Analysis of Wind Turbine’s Velocity Deficit, Recovery and Output Power Losses using a Hybrid CFD-Jensen’s Wake Model Scheme

Abstract

Owing to the depletion of the fossil fuels and their ill-effects posed on the environment, the alternative renewable energy resources are receiving ever increasing focus of the modern world. Amid these resources, prospects of harvesting energy form the wind stand out because of its inexhaustible availability and cost-effectiveness. In spite of all the pros associated with the wind power, a con exists in the shape of low power density. Hence, to generate an amount of energy comparable with the other sources, numerous wind turbines are arrayed in a single wind farm. With this, arises the problem of wake interaction amongst the turbine arrays, owing to which, the downstream wind turbines exhibit a reduced output yield. This instigates a significant diminution in the efficiency of the succeeding wind turbines and, hence, their service life gets adversely affected as well. Much work has been inspired to attain a proper understanding of the wake interactions by developing wake interaction models. Notable amongst these models are the infinite wind farm boundary layer model, the Jensen model and its variant Jensen Park model, the Larsen model, FUGA and Ellipsys 3D model with RANS and LES variants. There exists enough data in the literature to prove that the Jensen’s wake model has long maintained its dominance over other models. This owes to its less computational cost yet with adequate accuracy in its predictions. In this work, an analysis of the velocity deficit aft of the wind turbine and its recovery along the downstream distance as calculated by the Jensen’s model has been compared with a case when a hybrid CFD-Jensen model technique is employed. As wind farm layout optimization is concerned with the optimal energy harvest through placement of maximum wind turbines within a limited area of the wind farm, the magnitude of output power losses along the downstream distance, becomes quite a significant concern. Hence, this analysis has been further extended to the estimation of output power losses as manifested by the succeeding wind turbines operating in the wakes, at different downstream distances. Furthermore, a comparative analysis of the angular spread of the wakes, as they travel downstream, is also presented. This study will be particularly useful for the cases when very little or no experimental data is available at hand, as it provides initial estimates for the wind farm layout optimization for optimal energy harvest.