Abstract
The lift-type helical hydrokinetic turbine (LHHT) owns combined capabilities of low torque pulsations and high rotating speed, stimulating the researchers' attention towards power output enhancement compared to other cross-flow turbines. The blade tip vortex plays a key role in diminishing the performance; however, it can be countered by lengthening the rotor's blades. In this context, the numerical simulations are performed on the 3D-CFD LHHT model to investigate the influence of aspect ratio considered in the range of 0.75–1.75 on the performance at different tip speed ratios and water velocities. Besides, wake recovery analysis is carried out by measuring velocity deficit at various downstream locations of the rotor under constant 1.0 m/s velocity. The aspect ratio is seen to have a strong influence on power coefficient, torque pulsations and wake recovery as well. The simulation results show that the peak power coefficient is proportional to the aspect ratio and reached a value of 0.228 for 1.75 aspect ratio model, which is 32.5 % superior to the 0.75 model. It is noticed that for an aspect ratio greater than 1.25, the water velocity recovers 100 % at a distance of 21 times the rotor diameter along the channel where the second machine would be installed.