• International Journal of Fluid Machinery and Systems
• /
• 제2권4호
• /
• pp.418-425
• /
• 2009

A vertical bulb turbine unit with elbow type draft tube has been developed due to avoidance of complicated assembling and long standstill period at overhaul in comparison with conventional horizontal bulb turbine unit. Before designing the prototype vertical bulb unit, a hydrographic model test was carried out to establish the ideal design concept for this innovative generating unit. Froude similarity is not available for vortex occurrence. Consequently, an intake structure without air entraining vortices under all the flow conditions is developed, and it is confirmed that the surge wave at load rejection is not affected harmful influence for other constructions.

• International Journal of Fluid Machinery and Systems
• /
• 제10권2호
• /
• pp.164-175
• /
• 2017

Francis turbines are often operated over a wide load range due to high flexibility in electricity demand and penetration of other renewable energies. This has raised significant concerns about the existing designing criteria. Hydraulic turbines are not designed to withstand large dynamic pressure loadings on the stationary and rotating parts during such conditions. Previous investigations on transient operating conditions of turbine were mainly focused on the pressure fluctuations due to the rotor-stator interaction. This study characterizes the synchronous and asynchronous pressure and velocity fluctuations due to rotor-stator interaction and rotating vortex rope during load variation, i.e. best efficiency point to part load and vice versa. The measurements were performed on the Francis-99 test case. The repeatability of the measurements was estimated by providing similar movement to guide vanes twenty times for both load rejection and load acceptance operations. Synchronized two dimensional particle image velocimetry and pressure measurements were performed to investigate the dominant frequencies of fluctuations, vortex rope formation, and modes (rotating and plunging) of the rotating vortex rope. The time of appearance and disappearance of rotating and plunging modes of vortex rope was investigated simultaneously in the pressure and velocity data. The asynchronous mode was observed to dominate over the synchronous mode in both velocity and pressure measurements.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1027-1033
• /
• 2000

This paper describes the characteristics of vibration of a hydraulic turbine mainly due to cavitation occurrence. The analysis of vibration spectra of the turbine shaft shows that hub vortex cavitation occurs in the downstream of the turbine runner, which is verified from coherence analysis between shaft vibration displacement and dynamic pressure at the draft tube. Even though acceleration level measured at the guide vane lever, which is usually used for evaluation of cavitations performance, is decreased during forced aeration, it is found from the analysis of dynamic pressure spectra that cavitation around runner blades still remains unchanged. It is also found that lateral vibration of the turbine shaft is mainly due to the hub vortex cavitation of the turbine runner.

• International Journal of Fluid Machinery and Systems
• /
• 제3권1호
• /
• pp.80-90
• /
• 2010

The cavity oscillation with swirling flow in hydraulic power generating systems was studied by a simple experiment and numerical simulation. Several types of fluctuation were observed in the experiment, including the cavitation surge caused by the diffuser effect and the vortex precession by the swirling flow. Both cavitation surge and vortex precession were simulated by CFD. Detailed flow structure was examined through flow visualization and CFD.

• International Journal of Fluid Machinery and Systems
• /
• 제5권4호
• /
• pp.152-160
• /
• 2012

Model tests and CFD were carried out to find out the cause of cavitation surge in hydraulic power plants. In experiments the cavitation surge was observed at flow rate, both with and without a surge tank placed just upstream of the inlet volute. The surge frequency at smaller flow rate was much smaller than the swirl mode frequency caused by the whirl of vortex rope. An unsteady CFD was carried out with two boundary conditions: (1) the flow rate is fixed to be constant at the volute inlet, (2) the total pressure is kept constant at the volute inlet, corresponding to the experiments without/with the surge tank. The surge was observed with both boundary conditions at both higher and lower flow rates. Discussions as to the cause of the surge are made based on additional tests with an orifice at the diffuser exit, and with the diffuser replaced with a straight pipe.