Designing an optimization of vertical axis wind turbine

Designing an optimization of vertical axis wind turbine

Wind turbines have in the recent past been adopted as the main source of renewable energy. The vertical wind turbines have proved to be very efficient due to their ability to be used in small scale. A report authored by Hamid Rahai and Hamid Hefazi (2005) entitled: Development for Optimum Design configuration and Performance of Vertical Axis Wind Turbine(VAWT), points out that vertical axis turbines are cheaper to install than the horizontal axis wind turbines. However, the report shows that the research have shown that they are less efficient than their counterparts. This is the biggest impediment to the full commercial adoption of these machines. This report that was prepared for the California Energy Commission points out that through optimization, redesigns can be done to increase their efficiency (p. 5). Hamid Rahai and Hamid Hefazi (2005) report in this article that one of the ways of achieving efficiency is the ability to have a design that would increase the toque. To prove this, a research is done by modification of the blades. Using thin airfoils blades that are highly cambered result in higher drag than the thick less cambered airfoils. The research proves the reality of this modification. Their investigation has shown that optimizing the blades of the vertical axis wind turbines leads to generation of 1KW of power at average wind speed of 10-15 miles/hr. This is an improved efficiency that almost equals that of the horizontal axis wind turbines. The result of Liebeck’s (1973) experimental and theoretical studies on the single element foil shows the maximum lift at the design angle. He approaches the issue by first getting the optimum velocity distributions to help him get practical airfoil shapes. He does by the use of calculus variation and boundary layer theory. The results of his experiments confirm the theoretical arguments that increase in the lift occurs without separation by thin airfoils. It is therefore evident that optimization of the blades can lead to a higher efficiency of the vertical axis wind turbines. This can only be achieved on the designs. A thesis by Brian Kirke (1998) on Evaluation Self-starting Vertical Axis Wind Turbine for Stand Alone Application examines the possibility of using VAWT for the provision of stand alone power that can directly drive mechanical appliances. For instance, it could directly be used to pump water, heating and cooling using vapor compression pumps, and desalinating water by reverse osmosis. He points out that this has been possible due to the fact that VAWT has a disadvantage of inconsistent starting and low speed toque. His research finds out that above obstacles can be overcome by the following modifications: use of either passive variable pitch and the use of a combination of different aerofoil sections (fixed or variable). Moreover, the findings also indicate that also finds out that the starting toque can be eliminated by a system of transmission that unloads the rotor at low speeds (p. 319). Kirke’s research is an example of the benefits of VAWT optimization to the society. On the performance of Savonius Wind Turbines by Modi and Fernando (1989) shows results on the wind tunnel tests on VAWT. The experiment encompassed the modification blades to achieve higher efficiency. The investigation of the blade overlap, blade size, gap, shape and angle parameters. The outcome of Modi and Fernando’s research shows that Savonius rotor, at small of attacks, acts to contribute power for uplift. This is shown to increase the peak power coefficient from 12-15% to nearly 32% with tip speed ratio of 0.79 (p. 80). Studies by Benesh (1988) have also shown that for the efficiency of VAWT to be realized, the lift force has to be improved. References Modi, V.J., and Fernando. (1989) “On the Performance of the Savonius Wind Turbine.” Journal of Solar Energy Engineering, Vol. 111, pp 71-81. Benesh, A. H., 1988, ``Wind Turbine System Using a Vertical Axis Savonius Type Rotor, United States Patent, Patent No. 4,784,568. Benesh, A. H., 1989, ``Wind Turbine System Using a Savonius Type Rotor”. United States Patent, Patent No. 4,838,757. Hamid, R. and Hamid, H. (2005). Development for Optimum Design configuration and Performance of Vertical Axis Wind Turbine. California: California State University, Long Beach. Kirke, B. (1998) Evaluation Self-starting Vertical Axis Wind Turbine for Stand Alone Application. California: California State University. Liebeck, R. H., and Ormsbee, A.I. (1970) “Optimization of Airfoils for Maximum Lift” Journal of Aircraft, Vol. 7, No. 5.