Frequent shifts of output and operating mode require a pump turbine with excellent stability. Current researches show that large partial flow conditions in pump mode experience positive-slope phenomena with a large head drop. The pressure fluctuation at the positive slope is crucial to the pump turbine unit safety. The operating instabilities at large partial flow conditions for a pump turbine are analyzed. The hydraulic performance of a model pump turbine is tested with the pressure fluctuations measured at unstable operating points near a positive slope in the performance curve. The hydraulic performance tests show that there are two separated positive-slope regions for the pump turbine, with the flow discharge for the first positive slope from 0.85 to 0.91 times that at the maximum efficiency point. The amplitudes of the pressure fluctuations at these unstable large partial flow conditions near the first positive slope are much larger than those at stable operating condtions. A dominant frequency is measured at 0.2 times the impeller rotational frequency in the flow passage near the impeller exit, which is believed to be induced by the rotating stall in the flow passage of the wicket gates. The test results also show hysteresis with pressure fluctuations when the pump turbine is operated near the first positive slope. The hysteresis creates different pressure fluctuations for those operation points even though their flow rates and heads are similar respectively. The pressure fluctuation characteristics at large partial flow conditions obtained by the present study will be helpful for the safe operation of pumped storage units.
RAN HongjuanLUO XianwuZHU LeiZHANG YaoWANG XinXU Hongyuan
A novel double suction shaft-less mini pump was developed for heat control of small energy systems in this study.The mini pump impeller with an exit diameter of 40 mm was combined with the motor rotor supported by the hybrid dynamic bearing.The specific speed of the pump was 125 min-1 m3 min-1 m.The hydraulic performance of the pump was investigated experimen-tally under four rotational speeds.From the test results,it was recognized that the pump could provide a flow discharge of 5 L/min and head of 1.5 m,which are applicable for the heat control system of a 3 kW fuel cell.A three-dimensional turbulent flow simulation in the pump was also conducted near the design point.The numerical results showed that the average hydraulic performance of the mini pump was predicted reasonably.From the internal flow simulation,it was revealed that the favorable inflow condition upstream of impeller inlet could be attained by applying the double suction shaft-less design for the mini pump.
This paper describes the development of a miniature pump having an impeller with an exit diameter of 24 mm supported with the motor rotor by a fluid dynamic bearing.Tests verify that the miniature pump is stable and quiet for rotational speeds larger than 4000 min-1.The three-dimensional turbulent flow in the entire pump flow passage and the laminar flow in the fluid dynamic bearing were then simulated numerically.The average pump performance was well predicted by the simulations.Both the tests and the simulations show that there is no obvious Reynolds effect for the miniature pump within the tested range of rotational speeds.The numerical results also show that the bearing capacity of the fluid dynamic bearing increases with the pump rotor rotational speed and the eccentricity ratio of the journal to the bushing.This pump is very compact,so it is a promising device for surgical use.
LUO XianWuJI BinZHUANG BaoTangZHU LeiLU LiXU HongYuan
