旋转圆盘涡动过程中的流体力矩试验

Experiment of fluid force moment on a rotational disk in whirling motion

本试验模拟了混流式水轮机转轮上冠在不均匀径向间隙情况下产生涡动时所受的流体力矩。通过模型实验和数值模拟研究了混流式水轮机涡动过程中作用在其上冠的转动流体力矩的基本特性。模型实验中水轮机转轮用一个圆盘来模拟,其上冠与外壳之间形成一个很小的轴向间隙。用圆盘圆周和外壳之间的径向间隙来模拟实际水轮机中的密封。内向流由外部水泵供给。设计了在不同的泄漏流速、预旋速度、轴向间隙的情况下测量流体力矩的实验。通过整体流动模型对涡动过程中间隙流的特性进行了数值模拟。通过比较流体力矩的实验和数值结果,讨论了转子动力稳定性。最后得出在混流式水轮机涡动过程中,作用在转轮上冠的流体力矩除了几个较小涡动速率比以外,在其它很大的涡动速率比区间内都能够助长涡动的运动状态,从而使系统产生自激振动。

This experiment simulates the fluid force moments acting on the backshroud of a Francis turbine runner in whirling motion caused by the uneven inlet clearance.These moments were studied by model tests and numerical computations.The backshroud was modeled by a disk set close to the casing with a small radial clearance to the outer periphery.The moment was caused by an inward leakage flow which was produced by a pump.The moments were measured under the test conditions of different leakage velocity,pre-swirl intensity and axial clearance between the backshroud and the casing.Computation was made by a bulk flow model.The measured and calculated moments were compared to analyze the rotordynamic stability.It was found that this moment has a destabilizing effect in a wide region except for a small region of positive whirling speed ratio.