Abstract
We report on experimental studies of the formation of vortex ropes in a laboratory simplified model of hydroturbine draft tube. Work is focused on the observation of various flow patterns at the different rotational speed of turbine runner at fixed flow rate. The measurements involve high-speed visualization and pressure pulsations recordings. Draft tube wall pressure pulsations are registered by pressure transducer for different flow regimes. Vortex rope precession frequency were calculated using FFT transform. The experiments showed interesting features of precessing vortex rope like twin spiral and formation of vortex ring.
Highlights
Vortex ropes are often formed in draft tubes of hydraulic turbines operating under partial load or overload conditions
The main vortex can be replaced by twin spiral vortex, whereby the frequency of the pressure pulsations in hydraulic unit becomes unpredictable in certain part load conditions [4, 5]
Conical draft tube model excludes the effect of interaction between precessing vortex core (PVC) and draft tube elbow
Summary
Vortex ropes are often formed in draft tubes of hydraulic turbines operating under partial load or overload conditions. The precessing vortex core (PVC) is associated with strong pressure pulsation commonly called draft-tube surge. Draft tube surge has been investigated for a long time both numerically and experimentally, usually on scaled hydro turbine models. It is well known that the pattern, precession frequency and intensity of the vortex rope dependent on the operating mode of hydraulic turbine. A large number of swirl devices used as a model of the runner constantly expand and complement the information on a variety of PVC patterns. The main vortex can be replaced by twin spiral vortex, whereby the frequency of the pressure pulsations in hydraulic unit becomes unpredictable in certain part load conditions [4, 5]. Experimental modelling of swirling flow under the hydraulic turbine runner have been conducted. Experiments include high-speed visualization and pressure measurements at a fixed flow rate of fluid and varying the speed of the runner
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