叶根间隙对双向轴流泵水力性能的影响

Effect of Hub Clearance on Hydraulic Performance in Bidirectional Axial-flow Pump

为了保证双向轴流泵叶片安放角的可调节性,在叶轮结构设计时,叶片与轮毂之间均会保留一定的间隙,并且该间隙也会随着叶片安装角的调节而发生改变。根据工程经验,叶轮叶根间隙设计不合理会对轴流泵水力性能产生显著影响。为了探究叶根间隙在不同流量下对双向轴流泵正、反运行工况下水力性能的影响,设计了5种叶根径向间隙半径(0、1、3、5、8 mm),基于CFX对5种方案在不同运行工况下的水力性能与内部流态进行预测模拟,并将计算结果与试验测量值进行了验证对比。研究结果表明:当叶根径向间隙大于一定数值时,双向轴流泵在正、反运行工况下的扬程与扭矩会出现明显下降。在大流量条件下,泵效率由于叶根径向间隙半径增加而产生的下降幅度较大,正、反运行工况下泵效率最大下降5.72个百分点和3.48个百分点。在研究叶轮流道内部的流场时发现,正、反运行工况下的间隙泄漏量均随着叶根径向间隙半径的增大而上升。对于叶轮出口处的速度分布而言,轮毂附近的轴向速度与绝对速度环量受叶根径向间隙半径影响较为明显,均随着间隙增大而呈现显著的下降趋势。

Variable angle adjustment is an effective measure which is usually used to widen the operating range of axial-flow pump. In order to ensure the adjustability of blade placement angle in bidirectional axial-flow pump,a certain clearance will be reserved between blade and hub during structure design of the impeller. The hub clearance will change with the adjustment of the blade installation angle.According to engineering experience,inappropriate size of the hub clearance will significantly affect the hydraulic performance of the axial flow pump. Therefore,the effects of hub clearance on hydraulic performance of bidirectional axial-flow pump should be analyzed. Five clearance radii of impeller hub( 0 mm,1 mm,3 mm,5 mm and 8 mm) were designed. Three-dimensional Reynolds-averaged NavierStokes equations was solved by CFX to predict external characteristics of bidirectional axial-flow pump.The results were verified by experimental data. It was shown that when hub clearance was too large,head and torque of pump were decreased significantly both under forward and reverse condition. The decline of pump efficiency due to increase of hub clearance under large flowrate was more obvious. And the maximum relative decline ratios of pump efficiency under forward and reverse condition were 5. 72 percentage points and 3. 48 percentage points respectively. In impeller passage,the leakage rate of hub clearance was increased with the increase of clearance radius. Near impeller hub,the axial velocity and circulation of impeller outlet declined remarkable with the increase of clearance radius. This result can provide useful suggestion to structural design of bidirectional axial-flow pump.