الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 129 |  |  |
| | | from | 129 | | |
Abstract
Winglet (WL) has recently been used to improve the performance of horizontal axis wind turbine (HAWT). The WL geometry is a key parameter for diverging blade tip vortices away
from turbine blades and reducing their induced drag. The present study focuses on the effect of winglet height (H) and toe angle (αw) on the turbine performance and turbine wake
characteristics. Both computational and experimental investigations are carried out. The performance of a three-bladed rotor of 1m diameter with SD8000 aerofoil is numerically investigated using ANSYS 17.2 CFD on a polyhedral mesh. The model is hence
validated by comparing results for power coefficient (Cpw) with experimental values available
in the literature. The pressure coefficient (Cp) results around blade aerofoil are compared to those of the literature. Four upwind WLs with different values of H are considered while keeping αw constant at 0o
. The winglet of H=0.8%R is proved to be the best height for performance enhancement. It increases Cpw by 2.4% at tip speed ratio =7. The toe angle effect is studied for upwind and downwind WLs while keeping H=0.8%R.
The results show that Cpw increases as αw increases up to αw=+20o at all values of . Cpw increases by 6% at =7. Downwind WL always reduces Cpw. The present results are well
explained by the resulting vectors map near the blade tip. Using WL with the optimum H and αw, causes 6% increase in Cpw as compared to rotor blades without WL. The effects of four selected WLs namely H=8%R, H=0.8%R (αw=0), αw=+20o and αw=- 30o
(H=0.8%R) on the wake up to X/R=5.4 downstream of the turbine are studied numerically at λ=7. The optimum WL (H=0.8%R and αw=+20o ) increases the velocity deficit in the mixing
region as a result of thrust increase. It produces higher Reynolds’s shear stress and wider mixing region by comparison to the other WLs. The results prove that optimum winglet plays crucial role in wake re-energizing process. Experiments are performed using free-jet wind tunnel and three-dimensional printed
model with the same CFD model dimensions. Four samples of WLs are manufactured for the experimental study. The WL of αw=+20o shows experimentally the same percent of p ower enhancement (6% at λ=7) that is previously predicted by the present CFD.