Tether and bridle line drag in airborne wind energy applications

Abstract

This chapter discusses the physics of tether and bridle line drag based on literature, describes the typical flight regimes for airborne wind energy and identifies regimes of elevated drag caused by vortex-induced vibration and movement-induced excitation such as galloping. The presented laboratory tests show increases of aerodynamic drag due to vortex-induced vibration up to 300% and due to galloping up to 210%. Given that tether drag is a primary limitation to an airborne wind energy system’s ability to fly faster and produce more energy, understanding the regimes of elevated drag as well as the mechanisms to suppress the causing phenomena are important. The chapter provides a basic overview of these phenomena as well as potential solutions for drag reduction. The information and material presented should provide an airborne wind energy developer a useful introduction to the considerations of tether and bridle line aerodynamic drag.