Numerical investigation of stand-still characteristics of a bio-inspired vertical axis wind turbine rotor

This paper reports the preliminary findings of a numerical study of a 500 W bio-inspired Vertical Axis Wind Turbine (VAWT) rotor for an urban environment. The rotor shapes are inspired by seed pods of two trees found commonly in India viz. Mimosa and Bauhinia Variegata. 15 samples of seed pods were collected from each of these trees and their diameter-to-height ratio (d/h) & helix pitch-to-height ratio (p/h) were measured. Baseline rotor shapes were based on these measurements. Subsequently, d/h and p/h ratios were varied and a 3D parametric CFD analysis was carried out using an open-source CFD solver, OpenFOAM. 3D CAD models of the rotors were created using SOLIDWORKS. Grids were generated by blockMesh and snappyHexMesh tools of OpenFOAM. Numerical simulations revealed that for a d/h of 0.27 and p/h of 0.7, the single bladed helical shaped rotor produced a stand-still aerodynamic torque of about 0.26 Nm at a wind speed of 2 m/s. This was higher than the typical cogging torque of a 500 W permanent magnet generator. Hence, the bio-inspired single bladed helical shaped rotor with d/h of 0.27 and p/h of 0.7 would exhibit early start-up at wind speeds as low as 2 m/s and would be suitable for optimally operating in an urban environment. (paper)