Analyses of the Unsteady Fluid Force on the Impeller of a Centrifugal Blood Pump

本文研究了一种用于左心室辅助装置的微型离心泵叶轮上的转子动态流体力。最终目的是澄清磁耦合离心泵叶轮运动不稳定问题的原因，并提出振动问题的设计标准。本研究选择原设计为左心室辅助装置的内部血泵作为目标泵。利用两台激光位移仪测量叶轮的位移，得到叶轮在大范围工况下的横向轨迹。在所有被调查的转速（1500 - 3000转/分）下，随着流量的增加，叶轮的平均位置向出口方向移动。叶轮的旋转运动频率在0.7 ~ 0.5之间，叶轮轴套周围的转速分量对旋转运动频率有影响。该流也作为泄漏流工作，它有望冲洗泵壳体的底部区域，以避免泵内形成血栓。泵的实际运行工况包括由于患者自身心脏跳动引起的较大的流量波动。在脉动工况下，通过在试验泵的上游放置脉动血泵来测量叶轮的位移。结果表明，与稳态流量条件下的轨迹无显著差异。为了测量转子动力流体力，制作了叶轮的7.5倍放大模型，并进行了旋转运动下的试验。结果表明：无叶冠开叶时，叶轮产生非定常力，非定常力在频率比为0.7 ~ 0.8时趋于稳定；

The present study deals with the analyses of the rotor-dynamic fluid force acting on the impeller of a miniature centrifugal pump developed as a left ventricular assist device. The final goals are to clarify the causes of the unstable problems on the impeller motion of a magnetically-coupled centrifugal pump and to present the design standards for vibration problems. The in-house blood pump originally designed as a left ventricular assist device was selected as the object pump. The displacement of the impeller was measured using two laser displacement meters to obtain the lateral loci of the impeller under the wide range of working conditions. The average position of the impeller shifted in the direction of the outlet port as the flow rates increased at the all investigated rotational speeds (1500 - 3000 rpm). The frequencies of the whirling motion of the impeller were between 0.7 and 0.5, and the rotational velocity components around the impeller bush was influential on the frequency of the whirling motion. This flow works also as the leakage flow, which is expected to wash the bottom area of the pump casing to avoid thrombus formation inside the pump. The practical operational conditions of the pump include flow fluctuation of a large-scale, which was caused by the beatings of the native heart of the patients. The impeller displacements were also measured under the pulsatile conditions by the use of pulsatile blood pump placed at the upstream of the test pump. The results showed no significant difference from the loci of the steady flow rate conditions.For the measurements of the rotordynamic fluid forces, a 7.5 time scale-up model of -the impeller was manufactured and tested under whirling motion. The results are that the unsteady forces are generated on the impeller with the open-blades without the shroud, and that unsteady force becomes steady at the frequency ratio of 0.7 to 0.8.