离心泵浮动叶轮自动平衡轴向力技术基础理论及实验

The research on axial force balance method and the theory is the major topic in the study of pump. At present it can say that the basic principles and structural form of device adopted to balancing axial force have no change, and Axial force calculation is the most vulnerable part in the pump design. In this study the technology of floating impeller automatic balance axial force has essential differences compared to the traditional one, and it integrates the balance hole and balance disc that are two traditional technology used to balance axial force into the impeller, by the axial displacement leading to leakage quantity change, adjusting the pressure in pump chamber and balance cavity, skillfully using of the pressure difference acting on the front and back cover of impeller, which is a new technology of realizing the axial force automatically balanced, and breaks through the constraint of the traditional balance method and calculation on the axial force..This study adopts experiment, numerical simulation and theory to research clearance rotating liquid flow characteristics of forced radial flow in the side of floating impeller cover plate; research pressure distribution mathematical model of liquid in pump chamber and balance cavity with floating impeller, leakage characteristics and calculation of balance hole, axial force characteristics and automatic balancing conditions and other basic theory. The research results not only solve the axial force problem of high speed and high head pump, and especially multistage pumps can cancel specific axial force balance device, but also provide beneficial reference for the study of the mechanical impeller clearance flow , which will produce profound influence on the technology development of pumps.

泵轴向力平衡法及理论是泵研究中的关键问题。目前泵采用平衡轴向力措施其基本原理、结构形式可以说没有改变，轴向力计算又是泵设计中最薄弱环节。本研究的浮动叶轮自动平衡轴向力技术较传统轴向力平衡法有质的区别，它将平衡孔和平衡盘这两种平衡轴向力技术集成在叶轮上，通过叶轮轴向位移引起泄漏量变化，调节泵腔、平衡腔内压力，巧妙地利用了液体作用在叶轮前、后盖板压力差，实现轴向力自动平衡的新技术，突破了传统轴向力平衡方法及计算的约束。本研究采用实验、数值模拟、理论研究的方法，研究浮动叶轮盖板侧具有强迫径向流的间隙旋转液体流动特性；研究浮动叶轮的泵腔和平衡腔液体压力分布数学模型、平衡孔泄漏量特性及计算、轴向力计算及自动平衡判别条件等基础理论。本研究成果不但解决了高转速、高扬程泵轴向力问题，尤其是多级泵可取消专门的轴向力平衡装置，而且对研究叶轮机械中的间隙流动提供借鉴和有益参考，并对泵技术发展将会产生深远影响。

浮动叶轮盖板侧间隙液体压力分布及计算，以及叶轮轴向位移对泵性能的影响是浮动叶轮轴向力的核心研究问题。通过求解泵腔液体流动的Navies-Stokes方程，推导出了设计工况下泵腔液体压力数学模型及其液体压力损失系的理论值为1.2。依据试验数据绘制出了不同比面积的泵腔液体压力损失系数与相对半径的关系曲线。结果表明，相对半径小于0.8，前、后泵腔液体压力损失系数分别为1.592、1.272，这与理论值基本一致。相对半径大于等于0.8，前、后泵腔液体压力损失系数的试验与理论的值相差较大，为此给出了计算其压力损失系数的拟合公式。从控制轴向力降低泵泄漏量的角度，提出平衡孔直径取6～8mm较为合适；为了解决设计工况下平衡腔液体压力计算问题，引入了压力系数和比面积两个无因特征参数，推导出了设计工况下平衡腔液体压力数学模型，建立了扬程、叶轮平衡孔直径大小及数量、叶轮后密封环直径及间隙和平衡腔液体压力的关系，试验验证了该数学模型是可行和可靠的；为了计算泵腔流道液体泄漏量，提出了泵腔流道液体泄漏量的测量方法和计算公式，依据试验数据绘制出了不同压力系数下速度系数与隙径比的试验曲线，并提出泵腔轴向间隙最佳取值为1～5mm；针对浮动叶轮结构特点，将其径向和轴向的间隙液体流动分别简化为平行平板间粘性层流运动和轴对称二维粘性层流运动，推导出了轴向间隙液体泄漏量及压力、液体作用在不锈钢盘上轴向力的数学表达式。通过设计实例计算，绘制出了轴向间隙泄漏量和不锈钢盘上轴向力与轴向间隙的关系曲线，从控制泄漏量减少轴向力的角度，提出轴向间隙选取0.4～0.8mm较为适宜；针对浮动叶轮轴向移动对泵性能影响的问题，试验获得了叶轮轴向位移对泵的性能和平衡腔区域液体作用在叶轮上轴向力的影响规律。这些研究成果，构建了离心泵浮动叶轮自动平衡轴向力技术的基础理论框架，它不但为离心泵浮动叶轮结构设计及轴向力计算提供了基础理论，也对常规离心泵轴向力研究提供了借鉴和有益参考，对促进泵技术进步具有较大影响。