With the booming growth of the economy in this century, the global energy demand increasingly rockets by year. Renewable energy is considered a feasible solution to address the thorny problem of energy supply and contribute to restraining the greenhouse effects. Among several types of renewable energy, tidal power, which is based on the surge of enormous amounts of water as ocean tides rise and fall, shows its potential to play an essential role as environmentally friendly energy. Tidal energy is not only friendly to the environment but also is a highly predictable energy source. Tidal turbines farm is more compact compared to that for wind power. There are numerous types of tidal converter devices for different power scale plants. For large-scale tidal power projects, horizontal axis turbines and bulb turbines working in tidal farms or tidal barrages can generate hundreds of MW of electricity. Meanwhile, the propeller turbine is a promising candidate suitable for small-scale projects because it is considered the most proper option for low-head hydropower schemes. Due to the fact that pico-propeller turbines possess many advantages, including low-cost investment, simple structure, and high flexibility, this type of hydro turbine increasingly receives more attention from researchers and engineers.
The target of this study is to develop a tidal propeller turbine, which is capable of generating a 3 kW output power and effectively operating in the tidal range with a low head of 2 m. With constant thickness, simple profile runner blades, the turbine not only can be built in a barrage configuration for industrial application but also suitable to apply for household purposes in remote areas because of the simple manufacture and installation. The design process was conducted based on the well-known free vortex theory, while the turbine performance evaluation was implemented by applying the numerical simulations using a computational reliable commercial code. The numerical method was validated by utilizing a set of experimental results for a similar propeller turbine. The generating power and hydraulic efficiency of the turbine in this study were numerically evaluated under a series of working circumstances with various values of flow rate and rotational speeds. Besides, the velocity and pressure of the flow field were also visually illustrated by the surface streamlines located on the turbine blades and the distribution of pressure coefficient, respectively.
Unavoidable tip clearance between the blade tip and casing wall significantly affects the performance and characteristics of the tidal propeller turbine. The numerical simulations investigating the formation of tip-leakage vortices and the effects of tip-clearance size on the turbine behavior were carried out. The swirling strength criterion was employed to visualize the tip-leakage vortex trajectory and investigate vortex evolution according to the change of clearance size. Although TLV occurs in both design and off-design conditions, the results showed that vortices develop strongly under excess flow rate with increased tip gap. The significant influence of TCS on absorbing power, turbine efficiency, and pressure fluctuation was predicted in simulations for four TCS cases: δ = 0%, 0.25%, 0.5%, and 0.75%.
Finally, a study on the interaction between the fluid flow and the turbine blade was executed with one-way FSI simulations to investigate the mechanical response of the turbine blade concerning various flow conditions and assess the safety level of the turbine blade under hazardous working conditions. Several structural factors, including stress and strain concentration, blade deflection, and safety factor, were computationally calculated in this section. The observed results assisted in determining the high-risk regions and evaluate the influence of flow on the turbine blade with respect to the increase of flow rate.