Transient performance of fluid machinery during transient operating periods, such as startup and stopping, has been drawn more attentions recently due to the growing engineering needs. In this paper, the transient beh...Transient performance of fluid machinery during transient operating periods, such as startup and stopping, has been drawn more attentions recently due to the growing engineering needs. In this paper, the transient behavior of a prototype centrifugal pump with an open impeller during rapid startup period is studied experimentally. The variations of the rotational speed, flow rate, head, and shaft power during rapid startup period are recorded in ex- periments at different discharge valve openings. In addition, the non-dimensional flow rate and head are also used to analyze the transient behavior. The research result shows that the rise characteristic of the rotational speed is not basically changed by working points, while mainly depends on the startnp characteristics of the driving motor. Compared with the rapid rise of the rotational speed, the flow rate rises slowly in the initial stage of startup. Moreover, the flow rate lags behind the rotational speed to rise to final stable value, and the delay becomes more severe with the increase of the discharge valve opening. The shaft power impact phenomenon generally exists in the process of startup. The non-dimensional analysis shows that the non-dimensional head is very high at the very beginning of startup, and quickly falls to the minimum, then gradually rises to final stable value, while the non-dimensional flow rate always shows the rise tendency during whole startup period. In conclusion, it is found from the non-dimensional results that the quasi-steady analysis is unable to accurately assess the transient flow during startup period.展开更多
We consider inviscid,incompressible shear flows with variable density and variable cross section.For this problem,we derived a new estimate for the growth rate of an unstable mode and a parabolic instability region wh...We consider inviscid,incompressible shear flows with variable density and variable cross section.For this problem,we derived a new estimate for the growth rate of an unstable mode and a parabolic instability region which intersects semiellipse instability region under some condition.展开更多
基金supported by the National Natural Science Foundation of China(No.21076198,51249003)the National Basic Research Program ("973" Program,No.2009CB724303)
文摘Transient performance of fluid machinery during transient operating periods, such as startup and stopping, has been drawn more attentions recently due to the growing engineering needs. In this paper, the transient behavior of a prototype centrifugal pump with an open impeller during rapid startup period is studied experimentally. The variations of the rotational speed, flow rate, head, and shaft power during rapid startup period are recorded in ex- periments at different discharge valve openings. In addition, the non-dimensional flow rate and head are also used to analyze the transient behavior. The research result shows that the rise characteristic of the rotational speed is not basically changed by working points, while mainly depends on the startnp characteristics of the driving motor. Compared with the rapid rise of the rotational speed, the flow rate rises slowly in the initial stage of startup. Moreover, the flow rate lags behind the rotational speed to rise to final stable value, and the delay becomes more severe with the increase of the discharge valve opening. The shaft power impact phenomenon generally exists in the process of startup. The non-dimensional analysis shows that the non-dimensional head is very high at the very beginning of startup, and quickly falls to the minimum, then gradually rises to final stable value, while the non-dimensional flow rate always shows the rise tendency during whole startup period. In conclusion, it is found from the non-dimensional results that the quasi-steady analysis is unable to accurately assess the transient flow during startup period.
文摘We consider inviscid,incompressible shear flows with variable density and variable cross section.For this problem,we derived a new estimate for the growth rate of an unstable mode and a parabolic instability region which intersects semiellipse instability region under some condition.
