongue of the volute is more.