A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid acceleration from standstill to final speed. Instantaneous rotatinal speed, flow-rate, and total pressure rise are measured for various start-up schemes. Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results. As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopump during its starting period.
A series of studies on the dynamic characteristics of noncavitating centrifugal pumps were extended to the cavitating case. An experimental study was carried out on the transient behavior of a cavitating centrifugal pump at the sudden opening/closure of the discharge valve. Cavitation behavior in the centrifugal pump was visualized during the transient period by using high speed video camera, and instantaneous pressure and flowrate were measured at the pump suction and discharge section with rotational speed during the transient period. Unsteady pressure, as well as flowrate, was related to the time-dependent cavitation behavior. As a result of the present study, pressure and flowrate fluctuations were found to occur due to oscillating cavitation or water column separation at rapid transient operations.
This paper presents a numerical methodology developed for predicting off-design performance of diffuser pumps. In off-design conditions, the effects of rotor/stator interaction and the pump system characteristics become significant, and both need to be taken into account. The pump computational fluid dynamics (CFD) model and the system characteristic equation were incorporated to allow for flow dynamics in the duct. Flow analysis was applied to an entire circumference to capture the asymmetric flow feature at part-flow caused by rotating stall. An arbitrary sliding interface was exploited to consider the influence of rotor/stator interaction.
The methodology was applied to a diffuser pump stage which includes a suction pipe, impeller, diffuser, U-bend, return channel and discharge pipe. Predicted results of the head-flow curve, pressure field and impeller radial forces were validated by the experimental data over the entire flow range. Back flow in the shroud region at small flowrates (from 0 to 40 per cent of design flow) was realistically exhibited. Flow in the region of 81 per cent of design flow displayed unstable features being caused by the occurrence of rotating stall in the impeller, such unsteady phenomena manifest themselves as a drop in the pump head rise, and larger fluctuations in impeller inlet pressure and radial forces.
The present study has demonstrated that incorporation of the pump system characteristic equation and the pump CFD model produces a good prediction of pump off-design performance. The developed methodology can provide an alternative to dealing with pump off-design performance.
Recently, aerial Mars exploration systems have been actively researched. Because the atmospheric density of Mars is almost one-hundredth to that of Earth's, the flight Reynolds number becomes low (Re = 10 4 ~ 10 5 ). In low Reynolds numbers, the flow around a wing tends to separate and conventional airfoils cannot satisfy the given performance requirements for Mars exploration aircraft. In recent years, Sasaki et al. researched new airfoils that have high lift-to-drag ratio at low Reynolds number using evolutionary multi-objective optimization and computational fluid dynamics. In this research, two-dimensional wind tunnel test of three airfoils proposed by Sasaki et al. is conducted to investigate their actual aerodynamic characteristics at Reynolds number 2.0 × 10 4 . The Ishii airfoil with good performance at low Reynolds number is used as the benchmark. The result of the wind tunnel test showed that the lift curve of the three airfoils is linear, and their maximum lift coefficient and stall angle are larger than those of Ishii. Particularly, the three airfoils' lift-to-drag ratio is superior to the Ishii airfoil by more than 30%.
NomenclatureRe : Reynolds number L : lift
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