Experimental Investigation on the Characteristics of Hydrodynamic Stabilities in Francis Hydroturbine Models

Abstract

This paper presents an experimental investigation of flow phenomena related to the characteristic frequencies of pressure fluctuation in Francis hydroturbine models. The experiments were carried out on two test rigs with two model runners having hydraulic similarities. Flow field around the guide vanes was measured with a particle image velocimetry (PIV) on the first PIV test rig. Flow structures at the inlet region of runner and in draft tube at different operating conditions were visualized on another hydrodynamic test rig. Analyses of dominant frequency of unsteady hydraulic behaviors in the tested hydroturbines were performed. It was observed that the main frequency of flow over the guide vanes and the dominant frequency of channel vortex equal the blade passing frequency; the dominant frequency of flow separation at the suction side of blade inlet equals the vane passing frequency; the vortex rope in the draft tube displays a low-frequency nature. The flow instabilities and fluctuations directly influence the running of hydroturbine, thus these experimental results could provide important evidence for the stability study of a real hydroturbine.

On the Flow Instabilities and Turbulent Kinetic Energy of Large-Scale Francis Hydroturbine Model at Low Flow Rate Conditions

“…Figure 6 just displays the helical form of vortex rope at operating condition of = 14mm and 11 = 55.0 r/min, showing excellent agreement with former experimental results [35]. The results of other conditions have similar patterns, and all considerably reproduce the patterns in the experiments.…”

“…The threshold for channel vortex illustration is half of the ensemble average value of vorticity magnitude in the runner, that is, 0.5⟨| |⟩. Compared with experiments [35], it is found that the multiphase calculation can well reproduce the cavitating flow in the channel passages. They both present a main stripe of cavitating region along the flow direction with separately isolated secondary cavitating bubbles at the transverse direction, indicating results based on cavitation model can capture most of the features of channel vortices accurately.…”

“…We have compared the average flow field for the guide vanes' opening of 14 mm with the PIV experiments [35], as shown in Figure 8. Both results are derived from 200 samples of instantaneous data at the halfheight plane of guide vanes, and the flow conditions keep the same, that is, 11 = 65.4 r/min.…”

Vortex rope instabilities in a model of conical draft tube

“…Numerous publications related to investigations of flow regimes in draft tube can be found in literature [1][2][3]. It is well known that the pattern, precession frequency and intensity of the vortex rope dependent on the operating mode of hydraulic turbine.…”

Study of the simultaneous effects of secondary flow and sediment erosion in Francis turbines

“…The experimental details of this study are shown inFig. 8.Su et al[32] performed a PIV experiment in a complete Francis hydro-turbine model of diameter 0.15 m, with 15 runner blades, 24 guide vanes and 23 stay vanes. The visualization of the flow field inside the turbine was done by making some guide vanes and stay vanes transparent and drilling a hole on the casing at a corresponding position.…”