Inventi Impact: Energy & Power

Inventi:eep/23593/17

Optimization of the Runner for Extremely Low Head Bidirectional Tidal Bulb Turbine

This paper presents a multi-objective optimization procedure for bidirectional bulb turbine\nrunners which is completed using ANSYS Workbench. The optimization procedure is able to\ncheck many more geometries with less manual work. In the procedure, the initial blade shape is\nparameterized, the inlet and outlet angles (�²1, �²2), as well as the starting and ending wrap angles (�¸1,\n�¸2) for the five sections of the blade profile, are selected as design variables, and the optimization\ntarget is set to obtain the maximum of the overall efficiency for the ebb and flood turbine modes.\nFor the flow analysis, the ANSYS CFX code, with a SST (Shear Stress Transport) k-Ï� turbulence\nmodel, has been used to evaluate the efficiency of the turbine. An efficient response surface model\nrelating the design parameters and the objective functions is obtained. The optimization strategy\nwas used to optimize a model bulb turbine runner. Model tests were carried out to validate the final\ndesigns and the design procedure. For the four-bladed turbine, the efficiency improvement is 5.5%\nin the ebb operation direction, and 2.9% in the flood operation direction, as well as 4.3% and 4.5%\nfor the three-bladed turbine. Numerical simulations were then performed to analyze the pressure\npulsation in the pressure and suction sides of the blade for the prototype turbine with optimal\nfour-bladed and three-bladed runners. The results show that the runner rotational frequency (fn) is\nthe dominant frequency of the pressure pulsations in the blades for ebb and flood turbine modes,\nand the gravitational effect, rather than rotor-stator interaction (RSI), plays an important role in a low\nhead horizontal axial turbine. The amplitudes of the pressure pulsations on the blade side facing the\nguide vanes varies little with the water head. However, the amplitudes of the pressure pulsations on\nthe blade side facing the diffusion tube linearly increase with the water head. These results could\nprovide valuable insight for reducing the pressure amplitudes in the bidirectional bulb turbine.