Assessment of wind energy potential in some locations of north eastern region of India and CFD analysis of vertical axis wind turbine

Abstract

In the application of wind energy conversion technology the kinetic energy of the wind is converted into useful electrical energy. However, as the wind energy is stochastic in nature, the analysis of wind characteristics and assessment of wind energy potential is vitally important for the selection or design of appropriate wind turbine of the concerned site before its installation. Therefore, this thesis is concerned with the assessment of wind power potential of some locations in Northeastern and Eastern regions of India and then CFD analysis of vertical axis wind turbine which can be deployed in such regions to assess the performance of rotors with some new airfoils section. Simultaneously, the present study also includes development of a new proposed estimation method namely, Energy Variance method (EVM) which can be effectively used in the assessment of wind energy potential. For the assessment of wind energy potential four important locations namely, Imphal, Shillong, Guwahati and Kolkata the capital or the business capital of Manipur, Meghalaya, Assam and West Bengal respectively have been selected from the Northeastern and Eastern regions of India. Analysis of the wind characteristics and wind profiles of the all the selected sites reveal that all the sites fall in the low wind speed range and among them Kolkata provides the highest wind power potential followed by Guwahati site while Shillong provides the least wind power potential. Sessional variations show that wind potential is higher during summer and lower during winter for all the sites. Even after extrapolating the data to twice the height of measurement, the available wind power of all the selected sites fall in the low wind power scale and in such situation deployment of vertical axis wind turbine is feasible. Several previous studies showed that two-parameter Weibull distribution model associated with shape and scale parameters is an effective, simple, flexible and best statistical distribution method. However, from the earlier study it is also known that Weibull is properly unable to represent very low speeds in the set of wind speed data to be assessed. Therefore, an alternative model namely, Rayleigh distribution model is employed to assess the available data and the performance of both Weibull and Rayleigh models are compared. The results show that the overall performance of Weibull model is better than the same of the Rayleigh model except in case of Shillong site. It may be concluded that Weibull is still better for the assessment of low to higher wind speed range while Rayleigh model showed better result for the region having extremely low wind speed range. Evaluating the exact and efficient parameters is imperative to get the best fit for the distribution for both Weibull and Rayleigh models. The Weibull parameters are estimated by utilizing four effective methods such as Moment method, Empirical method, Power Density method, and Maximum Likelihood method. Simultaneously, a new approach namely, Energy Variance method is developed which utilizes a non-iterative method to find out the Weibull distribution parameters effectively. Therefore, one of the objectives of the present work is to perform the comparative analysis of the proposed new method with four effective widely accepted estimation methods. The performance shows that the proposed Energy Variance method is a potential which provides the least error in case of Guwahati and Kolkata sites while the maximum likelihood method and moment method show the least error in case of Shillong and Imphal sites respectively. However, the overall performance shows that Energy Variance method is an effective and the most accurate method for estimating Weibull parameters followed by Maximum Likelihood method and Moment method for this region. Therefore, this new method may be considered as an improved, efficient and alternative estimation method for estimating Weibull parameters for wind energy applications. Further, once the assessment of wind potential is completed, the next phase is to find suitable device to tap maximum possible energy from the stated energy source. A wind turbine is a device that can harness useful energy from wind energy source. Although there are two types of wind turbines: Horizontal Axis Wind Turbines and Vertical Axis Wind Turbine, the latter is more suited for the Northeastern and eastern regions as stated above. However, efficiency of vertical axis wind turbine is remarkably less than horizontal axis wind turbine and consequently the most important challenge of the former one is to enhance its aerodynamic performance. Earlier study showed that selection of efficient airfoil shape is an important criterion to enhance overall performance of wind turbine. Therefore, the last objective of the present work is to do two dimensional Computational Fluid Dynamics analysis of three bladed H-type Darrieus wind turbine having blade profile of NACA0019 and NACA0016 which are neither too thick nor too thin and the effectiveness of these profiles for harnessing wind energy are not reported till date. Prior to the Computational Fluid Dynamics simulation two dimensional mesh is generated using Ansys Meshing tool and then sliding mesh technique is used to simulate the rotational motion of the wind turbine. SST k-ω turbulence model is employed for the flow simulation. Initially both mesh and time step are optimized to reach independent solutions. Then the results from the simulation are compared with the pre- existing experimental result for the purpose of validation. xiii For this study several parameters such as lift coefficient, drag coefficient and torque coefficient are considered. The vortical structures at three different input wind speeds are also compared. Finally, the power coefficient curves at different speeds with respect to optimal value of tip speed ratio are compared. It is observed that power coefficient increases as the input wind speed increases. Further, the performance of these two new airfoils are compared with an effective airfoil namely, NACA0015 which has been already accepted for excellent performance in wind turbine applications. The analysis reveals that the power coefficient of NACA0019 airfoils resulting from the CFD simulation is comparatively high and may be considered as one of the effective and alternative airfoil for the Darrieus VAWT which also provides better structural strength than thinner NACA 4 digit series like NACA0018, NACA0016 and NACA0015.