Theoretical investigation of performance characteristics and design of VAWT with pitching

Abstract

Performance prediction and design of a straight-bladed vertical-axis Darrieus Wind Turbine is done with the cascade theory. In this prediction model the effect of dynamic stall and flow curvature is taken into consideration with blade pitching. For dynamic stall consideration, Boeing-Vertol stall model with modification is taken into account. An empirical relation is used to determine the drag characteristics. In the prestall condition, the ECN stall model is followed to calculate the lift characteristics. For the flow curvature effect the lift values are corrected only by a factor that is determined using the thin airfoil theory. However, the drag values are modified for the effect of chord-radius ratio, thus further correction of them due to the effect of flow curvature is not necessary. The finite aspect ratio effect is also incorporated in the prediction model. Incorporation of blade pitching with dynamic stall and flow curvature effects in the performance prediction model is the prime objective of the thesis. Different important parameters, like normal and tangential forces, power coefficients, torque coefficients, drag coefficients etc. at different fixed pitch angles are obtained in this investigation and they are presented in graphical form. Also design of a I KW straight-bladed vertical axis Darrieus wind turb.ine is done with mean wind velocity for the coastal regions of Bangladesh. The design wind speed is taken as 5 m/s and cutout wind speed as 15 m/s. The effect of dynamic stall and flow curvature is taken into consideration with fixed and variable blade pitching.