The IUP Journal of Mechanical Engineering
Understanding the Performance Degradation of Small Stall-Regulated Wind Turbines Due to Typical Manufacturing Defects

Article Details
Pub. Date : Feb, 2020
Product Name : The IUP Journal of Mechanical Engineering
Product Type : Article
Product Code : IJME20220
Author Name : Amool Raina, Kyle Wetzel, Saeed Farokhi
Availability : YES
Subject/Domain : Engineering
Download Format : PDF Format
No. of Pages : 14

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Abstract

A computational flow simulation is conducted to study the underperformance of some stall-regulated wind turbine blades. A hypothesis was proposed explaining the causes for the underperformance of an 8 kW stall-regulated wind turbine machine. The two main causes affecting the performance were poor manufacturing techniques and the aerodynamic design of the airfoil. CFD studies confirmed the causes for the underperformance of these blades and a good comparison with field data was obtained for the study.


Description

Small wind turbines of the lower kW range (8-100 kW) have been growing in popularity in recent years since they increasingly serve as good sources of small-scale economical independent energy for agricultural and industrial consumers. Unfortunately, a number of studies show evidence that many small turbines are underperforming in the field compared to design projections. The authors' direct and recent experience with a small-stall regulated wind turbine confirms this problem. Based on the extensive field testing and customer feedback, it is concluded that the expected power performance does not match the power projections generated using the rotor blade airfoils' design performance data. In some cases, losses were recorded to be as high as 50% of the original power prediction. An initial aerodynamic investigation of the wind turbine airfoils using Computational Fluid Dynamics (CFD) focused on two possible causes-blade manufacturing defects that could cause the initial airfoil geometry to change drastically near the leading edge or the aerodynamic properties of the designed airfoil itself did not exhibit the predicted aerodynamic performance. On further investigation, the root cause of the problem for loss in performance was found to be due to the effect of laminar separation bubble formation on both the upper and lower surfaces of the blade. It is well known that separation and transition play a critical role in the aerodynamic performance of the airfoil (Mueller, 1984; and Eppler, 1990). The problem gets even more complicated as the blade-chord Reynolds number approaches the range of 100 K to 500 K where a small disturbance amplifies and easily triggers separation. The paper mainly addresses the approach used and the validation study undertaken to shed light on the problem of small wind turbine underperformance. The analyses of the results obtained corroborated the initial prediction of the possible causes for the poor performance reported in the chosen small wind turbine machine. Two case studies have been presented as a part of this study.


Keywords

Wind turbine, Aerodynamics, Manufacturing, Blade performance

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