Design of modified Magnus wind rotors using computational fluid dynamics simulation and multi-response optimization

Abstract

Concerns on climate change and dwindling fossil fuel supply have renewed interest on alternative ways of harnessing renewable energy. Using rotating cylinders to generate lift from a fluid stream, a Magnus rotor can produce up to 10 times more lift compared to an airfoil. However, it is also producing more drag. Recent studies have demonstrated improvement on the aerodynamic efficiency of a Magnus rotor through the application of surface modifications such as grooves, bumps, dimples, and even changing the shape of the cylinder into a frustum. However, it is unknown which is most desirable among those modifications; moreover, if some may be combined for even better performance. This present study seeks to fill the mentioned research gap with the aid of computer simulation tool ANSYS CFX. Simulation results showed that modifying cylinder shape into a frustum generates the most lift force. However, it is also increasing the drag on the cylinder. Interestingly, a helical groove may be employed around the frustum cylinder to mitigate the increase in drag, making the two modifications a promising combination. Multiple response surface analysis using desirability function was used to investigate the sensitivity of the rotor design to the different modifications. Furthermore, a new perspective is introduced wherein the rotor may be able to withstand more drag in exchange for more lift. For lift generation purposes, bumps are not desirable. Finally, the aerodynamic performances of the modified rotors are compared against other published results by means of a drag polar plot.