Abstract:
As it is well understood that utilizing crude oil or coal for electricity production has adverse effect on environment, due to excess emission of greenhouse gasses. Wind power is one of the most favorable solution for the production of energy as it has least effect when compared with other sources of renewable energy. Wind power generation has so far preferred the multi-megawatt horizontal axis wind turbine (HAWT) over the vertical axis wind turbine (VAWT) technology. Main benefits of the VAWT technology are: (a) Omni-directional operation, which is independent of the directional changes in the wind, (b) heavy components such as the electric generator installed close to the ground, (c) simple design, less manufacturing and maintenance costs, (d) small operating space requirement (high farm power density), and (e) low environmental impact and noise signature. These properties support the application of VAWT in urban environments. However, the VAWT characterizes lower power coefficient Cp compared to the HAWT owing to the presence of dynamic stall and associated blade-wake interaction induced vibrations.
Generally, wind turbines are designed at rated wind speeds of 10-12 m/s. However, for low wind speed corridors such as those in Pakistan, maximum wind speeds of 7-8 m/s are available. For such low wind speeds, a turbine has to be significantly large compared to the ones made for higher wind speed. In addition, a small-scale application will also incur low Reynolds number effects. The current study is therefore focused on designing a VAWT rotor for low wind speeds of 7-8 m/s by considering a number of design variables and parameters.
The double multiple stream tube (DMST) method, the most reliable of all stream tube models is utilized to design the VAWT rotor. The DMST model is coupled to an optimizer in order to obtain optimum rotor geometry for low wind speeds. The chord length, rotor radius and number of blades collectively affects the performance when varied. An optimal selection of different design variables can lead to a smaller yet effective VAWT rotor design in terms of performance. Finally, the results obtain from DMST model are validated with CFD using ANSYS 15.
