Transient characteristics of a centrifugal pump at rapid startup

Experimental and CFD studies were carried out on transient behaviors of a centrifugal pump during rapid startup. Relationship between the transient characteristics and a flow field in the centrifugal pump was investigated during the transient period of the centrifugal pump. Instantaneous pressure and flow rate were measured at suction and discharge ports with rotational speed during the transient operations. The pump suction and delivery pressures were measured using strain gauge type pressure transducers. And unsteady flow rate was calculated from pressure difference between two pressure measurement points in the straight pipe of the pump suction and discharge lines using the difference of inertia force. Transient characteristics during transient period were related to the time-dependent flow field, which was investigated using CFD, in the pump. As a result of the present study, it was shown that the transient characteristics in experiments were larger than a quasi-steady change at early transient stage, and then that characteristics gradually approaches to the quasi-steady change. And from CFD results, it was shown that the flow field in pump at this early transient stage did not develop enough compared with that at the quasi-steady change. Moreover, from the experimental and CFD results, the deviation of dynamic operation loci from the quasi-steady change during pump startup period occurs at a large flow rate acceleration. The reason is thought to be due to that the flow field at large flow rate change cannot develop compared with that at the quasi-steady change.