Response Tests on the Unsteady Fluid Forces for the Oscillating Centrifugal Impeller

第一年致力于从非定常压力测量估计进动叶轮护罩上的流体力矩。结果表明，由于泄漏流的平均切向速度增大，失稳区域随着泄漏量的增大而增大。研究还发现，外径处阻力的增加导致了测力的增加。基于体流模型进行了数值分析。结果表明，该分析方法可以模拟大多数重要方面的实验。第二年，对前年设计制造的旋转开式压气机叶轮进行了直接测力试验。为了识别叶轮旋转和旋转运动的相位关系，将来自主轴和旋转套筒的两个触发信号输入AND电路，当旋转和旋转信号都打开时，输出触发信号。触发信号被用来开始累加FFT中的力信号，得到了一个有趣的结果，表明存在向前和向后旋转不稳定的可能性。然而，对脉动力的详细检查表明，存在意外的轴振动。因此，我们应该继续进行实验，以获得更可靠的数据。

The first year was devoted to the estimation of the fluid force moment on the shroud of precessing impeller, from unsteady pressure measurements. It was shown that the destabilizing region increases as the increase is leakage flow rate, caused by the increase in the mean tangential velocity of the leakage flow. It was also found the increase of resistance at the outerradius causes the increase in the force measurements. A numerical analysis based on the bulk flow model was made. It was found that analysis can simulate most of important aspects experiments. It was also made clear that the leakage flow can be basically treated as a 2-D inviscid unsteady flow within variable clearance.In the 2nd year, direct force measurements on a whirling open-type compressor impeller which was designed and manufactured in the preceding year. To identify the phase relationship of the impeller rotation and the whirling motion, two triggering signals from the main shaft and the whirling sleeve was put in an AND circuit and a triggering signal was put out when the rotational and whirl signal were both on. The triggering signal was used to start accumulating the force signal in a FFT.An interesting result which suggests the possibility of both forward and backward whirl instability was obtained. However, a detailed inspection of the fluctuating force suggests the existence of unexpected shaft vibration. Hence we should continue the experiments to obtain more reliable data.