Abstract
The runaway condition is a damage condition for pumps and turbines which can induce the wake vortex, reverse flow, and severe pressure pulsation. This study aimed to research the characteristics of pressure pulsation of axial flow pumps under different runaway conditions, and the runaway model test was performed with different blade angles and heads. Moreover, four pressure sensors were uniformly arranged at the impeller inlet section to eliminate the random error. The time domain and frequency domain analysis were the main methods to obtain the change regulations. Results showed that the pressure pulsation under the runaway condition are mainly influenced by the rotation frequency, blade passing frequency, and wake vortex frequency. The dimensionless pressure pulsation coefficient of rotation frequency and wake vortex frequency increased obviously with the runaway head increasing, but changed little with different blade angles. In addition, the dimensionless pressure coefficient of wake vortex frequency of the sensors around the impeller inlet section differed a lot, which means that the wake vortex core is not in center of the rotation axis. The average dimensionless pressure pulsation coefficient of wake vortex frequency is higher than that of rotation frequency with the same runaway head, owing to the severer wake vortex.
Highlights
Accepted: 4 September 2021The runaway condition of pumps is an extreme turbine condition in which the flow and rotation direction are the same with those of turbine condition
In order to compare the characteristics of pressure fluctuation under different runaway conditions, four different water heads and four different blade angles were adopted when sampling the pressure signal during the runaway process
To deeply analyze the pressure pulsation coefficient Cp at different locations, MP1–4 were uniformly arranged at the impeller inlet section and, MP5 and MP6 were placed above and below the inlet conduit respectively
Summary
The runaway condition of pumps is an extreme turbine condition in which the flow and rotation direction are the same with those of turbine condition. When a pump or turbine suddenly loses power by incident, the water in the pipe system will flow back and the impeller will rotate in the opposite direction [1,2]. Under the influence of the water level difference between the upstream and the downstream, the rotation speed of the impeller continues to speed up until the maximum value, called runaway speed. The centrifugal force in the impeller and the vortex rope in the inlet pipe are produced inevitably [3], which will cause harm to the rotation device and constraint components [4]. Studying the runaway condition is of great importance for the safety of pumps or turbines
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