Abstract
A gravitation vortex type water turbine, which mainly comprises a runner and a tank, generates electricity by introducing a flow of water into the tank and using the gravitation vortex generated when the water drains from the bottom of the tank. This water turbine is capable of generating electricity using a low head and a low flow rate with relatively simple structure. However, because its flow field has a free surface, this water turbine is extremely complicated, and thus its relevance to performance for the generation of electricity has not been clarified. This study aims to clarify the performance and flow field of a gravitation vortex type water turbine. We conducted experiments and numerical analysis, taking the free surface into consideration. As a result, the experimental and computational values of the torque, turbine output, turbine efficiency, and effective head agreed with one another. The performance of this water turbine can be predicted by this analysis. It has been shown that when the rotational speed increases at the runner inlet, the forward flow area expands. However, when the air area decreases, the backward flow area also expands.
Highlights
Many large-scale conventional hydraulic power generations mainly use medium- or high-heads and water turbines [1, 2] for conduits, such as the Francis water turbine
A flow in the tank of this water turbine is not a perfect free vortex, and it is greatly influenced by the rotation of the runner near the runner inlet
The following matters were determined by our research of the performance of a gravitation vortex type water turbine and the flow field at the center of blade width through experiments and free surface flow analysis: (1) The experimental and computational values of the torque, turbine output, turbine efficiency, and effective head agree well with one another
Summary
Many large-scale conventional hydraulic power generations mainly use medium- or high-heads and water turbines [1, 2] for conduits, such as the Francis water turbine. As public consciousness about renewable energies has risen, the demand for small-scale hydraulic power generation with a water turbine [3,4,5,6,7] for open channels has been increasing, with the use of so-far unused common rivers or waterways that have low heads and low flow rates. We focused on a water turbine used in the Gravitation Water Vortex Power Plant (GWVPP) [8], which generates electricity with a low head and a low flow rate. This gravitation vortex type water turbine mainly comprises a runner and a tank. It has started to be applied to a spiral water turbine [13], an undershot cross-flow water turbine [14, 15], and a propeller water turbine [16, 17]
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