Numerical investigation and evaluation of optimum hydrodynamic performance of a horizontal axis hydrokinetic turbine

Abstract

The hydrodynamic performance of horizontal axis hydrokinetic turbines (HAHkTs) under different turbine geometries and flow conditions is discussed. Hydrokinetic turbines are a class of zero-head hydropower systems which utilize kinetic energy of flowing water to drive a generator. However, such turbines very often suffer from low-efficiency which is primarily due to its operation in a low tip-speed ratio (≤4) regime. This makes the design of a HAHkT a challenging task. A detailed computational fluid dynamics study was performed using the k-ω shear stress transport turbulence model to examine the effect of various parameters like tip-speed ratio, solidity, angle of attack, and number of blades on the performance HAHkTs having power capacities of ∼12 kW. For this purpose, a three-dimensional numerical model was developed and validated with experimental data. The numerical studies estimate optimum turbine solidity and blade numbers that produce maximum power coefficient at a given tip speed ratio. Simulations were also performed to observe the axial velocity ratios at the turbine rotor downstream for different tip speed ratios which provide quantitative details of energy loss suffered by each turbine at an ambient flow condition. The velocity distribution provides confirmation of the stall-delay phenomenon due to the effect of rotation of the turbine and a further verification of optimum tip speed ratio corresponding to maximum power coefficient obtained from the solidity analysis.