Abstract
There are two main types of lift driven vertical axis turbine which can be used for capturing energy from tidal streams. These are the straight bladed ”Darrieustype” and the helically shaped ”Gorlov-type”. The Darrieus-type turbine can suffer from vibrations in the shaft due to torque variations, known as ”torque ripple”. Gorlov-type turbines ought to reduce this problem but suffer from variations in force distribution along the length of turbine blade. The double multiple streamtube model (a blade element momentum model), with the Gormont-Berg adaptation for dynamic stall, is used to analyse the blade forces and shaft torques. The results show the extent to which torque ripple or variable blade force is effected by various other design choices, such as blade thickness, blade camber or turbine solidity. From these some of the requisite turbine characteristics are derived.