非均匀进流下喷水推进泵进流速度场的数值分析

为具体描述喷水推进泵非均匀进流的结构特点,并深入探究非均匀流对喷水推进泵性能的影响,运用CFD-Post软件提取进水流道的出流速度场,将其Profile Data文件定义为喷水推进泵的附加进流条件,数值计算非均匀进流下泵的水动力性能,并与均匀进流下的仿真结果进行比较,获得了喷水推进泵扬程和效率的降幅曲线,其下降幅值随进流场不均匀度的增大而上升.围绕喷水推进泵叶轮进口边的周向平均速度分量,具体分析泵在非均匀进流场中性能下降的原因.结果表明,喷水推进泵的传统设计方法无法满足实际工作要求,相关假设在非均匀进流中也不再适用.其中,非均匀进流场中进口预旋不可忽略;叶轮进口轴面速度和环量不再遵循线性分布规律;圆柱面无关假设也不再成立.非均匀进流对叶轮的干扰集中于叶片进口轮缘处,二次回流的出现堵塞了流道,降低了泵的过流能力,同时诱发叶片轮缘处的载荷突变,降低了泵的做功能力.

Numerical analysis on velocity field of water-jet pump under non-uniform inflow

To research the correlation between non-uniform inflow and the hydrodynamics of water-jet pump, the outflow velocity field in the intake duct was analyzed by the CFX-Post software. The velocity field of non-uniform outflow was selected as the inflow boundary condition in the process of simulation, and the hydrodynamics of water-jet pump was achieved. Then the comparison of hydrodynamics between non-uniform and uniform inflow conditions was carried out. The results show that the hydrodynamics of water-jet pump in the non-uniform inflow condition is lower than that in the uniform inflow condition. With the non-uniformity of the inflow field increasing, the decreasing amplitude of the head and efficiency is increasing. According to velocity components of non-uniform, the reason that the pump hydrodynamics reduced in the non-uniform inflow condition was analyzed. Results show that the traditional design method can not meet the working requirements, and the correlation assumptions are unavailable to the condition of non-uniform inflow. The existence of inlet pre-swirling in the non-uniform inflow field is against the "no pre-swirling" hypothesis, so the angle of attack and the lift coefficient of airfoils decrease. The interaction between axial and radial velocity in the non-uniform inflow field results in the nonlinear distribution of the meridional velocity and circulation. The circumference independence assumption is invalid owing to the change of radial velocity. The non-uniform inflow also impacts the field of blades, which is concentrated at the shroud. The secondary circumfluence blocks the flow passages, and weakens the flow capacity of the water-jet pump. Meanwhile, it contributes to the deviation curve of blade loading at the shroud, and impairs the working ability of the water-jet pump. In conclusion, the non-uniform inflow is the major reason for the decrement of propulsion efficiency,therefore the non-uniform inflow condition should be considered during the process of water-jet pump designing.