Experimental investigations of pressure fluctuations in low-head francis turbine model

The present study emphasizes the experimental investigations of pressure fluctuations characteristics of the steady flow behavior in a low-head Francis turbine model operating under various load conditions. The experimental study was conducted on a scaled model of the Francis turbine with a runner diameter of 0.31847 m with a head of 17.66 m and operated at a speed of 950 rpm. The pressure fluctuations ranged their operating points from 70% during part load, 100% at the best efficiency point, to 110% under overload conditions. Pressure field measurements were conducted using miniature-type pressure sensors. Eight sensors were strategically placed at various locations, ranging from the spiral casing inlet to the draft tube. The outcomes facilitated identifying the sources of pressure fluctuations. Substantial pressure oscillation occurs on the model runner, vaneless space, and draft tube cone. The rotating vortex rope was formulated during the part load operation. The results show that the fundamental frequency of pressure fluctuations was 0.375 times the rotational runner frequency and strong pressure fluctuations were observed during part load operation.