A classical image of fluid flowing around a cylinder shows it speeding up at the sides and slowing or stagnating at the front and back. This let Majid Rashidi, Professor of Mechanical Engineering at Cleveland State University, realize that placing wind turbines in the naturally forming high-speed areas at the sides would let them generate more power than if the turbines were free standing. To test his hypothesis, Rashidi applied for a two-year grant from the Dept. of Energy and NREL, won it, and built a 25-ft diameter cylindrical tower on the roof of a CSU building. His idea mounts a pivoted truss across the top of a cylindrical tower to extend beyond its circumference. Arms extend down from the end of the truss to hold four 2-m diameter turbines (two on each side). The turbines are the off-the-shelf Swift design from Cascade Renewable Energy Solutions, Grand Rapids, Mich. Each is rated for about 2 kW at max wind speed.
Controls and monitors nearby show what each turbine is producing. During my visit, an almost calm morning, the control turbine some 150 ft away was barely turning in the light breeze while those by Rashidi’s cylinder were spinning much faster. And when the wind picked up, the turbines made no discernable noise, partially because the circular rim prevents vortex shedding at the blade tip, a noise source. The existing design uses a time averaged control to turn the device into the wind. But Rachidi plans on testing a passive less expensive directional fin, like a weather vane, for the same function.
The CSU professor says his design improves power capture by three to four fold. In addition, the design would be ideal for retrofitting existing round structures such as silos or water towers that adorn many rooftops in large cities. Rashidi says the school owns the technology and is still in the proof of concept stage. Commercialization would be a next step.
Filed Under: News, Turbines