The hydrodynamic analysis of a novel vertical axis tidal turbine concept is presented for identification of optimum operating conditions. The model uses a blade element momentum approach, adapted for the complex spiral geometry of the blades. A range of blade designs is considered, based on different rotor height to diameter ratios, leading to a range of hydrodynamic power curves with different optimal tip speed ratios and peak power levels. The model is validated against experimental data and previous similar work. It is found that decreasing the turbine height to diameter ratio results in increased maximum power coefficient.
The development of new technologies for clean, sustainable renewable energy is a key challenge for society. Tidal energy is a leading renewable energy source with significant advantages over competing sources, including predictability and repeatability.
This paper is concerned with establishing the optimum operating performance of a range of novel vertical axis tidal turbines for micro-hydro power through analytical modelling. The development of wind turbine technology is significantly more advanced in this area, leading to potential technology transfer opportunities for tidal turbine developers. Khalid et al. (2013) have assessed a number of tidal turbines and identified key challenges faced by these emerging technologies.
A number of methods have been established for investigating the power performance of turbines including vortex models, by Strickland (1975), and computational fluid dynamics (CFD) models, developed by Le et al. (2014), for example. These methods have proven to provide accurate results but are computationally expensive.
Blade element momentum (BEM) modelling is another method which offers a computational inexpensive means of analysing both wind and tidal turbines. For BEM theory the rate of change in the momentum of the fluid is equated to the streamwise hydrodynamic forces on the hydrofoils. A number of BEM models have been developed over the years. Templin (1974) was the first to develop a momentum based model for vertical axis wind turbines. This model is based on actuator disk theory and assumes the induced velocity at the turbine to be constant. It is therefore referred to as a single streamtube model.