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Professors Doing Their Part to Improve Energy Sustainability

Published: December 15, 2008

Hamid Rahai and Hamid Hefazi
Photo by David J. Nelson
Engineering professors Hamid Hefazi (l) Hamid Rahai

Doing their part to improve energy sustainability and to reduce costs and pollution, CSULB engineering professors Hamid Rahai and Hamid Hefazi have designed and patented a high-efficiency vertical axis wind turbine.

Rahai is a professor of mechanical and aerospace engineering (MAE) and director of the Center for Energy and Environmental Research and Services at CSULB. Hefazi is chair of the MAE Department. The duo developed the turbine with a nearly $70,000 grant from the California Energy Commission.

Rahai, who received his doctorate in mechanical engineering from the UC Irvine in 1988, has been involved in a variety of projects related to renewable energy, air pollution and diesel emissions assessment and control. His areas of expertise are aerodynamics, convective heat and mass transfer and turbulence. He has been teaching, consulting and performing research in the area of fluid and thermal sciences since 1988.

“A high-efficiency vertical axis wind turbine allows us to harness wasted wind energy within urban areas,” explained Rahai. “Areas with moderate wind speed such as the beaches, on the top of buildings and even along freeways are also potential sites for installing such turbines.”

Hefazi received his Ph.D. in aerospace engineering from USC in 1985. He has been involved in a broad range of research activities in fluid mechanics, including geophysical fluid mechanics and computational fluid dynamics, with an emphasis on aerodynamic optimization.

“Aerodynamic optimization, for improving performance, is widely used in the aerospace industry. Our idea was to apply the same principles to a wind turbine,” said Hefazi. “With Professor Rahai’s expertise in experimental aerodynamics, we were able to test our optimized design and verify its performance.”

The professors’ invention is a high-efficiency vertical axis wind turbine with an asymmetric blade. Compared to vertical axis wind turbines with traditional blade profiles, such as the windmills that dot the desert landscape on the way to Palm Springs, their optimized blade shape produces higher torque and power output.

Today’s common wind turbines are comprised of two general types, horizontal axis and vertical axis. The vertical axis wind turbine is the simpler design. Neither type of turbines creates pollution (other than moderate noise pollution), and both are known for generating power at a low operational cost in areas of relatively consistent wind.

However, these commonly used wind turbines have a high initial investment cost, and their performance can vary depending on wind direction and the guidance machinery designed to keep the turbine in the correct position for maximum power output.

“With geometrical optimization, we were able to reduce flow separation near the leading edge of the airfoil and increase contribution of the lift force to the torque, which improved its power generation capacity,” said Rahai.

Experimental testing on the professors’ new blade shape showed an improvement of nearly 17 percent, a 40 percent increase in the power coefficient and a mean velocity improvement of 6.8 seconds. For both single and two-blade configurations with the improved geometry, tests showed a nearly 27 percent improvement in torque.

“The results of the laboratory tests were very exciting and promising. The next step in development of this turbine is to verify its performance in long-term, real-life applications,” said Hefazi.