Analysis of Wake Flow Structure around the Horizontal AxisWind Turbines under Ground Effects

Finding air flow pattern and wake structure aroundwind turbine blades is primarily needed for aerodynamicperformance investigation. One of the most importantanalytical methods for this purpose is based on Prandtl's liftingline theory. The aim of this study is to investigate ground effecton the wake of wind turbine by an analytical code based onPrandtl's lifting line Theory. The wake is modelled by aprescribed method somehow all the modelling equations areobtained from experimental results. To obtain a more accurateprediction of ground effect on aerodynamic performance ofwind turbines, blade element momentum (BEM) theory is usedfor design, while the analysis of the wake structure is carried outby a vortex wake method. Therefore, trailing vortices that shedalong the blade span are modelled. Results represent that theforces imposed on the blade of two-bladed turbine are higherthan the forces on the three-bladed one, unlike lift to drag ratio(L/D). Ground effect removes the axial symmetry of the wakeand pushes it downwards. The new model is applicable andrelatively accurate for prediction of wake structures behind theHAWTs and aerodynamic behavior in presence of the groundeffect.

Keywords:

Prandtl's Lifting Line Theory , Ground Effect , Wake Modelling , Number of Blades , Aerodynamic Efficiency