Innovative Design of a Darrieus Straight Bladed Vertical Axis Wind Turbine by using Multi Element Airfoil

30% of electrical energy is being consumed by households, and the demand for energy is increasing rapidly causing a strain on existing electricity solutions. Electricity production plants have been seen on larger scales but they have failed to reach every single potential user of electricity. The demand for electricity is rapidly growing in urban areas as people are migrating towards the big cities. So governments around the world are focusing on the electricity needs in urban areas and on the industrialized special economic zones consuming all their resources and leaving behind rural electrification. However, electricity demand in developed countries is far more different than the developing countries. Developed countries need massive supply of electricity for its own cities for future exponential demand whereas developing countries needs to lift up their un-electrified population with supplying electricity for livelihood alongside with urban demand. The price of electricity is increasing every day as well.

With this immense opportunity for off-grid electricity production in energy field new renewable energy and technological devices are getting lots of attention around the world. A wind energy convertor is seen as the most potential energy convertor to supply electricity and has gone through technological developments in last two decades. Wind energy convertors are growing bigger in size and going through new design procedures on a massive scale that the world has never seen before, as big as 10 MW wind energy convertors. Today wind turbines are the biggest structures on the earth. The knowledge and experiences from aviation and a construction industry has made quicker developments in the wind turbines. This research work is aimed at design and development of a small wind turbine.

Mainly, there is the horizontal axis wind turbine (HAWT) and vertical axis wind turbine (VAWT). HAWTs are more popular than VAWTs due to failure of VAWT commercialization during the late of 1980s on a large scale. However, in recent research work it has been documented that VAWTs are more economical and suitable for urban use due to their noise-free and aesthetic design. Still there is a room to improve the efficiency of the VAWTs since they are not completely understood. The reason for smaller development of VAWTs is the non-availability of an accurate aerodynamic model and very few experimental data for validation. In this PhD research, a development of wind turbine rotor is planned based on the multi-element airfoil technology used in aviation for aeroplanes.

A method of experimental and numerical analysis is combined together for successful research. A double-element airfoil design is carried out, and the wind tunnel testing of double-element airfoil is performed. It is found that the aerodynamic characteristics of the airfoil increased considerably by delaying the angle of stall. These two facts are very suitable for vertical axis wind turbine since they operate in a larger range of angle of attack, ±40_, compared to the horizontal axis wind turbines which operate in the range of attack, ±15_. A new design of vertical axis wind turbine is then proposed, and aerodynamic performance is evaluated based on double multiple stream tube methods. The performance parameters are almost doubled compared to the traditional straight-bladed vertical axis wind turbine. Theoretical study of blade pitch control methods for a vertical axis wind turbine has also been carried and compared with each other.