Abstract
This paper presents a multi-objective optimization procedure for bidirectional bulb turbine runners which is completed using ANSYS Workbench. The optimization procedure is able to check many more geometries with less manual work. In the procedure, the initial blade shape is parameterized, the inlet and outlet angles (β1, β2), as well as the starting and ending wrap angles (θ1, θ2) for the five sections of the blade profile, are selected as design variables, and the optimization target is set to obtain the maximum of the overall efficiency for the ebb and flood turbine modes. For the flow analysis, the ANSYS CFX code, with a SST (Shear Stress Transport) k-ω turbulence model, has been used to evaluate the efficiency of the turbine. An efficient response surface model relating the design parameters and the objective functions is obtained. The optimization strategy was used to optimize a model bulb turbine runner. Model tests were carried out to validate the final designs and the design procedure. For the four-bladed turbine, the efficiency improvement is 5.5% in the ebb operation direction, and 2.9% in the flood operation direction, as well as 4.3% and 4.5% for the three-bladed turbine. Numerical simulations were then performed to analyze the pressure pulsation in the pressure and suction sides of the blade for the prototype turbine with optimal four-bladed and three-bladed runners. The results show that the runner rotational frequency (fn) is the dominant frequency of the pressure pulsations in the blades for ebb and flood turbine modes, and the gravitational effect, rather than rotor-stator interaction (RSI), plays an important role in a low head horizontal axial turbine. The amplitudes of the pressure pulsations on the blade side facing the guide vanes varies little with the water head. However, the amplitudes of the pressure pulsations on the blade side facing the diffusion tube linearly increase with the water head. These results could provide valuable insight for reducing the pressure amplitudes in the bidirectional bulb turbine.
Highlights
Seventy-one percent of the Earth’s surface is covered by sea with an enormous source of renewable energy, including tidal energy, marine current energy, wave energy, ocean thermal energy, and salinity gradient energy
Tidal power uses the twice-daily variation in sea level caused by the gravitational effect of the moon and sun on the ocean
Optimization processes are based on the relationships between input design parameters and output targets
Summary
Seventy-one percent of the Earth’s surface is covered by sea with an enormous source of renewable energy, including tidal energy, marine current energy, wave energy, ocean thermal energy, and salinity gradient energy. Of which tidal energy is a form of hydroelectric generation in which the water resource is replenished by tidal movements. It is truly renewable green power and a clean source of energy without pollution. Tidal power uses the twice-daily variation in sea level caused by the gravitational effect of the moon and sun on the ocean. Tides are the daily movements with every rise and fall, storing large amounts of potential energy [1]. The tidal change in sea level can be used to Energies 2017, 10, 787; doi:10.3390/en10060787 www.mdpi.com/journal/energies generate electricity by building a dam across a coastal bay or estuary with large differences2between
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