Torque and power coefficients of a vertical axis wind turbine with optimal pitch control

Jim Shih Jiun Chen, Zhi Chen, Saroj Biswas, Jiun Jih Miau, Cheng Han Hsieh

Research output: Chapter in Book/Report/Conference proceedingConference contribution

6 Citations (Scopus)


Vertical axis wind turbines (VAWT) have been valued in recent years for their low manufacturing cost, structural simplicity and convenience of applications in urban settings. Despite their advantages, VAWTs have several drawbacks including low power coefficient, poor self-starting ability, negative torque and the associated cyclic stress at certain azimuth angles. Using pitch control ideas, our research is aimed at solving the above problems. In this study, a small-scale Giromill VAWT using three NACA-0015 airfoils with a cord length of 0.09 m and a wind turbine radius of 0.6 m is investigated. During each rotation, the angle of attack depends on the wind velocity, angular velocity and current azimuth angle for each turbine blade. Negative torques at certain angles are attributed to the inherent unsteady aerodynamic behavior at high angles of attack. Without optimal pitch control, the Double-Multiple Streamtube (DMS) model predicts negative torques at certain azimuth angles and very low power coefficients for tip speed ratios below 2.5. The unfavorable negative torques are eliminated using an optimal pitch control strategy, which maximizes the tangential force coefficients and thus the torque coefficients by iterations of all possible relative angles of attack for various tip speed ratios. As a result, the power coefficient is significantly improved especially at low tip speed ratios in the range of zero to three (Λ = 0 - 3). Blade pitch control can also solve the self-starting problem and reduce the vibration of vertical axis wind turbines.

Original languageEnglish
Title of host publicationASME 2010 Power Conference, POWER 2010
Number of pages8
Publication statusPublished - 2010
EventASME 2010 Power Conference, POWER 2010 - Chicago, IL, United States
Duration: 2010 Jul 132010 Jul 15

Publication series

NameAmerican Society of Mechanical Engineers, Power Division (Publication) POWER


OtherASME 2010 Power Conference, POWER 2010
Country/TerritoryUnited States
CityChicago, IL

All Science Journal Classification (ASJC) codes

  • Mechanical Engineering
  • Energy Engineering and Power Technology


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