Fluid Force Testing Machine for Centrifugal Impellers in Precession Motion

外伸离心叶轮的振动运动可以看作是涡动和旋进运动的叠加。本研究旨在研制一台能测量离心式叶轮在旋进运动中所受流体力和力矩的试验机，第一年（1989年）进行了试验机的设计和建造。第二年（1990年），终于沿着调试好试验机及其子系统，并投入试验。选择直径为350 mm的离心叶轮（锅炉给水泵模型）作为试验叶轮。在五个给定流量下，测量了该叶轮在不同旋进/转速比下的旋进运动过程中所受的流体力和力矩。将叶轮分别安装在无叶扩压器和有叶扩压器上，试验机达到预期的效果。试验结果表明：1）当转速大于2倍临界转速时，叶轮上的力矩对轴的振动有失稳作用; 2）由于旋进运动所产生的力被涡动运动所抵消，叶轮上的力对轴的振动影响不大。

The vibration motion of an overhung centrifugal impeller can be considered as the superposition of whirling and precession motion. The present study is to develop a testing machine, by which the fluid force and moment acting on a centrifugal impeller in the precession motion can be measured.In the first year (1989), the design and construction of the testing machine was conducted. Measuring devices including 4-element rotating force sensor and data acquisition and processing system were also planned.In the second year (1990), the testing machine was finally adjusted along with its subsystems and set into experiment. A centrifugal impeller (model of a boiler feed pump) with 350 mm diameter was chosen as test impeller. The fluid force and moment on this impeller were measured during precession motion with various precession/rotational speed ratio at five given flow rate. The impeller was installed in vaneless diffuser and in vaned diffuser.The testing machine functioned as expected. The test result revealed that :1) The moment on the impeller exerts destabilizing effect on the shaft vibration when the rotational speed is higher than twice the critical speed of the shaft.2) The force plays less important role for the shaft vibration, since the force associated with precession motion is canceled by that associated with whirling motion.