Research on Energy Characteristics of Bidirectional Tubular Turbine

Combining a tidal power station in China, numerical simulation on energy characteristics of bidirectional tubular turbine is performed using standard k–ε model, which was used to simulate turbulent flow with high Reynolds number and is applicable to fully developed turbulent flow. This simple and economical model ensures sufficient precision in the large project simulation. Structural mesh is applied in the mesh division, for it was convenient to dispose of boundary conditions with high precision. By using high performance implicit algorithm and multi-grid algorithm, the efficiency of simulation using structural mesh is higher than other models. The simulation control zones are comprised of inlet (including bulb unit), guide vane, runner and draft tube. Boundary conditions were comprised of entrance of intake tube and export of draft tube. The inlet of turbine is a regular circular tube, where the velocity of flow is perpendicular to inlet. The water is directly discharged to downstream thus free outflow is adopted in the simulation. The numerical simulation is divided into positive and negative conditions. On the positive condition, the simulation results show that to the same guide vane opening, the discharge becomes larger and the rotational speed becomes slower with the angle of runner blade increasing. To the same angle of runner blade, the discharge becomes larger and the rotational speed becomes higher when the guide vane opening becomes larger. The highest efficiency of positive direction in the simulation is 75.8% and the optimist angle of runner blade is 15°. The simulation results agree with the results of model test generally, and the efficiency in simulation is lower than that in model test with value of 2%∼9%. And the results of simulation are close to the tested ones when the guide vane opening is near 60°. Under this guide vane opening, when the runner blade is 15°, the efficiency in the simulation was 72% while in the test the value is 74%, thus the difference between numerical simulation and model test is 2%. So, good results are obtained through numerical simulation. Under the negative condition, the discharge becomes larger with the angle of runner blade increasing in the same unit speed. The discharge becomes larger with the unit speed increasing with the same angle of blade. The highest calculated efficiency is 66.6% in this condition, and the optimist angel of the runner blade is 10°. The efficiency in the numerical simulation is lower than the value in model test, which also occurs in the positive condition. However, the difference between simulation and test is less than the one in the positive condition. The average difference is 2.5%, and it can be concluded that the difference value becomes smaller with the unit speed increasing. The values in the numerical simulation are near to the test ones. From results obtained above, numerical simulation can make comparatively accurate estimation for the energy characteristics of tubular turbine, and direct to the hydraulic design of turbine units.